Atmospheric Environment (v.99, #C)

On-road measurement of regulated pollutants from diesel and CNG buses with urea selective catalytic reduction systems by Jiadong Guo; Yunshan Ge; Lijun Hao; Jianwei Tan; Jiaqiang Li; Xiangyu Feng (1-9).
In this study, emissions from 13 buses operated in Beijing, including two Euro-III diesel buses, four Euro-IV diesel buses, three Euro-V diesel buses and four Euro-V CNG buses, were characterized in real world conditions. All of the buses tested were fitted with selective catalytic reduction (SCR) systems except for the Euro-III diesel buses. A SEMTECH-DS was used for testing the gaseous pollutants, and an electric low pressure impactor (ELPI) was used for measuring of particle numbers and size distributions. A comparison was made based on emission performance of these buses by employing the VSP approach and fuel- based emissions factors. Diesel buses emitted less CO and THC but more NO x and PM pollutants than CNG buses. The NO x reduction efficiencies of the SCR systems for CNG buses were higher because of the high exhaust temperature and high NO2/NO x ratio, whereas the efficiencies for diesel buses were lower. This resulted in extremely low NO x emissions from CNG buses, but the high NO2/NO x ratio needs further study. Failures of urea injection in the SCR systems were detected in this research, which resulted in very high NO x emissions. The CNG buses also emitted smaller numbers of particles and less particle mass with the presence of oxidation catalysts. Diesel buses satisfying the Euro-V standard performed better than Euro-IV and Euro-III diesel buses in terms of emission performance, except for more nuclei mode particles. Most of time, the Euro-IV diesel buses show no advantages in CO and NO x emissions compared with the Euro-III diesel buses.
Keywords: SCR; Diesel; CNG; NO x ; Particulate;

Daily precipitation samples were collected from June 2012 to May 2013 at four observation sites in Xiamen, a coastal city of Southeast China. Concentrations of Total mercury (THg) and methyl mercury (MeHg) in precipitation were rigorously treated and determined. The annual volume-weighted mean concentrations of THg and MeHg at four sites were 12.3 and 0.053 ng L−1, and wet deposition fluxes of THg and MeHg were 14.04 μg m−2 yr−1 and 58.2 ng m−2 yr−1, respectively. MeHg could account for 0.43% of THg, and dissolved Hg contributed 55.4% to THg. There was no significant difference in THg concentration between monsoon and non-monsoon seasons, which was consistent with neither the general seasonal pattern of inland cities of China nor the report from the Gulf coast. Higher wet deposition flux of THg in monsoon season was a function of intense rainfall, whereas higher MeHg flux in non-monsoon season could attribute to increased MeHg concentration. Atmospheric Hg was more efficiently scavenged during the earlier period of the rain event. Positive correlations between precipitation depth and wet deposition fluxes suggested that rainfall played an important role in scavenging atmospheric Hg rather than diluting concentrations. Pearson correlation analysis combined with ions ratios implied that sea salt aerosols had an important impact on rainwater, but coal combustion and traffic emission could be the dominant factors influencing THg in precipitation.
Keywords: Total mercury; Methyl mercury; Precipitation; Wet deposition flux; Seasonal variation;

Inventory and mitigation opportunities for HFC-134a emissions from nonprofessional automotive service by Tao Zhan; Winston Potts; John F. Collins; Jeff Austin (17-23).
Many vehicle owners in the United States recharge their vehicles' air conditioning systems with small containers of hydrofluorocarbon-134a (HFC-134a, CH2FCF3), at a frequency estimated to be once every year on average. Such nonprofessional service produces immediate emissions of this potent greenhouse gas during service and from the residual heel in partially used containers. The nonprofessional operations are also associated with increased delayed refrigerant emissions that occur because owners are less likely to repair leaks than professional technicians. In California, an estimated 1.3 million nonprofessional service operations performed each year generate 0.27 ± 0.07 million metric ton CO2 equivalent (MMTCO2e) of immediate emissions and 0.54 ± 0.08 MMTCO2e of delayed emissions, using a Global Warming Potential of 1300 for HFC-134a. The immediate emissions can be largely mitigated by a regulation that requires self-sealing valves and improved labeling instructions on the containers, a deposit-return-recycling program for the containers, and a consumer education program. If 95% of the used containers were to be returned by consumers for recycling of the container heel, the annual immediate emissions would be reduced by 0.26 ± 0.07 MMTCO2e. In the United States, an estimated 24 million nonprofessional service operations are performed each year, generating 5.1 ± 1.4 MMTCO2e of immediate emissions and 10.4 ± 1.5 MMTCO2e of delayed emissions. Mitigation measures equivalent to the California regulation would reduce nationwide immediate emissions by 4.9 ± 1.4 MMTCO2e, if 95% of the used cans were returned for recycling. These business-as-usual emissions and mitigation potentials are projected to stay approximately constant until around 2022, and remain at significant levels into the 2030s.Display Omitted
Keywords: HFC-134a; Greenhouse gas; Motor vehicle air conditioning; Nonprofessional service; Emission inventory; Mitigation;

Liquid water content (LWC) is the amount of liquid water on aerosols. It contributes to visibility degradation, provides a surface for gas condensation, and acts as a medium for heterogeneous gas/particle reactions. In this study, 520 half-hourly measurements of ionic chemical composition in PM2.5 at a receptor site in Hong Kong are used to investigate the dependence of LWC on ionic chemical composition, particularly on the relative abundance of sulfate and nitrate. LWC was estimated using a thermodynamic model (AIM-III). Within this data set of PM2.5 ionic compositions, LWC was highly correlated with the multivariate combination of sulfate and nitrate concentrations and RH (R 2 = 0.90). The empirical linear regression result indicates that LWC is more sensitive to nitrate mass than sulfate. During a nitrate episode, the highest LWC (80.6 ± 17.9 μg m−3) was observed and the level was 70% higher than that during a sulfate episode despite a similar ionic PM2.5 mass concentration. A series of sensitivity tests were conducted to study LWC change as a function of the relative nitrate and sulfate abundance, the trend of which is expected to shift to more nitrate in China as a result of SO2 reduction and increase in NO x emission. Starting from a base case that uses the average of measured PM2.5 ionic chemical composition (63% SO4 2−, 11% NO3 , 19% NH4 +, and 7% other ions) and an ionic equivalence ratio, [NH4 +]/(2[SO4 2−] + [NO3 ]), set constant to 0.72, the results show LWC would increase by 204% at RH = 40% when 50% of the SO4 2− is replaced by NO3 mass concentration. This is largely due to inhibition of (NH4)3H(SO4)2 crystallization while PM2.5 ionic species persist in the aqueous phase. At RH = 90%, LWC would increase by 12% when 50% of the SO4 2− is replaced by NO3 mass concentration. The results of this study highlight the important implications to aerosol chemistry and visibility degradation associated with LWC as a result of a shift in PM2.5 ionic chemical composition to more nitrate in atmospheric environments as is expected in many Chinese cities.
Keywords: Aerosol chemistry; Liquid water content; Aerosol chemical composition; Chinese aerosols; Ionic aerosol constituents;

Anthropogenic emissions in Nigeria and implications for atmospheric ozone pollution: A view from space by E.A. Marais; D.J. Jacob; K. Wecht; C. Lerot; L. Zhang; K. Yu; T.P. Kurosu; K. Chance; B. Sauvage (32-40).
Nigeria has a high population density and large fossil fuel resources but very poorly managed energy infrastructure. Satellite observations of formaldehyde (HCHO) and glyoxal (CHOCHO) reveal very large sources of anthropogenic nonmethane volatile organic compounds (NMVOCs) from the Lagos megacity and oil/gas operations in the Niger Delta. This is supported by aircraft observations over Lagos and satellite observations of methane in the Niger Delta. Satellite observations of carbon monoxide (CO) and nitrogen dioxide (NO2) show large seasonal emissions from open fires in December–February (DJF). Ventilation of central Nigeria is severely restricted at that time of year, leading to very poor ozone air quality as observed from aircraft (MOZAIC) and satellite (TES). Simulations with the GEOS-Chem chemical transport model (CTM) suggest that maximum daily 8-h average (MDA8) ozone exceeds 70 ppbv over the region on a seasonal mean basis, with significant contributions from both open fires (15–20 ppbv) and fuel/industrial emissions (7–9 ppbv). The already severe ozone pollution in Nigeria could worsen in the future as a result of demographic and economic growth, although this would be offset by a decrease in open fires.
Keywords: Nigeria; NMVOC; Atmospheric ozone pollution; Satellite; AMMA;

Total global solar shortwave (G) irradiation and sunshine duration were recorded at nine Spanish stations located in the Iberian Peninsula. G irradiation under cloudless conditions was simulated by means of a radiative transfer model using satellite data as input. A method based on these cloudless simulations and sunshine duration records was developed to reconstruct G series. This model was validated against experimental data, providing a good agreement for cloudless skies (mean bias error of 0.4% and root mean square error of 5.8%). Monthly averages of modelled and measured G irradiation presented a mean bias error of 0.5% and a root mean square error of 3%. Differences between modelled and measured G irradiation were in agreement within the model uncertainties. The reconstruction model was applied to sunshine duration measurements, giving long-term G series at the nine locations. Monthly, seasonal, and annual G anomalies were calculated and analysed. Averaged series (using the nine locations) showed a statistically significant decrease in annual G from 1950 to the mid 1980s (−1.7%dc−1) together with a significant increase from the mid 1980s to 2011 (1.6%dc−1). The effect of uncertainty in the reconstructed series on statistically significant trends was studied.
Keywords: Solar radiation; Global dimming; Brightening; Sunshine duration; Series reconstruction; Shortwave trends;

This work analyses the potential air quality improvements resulting from three fleet electrification scenarios (∼13, 26 and 40%) by replacing conventional vehicles with Electric Battery Vehicles (EBVs), Plug-in Hybrid Electric Vehicles (PHEVs) and Hybrid Electric Vehicles (HEVs). This study has been performed for the cities of Barcelona and Madrid (Spain), where road transport is the primary emission source. In these urban areas, several air quality problems are present, mainly related to NO2 and particulate matter. The WRF-ARW/HERMESv2/CMAQ model system has been applied at high spatial (1 × 1 km2) and temporal (1 h) resolution. The results show that fleet electrification offers a potential for emission abatement, especially related to NOx and CO. Regarding the more ambitious scenario (∼40% fleet electrification), reductions of 11% and 17% of the total NOx emissions are observed in Barcelona and Madrid respectively. These emissions reductions involve air quality improvements in NO2 maximum hourly values up to 16%: reductions up to 30 and 35 μg m−3 in Barcelona and Madrid, respectively. Furthermore, an additional scenario has been defined considering electric generation emissions associated with EBVs and PHEVs charging from a combined-cycle power plant. These charging emissions would produce slight NO2 increases in the downwind areas of <3 μg m−3. Thus, fleet electrification would improve urban air quality even when considering emissions associated with charging electric vehicles. However, two further points should be considered. First, fleet electrification cannot be considered a unique solution, and other management strategies may be defined. This is especially important with respect to particulate matter emissions, which are not significantly reduced by fleet electrification (<5%) due to the high weight of non-exhaust emissions. Second, a significant introduction of electric vehicles (26–40%) involving all vehicle categories is required to improve urban air quality.
Keywords: Air quality modelling; Air quality management; Emission inventory; Electric vehicles; Plug-in hybrid electric vehicle;

A multi-method and multi-scale approach for estimating city-wide anthropogenic heat fluxes by Winston T.L. Chow; Francisco Salamanca; Matei Georgescu; Alex Mahalov; Jeffrey M. Milne; Benjamin L. Ruddell (64-76).
A multi-method approach estimating summer waste heat emissions from anthropogenic activities (Q F ) was applied for a major subtropical city (Phoenix, AZ). These included detailed, quality-controlled inventories of city-wide population density and traffic counts to estimate waste heat emissions from population and vehicular sources respectively, and also included waste heat simulations derived from urban electrical consumption generated by a coupled building energy – regional climate model (WRF-BEM + BEP). These component Q F data were subsequently summed and mapped through Geographic Information Systems techniques to enable analysis over local (i.e. census-tract) and regional (i.e. metropolitan area) scales. Through this approach, local mean daily Q F estimates compared reasonably versus (1.) observed daily surface energy balance residuals from an eddy covariance tower sited within a residential area and (2.) estimates from inventory methods employed in a prior study, with improved sensitivity to temperature and precipitation variations. Regional analysis indicates substantial variations in both mean and maximum daily Q F , which varied with urban land use type. Average regional daily Q F was ∼13 W m−2 for the summer period. Temporal analyses also indicated notable differences using this approach with previous estimates of Q F in Phoenix over different land uses, with much larger peak fluxes averaging ∼50 W m−2 occurring in commercial or industrial areas during late summer afternoons. The spatio-temporal analysis of Q F also suggests that it may influence the form and intensity of the Phoenix urban heat island, specifically through additional early evening heat input, and by modifying the urban boundary layer structure through increased turbulence.
Keywords: Anthropogenic heat; Waste heat; Urban climate;

Reassessing the photochemical production of methanol from peroxy radical self and cross reactions using the STOCHEM-CRI global chemistry and transport model by M.A.H. Khan; M.C. Cooke; S.R. Utembe; P. Xiao; R.G. Derwent; M.E. Jenkin; A.T. Archibald; P. Maxwell; W.C. Morris; N. South; C.J. Percival; D.E. Shallcross (77-84).
Methanol (CH3OH) is an oxygenated volatile organic compound (VOC) and one of the most abundant species present in the troposphere. The mass of CH3OH in the atmospheric reservoir, its annual mass flux from sources to sinks, and its global budget have been investigated using STOCHEM-CRI, a global three-dimensional chemistry transport model. Our study shows that the global burden of methanol is 5 Tg. The atmospheric life-time of CH3OH is found to be 6.1 days which falls within the range of previous modelling studies. The impact of peroxy radicals on the photochemical production of CH3OH has been studied and suggests that NMVOCs (non-methane Volatile Organic Compounds) are an important source of both peroxy radicals and CH3OH. The photochemical production routes of CH3OH are found to be 48 Tg/yr, which are higher than the previous studies and contributes significantly to the total global methanol sources of 287 Tg/yr. An additional CH3OH production of 8.2 Tg/yr from the reaction of methyl peroxy radicals (CH3O2) with hydroxyl radicals (OH) could be a significant additional source of CH3OH particularly over the tropical oceans which would lead to a revision of the global sources and life cycle of CH3OH.
Keywords: Methanol; STOCHEM-CRI model; Photochemical source; Global burden; Atmospheric life-time;

Objective. This study explores the statistical relations between the accumulation of heavy metals in moss and natural surface soil and potential influencing factors such as atmospheric deposition by use of multivariate regression-kriging and generalized linear models. Based on data collected in 1995, 2000, 2005 and 2010 throughout Norway the statistical correlation of a set of potential predictors (elevation, precipitation, density of different land uses, population density, physical properties of soil) with concentrations of cadmium (Cd), mercury and lead in moss and natural surface soil (response variables), respectively, were evaluated. Spatio-temporal trends were estimated by applying generalized linear models and geostatistics on spatial data covering Norway. The resulting maps were used to investigate to what extent the HM concentrations in moss and natural surface soil are correlated. Results. From a set of ten potential predictor variables the modelled atmospheric deposition showed the highest correlation with heavy metals concentrations in moss and natural surface soil. Density of various land uses in a 5 km radius reveal significant correlations with lead and cadmium concentration in moss and mercury concentration in natural surface soil. Elevation also appeared as a relevant factor for accumulation of lead and mercury in moss and cadmium in natural surface soil respectively. Precipitation was found to be a significant factor for cadmium in moss and mercury in natural surface soil. The integrated use of multivariate generalized linear models and kriging interpolation enabled creating heavy metals maps at a high level of spatial resolution. The spatial patterns of cadmium and lead concentrations in moss and natural surface soil in 1995 and 2005 are similar. The heavy metals concentrations in moss and natural surface soil are correlated significantly with high coefficients for lead, medium for cadmium and moderate for mercury. From 1995 up to 2010 the modelled moss and natural surface soil estimates indicate a decrease of lead concentration in both moss and natural surface soil. In the case of the moss data the decrease of accumulation is more pronounced. By contrast, the modelled cadmium and mercury concentrations do not exhibit any significant temporal trend. Conclusions. In Europe, there is hardly any nation-wide investigation of statistical correlations between the accumulation of heavy metals in moss and natural surface soil and potential influencing factors such as atmospheric deposition. This study could show that assessments of heavy metal concentrations in natural surface soil could complement biomonitoring with moss but should not replace it since the heavy metal concentrations in mosses reliably traces the spatial pattern of respective atmospheric deposition. Generalized linear models extend established methods for estimating spatial patterns and temporal trends of HM concentration in moss and natural surface soil.
Keywords: Cadmium; Generalized linear models; Geostatistics; Lead; Mercury; Multivariate regression;

Anomalous features of mid-tropospheric CO2 during Indian summer monsoon drought years by Yogesh K. Tiwari; J.V. Revadekar; K. Ravi Kumar (94-103).
In this study, we have examined the impact of droughts on the atmospheric CO2 spatial variability and changes its emission scenario over India. Surface monitoring over India is very sparse and have started recently. Satellite retrievals from AIRS/Aqua during 2004–2011 are used here to understand CO2 variability over India. During recent decade, Indian region witnessed two drought years 2004 and 2009 and no flood. Year 2009 was mega drought for India ever seen, when actual rainfall was approx −23% below the mean rainfall over most part of India. Satellite retrieved mid-tropospheric CO2 indicates increase of about 3 ppm during summer monsoon drought. Enhanced impact of drought conditions is also seen on subsequent seasons, winter (JF) and hot pre-monsoon season (MAM). Post-monsoon season (OND) does not show any clear impact, as rainfall during this season has its own variability quite different than summer monsoon (JJAS) may be compensating changes in CO2 values. Decrease in vegetation and weak circulation patterns during drought conditions may have influences on distribution of CO2 over Indian region.
Keywords: AIRS CO2; Rainfall; Temperature; Vegetation; Indian sub-continent;

Fire environment effects on particulate matter emission factors in southeastern U.S. pine-grasslands by Kevin M. Robertson; Yuch P. Hsieh; Glynnis C. Bugna (104-111).
Particulate matter (PM) emission factors (EFPM), which predict particulate emissions per biomass consumed, have a strong influence on event-based and regional PM emission estimates and inventories. PM < 2.5 μm aerodynamic diameter (PM2.5), regulated for its impacts to human health and visibility, is of special concern. Although wildland fires vary widely in their fuel conditions, meteorology, and fire behavior which might influence combustion reactions, the EFPM2.5 component of emission estimates is typically a constant for the region or general fuel type being assessed. The goal of this study was to use structural equation modeling (SEM) to identify and measure effects of fire environment variables on EFPM2.5 in U.S. pine-grasslands, which contribute disproportionately to total U.S. PM2.5 emissions. A hypothetical model was developed from past literature and tested using 41 prescribed burns in northern Florida and southern Georgia, USA with varying years since previous fire, season of burn, and fire direction of spread. Measurements focused on EFPM2.5 from flaming combustion, although a subset of data considered MCE and smoldering combustion. The final SEM after adjustment showed EFPM2.5 to be higher in burns conducted at higher ambient temperatures, corresponding to later dates during the period from winter to summer and increases in live herbaceous vegetation and ambient humidity, but not total fine fuel moisture content. Percentage of fine fuel composed of pine needles had the strongest positive effect on EFPM2.5, suggesting that pine timber stand volume may significantly influence PM2.5 emissions. Also, percentage of fine fuel composed of grass showed a negative effect on EFPM2.5, consistent with past studies. Results of the study suggest that timber thinning and frequent prescribed fire minimize EFPM2.5 and total PM2.5 emissions on a per burn basis, and that further development of PM emission models should consider adjusting EFPM2.5 as a function of common land use variables, including pine timber stocking, surface vegetation composition, fire frequency, and season of burn.
Keywords: Prescribed fire; Biomass burning; Fire behavior; Combustion efficiency; Structural equation model;

Hourly atmospheric measurements of halocarbons and chlorofluorocarbon (CFC) replacements were conducted at an urban site of Lukang, Changhua, in central Taiwan from May to August, 2013. The temporal distribution of different groups of halocarbons in the Lukang urban atmosphere, including chlorofluorocarbons (CFCs), Chlorodifluoromethane (HCFC-22), Bromochlorodifluoromethane (Halon-1211), and other chlorinated compounds, is presented and discussed. The concentrations (mixing ratios) of HCFC-22, Dichlorodifluoromethane (CFC-12), Halon-1211, Trichlorofluoromethane (CFC-11), Dichloromethane (CH2Cl2), and Trichloroethylene (TCE) were enhanced with respect to the local background levels; the atmospheric mixing ratio of carbon tetrachloride (CCl4) was slightly higher than its local background level; on the other hand, 1,1,2-Trichlorotrifluoroethane (CFC-113) was relatively uniform and not very different from background atmospheric level in non-urban areas. Among these compounds, HCFC-22, Halon-1211 and the halogenated compounds, CH2Cl2 and TCE, used as solvents were strongly enhanced. The average mixing ratio of Halon-1211 was higher than the local background of ∼4.5 ppt by ∼60% although Halon-1211 production had been phased out by 1996.Hourly average mixing ratios of halocarbons (HCFC-22, CFC-12, Halon-1211, CFC-11, CH2Cl2, and TCE) illustrated a distinct diurnal cycle characterized with a pattern of elevated mixing ratio and large mixing ratio variability amplitude at night relative to that in daytime. Although emission sources of these halocarbons were complex, hourly average mixing ratios for most of these high variability halocarbons peaked at ∼5:00 AM when the hourly average wind speed reached the minimum value of the day; by contrast, the hourly average mixing ratio of CO peaked at ∼8:30 AM when the ambient atmospheric wind condition was strongly influenced by sea breezes during the traffic rush hours. This phenomenon revealed that meteorological factors predominated the distribution of halocarbon mixing ratio in the urban atmosphere and the traffic emission of CFC-12 derived from old vehicles manufactured before 1994 was insignificant to the CFC-12 mixing ratio in the urban atmosphere. The meteorological condition of nighttime atmospheric temperature inversion and low wind speed facilitated the accumulation of terrestrial airborne pollutants near the ground; consequently the hourly average mixing ratios at night were higher than those in daytime by up to ∼2% (CFC-11), ∼7% (CFC-12), ∼75% (HCFC-22), ∼72% (Halon-1211), ∼280% (CH2Cl2), and ∼155% (TCE).
Keywords: Halocarbons; CFC replacements; Diurnal variability; Enhancement; Lukang;

Needle trap samplers (NTS) are packed with 80–100 mesh divinylbenzene (DVB) particles to extract indoor volatile organic compounds (VOCs). This study compared extraction efficiency between an NTS and a commercially available 100 μm polydimethylsiloxane-solid phase microextration (PDMS-SPME) fiber sampler used to sample gaseous products in heated tea tree essential oil in different evaporation modes, which were evaporated respectively by free convection inside a glass evaporation dish at 27 °C, by evaporation diffuser at 60 °C, and by thermal ceramic wicks at 100 °C. The experimental results indicated that the NTS performed better than the SPME fiber samplers and that the NTS primarily adsorbed 5.7 ng ethylbenzene, 5.8 ng m/p-xylenes, 11.1 ng 1,2,3-trimethylbenzene, 12.4 ng 1,2,4-trimethylbenzene and 9.99 ng 1,4-diethylbenzene when thermal ceramic wicks were used to evaporate the tea tree essential oil during a 1-hr evaporation period. The experiment also indicated that the temperature used to heat the essential oils should be as low as possible to minimize irritant VOC by-products. If the evaporation temperature does not exceed 100 °C, the concentrations of main by-products trimethylbenzene and diethylbenzene are much lower than the threshold limit values recommended by the National Institute for Occupational Safety and Health (NIOSH).
Keywords: Solid phase microextraction; Needle trap sampler; Sampling; Indoor air; Volatile organic compounds; Essential oil;

On the relation between tree crown morphology and particulate matter deposition on urban tree leaves: A ground-based LiDAR approach by Jelle Hofman; Harm Bartholomeus; Kim Calders; Shari Van Wittenberghe; Karen Wuyts; Roeland Samson (130-139).
Urban dwellers often breathe air that does not meet the European and WHO standards. Next to legislative initiatives to lower atmospheric pollutants, much research has been conducted on the potential of urban trees as mitigation tool for atmospheric particles. While leaf-deposited dust has shown to vary significantly throughout single tree crowns, this study evaluated the influence of micro-scale tree crown morphology (leaf density) on the amount of leaf-deposited dust. Using a ground-based LiDAR approach, the three-dimensional tree crown morphology was obtained and compared to gravimetric measurements of leaf-deposited dust within three different size fractions (>10, 3–10 and 0.2–3 μm). To our knowledge, this is the first application of ground-based LiDAR for comparison with gravimetric results of leaf-deposited particulate matter. Overall, an increasing leaf density appears to reduce leaf-deposition of atmospheric particles. This might be explained by a reduced wind velocity, suppressing turbulent deposition of atmospheric particles through impaction. Nevertheless, the effect of tree crown morphology on particulate deposition appears almost negligible (7% AIC decrease) compared to the influence of physical factors like height, azimuth and tree position.
Keywords: Particulate matter; Urban green; Light detection and ranging (LiDAR); Leaf-deposition; Tree morphology;

Concentrations of organobromine (BFRs), organochlorine (CFRs) and organophosphate esters flame retardants and plasticizers (PFRs) in air were monitored for over one year at an urban site in Toronto, Canada during 2010–2011. The mean value for polybrominated diphenyl ethers (BDEs) (gas + particle phase) was 38 pg/m3 with BDE-47 and BDE-99 as the dominant congeners. The mean concentrations in air for ∑non-BDE (BFRs and CFRs), was 9.6 pg/m3 – about four times lower than the BDEs. The brominated FRs: TBP-AE, BTBPE, EH-TBB, BEH-TEBP and the chlorinated syn- and anti-DP were detected frequently, ranging from 87% to 96%. Highest concentrations in air among all flame retardant classes were observed for the Σ-PFRs. The yearly mean concentration in air for ΣPFRs was 2643 pg/m3 with detection frequency higher than 80%. Except for TBP-AE and b- DBE-DBCH, non-BDEs (BFRs, CFRs and PFRs) were mainly associated with the particle phase. BDE concentrations in air were positively correlated with temperature indicating that volatilization from local sources was an important factor controlling levels in air. This correlation did not hold for most BFRs, CFRs and PFRs which were mainly on particles. For these compounds, air concentrations in Toronto are likely related to emissions from point sources and advective inputs. This study highlights the importance of urban air monitoring for FRs. Urban air can be considered a sentinel for detecting changes in the use and application of FRs in commercial products.
Keywords: Flame retardants; Air concentrations; Organobromine flame retardants; Organophosphate; NBFRs; BFRs; OPFRs;

Near source modeling is needed to assess primary and secondary pollutant impacts from single sources and single source complexes. Source–receptor relationships need to be resolved from tens of meters to tens of kilometers. Dispersion models are typically applied for near-source primary pollutant impacts but lack complex photochemistry. Photochemical models provide a realistic chemical environment but are typically applied using grid cell sizes that may be larger than the distance between sources and receptors. It is important to understand the impacts of grid resolution and sub-grid plume treatments on photochemical modeling of near-source primary pollution gradients. Here, the CAMx photochemical grid model is applied using multiple grid resolutions and sub-grid plume treatment for SO2 and compared with a receptor mesonet largely impacted by nearby sources approximately 3–17 km away in a complex terrain environment. Measurements are compared with model estimates of SO2 at 4- and 1-km resolution, both with and without sub-grid plume treatment and inclusion of finer two-way grid nests. Annual average estimated SO2 mixing ratios are highest nearest the sources and decrease as distance from the sources increase. In general, CAMx estimates of SO2 do not compare well with the near-source observations when paired in space and time. Given the proximity of these sources and receptors, accuracy in wind vector estimation is critical for applications that pair pollutant predictions and observations in time and space. In typical permit applications, predictions and observations are not paired in time and space and the entire distributions of each are directly compared. Using this approach, model estimates using 1-km grid resolution best match the distribution of observations and are most comparable to similar studies that used dispersion and Lagrangian modeling systems. Model-estimated SO2 increases as grid cell size decreases from 4 km to 250 m. However, it is notable that the 1-km model estimates using 1-km meteorological model input are higher than the 1-km model simulation that used interpolated 4-km meteorology. The inclusion of sub-grid plume treatment did not improve model skill in predicting SO2 in time and space and generally acts to keep emitted mass aloft.
Keywords: CAMx; Dispersion; Air quality modeling; Grid resolution; Sub-grid plume; Martins Creek;

Atmospheric reactions between E,E-2,4-hexadienal and OH, NO3 radicals and Cl atoms by I. Colmenar; P. Martín; B. Cabañas; S. Salgado; E. Martínez (159-167).
E,E-2,4-Hexadienal is an α,β-unsaturated aldehyde whose presence in the atmosphere can arise from different sources. The rate coefficients for the reaction of this compound with Cl atoms, OH and NO3 radicals and for the photolysis process have been determined at atmospheric pressure and room temperature. A relative method has been developed with a Fourier Transform Infrared spectrometer (FTIR) or Solid Phase Micro Extraction fiber/chromatography-mass spectrometer (SPME/GC-MS) used as sampling/detection techniques. The absolute rate coefficients k (in units of cm3 molecule−1 s−1) obtained for Cl, OH and NO3 were (3.98 ± 0.44) × 10−10, (6.78 ± 0.47) × 10−11 and (1.34 ± 0.56) × 10−12, respectively. An estimation of the rate coefficient for the reaction of E,E-2,4-hexadienal with OH and NO3 radicals and Cl atoms has been carried out using correlations and SAR methods. The SAR substituent factor for the –C(O)H group, [G-(C(O)H)] = 3.58 × 10−3, has been obtained. This group reactivity factor allows the rate coefficients to be estimated for the reaction of unsaturated aldehydes with NO3 radicals. The results of this study confirm that the reaction of unsaturated aldehydes with Cl atoms is very fast and that the structure of the compound has little influence, with the influence of the structure being more marked in the case of the OH radical reaction and relatively large for the NO3 reaction. The results are consistent with a mechanism in which the first stage is addition of an atom or radical to the double bond of E,E-2,4-hexadienal as the main reaction channel and, to a minor extent, the abstraction of aldehydic hydrogen. These are the first data reported for the atmospheric reactions of this compound and this study therefore contributes to the database of rate coefficients for atmospheric reactions.Display Omitted
Keywords: E,E-2,4-Hexadienal; Gas-phase reactions; Rate coefficients; Atmospheric oxidants; Relative method;

Indian cities are among the most polluted areas globally, yet assessments of short term mortality impacts due to pollution have been limited. Furthermore, studies examining temperature – pollution interactions on mortality are largely absent. Addressing this gap remains important in providing research evidence to better link health outcomes and air quality standards for India. Daily all-cause mortality, temperature, humidity and particulate matter less than 10 microns (PM10) data were collected for five cities – Ahmedabad, Bangalore, Hyderabad, Mumbai and Shimla spanning 2005–2012. Poisson regression models were developed to study short term impacts of PM10 as well as temperature – pollution interactions on daily all-cause mortality. We find that excess risk of mortality associated with a 10 μg/m3 PM10 increase is highest for Shimla (1.36%, 95% CI = −0.38%–3.1%) and the least for Ahmedabad (0.16%, 95% CI = −0.31%–0.62%). The corresponding values for Bangalore, Hyderabad and Mumbai are 0.22% (−0.04%–0.49%), 0.85% (0.06%–1.63%) and 0.2% (0.1%–0.3%) respectively. The relative health benefits of reducing pollution are higher for cleaner cities (Shimla) as opposed to dirtier cities (Mumbai). Overall we find that temperature and pollution interactions do not significantly impact mortality for the cities studied. This is one of the first multi-city studies that assess heterogeneity of air pollution impacts and possible modification due to temperature in Indian cities that are spread across climatic regions and topographies. Our findings highlight the need for pursuing stringent pollution control policies in Indian cities to minimize health impacts.
Keywords: Particulate matter; PM10; Health effect; Temperature-pollution interactions; Time-series; GAM;

A quantitative estimation of the exhaust, abrasion and resuspension components of particulate traffic emissions using electron microscopy by Stephan Weinbruch; Annette Worringen; Martin Ebert; Dirk Scheuvens; Konrad Kandler; Ulrich Pfeffer; Peter Bruckmann (175-182).
The contribution of the three traffic-related components exhaust, abrasion, and resuspension to kerbside and urban background PM10 and PM1 levels was quantified based on the analysis of individual particles by scanning electron microscopy. A total of 160 samples was collected on 38 days between February and September 2009 at a kerbside and an urban background station in the urban/industrial Ruhr area (Germany). Based on size, morphology, chemical composition and stability under electron bombardment, the 111,003 particles studied in detail were classified into the following 14 particle classes: traffic/exhaust, traffic/abrasion, traffic/resuspension, carbonaceous/organic, industry/metallurgy, industry/power plants, secondary particles, (aged) sea salt, silicates, Ca sulfates, carbonates, Fe oxides/hydroxides, biological particles, and other particles. The traffic/exhaust component consists predominantly of externally mixed soot particles and soot internally mixed with secondary particles. The traffic/abrasion component contains all particles with characteristic tracer elements (Fe, Cu, Ba, Sb, Zn) for brake and tire abrasion. The traffic/resuspension component is defined by the mixing state and comprises all internally mixed particles with a high proportion of silicates or Fe oxides/hydroxides which contain soot or abrasion particles as minor constituent. In addition, silicates and Fe oxides/hydroxides internally mixed with chlorine and sulphur containing particles were also assigned to the traffic/resuspension component. The total contribution of traffic to PM10 was found to be 27% at the urban background station and 48% at the kerbside station, the corresponding values for PM1 are 15% and 39%. These values lie within the range reported in previous literature. The relative share of the different traffic components for PM10 at the kerbside station was 27% exhaust, 15% abrasion, and 58% resuspension (38%, 8%, 54% for PM1). For the urban background, the following relative shares were obtained for PM10: 22% exhaust, 22% abrasion and 56% resuspension (40%, 27%, 33% for PM1). Compared to previous publications we have observed a significantly lower portion of exhaust particles and a significantly higher portion of resuspension particles. The high abundance of resuspension particles underlines their significance for the observed adverse health effects of traffic emissions and for mitigation measures.
Keywords: Particulate matter; Urban air pollution; Traffic; Electron microscopy;

Rate coefficients for the reaction of Cl atoms with limonene (C10H16) were measured between 278–350 K and 800 Torr of N2, using the relative rate technique, with 1,3-butadiene (C4H6), n-nonane (C9H20), and 1-pentene (C5H10) as reference compounds. Cl atoms were generated by UV photolysis of oxalyl chloride ((COCl)2) at 254 nm. A gas chromatograph equipped with a flame ionization detector (GC-FID) was used for quantitative analysis of the organics. The rate coefficient for the reaction of Cl atoms with limonene at 298 K was measured to be (8.65 ± 2.44) × 10−10 cm3 molecule−1 s−1. The rate coefficient is an average value of the measurements, with two standard deviations as the quoted error, including uncertainties in the reference rate coefficients. The kinetic data obtained over the temperature range of 278–350 K were used to derive the following Arrhenius expression: k(T) = (9.75 ± 4.1) × 10−11 exp[(655 ± 133)/T] cm3 molecule−1 s−1. Theoretical kinetic calculations were also performed for the title reaction using conventional transition state theory (CTST) in combination with G3(MP2) theory between 275 and 400 K. The kinetic data obtained over the temperature range of 275–400 K were used to derive an Arrhenius expression: k(T) = (7.92 ± 0.82) × 10−13 exp[(2310 ± 34)/T] cm3 molecule−1 s−1. The addition channels contributes maximum to the total reaction and H-abstraction channels can be neglected in the range of studied pressures. The Atmospheric lifetime (τ) of limonene due to its reaction with Cl atoms was estimated and concluded that the reaction with chlorine atoms can be an effective tropospheric loss pathway in the marine boundary layer and in coastal urban areas.Display Omitted
Keywords: Limonene; Cl atoms; Rate coefficient; Relative rate technique; Conventional transition-state theory (CTST); Atmospheric lifetime;

Particle number (PN) concentrations and particle size distributions (PSD) in the size range of 5.5–350 nm were continuously measured from 22 December 2010 to 20 January 2011 at an urban site in Hong Kong when northeastern monsoon prevailed. Apart from the PN peaks appeared in traffic rush hours (i.e. 08:00–09:00 and 17:00–18:00), a distinct peak of PN concentrations in the afternoon (11:00–16:00) was observed during the sampling period. Concurrent measurement data of PSD, ozone (O3) and proxy sulfuric acid (H2SO4) concentrations revealed that the afternoon peaks observed were likely due to new particle formation (NPF) via photochemical reactions. These NPF events were frequently observed under a clean and dry weather in Hong Kong. The occurrence of NPF was closely associated with high solar radiation (SR), low relative humidity (RH) and low condensation sink (CS) in the atmosphere. Besides the NPF events, we also found four nucleation mode particle burst events, typically with increased number concentrations of nucleation mode particles (Nnuc) without growth to larger size particles. These burst events were generally accompanied by high-level primary air pollutants, i.e. sulfur dioxide (SO2), nitrogen oxide (NOx) and carbon monoxide (CO), low SR and high CS conditions. The very different characteristics of the burst events from those of the NPF events indicated that these nucleation mode particle burst events were not caused by the photochemical reactions, but by the primary emission from the local combustion source(s).
Keywords: Nucleation mode particle; New particle formation; Primary emission; Nucleation burst;

UV-induced N2O emission from plants by Dan Bruhn; Kristian R. Albert; Teis N. Mikkelsen; Per Ambus (206-214).
Nitrous oxide (N2O) is an important long-lived greenhouse gas and precursor of stratospheric ozone-depleting mono-nitrogen oxides. The atmospheric concentration of N2O is persistently increasing; however, large uncertainties are associated with the distinct source strengths. Here we investigate for the first time N2O emission from terrestrial vegetation in response to natural solar ultra violet radiation.We conducted field site measurements to investigate N2O atmosphere exchange from grass vegetation exposed to solar irradiance with and without UV-screening. Further laboratory tests were conducted with a range of species to study the controls and possible loci of UV-induced N2O emission from plants.Plants released N2O in response to natural sunlight at rates of c. 20–50 nmol m−2  h−1, mostly due to the UV component. The emission response to UV-A is of the same magnitude as that to UV-B. Therefore, UV-A is more important than UV-B given the natural UV-spectrum at Earth's surface. Plants also emitted N2O in darkness, although at reduced rates. The emission rate is temperature dependent with a rather high activation energy indicative for an abiotic process. The prevailing zone for the N2O formation appears to be at the very surface of leaves. However, only c. 26% of the UV-induced N2O appears to originate from plant-N. Further, the process is dependent on atmospheric oxygen concentration. Our work demonstrates that ecosystem emission of the important greenhouse gas, N2O, may be up to c. 30% higher than hitherto assumed.
Keywords: Epicuticular wax; Greenhouse gas; Nitrous oxide; Plant; Ultra violet radiation; Vegetation;

The number of motorcycles has increased significantly in Asia, Africa, Latin American and Europe in recent years due to their reasonable price, high mobility and low fuel consumption. However, motorcycles can emit significant amounts of air pollutants; therefore, the emission characteristics of motorcycles are an important consideration for the implementation of control measures for motorcycles in urban areas. Results of this study indicate that most volatile organic compound (VOC) emission factors were in the range of several decades mg/km during on-road driving. Toluene, isopentane, 1,2,4-trimethylbenzene, m,p-xylene, and o-xylene were the most abundant VOCs in motorcycle exhaust, with emission factors of hundreds mg/km. Motorcycle exhaust was 15.4 mg/km for 15 carbonyl species. Acetaldehyde, acetone, formaldehyde and benzaldehyde were the major carbonyl species, and their emission factors ranged from 1.4 to 3.5 mg/km 1,2,4-trimethylbenzene, m,p-xylene, 1-butene, toluene, o-xylene, 1,2,3-trimethylbenzene, propene, 1,3,5-trimethylbenzene, isoprene, m-diethylbenzene, and m-ethyltoluene were the main ozone formation potential (OFP) species, and their OFP was 200 mg-O3/km or higher.
Keywords: Emission factor; Real world driving mode; On-board emission measurements; Carbonyls; Ozone formation potential (OFP);

This study elucidates the seasonality in aerosol vertical profiles acquired using LiDAR measurements and compares it with the CALIPSO level-2 data products over central Himalayas. A detailed analysis on the vertical distribution of aerosols over the central Himalayan region is carried out during different seasons. We present intermittent observations that were made over Manora Peak (29.36° N, 79.45° E, 1951 m, AMSL) Nainital, during March 2012 to May 2013 amounting to a total of 360 h of LiDAR operation, out of which 57 suitable cases were subjected to further analysis. Aerosol loading in the vertical column was found to be highest with 3.40 (Mm sr)−1 at 3.3 km during the spring and summer seasons (MAMJ-2012), and the lowest with 0.48 (Mm sr)−1 at 2.5 km, during winter season (DJF 2012–13). The aerosol layer reaches to the maximum altitude of 5.6 km in the period of MAMJ-2012 and a minimum at 2.8 km in the winter (DJF). The highest value (124 Mm 1) of extinction coefficient is found at 3.3 km, during MAMJ-2012 and minimum (7 Mm 1) at 2.5 km during the winter season. A comparison of ground based LiDAR observations with the CALIPSO satellite derived aerosol backscatter profiles has been carried out for 37 suitable cases. To determine the LiDAR ratio, AOD measurements from MODIS were used as constrain. The mean percent bias for different seasons is found to be +18 ± 42%, +22 ± 28%, +32 ± 36% and +18 ± 51% for MAMJ-2012, SON-2012, DJF-2012–13 and MAM-2013 respectively.
Keywords: LiDAR; Aerosol backscatter; LiDAR ratio; Long range transport; CALIPSO; Bias;

Twenty years of continuous high time resolution volatile organic compound monitoring in the United Kingdom from 1993 to 2012 by R.G. Derwent; J.I.R. Dernie; G.J. Dollard; P. Dumitrean; R.F. Mitchell; T.P. Murrells; S.P. Telling; R.A. Field (239-247).
Continuous, high frequency observations of C2 – C8 hydrocarbons began in the United Kingdom in 1993 and have continued through to the present day at a range of kerbside, urban background and rural locations. Most of the monitored hydrocarbons have shown dramatic declines in concentrations over the study period, with present levels close to an order of magnitude below their levels in the 1990s. The concentrations of 23 selected hydrocarbons have been aggregated up to give an estimate of the total VOC concentrations. These annual values have shown an exponential decline of −18% yr−1 at the London Marylebone Road kerbside site, −11% yr−1 at the London Eltham urban background site and −22% yr−1 at the rural Harwell site. Similar declines have been reported in UK road transport VOC emissions, demonstrating how the VOC emission inventories have apparently captured the salient features influencing real-world VOC emissions over the 1994–2012 period.
Keywords: VOCs; Hydrocarbons; Monitoring; VOC emission inventories;

Analyzing source apportioned methane in northern California during Discover-AQ-CA using airborne measurements and model simulations by Matthew S. Johnson; Emma L. Yates; Laura T. Iraci; Max Loewenstein; Jovan M. Tadić; Kevin J. Wecht; Seongeun Jeong; Marc L. Fischer (248-256).
This study analyzes source apportioned methane (CH4) emissions and atmospheric mixing ratios in northern California during the Discover-AQ-CA field campaign using airborne measurement data and model simulations. Source apportioned CH4 emissions from the Emissions Database for Global Atmospheric Research (EDGAR) version 4.2 were applied in the 3-D chemical transport model GEOS-Chem and analyzed using airborne measurements taken as part of the Alpha Jet Atmospheric eXperiment over the San Francisco Bay Area (SFBA) and northern San Joaquin Valley (SJV). During the time period of the Discover-AQ-CA field campaign EDGAR inventory CH4 emissions were ∼5.30 Gg day−1 (Gg = 1.0 × 109 g) (equating to ∼1.90 × 103 Gg yr−1) for all of California. According to EDGAR, the SFBA and northern SJV region contributes ∼30% of total CH4 emissions from California. Source apportionment analysis during this study shows that CH4 mixing ratios over this area of northern California are largely influenced by global emissions from wetlands and local/global emissions from gas and oil production and distribution, waste treatment processes, and livestock management. Model simulations, using EDGAR emissions, suggest that the model under-estimates CH4 mixing ratios in northern California (average normalized mean bias (NMB) = −5.2% and linear regression slope = 0.20). The largest negative biases in the model were calculated on days when large amounts of CH4 were measured over local emission sources and atmospheric CH4 mixing ratios reached values >2.5 parts per million. Sensitivity emission studies conducted during this research suggest that local emissions of CH4 from livestock management processes are likely the primary source of the negative model bias. These results indicate that a variety, and larger quantity, of measurement data needs to be obtained and additional research is necessary to better quantify source apportioned CH4 emissions in California.
Keywords: Methane; Source apportionment; Emission inventory; Livestock emissions;

Seasonal and spatial variation of trace elements in multi-size airborne particulate matters of Beijing, China: Mass concentration, enrichment characteristics, source apportionment, chemical speciation and bioavailability by Jiajia Gao; Hezhong Tian; Ke Cheng; Long Lu; Yuxuan Wang; Ye Wu; Chuanyong Zhu; Kaiyun Liu; Junrui Zhou; Xingang Liu; Jing Chen; Jiming Hao (257-265).
The seasonal and spatial variation characteristics of 19 elements (Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sb, Se, Zn) in TSP/PM10/PM2.5 samples were investigated, which were collected from April 2011 to January 2012 simultaneously at an urban downtown site, a traffic roadside site, a suburban site, and a rural site in Beijing. The elevated concentrations of several toxic trace elements (As, Cd, Mn, Ni, Pb, etc.) in particles revealed that the contamination of toxic elements in Beijing could not be neglected. Positive matrix factorization method (PMF) was applied for source apportionment of trace elements in PM, and three factors (crust related sources, combustion sources, and traffic and steel industrial related sources) were identified. Furthermore, the chemical speciation and bioavailability of various elements were identified by applying European Community Bureau of Reference (BCR) procedure. Our results showed that eight toxic elements (As, Cd, Cr, Cu, Ni, Pb, Sb and Zn) exhibited higher mobility in PM2.5 than in PM10. Notably, elements of As, Cd, Pb and Zn were presented with higher mobility than the other elements, and these elements were lightly to release into the environment and easily available to human body. Additionally, As, Cd, Pb and Zn also accounted for higher percentages in the bound to mobile fractions at the central urban areas of Beijing. Therefore, special concerns should be paid to these toxic trace elements which had relatively high mobility in fine particles, when planning and implementing the comprehensive air pollution mitigation policies in Beijing.
Keywords: Atmospheric aerosol; Trace elements; Positive matrix factorization (PMF); Enrichment factor (EF); Chemical speciation;

A modeling analysis of alternative primary and secondary US ozone standards in urban and rural areas by Uarporn Nopmongcol; Chris Emery; Tanarit Sakulyanontvittaya; Jaegun Jung; Eladio Knipping; Greg Yarwood (266-276).
This study employed the High-Order Decoupled Direct Method (HDDM) of sensitivity analysis in a photochemical grid model to determine US anthropogenic emissions reductions required from 2006 levels to meet alternative US primary (health-based) and secondary (welfare-based) ozone (O3) standards. Applying the modeling techniques developed by Yarwood et al. (2013), we specifically evaluated sector-wide emission reductions needed to meet primary standards in the range of 60–75 ppb, and secondary standards in the range of 7–15 ppm-h, in 22 cities and at 20 rural sites across the US for NOx-only, combined NOx and VOC, and VOC-only scenarios. Site-specific model biases were taken into account by applying adjustment factors separately for the primary and secondary standard metrics, analogous to the US Environmental Protection Agency's (EPA) relative response factor technique. Both bias-adjusted and unadjusted results are presented and analyzed. We found that the secondary metric does not necessarily respond to emission reductions the same way the primary metric does, indicating sensitivity to their different forms. Combined NOx and VOC reductions are most effective for cities, whereas NOx-only reductions are sufficient at rural sites. Most cities we examined require more than 50% US anthropogenic emission reductions from 2006 levels to meet the current primary 75 ppb US standard and secondary 15 ppm-h target. Most rural sites require less than 20% reductions to meet the primary 75 ppb standard and less than 40% reductions to meet the secondary 15 ppm-h target. Whether the primary standard is protective of the secondary standard depends on the combination of alternative standard levels. Our modeling suggests that the current 75 ppb standard achieves a 15 ppm-h secondary target in most (17 of 22) cities, but only half of the rural sites; the inability for several western cities and rural areas to achieve the seasonally-summed secondary 15 ppm-h target while meeting the 75 ppb primary target is likely driven by higher background O3 that is commonly reported in the western US. However, a 70 ppb primary standard is protective of a 15 ppm-h secondary standard in all cities and 18 of 20 rural sites we examined, and a 60 ppb primary standard is protective of a 7 ppm-h secondary standard in all cities and 19 of 20 rural sites. If EPA promulgates separate primary and secondary standards, exceedance areas will need to develop and demonstrate control strategies to achieve both. This HDDM analysis provides an illustrative screening assessment by which to estimate emissions reductions necessary to satisfy both standards.
Keywords: Ozone; Photochemical modeling; HDDM; US emissions; US ozone standard; W126;

Evaluation of impacts of trees on PM2.5 dispersion in urban streets by Sijia Jin; Jiankang Guo; Stephen Wheeler; Liyan Kan; Shengquan Che (277-287).
Reducing airborne particulate matter (PM), especially PM2.5 (PM with aerodynamic diameters of 2.5 μm or less), in urban street canyons is critical to the health of central city population. Tree-planting in urban street canyons is a double-edged sword, providing landscape benefits while inevitably resulting in PM2.5 concentrating at street level, thus showing negative environmental effects. Thereby, it is necessary to quantify the impact of trees on PM2.5 dispersion and obtain the optimum structure of street trees for minimizing the PM2.5 concentration in street canyons. However, most of the previous findings in this field were derived from wind tunnel or numerical simulation rather than on-site measuring data. In this study, a seasonal investigation was performed in six typical street canyons in the residential area of central Shanghai, which has been suffering from haze pollution while having large numbers of green streets. We monitored and measured PM2.5 concentrations at five heights, structural parameters of street trees and weather. For tree-free street canyons, declining PM2.5 concentrations were found with increasing height. However, in presence of trees the reduction rate of PM2.5 concentrations was less pronounced, and for some cases, the concentrations even increased at the top of street canyons, indicating tree canopies are trapping PM2.5. To quantify the decrease of PM2.5 reduction rate, we developed the attenuation coefficient of PM2.5 (PMAC). The wind speed was significantly lower in street canyons with trees than in tree-free ones. A mixed-effects model indicated that canopy density (CD), leaf area index (LAI), rate of change of wind speed were the most significant predictors influencing PMAC. Further regression analysis showed that in order to balance both environmental and landscape benefits of green streets, the optimum range of CD and LAI was 50%–60% and 1.5–2.0 respectively. We concluded by suggesting an optimized tree-planting pattern and discussing strategies for a better green streets planning and pruning.
Keywords: PM2.5; Air pollution; Urban street canyon; Canopy density; Leaf area index; Wind speed; Green street planning;

Partially-irreversible sorption of formaldehyde in five polymers by Wei Ye; Steven S. Cox; Xiaomin Zhao; Charles E. Frazier; John C. Little (288-297).
Due to its environmental ubiquity and concern over its potential toxicity, the mass-transfer characteristics of formaldehyde are of critical importance to indoor air quality research. Previous studies have suggested that formaldehyde mass transfer in polymer is partially irreversible. In this study, mechanisms that could cause the observed irreversibility were investigated. Polycarbonate and four other polymeric matrices were selected and subjected to formaldehyde sorption/desorption cycles. Mass transfer of formaldehyde was partially irreversible in all cases, and three potential mechanisms were evaluated. First, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis was used to investigate possible formaldehyde polymerization on polymer surfaces. ATR-FTIR showed no detectable paraformaldehyde or formaldehyde on the film surfaces that had been exposed to formaldehyde and air. ATR-FTIR did detect aliphatic acids suggesting oxidation had occurred on film surfaces as a result of exposure to formaldehyde. However, additional study suggested that air is not the primary cause for irreversibility. Second, statistical physics theory was tested as a possible explanation. According to this theory, reversible and irreversible sorption could be taking place simultaneously. The irreversible fraction should be constant during sorption and the fraction could be determined by performing a complete sorption/desorption test. The sorption/desorption data was consistent with this theory. Third, chemisorption was considered as another possible cause for irreversibility. Extraction/fluorimetry testing of post-sorption and post-desorption polymer films showed measurable quantities of formaldehyde suggesting that some of the chemisorbed formaldehyde was reversible at the higher extraction temperature. Further quantitative study on chemical reaction products is needed.
Keywords: Polycarbonate; Statistical physics; ATR-FTIR; Extraction; Physisorption; Chemisorption;

Seasonal characteristics of biogenic and anthropogenic isoprene in tropical–subtropical urban environments by Chih-Chung Chang; Jia-Lin Wang; Shih-Chun Candice Lung; Chih-Yuan Chang; Po-Ju Lee; Clock Chew; Wei-Cheng Liao; Wei-Nai Chen; Chang-Feng Ou-Yang (298-308).
Measurements of atmospheric isoprene and other selected volatile organic compounds (VOCs) were conducted in Taipei, a tropical–subtropical metropolis, to investigate diurnal variations, seasonal diversity and spatial differences in terms of the levels and sources of isoprene. Our study also investigated the responses of biogenic isoprene to both light flux and temperature in real urban settings that have a variety of plant species and traffic volumes. The robust ratio of isoprene/1,3-butadiene obtained from pure traffic emissions was used as a gauge to separate biogenic isoprene from traffic emissions. The four seasonal measurements at a typical urban site in the city showed that biogenic contributions overwhelmed their anthropogenic counterparts in summer and dominated the daytime isoprene levels in spring and autumn. Even in winter, biogenic sources still contributed a non-negligible fraction of approximately 44% to daytime isoprene. Furthermore, the concentration contour of isoprene extrapolated from the data at 38 sites throughout the city revealed that high levels of biogenic isoprene were generally a widespread phenomenon in summer in the tropical–subtropical city. A three-dimensional plot of the isoprene/1,3-butadiene ratio, ambient temperatures and radiation flux showed a temperature threshold of biogenic isoprene emissions, beyond which the biogenic contribution began to increase exponentially with enhanced ambient temperature. However, when the ambient temperature was below the threshold, there was no or negligible biogenic contribution to the ambient isoprene, regardless of the strength of the radiation flux. The temperature threshold (approximately 17–21 °C) of isoprene emissions in the tropical–subtropical city was much higher than the thresholds in cities and areas at temperate latitudes, indicating that the adaptation of vegetation to different temperature zones via isoprene emission may be characteristic.
Keywords: Isoprene; BVOC; Vehicular tracer; SOA; Ozone; Urban air;

Spatial and temporal differences in traffic-related air pollution in three urban neighborhoods near an interstate highway by Allison P. Patton; Jessica Perkins; Wig Zamore; Jonathan I. Levy; Doug Brugge; John L. Durant (309-321).
Relatively few studies have characterized differences in intra- and inter-neighborhood traffic-related air pollutant (TRAP) concentrations and distance-decay gradients in neighborhoods along an urban highway for the purposes of exposure assessment. The goal of this work was to determine the extent to which intra- and inter-neighborhood differences in TRAP concentrations can be explained by traffic and meteorology in three pairs of neighborhoods along Interstate 93 (I-93) in the metropolitan Boston area (USA). We measured distance-decay gradients of seven TRAPs (PNC, pPAH, NO, NOX, BC, CO, PM2.5) in near-highway (<400 m) and background areas (>1 km) in Somerville, Dorchester/South Boston, Chinatown and Malden to determine whether (1) spatial patterns in concentrations and inter-pollutant correlations differ between neighborhoods, and (2) variation within and between neighborhoods can be explained by traffic and meteorology. The neighborhoods ranged in area from 0.5 to 2.3 km2. Mobile monitoring was performed over the course of one year in each pair of neighborhoods (one pair of neighborhoods per year in three successive years; 35–47 days of monitoring in each neighborhood). Pollutant levels generally increased with highway proximity, consistent with I-93 being a major source of TRAP; however, the slope and extent of the distance-decay gradients varied by neighborhood as well as by pollutant, season and time of day. Spearman correlations among pollutants differed between neighborhoods (e.g., ρ = 0.35–0.80 between PNC and NOX and ρ = 0.11–0.60 between PNC and BC) and were generally lower in Dorchester/South Boston than in the other neighborhoods. We found that the generalizability of near-road gradients and near-highway/urban background contrasts was limited for near-highway neighborhoods in a metropolitan area with substantial local street traffic. Our findings illustrate the importance of measuring gradients of multiple pollutants under different ambient conditions in individual near-highway neighborhoods for health studies involving inter-neighborhood comparisons.Display Omitted
Keywords: Near-highway; Distance-decay gradients; Mobile monitoring; Traffic-related air pollution; Metropolitan Boston (USA);

Urban influence on increasing ozone concentrations in a characteristic Mediterranean agglomeration by M. Escudero; A. Lozano; J. Hierro; J. del Valle; E. Mantilla (322-332).
Air quality in cities has been extensively studied due to the high population density potentially exposed to high levels of pollutants. The main problems in urban areas have been related to particulate matter (PM) and NO2. Less attention has been directed towards O3 because urban levels are generally lower than those recorded in rural areas. The implementation of air quality plans, together with technological improvements, have resulted in reductions of PM and NO2 levels in many European cities. In contrast, urban O3 levels have experimented increases which may respond to declining NO x emission trends. It is therefore necessary to intensify the study of urban O3 and its potential relation with NO x variations. In the agglomeration of Zaragoza (NE Spain), traffic circulation through the centre has dropped by 28.3% since 2008 due to several factors such as the implementation of a mobility plan, the completion of major construction projects and the economic crisis in Spain. The study of this case offers a unique opportunity to evaluate the impact of reductions in NO x emissions on the levels of O3 in a characteristic Mediterranean city. This work analyses the variability and trends of ambient air levels of O3 and NO x in Zaragoza and the Ebro valley from 2007 to 2012. Results demonstrate that, although the main factor explaining O3 variability is still linked to meteorology, changes in NO x emissions strongly influence O3 variability and trends, mainly due to interaction with fresh NO. Specific analysis of the O3 “weekend effect” show a significant correlation (r 2 = 0.81) between the drop of NO concentrations (associated to emissions) and the increment of O3 levels during weekends. Moreover, trend analyses reveal that the decline in NO x emissions in Zaragoza from 2007 to 2012 can be associated with significant increments in O3 levels.
Keywords: Ozone; Urban areas; NO x ; Emission reductions; Weekend effect;

Quantifying uncertainties in pollutant mapping studies using the Monte Carlo method by Yi Tan; Allen L. Robinson; Albert A. Presto (333-340).
Routine air monitoring provides accurate measurements of annual average concentrations of air pollutants, but the low density of monitoring sites limits its capability in capturing intra-urban variation. Pollutant mapping studies measure air pollutants at a large number of sites during short periods. However, their short duration can cause substantial uncertainty in reproducing annual mean concentrations. In order to quantify this uncertainty for existing sampling strategies and investigate methods to improve future studies, we conducted Monte Carlo experiments with nationwide monitoring data from the EPA Air Quality System. Typical fixed sampling designs have much larger uncertainties than previously assumed, and produce accurate estimates of annual average pollution concentrations approximately 80% of the time. Mobile sampling has difficulties in estimating long-term exposures for individual sites, but performs better for site groups. The accuracy and the precision of a given design decrease when data variation increases, indicating challenges in sites intermittently impact by local sources such as traffic. Correcting measurements with reference sites does not completely remove the uncertainty associated with short duration sampling. Using reference sites with the addition method can better account for temporal variations than the multiplication method. We propose feasible methods for future mapping studies to reduce uncertainties in estimating annual mean concentrations. Future fixed sampling studies should conduct two separate 1-week long sampling periods in all 4 seasons. Mobile sampling studies should estimate annual mean concentrations for exposure groups with five or more sites. Fixed and mobile sampling designs have comparable probabilities in ordering two sites, so they may have similar capabilities in predicting pollutant spatial variations. Simulated sampling designs have large uncertainties in reproducing seasonal and diurnal variations at individual sites, but are capable to predict these variations for exposure groups.
Keywords: Uncertainty analysis; Air pollution; Pollutant mapping; Spatial-temporal variation; Long-term exposure;

Dispersed traditional combustion technologies, characterized by inefficient combustion and significant emissions, are widely used in residential cooking and “informal industries” including brick production, food and agricultural product processing operations like drying and cooking operations related to sugarcane juice, milk, food-grain, jute, silk, tea and coffee. In addition, seasonal agricultural residue burning in field is a discontinuous source of significant emissions. Here we estimate fuel consumption in these sectors and agricultural residue burned using detailed technology divisions and survey-based primary data for 2010 and projected between 1996 and 2015. In the residential sector, a decline in the fraction of solid biomass users for cooking from 79% in 1996 to 65% in 2010 was offset by a growing population, leading to a nearly constant population of solid biomass users, with a corresponding increase in the population of LPG users. Emissions from agriculture followed the growth in agricultural production and diesel use by tractors and pumps. Trends in emissions from the informal industries sector followed those in coal combustion in brick kilns. Residential biomass cooking stoves were the largest contributors to emissions of PM2.5, OC, CO, NMVOC and CH4. Highest emitting technologies of BC were residential kerosene wick lamps. Emissions of SO2 were largely from coal combustion in Bull's trench kilns and other brick manufacturing technologies. Diesel use in tractors was the major source of NO x emissions. Uncertainties in emission estimates were principally from highly uncertain emission factors, particularly for technologies in the informal industries.
Keywords: Aerosol; Ozone precursors; Greenhouse gases; Residential sector; Informal industries; Agricultural burning;

Emissions estimation, for research and regulatory applications including reporting to international conventions, needs treatment of detailed technology divisions and high-emitting technologies. Here we estimate Indian emissions, for 1996–2015, of aerosol constituents (PM2.5, BC and OC) and precursor gas SO2, ozone precursors (CO, NOx, NMVOC and CH4) and greenhouse gases (CO2 and N2O), using a common fuel consumption database and consistent assumptions. Six source categories and 45 technologies/activities in the industry and transport sectors were used for estimating emissions for 2010. Mean emission factors, developed at the source-category level, were used with corresponding fuel consumption data, available for 1996–2011, projected to 2015. New activities were included to account for fugitive emissions of NMVOC from chemical and petrochemical industries. Dynamic emission factors, reflecting changes in technology-mix and emission regulations, were developed for thermal power plants and on-road transport vehicles. Modeled emission factors were used for gaseous pollutants for on-road vehicles. Emissions of 2.4 (0.6–7.5) Tg y 1 PM2.5, 0.23 (0.1–0.7) Tg y 1 BC, 0.15 (0.04–0.5) Tg y 1 OC, 7.3 (6–10) Tg y 1 SO2, 19 (7.5–33) Tg y 1 CO, 1.5 (0.1–9) Tg y 1 CH4, 4.3 (2–9) Tg y 1 NMVOC, 5.6 (1.7–15.9) Tg y 1 NOx, 1750 (1397–2231) Tg y 1 CO2 and 0.13 (0.05–0.3) Tg y 1 N2O were estimated for 2015. Significant emissions of aerosols and their precursors were from coal use in thermal power and industry (PM2.5 and SO2), and on-road diesel vehicles (BC), especially superemitters. Emissions of ozone precursors were largely from thermal power plants (NOx), on-road gasoline vehicles (CO and NMVOC) and fugitive emissions from mining (CH4). Highly uncertain default emission factors were the principal contributors to uncertainties in emission estimates, indicating the need for region specific measurements.
Keywords: Short-lived pollutants; Aerosol; Ozone precursors; Greenhouse gases; Uncertainty;

Variability of atmospheric ammonia related to potential emission sources in downtown Toronto, Canada by Qingjing Hu; Leiming Zhang; Greg J. Evans; Xiaohong Yao (365-373).
The variability of atmospheric ammonia (NH3) in downtown Toronto was investigated through the analysis of 24 hr integrated denuder NH3 samples collected at a site above a street canyon every third day from July 2003 to September 2011 (Dataset 1). The measured NH3 mixing ratios ranged from below the detection limit to 14.7 ppb during the eight-year period. Distinctive seasonal variations were observed with summer averages (±standard deviation) of 3.9 ± 1.6 ppb and winter averages of 1.1 ± 0.6 ppb. Two other datasets, weekly/biweekly passive samples of NH3 monitored at 74 agricultural and remote sites across southern Ontario during the period of June 2006 to March 2007 (Dataset 2) and semi-continuous measurements of NH3 and ammonium (pNH4 +) in PM2.5 collected at a site inside a street canyon approximately 170 m away from the downtown site in December 2008 and February, March and May 2009 (Dataset 3), were further used to evaluate the potential NH3 sources in downtown Toronto. The NH3 mixing ratios at the downtown location were higher than those at the surrounding agricultural sites, and the mixing ratios within the street canyon were almost double those measured above it. These results suggested that the observed NH3 at the downtown location was mainly from local sources within the street canyon. Analysis of Dataset 3 showed that the diurnal cycles of NH3 at the downtown location cannot be simply explained by traffic and water consumption patterns. A green space inside the street canyon was identified as a potential important source contributing to the observed NH3 when T > 0 °C. However, the major NH3 emission sources at T ≤ 0 °C are yet to be investigated.
Keywords: NH3; Soil emission; Temperature effect; Seasonal variations; pNH4 +;

Atmospheric concentrations of non-sea-salt sulfate (nss-SO4 2−) and methanesulfonic acid (MSA) were measured over the Pacific Ocean between 48°N and 55°S during the KH-08-2 and MR08-06 cruises in summers of 2008 and 2009, in order to investigate spatial distributions of each species and MSA/nss-SO4 2− ratio. In the subarctic western North Pacific, mean concentrations of nss-SO4 2− and MSA in bulk (fine + coarse) aerosols were 1.1 μg m−3 and 0.061 μg m−3, whereas those in the South Pacific were 0.25 μg m−3 and 0.043 μg m−3, respectively. In the subtropical western North Pacific, it was observed that nss-SO4 2− concentration sharply increased from 0.45 μg m−3 up to 4.2 μg m−3 under the dominant influence of the Kilauea volcano, while that of MSA remained low. Mean MSA/nss-SO4 2− ratio observed in the South Pacific was approximately 3.7 times higher than that in the subarctic western North Pacific, although the mean MSA concentration in the subarctic western North Pacific was a factor of 1.4 higher than that in the South Pacific. The distributions of nss-SO4 2−, MSA, and MSA/nss-SO4 2− ratio suggested that aerosol nss-SO4 2− plays a key role in the latitudinal variation in MSA/nss-SO4 2− ratio over the North and South Pacific during summer periods, and that high MSA concentrations in the subarctic western North Pacific and the South Pacific were related to high biological productivity and low air temperature. During the cruises, an inverse relationship (r = −0.72, p < 0.01) was observed between satellite-derived chlorophyll a concentration and air temperature, showing that high biological productivity occurred at high latitudes, where air temperature were relatively low, in both hemispheres during the summer periods. Although both MSA concentration and MSA/nss-SO4 2− ratio showed inverse and positive relationships with air temperature and chlorophyll a concentration, respectively, the correlations between these variables were weak, suggesting that the distributions of MSA concentration and MSA/nss-SO4 2− ratio over the North and South Pacific during the summer periods were influenced by more complex factors. Estimates using the MSA/nss-SO4 2− ratios measured in different latitude regions in the Pacific Ocean indicated that the contributions from biogenic sources accounted for 9.6–58% of the total nss-SO4 2− in aerosols collected in the subarctic western North Pacific, 15–85% in the subtropical western North Pacific, 10–70% in the central North Pacific, and 12–97% in the South Pacific, showing strong influence of anthropogenic nss-SO4 2− in the subarctic western North Pacific despite the higher mean concentration of MSA in the subarctic western North Pacific than in the South Pacific.
Keywords: Non-sea-salt sulfate; Methanesulfonic acid; Methanesulfonic acid to non-sea-salt sulfate ratio; North and South Pacific; Marine aerosols;

UK concentrations of chromium and chromium (VI), measured as water soluble chromium, in PM10 by Richard J.C. Brown; Sivan Van Aswegen; William R. Webb; Sharon L. Goddard (385-391).
As a toxic metal found in respirable ambient particulate matter (PM10) chromium is being increasing recognised as an important environmental pollutant and its emissions from industrial facilities are controlled by legislation. Total chromium concentrations in ambient air are monitored by air quality monitoring stations across the UK and this work summarises for the first time the data recorded at these locations over the last 30 years. In addition, a novel assessment of chromium (VI) concentrations – measured as water soluble chromium, with the selectively of this technique being benchmarked against a more robust solid phase extraction procedure – across the UK, is presented. The results for soluble chromium concentrations typically lay within 5–15 % of the total chromium concentrations determined by the UK network, agreeing with ranges found in previous studies. The percentage of chromium (VI) as total chromium shows some correlation with proximity to industrial sources.UK concentrations of chromium and chromium (VI), measured as water soluble chromium, in PM10 are reported. Display Omitted
Keywords: Ambient air; Air quality networks; Chromium; Speciation; Particulate;

SO2 measurements at a high altitude site in the central Himalayas: Role of regional transport by Manish Naja; Chinmay Mallik; Tapaswini Sarangi; Varun Sheel; Shyam Lal (392-402).
Continuous measurements of a climatically important acidic gas, SO2, were made over Nainital (29.37°N, 79.45°E; 1958 m amsl), a regionally representative site in the central Himalayas, for the first time during 2009–2011. Unlike many other sites, the SO2 levels over Nainital are higher during pre-monsoon (345 pptv) compared to winter (71 pptv). High values during pre-monsoon are attributed to the transport of air masses from regions viz. Indo-Gangetic Plain (IGP), northern India and north-East Pakistan, which are dotted with numerous industries and power plants, where coal burning occurs. Transport from the polluted regions is evinced from good correlations of SO2 with wind speed, NO y and UV aerosol index during these periods. Daytime elevations in SO2 levels, influenced by ‘valley winds’ and boundary layer evolution, is a persistent feature at Nainital. SO2 levels are very much lower during monsoon compared to pre-monsoon, due to oxidation losses and wet scavenging. Despite this, SO2/NO y slopes are high (>0.4) both during pre-monsoon and monsoon, indicating impacts of point sources. The SO2 levels during winter are lower as the measurement site is cut off from the plains due to boundary layer dynamics. Further, the SO2 levels during winter nights are the lowest (lesser than 50 pptv) and resemble free tropospheric conditions.
Keywords: Sulfur dioxide; Boundary layer; Transport; NO y ; Free troposphere;

Biomass burning contribution to ambient volatile organic compounds (VOCs) in the Chengdu–Chongqing Region (CCR), China by Lingyu Li; Yuan Chen; Limin Zeng; Min Shao; Shaodong Xie; Wentai Chen; Sihua Lu; Yusheng Wu; Wei Cao (403-410).
Ambient volatile organic compounds (VOCs) were measured intensively using an online gas chromatography–mass spectrometry/flame ionization detector (GC–MS/FID) at Ziyang in the Chengdu–Chongqing Region (CCR) from 6 December 2012 to 4 January 2013. Alkanes contributed the most (59%) to mixing ratios of measured non-methane hydrocarbons (NMHCs), while aromatics contributed the least (7%). Methanol was the most abundant oxygenated VOC (OVOC), contributing 42% to the total amount of OVOCs. Significantly elevated VOC levels occurred during three pollution events, but the chemical composition of VOCs did not differ between polluted and clean days. The OH loss rates of VOCs were calculated to estimate their chemical reactivity. Alkenes played a predominant role in VOC reactivity, among which ethylene and propene were the largest contributors; the contributions of formaldehyde and acetaldehyde were also considerable. Biomass burning had a significant influence on ambient VOCs during our study. We chose acetonitrile as a tracer and used enhancement ratio to estimate the contribution of biomass burning to ambient VOCs. Biomass burning contributed 9.4%–36.8% to the mixing ratios of selected VOC species, and contributed most (>30% each) to aromatics, formaldehyde, and acetaldehyde.
Keywords: VOCs; Biomass burning; Enhancement ratio; Chemical reactivity;

Chemical properties of emission from biomass fuels used in the rural sector of the western region of India by Avirup Sen; T.K. Mandal; S.K. Sharma; Mohit Saxena; N.C. Gupta; R. Gautam; Anita Gupta; Tanvi Gill; Shalu Rani; T. Saud; D.P. Singh; Ranu Gadi (411-424).
This paper presents the emission factors (EF) of particulate matter (PM), organic carbon (OC), elemental carbon (EC), SO2, NO, NO2 and water soluble ions emitted by residential biomass fuels collected from the rural sector of Western India. Burning process has been simulated using a dilution chamber. Average EF of PM, OC and EC from fuel wood (FW), agricultural residues (AR) and dung cakes (DC) from Western India are estimated as: PM: 1.69 ± 0.98 g kg−1, 2.15 ± 1.00 g kg−1 and 5.37 ± 3.90 g kg−1; OC: 0.43 ± 0.29 g kg−1, 00.54 ± 0.22 g kg−1, 1.14 ± 0.67 g kg−1; EC: 0.25 ± 0.16 g kg−1, 0.23 ± 0.11 g kg−1 and 0.14 ± 0.08 g kg−1 respectively. Similarly, the average EF of SO2, NO and NO2 from FW, AR and DC are determined to be: SO2: 0.66 ± 0.37 g kg−1, 0.29 ± 0.45 g kg−1 and 0.74 ± 0.48 g kg−1; NO: 0.55 ± 0.25 g kg−1, 0.74 ± 0.37 g kg−1 and 0.50 ± 0.23 g kg−1; NO2: 1.05 ± 0.49 g kg−1, 1.41 ± 0.81 g kg−1 and 0.91 ± 0.45 g kg−1 respectively. Cl has the highest average EF (FW: 97.03 ± 74.98 mg kg−1, AR: 175.71 ± 145.78 mg kg−1, DC: 158.15 ± 109.07 mg kg−1) among the anions, followed by PO4 3−(FW: 116.59 ± 63.43 mg kg−1, AR: 58.45 ± 1.42 mg kg−1, DC: 85.77 ± 78.85 mg kg−1) and NO3 (FW: 64.23 ± 68.38 mg kg−1, AR: 36.78 ± 22.80 mg kg−1, DC: 50.25 ± 49.33 mg kg−1). Similarly, among the cations, the highest emitters are Na+ (FW: 40.25 ± 26.64 mg kg−1; AR: 47.96 ± 18.35 mg kg−1, DC: 30.51 ± 23.39 mg kg−1), K+ (FW: 29.32 ± 23.95 mg kg−1, AR: 50.89 ± 34.62 mg kg−1, DC: 18.23 ± 14.54 mg kg−1) and NH4 + (FW: 27.93 ± 22.59 mg kg−1; AR: 46.37 ± 41.79 mg kg−1, DC: 41.74 ± 36.01 mg kg−1). The total emissions of trace gases, PM and its chemical composition from FW, AR and DC have been calculated using laboratory generated EFs over Western India.
Keywords: Biomass burning; Emission factor; Particulate matter; Trace gases; Organic and elemental carbon; Water soluble ionic species;

Atmospheric deposition of lead in remote high mountain of eastern Tibetan Plateau, China by Haijian Bing; Yanhong Wu; Jun Zhou; Lili Ming; Shouqin Sun; Xiangdong Li (425-435).
Global warming has induced visible glacier retreat on many high mountains. The glacier forelands with the chronosequence and vegetation succession offer a good opportunity to assess natural (e.g., mineral weathering) and anthropogenic influence on trace element geochemical cycling in high mountain ecosystems. In the present study, the concentrations and isotope composition of lead (Pb) in soil profiles and mosses from the Hailuogou Glacier foreland in eastern Tibetan Plateau were investigated. The enrichment of Pb in the O and A horizons of soil layers and mosses indicated the influence from recently atmospheric deposition, while the local soil parent materials mainly affected the C horizon of soils. The lower 206Pb/207Pb (1.160–1.180) and higher 208Pb/206Pb (2.092–2.120) ratios were observed in the O horizon in comparison with the A (1.171–1.209 and 2.042–2.108, respectively) and C (1.183–1.206 and 2.070–2.130, respectively) horizons. The Pb isotope composition in the mosses was similar to those of the O horizon. The Pb-ore-involved industries and coal combustion in southwest China and South Asia were identified as the major sources of anthropogenic Pb at the glacier foreland. The estimations using binary mixing model indicated that the anthropogenic Pb contribution was about 45.2–61.3% for the O horizon, 8.6–34.8% for the A horizon, and 41.6–65.9% for the mosses. The results indicated that the anthropogenic Pb could reach the remote high mountains of eastern Tibetan Plateau through long distance atmospheric transport.
Keywords: Lead isotope; Source identification; High mountain; Hailuogou Glacier; China;

Elemental composition of current automotive braking materials and derived air emission factors by J.H.J. Hulskotte; G.D. Roskam; H.A.C. Denier van der Gon (436-445).
Wear-related PM emissions are an important constituent of total PM emissions from road transport. Due to ongoing (further) exhaust emission reduction wear emissions may become the dominant PM source from road transport in the near future. The chemical composition of the wear emissions is crucial information to assess the potential health relevance of these PM emissions. Here we provide an elemental composition profile of brake wear emissions as used in the Netherlands in 2012. In total, 65 spent brake pads and 15 brake discs were collected in car maintenance shops from in-use personal cars vehicles and analyzed with XRF for their metal composition (Fe, Cu, Zn, Sn, Al, Si, Zr, Ti, Sb, Cr, Mo, Mn, V, Ni, Bi, W, P, Pb and Co). Since car, engine and safety regulations are not nationally determined but controlled by European legislation the resulting profiles will be representative for the European personal car fleet. The brake pads contained Fe and Cu as the dominant metals but their ratio varied considerably, other relatively important metals were Sn, Zn and Sb. Overall a rather robust picture emerged with Fe, Cu, Zn and Sn together making up about 80–90% of the metals present in brake pads. Because the XRF did not give information on the contents of other material such as carbon, oxygen and sulphur, a representative selection of 9 brake pads was further analyzed by ICP-MS and a carbon and sulphur analyzer. The brake pads contained about 50% of non-metal material (26% C, 3% S and the remainder mostly oxygen and some magnesium). Based on our measurements, the average brake pad profile contained 20% Fe, 10% Cu, 4% Zn and 3% Sn as the dominant metals. The brake discs consisted almost entirely of metal with iron being the dominant metal (>95%) and only traces of other metals (<1% for individual metals). Non-metal components in the discs were 2–3% Silicon and, according to literature, ∼3% carbon. The robust ratio between Fe and Cu as found on kerbsides has been used to estimate the contribution of brake pads and brake discs to total brake wear. Based on this approach our hypothesis is that 70% of the brake wear originates from the discs and only 30% from the brake pads.
Keywords: Brake pads; Brake discs; Heavy metals; Iron; Copper; Non-exhaust emissions;

Pre-harvest sugarcane burning emission inventories based on remote sensing data in the state of São Paulo, Brazil by Daniela França; Karla Longo; Bernardo Rudorff; Daniel Aguiar; Saulo Freitas; Rafael Stockler; Gabriel Pereira (446-456).
The state of São Paulo is the largest sugarcane producer in Brazil, with a cultivated area of about 5.4 Mha in 2011. Approximately 2 Mha were harvested annually from 2006 to 2011 with the pre-harvest straw burning practice, which emits trace gases and particulate material to the atmosphere. The development of emission inventories for sugarcane straw burning is crucial in order to assess its environmental impacts. This study aimed to estimate annual emissions associated with the pre-harvest sugarcane burning practice in the state of São Paulo based on remote sensing maps and emission and combustion factors for sugarcane straw burning. Average estimated emissions (Gg/year) were 1130 ± 152 for CO, 26 ± 4 for NO x , 16 ± 2 for CH4, 45 ± 6 for PM2.5, 120 ± 16 for PM10 and 154 ± 21 for NMHC (non-methane hydrocarbons). An intercomparison among annual emissions from this study and annual emissions from four other different approaches indicated that the estimates obtained by satellite fire detection or low spatial resolution approaches tend to underestimate sugarcane burned area, due to unique characteristics of this type of biomass fire. Overall, our results also indicated that government actions to reduce sugarcane straw burning emissions are becoming effective.
Keywords: Biomass burning; Sugarcane; Emission inventories; Remote sensing;

Application of the complex step method to chemistry-transport modeling by Bogdan V. Constantin; Steven R.H. Barrett (457-465).
Sensitivity analysis in atmospheric chemistry-transport modeling is used to develop understanding of the mechanisms by which emissions affect atmospheric chemistry and composition, to quantify the marginal impact of emissions on air quality, and for other applications including improving estimates of emissions, developing fast first order air quality models, and validating adjoint models. Forward modeling sensitivities have predominantly been calculated using the finite difference approach, i.e. where the results of two separate simulations are subtracted. The finite difference approach incurs truncation and cancellation errors, which mean that exact sensitivities cannot be calculated and even approximate sensitivities cannot always be calculated for a sufficiently small perturbation (e.g. for emissions at a single location or time). Other sensitivity methods can provide exact sensitivities, but require the reformulation of non-linear steps (e.g. the decoupled direct method) or the development of adjoints of entire codes (partly automatically and partly manually). While the adjoint approach is widely applied and has significant utility in providing receptor-oriented information, in some applications the source-oriented information of forward approaches is needed. Here we apply an alternative method of calculating sensitivities that results in source-oriented information as with the finite difference approach, requires minimal reformulation of models, but enables near-exact computation of sensitivities. This approach – the complex step method – is applied for the first time to a complete atmospheric chemistry-transport model (GEOS-Chem). (The complex step method has been previously used in validating the adjoint of an aerosol thermodynamic equilibrium model.) We also introduce the idea of combining complex-step and adjoint sensitivity analysis (for the first time in any context to our knowledge) to enable the direct calculation of near-exact second order sensitivities.
Keywords: Sensitivity analysis; Adjoint; Finite difference; Chemistry-transport modeling;

Application of photochemical indicators to evaluate ozone nonlinear chemistry and pollution control countermeasure in China by Min Xie; Kuanguang Zhu; Tijian Wang; Haoming Yang; Bingliang Zhuang; Shu Li; Minggao Li; Xinsheng Zhu; Yan Ouyang (466-473).
Ozone sensitivity in China was investigated by using a comprehensive three-dimensional air quality model system WRF-CALGRID. A real case and two cases with 35% emission reduction for either NOx or VOC were conducted for the period of March in 2010. The simulation results of O3 agreed fairly well with the observation data. Based on the meaning of O3 sensitivity, the ratio Ra was defined, with the transition value of 1 to distinguish NOx-sensitive region from VOC-sensitive region. With the aid of Ra, VOC- and NOx-sensitive regions in China were preliminary located. The transition ranges for some photochemical indicators were quantified. Only those of H2O2/NOz and H2O2/HNO3 met the requirement that the 95th percentile VOC-sensitive value should be equal to or lower than the 5th percentile NOx-sensitive value. 0.16–0.40 for H2O2/HNO3 and 0.14–0.28 for H2O2/NOz were adopted to distinguish different O3 sensitivity in China. The results showed that the VOC-sensitive regions are primarily distributed over the urban centers and the developed industrial areas in eastern and southern China, while the NOx-sensitive regions are mainly located in the remote areas of northern and western China. High correlation between Ra and indicators was found, and a new approach to quantify the transition values of indicators was proposed. These indicators can play an important role in the air complex pollution control of urban clusters over East Asia.
Keywords: Ozone sensitivity; Photochemical indicators; Ozone precursors; Nonlinear chemistry; Ozone pollution prevention;

Levels, trends and health concerns of atmospheric PAHs in Europe by Adrián Garrido; Pedro Jiménez-Guerrero; Nuno Ratola (474-484).
Changes in climate can affect the concentration patterns of polycyclic aromatic hydrocarbons (PAHs) by altering the dispersion (wind speed, mixing layer height, convective fronts), deposition by precipitation, dry deposition, photochemistry, natural emissions and background concentrations. This means the evolution trends of these pollutants have to be studied under a multi-scale perspective, allowing the establishment of transport patterns and distribution of PAHs. In this sense, this work tries to unveil the atmospheric behaviour of these pollutants using temporal data series collected in different stations from the European Monitoring and Evaluation Programme (EMEP) air sampling network. These sites are thought to avoid the direct influence of emitting areas (background stations), allowing the study of long-range transport effects, intra- and trans-annual variability, relationships between concentrations patterns and meteorological variables and latitudinal gradients of PAH levels in Europe. Overall, a typical high concentration pattern was found for the colder months (and an opposite behaviour is found for summertime). Negative trends were detected over high latitudes, for instance, in Svalbard (Norway), whereas for the United Kingdom the pattern is the inverse. Also, negative latitudinal gradients were observed in 4 of the 15 PAHs studied. Finally, air quality parameters revealed concern over human health issues, given the recent increase of BaP levels in Europe.
Keywords: Polycyclic aromatic hydrocarbons; Atmospheric pollution; Temporal trends; Human health; Europe; EMEP;

Preliminary study of atmospheric carbon dioxide in a glacial area of the Qilian Mountains, west China by Chuanjin Li; Lingxi Zhou; Dahe Qin; Lixin Liu; Xiang Qin; Zebin Wang; Jiawen Ren (485-490).
Carbon dioxide represents the most important contribution to increased radiative forcing. The preliminary results of the atmospheric carbon dioxide mole fraction from the glacial region in the Qilian Mountains area, in the northeast of the Qinghai-Xizang (Tibetan) Plateau during July, 2009 to October, 2012 are presented. The annual mean CO2 mole fractions in 2010 and 2011 were 388.4 ± 2.7 ppm and 392.7 ± 2.6 ppm, respectively. These values were consistent with the CO2 mole fractions from the WMO/GAW stations located at high altitudes. However, both the concentration and seasonal variation were significantly lower than stations located adjacent to megacities or economic centers at low latitudes in eastern China. Shorter durations of photosynthesis of the alpine vegetation system that exceeded respiration were detected at the Qilian Mountains glacial area. The annual mean increase during the sampling period was 2.9 ppm yr−1 and this value was higher than the global mean values. Anthropogenic activities in the cities adjacent to the Qilian Mountains may have important influences on the CO2 mole fractions, especially in summer, when north and north-north-west winds are typical.
Keywords: Carbon dioxide; Qilian Mountains; Seasonal variations; Human activities;

Observed surface PM10 mass concentrations and weather records, satellite-derived aerosol and ocean color data, dust simulations, and a backward trajectory analysis were used to investigate a severe dust storm episode during 19–22 March 2010 and its impact on phytoplankton growth in the Yellow Sea. The observed PM10 concentrations and weather records showed that heavy dust pollution occurred along the transport pathway. The high MODIS AOD regions were consistent with the simulated high dust emission and deposition regions. Based on the CALIPSO satellite observations, the high dust aerosol layer was below 2 km above ground, indicating the dust transported to the sea was centered within the lower layer. The model simulation estimated that the total deposition flux over the southern Yellow Sea during 19–22 March 2010 was about 1.5 g m−2. Consequently, the chlorophyll a concentration was calculated to have increased four-fold. Ten to thirteen days later, a phytoplankton bloom occurred. The iron deposited by the severe dust episode could have increased the chlorophyll a concentration in the southern Yellow Sea by 10–68%. Our results suggest that severe dust storms containing readily bioavailable nutrients may enhance phytoplankton growth in the southern Yellow Sea.
Keywords: Dust storm; PM10; Vertical profile; Deposition; Chlorophyll; Yellow Sea;

Determination of PM mass emissions from an aircraft turbine engine using particle effective density by L. Durdina; B.T. Brem; M. Abegglen; P. Lobo; T. Rindlisbacher; K.A. Thomson; G.J. Smallwood; D.E. Hagen; B. Sierau; J. Wang (500-507).
Inventories of particulate matter (PM) emissions from civil aviation and air quality models need to be validated using up-to-date measurement data corrected for sampling artifacts. We compared the measured black carbon (BC) mass and the total PM mass determined from particle size distributions (PSD) and effective density for a commercial turbofan engine CFM56-7B26/3. The effective density was then used to calculate the PM mass losses in the sampling system. The effective density was determined using a differential mobility analyzer and a centrifugal particle mass analyzer, and increased from engine idle to take-off by up to 60%. The determined mass-mobility exponents ranged from 2.37 to 2.64. The mean effective density determined by weighting the effective density distributions by PM volume was within 10% of the unit density (1000 kg/m3) that is widely assumed in aircraft PM studies. We found ratios close to unity between the PM mass determined by the integrated PSD method and the real-time BC mass measurements. The integrated PSD method achieved higher precision at ultra-low PM concentrations at which current mass instruments reach their detection limit. The line loss model predicted ∼60% PM mass loss at engine idle, decreasing to ∼27% at high thrust. Replacing the effective density distributions with unit density lead to comparable estimates that were within 20% and 5% at engine idle and high thrust, respectively. These results could be used for the development of a robust method for sampling loss correction of the future PM emissions database from commercial aircraft engines.
Keywords: Aviation; Aircraft; Emissions; Particulate matter; Effective density; Black carbon;

Total ozone column, water vapour and aerosol effects on erythemal and global solar irradiance in Marsaxlokk, Malta by Julia Bilbao; Roberto Román; Charles Yousif; David Mateos; Argimiro de Miguel (508-518).
Observations of erythemal (UVER; 280–400 nm) and total solar shortwave irradiance (SW; 305–2800 nm), total ozone column (TOC), water vapour column (w), aerosol optical depth (AOD) and Ångström exponent (α) were carried out at Marsaxlokk, in south-east Malta. These measurements were recorded during a measurement campaign between May and October 2012, aimed at studying the influence of atmospheric compounds on solar radiation transfer through the atmosphere. The effects of TOC, AOD and w on UVER and SW (global, diffuse and direct) irradiance were quantified using irradiance values under cloud-free conditions at different fixed solar zenith angles (SZA). Results show that UVER (but not SW) irradiance correlates well with TOC. UVER variations ranged between −0.24% DU−1 and −0.32% DU−1 with all changes being statistically significant. Global SW irradiance varies with water vapour column between −2.44% cm−1 and −4.53% cm−1, these results proving statistically significant and diminishing when SZA increases. The irradiance variations range between 42.15% cm−1 and 20.30% cm−1 for diffuse SW when SZA varies between 20° and 70°. The effect of aerosols on global UVER is stronger than on global SW. Aerosols cause a UVER reduction of between 28.12% and 52.41% and a global SW reduction between 13.46% and 41.41% per AOD550 unit. Empirical results show that solar position plays a determinant role, that there is a negligible effect of ozone on SW radiation, and stronger attenuation by aerosol particles in UVER radiation.
Keywords: Erythemal ultraviolet irradiance; Total solar shortwave irradiance; Total ozone column; Water vapour column; Aerosol; Central Mediterranean;

A new method for derivatizing carbonyl compounds is presented. The conversion of a series of dicarbonyls to oximes in aqueous solution and from gas-phase sampling was achieved using O-tert-butylhydroxylamine hydrochloride (TBOX). Some advantages of using this derivatization agent include: aqueous reactions, lower molecular weight oximes, and shortened oxime-formation reaction time. Additionally, the TBOX derivatization technique was used to investigate the carbonyl reaction products from limonene ozonolysis. With ozone (O3) as the limiting reagent, four carbonyl compounds were detected: 7-hydroxy-6-oxo-3-(prop-1-en-2-yl)heptanal; 3-Isopropenyl-6-oxoheptanal (IPOH), 3-acetyl-6-oxoheptanal (3A6O) and one carbonyl of unknown structure. Using cyclohexane as a hydroxyl (OH•) radical scavenger, the relative yields (peak area) of the unknown carbonyl, IPOH, and 3A6O were reduced indicating the influence secondary OH radicals have on limonene ozonolysis products. The relative yield of the hydroxy-dicarbonyl based on the chromatogram was unchanged suggesting it is only made by the limonene + O3 reaction. The detection of 3A6O using TBOX highlights the advantages of a smaller molecular weight derivatization agent for the detection of multi-carbonyl compounds. The use of TBOX derivatization if combined with other derivatization agents may address a recurring need to simply and accurately detect multi-functional oxygenated species in air.
Keywords: Ozone; Reaction products; Oxygenated organic compounds; Derivatization;

Unit-based emission inventory and uncertainty assessment of coal-fired power plants by Linghong Chen; Yangyang Sun; Xuecheng Wu; Yongxin Zhang; Chenghang Zheng; Xiang Gao; Kefa Cen (527-535).
A unit-based emission inventory of coal-fired power plants in China was developed which contains unit capacity, coal consumption, emission control technology and geographical location. Estimated total emissions of SO2, NO x , particulate matter (PM) and PM2.5 in 2011 were 7251 kt, 8067 kt, 1433 kt and 622 kt, respectively. Units larger than 300 MW consumed 75% coal, while emitting 46% SO2, 58% NO x , 55% PM and 63.2% PM2.5. Emission comparisons between key regions such as the Yangtze River Delta, the Pearl River Delta and Shandong Province showed a general downward trend from 2005 to 2011, mainly because of the growing application ratio of desulphurisation, LNBs, denitration and dust-removal facilities. The uncertainties at unit level of SO2, NO x , PM and PM2.5 were estimated to be −10.1% ∼ +5.4%, −2.1% ∼ +4.6%, −5.7% ∼ +6.9% and −4.3% ∼ +6.5%, respectively. Meanwhile sector-based Monte Carlo simulation was conducted for better understanding of the uncertainties. Unit-based simulation yielded narrowed estimates of uncertainties, possibly caused by the neglected diversity of emission characteristics in sector-based simulation. The large number of plants narrowed unit-based uncertainties as large uncertainties were found in provinces with a small number of power plants, such as Qinghai. However, sector-based uncertainty analysis well depends on detailed source classification, because small NO x uncertainties were found in Shandong due to the detailed classification of NO x emission factors. The main uncertainty sources are discussed in the sensitivity analysis, which identifies specific needs in data investigation and field measures to improve them. Though unit-based Monte Carlo greatly narrowed uncertainties, the possibility of underestimated uncertainties at unit level cannot be ignored as the correlation of emission factors between units in the same source category was neglected.
Keywords: Unit-based emission inventory; Uncertainty assessment; Coal-fired power plant; SO2; NO x ; PM2.5; China;

Relationships between black carbon (BC) aerosols and haze with different intensities are analysed by using hourly averaged data of BC mass concentration (C BC) and meteorological parameters from April 2007 to March 2010 in Shanghai. The results show that the number of cumulative haze hours accounted for 59.6% of the all valid hours during the three-year test period, while slight, mild, moderate and severe haze contributed 64.4%, 24.3%, 8.8% and 2.5% of the haze hours, respectively. Seasonal haze hour percentages in all haze hours were 19.8, 19.5, 24.5 and 36.2 for spring, summer, fall and winter, respectively. The annual averaged C BC for haze hours and non-haze hours were 5.05 μg/m3 and 2.04 μg/m3 during the three test years, respectively. The observation results show a positive correlation between monthly averaged C BC and haze intensity, i.e., the higher the haze intensity, the higher the C BC. According to the test data, four ranges of C BC were introduced to show the relationships between BC aerosols and haze hour percentage, and found that the higher the CBC, the higher the percentage of haze hours in the corresponding range. When C BC was higher than 4.5 μg/m3, the haze hours accounted for 95.0% of the valid test hours of the three year time span, and it can be used as a sufficient condition of haze occurrence. In addition, a set of 96-h backward trajectories indicate that the air masses originated from north China were the main non-local sources of haze in spring, fall and winter in Shanghai, and emissions from south regions of Shanghai were the primary non-local sources of the haze in summer.
Keywords: Black carbon aerosols; Mass concentration; Haze intensity; Visibility; PM2.5;

Quantifying the air quality-CO2 tradeoff potential for airports by Akshay Ashok; Irene C. Dedoussi; Steve H.L. Yim; Hamsa Balakrishnan; Steven R.H. Barrett (546-555).
Aircraft movements on the airport surface are responsible for CO2 emissions that contribute to climate change and other emissions that affect air quality and human health. While the potential for optimizing aircraft surface movements to minimize CO2 emissions has been assessed, the implications of CO2 emissions minimization for air quality have not been quantified. In this paper, we identify conditions in which there is a tradeoff between CO2 emissions and population exposure to O3 and secondary PM2.5 – i.e. where decreasing fuel burn (which is directly proportional to CO2 emissions) results in increased exposure. Fuel burn and emissions are estimated as a function of thrust setting for five common gas turbine engines at 34 US airports. Regional air quality impacts, which are dominated by ozone and secondary PM2.5, are computed as a function of airport location and time using the adjoint of the GEOS-Chem chemistry-transport model. Tradeoffs between CO2 emissions and population exposure to PM2.5 and O3 occur between 2–18% and 5–60% of the year, respectively, depending on airport location, engine type, and thrust setting. The total duration of tradeoff conditions is 5–12 times longer at maximum thrust operations (typical for takeoff) relative to 4% thrust operations (typical for taxiing). Per kilogram of additional fuel burn at constant thrust setting during tradeoff conditions, reductions in population exposure to PM2.5 and O3 are 6–13% and 32–1060% of the annual average (positive) population exposure per kilogram fuel burn, where the ranges encompass the medians over the 34 airports. For fuel burn increases due to thrust increases (i.e. for constant operating time), reductions in both PM2.5 and O3 exposure are 1.5–6.4 times larger in magnitude than those due to increasing fuel burn at constant thrust (i.e. increasing operating time). Airports with relatively high population exposure reduction potentials – which occur due to a combination of high duration and magnitude of tradeoff conditions – are identified. Our results are the first to quantify the extent of the tradeoff between CO2 emissions and air quality impacts at airports. This raises the possibility of reducing the air quality impacts of airports beyond minimizing fuel burn and/or optimizing for minimum net environmental impact.
Keywords: Airports; Aircraft engines; Air quality-CO2 tradeoff;

Airborne measurements of HC(O)OH in the European Arctic: A winter – summer comparison by Benjamin T. Jones; Jennifer B.A. Muller; Sebastian J. O'Shea; Asan Bacak; Michael Le Breton; Thomas J. Bannan; Kimberley E. Leather; A. Murray Booth; Sam Illingworth; Keith Bower; Martin W. Gallagher; Grant Allen; Dudley E. Shallcross; Stephane J.-B. Bauguitte; John A. Pyle; Carl J. Percival (556-567).
This study represents the first airborne, in-situ measurements of HC(O)OH in the European Arctic, across the winter and summer seasons. HC(O)OH concentrations are under predicted at present, particularly in the mid to high northern latitudes. Data presented here probe unconfirmed sources of HC(O)OH in the Arctic, and would suggest an ocean source of HC(O)OH is more significant than proposed land sources in both winter and summer environments. A maximum concentration of 420 ppt was recorded over the ocean during the July 2012 campaign. This was more than 1.7 times greater than the maximum land concentration reported. Calculated estimates on HC(O)OH production would suggest diiodomethane photolysis could represent a significant source of HC(O)OH in marine environments in the European Arctic. Enhanced HC(O)OH concentrations observed at altitudes greater than 2 km particularly during the March campaign highlight the significance of long range transport on the European Arctic budget. In addition, two HC(O)OH vertical profiles between the altitudes 0.3–6.6 km are presented to provide a more representative vertical profile for this latitude which may be used to improve forthcoming regional and global modelling of the HC(O)OH budget.
Keywords: Organic acids; Formic acid; Criegee intermediate; Diiodomethane; Arctic; CIMS;

The hydroxyl radical (OH) in indoor air: Sources and implications by Sasho Gligorovski; Henri Wortham; Jörg Kleffmann (568-570).

The vast range of space-time scales associated with turbulent flow adjacent to rugged terrain is especially problematic to predictive dispersion modeling in atmospheric boundary layers (ABLs) partly due to the presence of non-linear flow features (e.g., recirculation zones, diffusion enhancement, etc.). It has been suggested that in such ABLs, explicitly modeling large turbulent eddies, through large-eddy simulation (LES), may help to curtail predicted concentration errors. In this work, passive scalars were introduced into the Weather Research and Forecasting (WRF) LES model for the purpose of simulating scalar plume interaction with an isolated terrain feature. Using measurements from the Cinder Cone Butte (CCB) field campaign, we evaluate the ability of WRF-LES to realistically simulate the impingement of Sulfur Hexafluoride (SF6) plumes onto CCB in both neutrally and stably stratified environments. Simulations reveal relatively accurate scalar trajectories with respect to thermal stability, including complex patterns such as plume splitting below the hill dividing streamline. Statistical accuracy varied with case study, but for the neutral case we recorded greater than 50% of predicted 1 h averaged surface concentrations within a factor of 2 of the observations. This metric, along with several others, indicates a performance accuracy similar to, or slightly better than, alternative Reynolds Averaged Navier–Stokes models. For the stably stratified case, the spatial distribution of surface concentrations was captured well; however, a positive concentration bias was observed which degraded quantitative accuracy scores. The variable accuracy of the WRF-LES model with respect to thermal stability is similar to what has been observed in regulatory analytical models (i.e., concentration under predictions in neutral environments and concentration over predictions in stable environments). Possible sources of error and uncertainty included the omission of mesoscale wind meandering (i.e., realistic boundary conditions) and sub-grid turbulence parameterization.
Keywords: Atmospheric boundary layer; Complex terrain; Dispersion modeling; Large-eddy simulation;

Local order and valence state of Fe in urban suspended particulate matter by Francesco d'Acapito; Simona Mazziotti Tagliani; Francesco Di Benedetto; Antonio Gianfagna (582-586).
X-ray absorption spectroscopy investigations were carried out on urban suspended particulate matter (PM2.5) with the aim of studying the local order and valence state of iron, a metal abundant in this type of material, particularly in urban environments. XANES results, based on the comparison with model compounds fayalite (Fe2+) and ferrihydrite (Fe3+), show that iron is prevalent as Fe3+, whereas EXAFS data attribute the prevalent Fe3+ to a nanocrystalline phase of ferrihydrite. The dominance of Fe3+ (less soluble than Fe2+) is further confirmed by the fact that previous leaching experiments did not show Fe presence in the solution.
Keywords: Urban PM2.5; XANES; EXAFS; Iron local order; Iron valence state;

Spatial and seasonal variability of carbonaceous aerosol across Italy by Silvia Sandrini; Sandro Fuzzi; Andrea Piazzalunga; Paolo Prati; Paolo Bonasoni; Fabrizia Cavalli; Maria Chiara Bove; Mariarosaria Calvello; David Cappelletti; Cristina Colombi; Daniele Contini; Gianluigi de Gennaro; Alessia Di Gilio; Paola Fermo; Luca Ferrero; Vorne Gianelle; Michele Giugliano; Pierina Ielpo; Giovanni Lonati; Angela Marinoni; Dario Massabò; Ugo Molteni; Beatrice Moroni; Giulia Pavese; Cinzia Perrino; Maria Grazia Perrone; Maria Rita Perrone; Jean-Philippe Putaud; Tiziana Sargolini; Roberta Vecchi; Stefania Gilardoni (587-598).
This paper analyses elemental (EC), organic (OC) and total carbon (TC) concentration in PM2.5 and PM10 samples collected over the last few years within several national and European projects at 37 remote, rural, urban, and traffic sites across the Italian peninsula.The purpose of the study is to obtain a picture of the spatial and seasonal variability of these aerosol species in Italy, and an insight into sources, processes and effects of meteorological conditions.OC and EC showed winter maxima and summer minima at urban and rural locations and an opposite behaviour at remote high altitude sites, where they increase during the warm period due to the rising of the Planetary Boundary Layer (PBL). The seasonal averages of OC are higher during winter compared to summer at the rural sites in the Po Valley (from 1.4 to 3.5 times), opposite to what usually occurs at rural locations, where OC increases during the warm period. This denotes the marked influence of urban areas on the surrounding rural environment in this densely populated region.The different types of sites exhibit marked differences in the average concentrations of carbonaceous aerosol and OC/EC ratio. This ratio is less sensitive to atmospheric processing than OC and EC concentrations, and hence more representative of different source types. Remote locations are characterised by the lowest levels of OC and especially EC, with OC/EC ratios ranging from 13 to 20, while the maximum OC and EC concentrations are observed at road-traffic influenced urban sites, where the OC/EC ratio ranges between 1 and 3. The highest urban impacts of OC and EC relative to remote and rural background sites occur in the Po Valley, especially in the city of Milan, which has the highest concentrations of PM and TC and low values of the OC/EC ratio.
Keywords: Particulate matter; Organic carbon; Elemental carbon; OC/EC ratio; SOA;

Carbon monoxide over Indian region as observed by MOPITT by I.A. Girach; Prabha R. Nair (599-609).
A comprehensive study has been carried out on tropospheric carbon monoxide (CO) over the Indian land mass and surrounding oceanic region using the CO retrievals from MOPITT (Measurements of Pollution in the Troposphere) for a period of ∼14 years (2000–2014). The lower-tropospheric CO maximises during winter and shows a broad minimum during summer-monsoon over most of the regions, but with regionally varying seasonal amplitudes. Tropospheric column CO also exhibits a seasonal pattern similar to lower-tropospheric CO. But the upper-tropospheric CO shows an opposite seasonal pattern which peaks during summer monsoon. Columnar CO showed strong positive correlation with fire counts over west, east and north-east India, indicating the dominant role of biomass burning in controlling the seasonal variation of CO. The lower-tropospheric and columnar CO showed decreasing trend of 2.0–3.4 ppb year−1 (1.1–2.0% year−1) and 6.0–13.6 × 1015 molecules cm−2 year−1 (0.3–0.6% year−1) respectively over most of the regions. However, over many land regions trend in columnar CO is not significant. Most strikingly, the upper tropospheric CO showed increasing trend of 1.4–2.4 ppb year−1 (1.8–3.2% year−1). The analysis of biases in the estimated trends due to temporal changes in the MOPITT averaging kernels shows that magnitude of the realistic trend may change depending upon the bias but the sign (positive or negative) of trend remains the same. The decreasing trend in lower tropospheric and columnar CO could be attributed partly to increase in lower tropospheric water vapour and/or tropospheric ozone. The strengthening of convective activity, uplifting the CO to higher altitudes, could be a reason for increasing trend in the upper-tropospheric CO.
Keywords: Carbon monoxide; Seasonal variation; Biomass burning; Long-term trend;

Combustion emissions constitute the largest source of anthropogenic emissions in the US, and lead to the degradation of air quality and human health. In Part I we computed the population fine particulate matter (PM2.5) exposure and number of early deaths caused by emissions from six major sectors: electric power generation, industry, commercial and residential activities, road transportation, marine transportation and rail transportation. In Part II we attribute exposure and early deaths to sectors, emissions species, time of emission, and location of emission. We apply a long-term adjoint sensitivity analysis and calculate the four dimensional sensitivities (time and space) of PM2.5 exposure with respect to each emissions species. Epidemiological evidence is used to relate increased population exposure to premature mortalities. This is the first regional application of the adjoint sensitivity analysis method to characterize long-term air pollution exposure. (A global scale application has been undertaken related to intercontinental pollution.) We find that for the electric power generation sector 75% of the attributable PM2.5 exposure is due to SO2 emissions, and 80% of the annual impacts are attributed to emissions from April to September. In the road transportation sector, 29% of PM2.5 exposure is due to NO x emissions and 33% is from ammonia (NH3), which is a result of emissions after-treatment technologies. We estimate that the benefit of reducing NH3 emissions from road transportation is ∼20 times that of NO x per unit mass. 75% of the road transportation ammonia impacts occur during the months October to March. We publicly release the sensitivity matrices computed, noting their potential use as a rapid air quality policy assessment tool.
Keywords: Adjoint sensitivity analysis; Early deaths; Particulate matter;

Implementation of plume rise and its impacts on emissions and air quality modelling by Marc Guevara; Albert Soret; Gustavo Arévalo; Francesc Martínez; José M. Baldasano (618-629).
This work analyses the impact of implementing hourly plume rise calculations over Spain in terms of: i) vertical emission allocations and ii) modelled air quality concentrations. Two air quality simulations (4 km × 4 km, 1 h) were performed for February and June 2009, using the CALIOPE-AQFS system (WRF-ARW/HERMESv2.0/CMAQ/BSC-DREAM8b) differing only by the vertical allocation of point source emissions: i) using fixed vertical profiles based on the stack height of each facility and ii) using an hourly bottom-up calculations of effective emission heights. When using plume rise calculations, emissions are generally allocated to lower altitudes than when using the fixed vertical profiles, showing significant differences depending on source sector and air pollutant (up to 75% between estimated average effective emission heights). In terms of air quality, it is shown that hourly plume rise calculations lead to improved simulation of industrial SO2 concentrations, thus increasing modelled concentrations (1.4 μg m−3 increase in February, 1.5 μg m−3 increase in June) and reducing the model biases for both months (31.1% in February, 73.7% in June). The increase of SO2 concentrations leads to an increase of SO 4 − 2 surface levels that varies according to the season and location (4.3% in February and 0.4% in June, on average). On the other hand, the impact on NO2 and PM10 concentrations is less significant, leading to average changes of a few μg·m3 at most (0.4 μg m−3 for NO2 and 0.2 μg m−3 for PM10). In order to maximize the precision of plume rise calculations, the use of stack parameters based on real-world data is mandatory.
Keywords: Air quality modelling; Vertical distribution; Vertical emission profiles; Point source; Spain;

Response of the summertime ground-level ozone trend in the Chicago area to emission controls and temperature changes, 2005–2013 by Ping Jing; Zifeng Lu; Jia Xing; David G. Streets; Qian Tan; Timothy O'Brien; Joseph Kamberos (630-640).
Despite strenuous efforts to reduce the emissions of ozone precursors such as nitrogen oxides (NOx), concentrations of ground-level ozone (O3) still often exceed the National Ambient Air Quality Standard in U.S. cities in summertime, including Chicago. Furthermore, studies have projected a future increase in O3 formation due to global climate change. This study examines the response of summertime O3 to emission controls and temperature change in the Chicago area from 2005 to 2013 by employing observations of O3, O3 precursors, and meteorological variables. We find that meteorology explains about 53% of the O3 variance in Chicago. O3 mixing ratios over Chicago are found to show no clear decline over the 2005–2013 period. The summertime ground-level O3 trend consists of a decrease of 0.08 ppb/year between 2005 and 2009 and an increase of 1.49 ppb/year between 2009 and 2013. Emissions of NOx and concentrations of NO2 have been decreasing steadily from 2005 to 2013 in the Chicago area. Concentrations of volatile organic compounds (VOCs) in Chicago, however, have more than doubled since 2009, even though emission inventories suggest that VOC emissions have decreased. We believe that O3 production in Chicago became more sensitive to VOCs starting in 2008/2009 and may have switched from being NOx-limited to VOC-limited. The warmer climate since 2008 has also contributed to the increasing ozone trend in the Chicago area. Increased attention should be paid to improving the quantification of VOC sources, enhancing the monitoring of reactive VOC concentrations, and designing VOC mitigation measures.
Keywords: Ozone trend; Temperature dependence of ozone; NOx and VOC emission control; Chicago;

Indoor PM2.5 and its chemical composition during a heavy haze–fog episode at Jinan, China by Junmei Zhang; Jianmin Chen; Lingxiao Yang; Xiao Sui; Lan Yao; Longfei Zheng; Liang Wen; Caihong Xu; Wenxing Wang (641-649).
PM2.5 samples were collected in both a typical laboratory (indoors) and adjacent courtyard (outdoors) in Jinan, China from 12 January to 4 February 2013. The samples were analysed for 10 inorganic water-soluble ions, 14 elements and carbonaceous species to investigate their chemical characteristics and relationships with indoor and outdoor PM2.5 during a severe haze–fog (HF) episode and a normal (NHF) period. The average indoor and outdoor PM2.5 concentrations during the HF episode were 236 μg/m3 and 409 μg/m3, respectively, whereas the corresponding figures for the NHF period were 62 μg/m3 and 87 μg/m3. The predominant component was (NH4)2SO4, which accounted for 55.07% and 44.43% of the total measured species of indoor and outdoor PM2.5, respectively, in the HF episode, and 40.31% and 32.93%, respectively, in the NHF period. The indoor NH4NO3 level was significantly lower than the outdoor level due to volatility. The indoor and outdoor concentration ratios, infiltration rates, and indoor-generated concentration of PM2.5 and chemical compounds (SO4 2−, NO3 and EC) indicate that the aforementioned species had primarily outdoor sources, whereas NH4 + and OC and all the measured elements appear to have indoor sources, Cu in particular.
Keywords: Indoor/outdoor sources; Indoor PM2.5; Haze–fog episode; I/O ratio; Infiltration rate;

Classification of observed aerosols into key types [e.g., clean-maritime (CM), desert-dust (DD), urban-industrial/biomass-burning (UI/BB), black carbon (BC), organic carbon (OC) and mixed-type aerosols (MA)] would facilitate to infer aerosol sources, effects, and feedback mechanisms, not only to improve the accuracy of satellite retrievals but also to quantify the assessment of aerosol radiative impacts on climate. In this paper, we report the results of a study conducted in this direction, employing a Cimel Sun-sky radiometer at the Indian Institute of Tropical Meteorology (IITM), Pune, India during 2008 and 2009, which represent two successive contrasting monsoon years. The study provided an observational evidence to show that the local sources are subject to heavy loading of absorbing aerosols (dust and black carbon), with strong seasonality closely linked to the monsoon annual rainfall cycle over Pune, a tropical urban station in India. The results revealed the absence of CM aerosols in the pre-monsoon as well as in the monsoon seasons of 2009 as opposed to 2008. Higher loading of dust aerosols is observed in the pre-monsoon and monsoon seasons of 2009; majority may be coated with fine BC aerosols from local emissions, leading to reduction in regional rainfall. Further, significant decrease in coarse-mode AOD and presence of carbonaceous aerosols, affecting the aerosol–cloud interaction and monsoon-rain processes via microphysics and dynamics, is considered responsible for the reduction in rainfall during 2009. Additionally, we discuss how optical depth, contributed by different types of aerosols, influences the distribution of monsoon rainfall over an urban region using the Monitoring Atmospheric Composition and Climate (MACC) aerosol reanalysis. Furthermore, predictions of the Dust REgional Atmospheric Model (DREAM) simulations combined with HYSPLIT (HYbrid Single Particle Lagrangian Integrated Trajectory) cluster model are also discussed in support of the observed features.
Keywords: Cimel sun-sky radiometer; Aerosol types; Monsoon rainfall; MACC aerosol reanalysis; Cluster trajectory analysis; DREAM simulations;

In order to investigate the impact of data assimilation on the assessment of ozone concentration in inland regions in the eastern area of the Korean Peninsula, several numerical experiments have been carried out using the Weather Research and Forecasting (WRF) model to estimate atmospheric circulations and the Community Multiscale Air Quality (CMAQ) model to assess air quality. Observations of wind that are assimilated into the modeling system are obtained from a wind profiler located at Changwon (CW), which is an urbanized coastal region in the Korean Peninsula.The simulated wind and temperature that is related to a well-developed sea breeze circulation are more consistent with observations in the experiment with dada assimilation than that without the assimilation. The ozone concentrations at both the coastal area of CW and the inland region of DG are well reproduced in the simulation with application of profiler data assimilation. Results from experiments without data assimilation are less realistic than that from the experiment with data assimilation.However, the improvement in simulation of meteorological variables and ozone concentration due to data assimilation is greater in the inland area than in the coastal area, where the wind profiler is located. The ozone concentration in CW changes only over a limited area and below the altitude of 1 km with a maximum change of 25 ppb. In contrast, the simulated ozone concentration in DG has been improved from the ground to upper levels of the planetary boundary layer (PBL), despite the fact that the observations are collected and assimilated into the model at the coastal region. Based on the results of process analysis, we find that the horizontal and vertical transportation of ozone related to the sea-breeze is more important than the local contribution of chemical production in determining the ozone concentration over the inland area. Therefore, observations of wind profiles in the coastal area and assimilation of these observations into the modeling system are important in our modeling study to assess the ozone concentration in inland areas. The assimilation of observations can greatly improve the model performance in both circulation simulation and ozone concentration simulation.
Keywords: Ozone concentration; Wind profiler; Data assimilation; Process analysis; WRF-CMAQ;