Atmospheric Environment (v.45, #5)

Haagen-Smit Prize 2010 (1065-1066).

Key unknowns in estimating atmospheric emissions from UK land management by T.H. Misselbrook; J.N. Cape; L.M. Cardenas; D.R. Chadwick; U. Dragosits; P.J. Hobbs; E. Nemitz; S. Reis; U. Skiba; M.A. Sutton (1067-1074).
Robust emission inventories of atmospheric pollutants are critical to understanding and predicting impacts, identifying key sources and mitigation opportunities. The objective of this study was to review the extent to which UK land management is accounted for as a source of emission of ammonia (NH3), nitrous oxide (N2O), nitrogen oxides (NOx), organic nitrogen (Norg), methane (CH4), non-methane volatile organic compounds (NMVOC), particulate matter (PM) and heavy metals (HM), in comparison with the current state of scientific knowledge; to ascertain whether there is evidence for significant gaps or that key emission sources have been overlooked. The processes leading to emissions of NH3, N2O and CH4 are largely understood and all major sources are thought to be captured in the current inventory. Quantification of uncertainties in the estimates for some of these sources is still required, as is an assessment of the potential improvement in accuracy of estimates through the development of country-specific emission factors for N2O and CH4 in particular. There is limited knowledge about sources and processes leading to emissions of Norg and the role that these may play in local and global nitrogen budgets. Land management is known to be a source of NOx, NMVOC and PM emissions, and potentially also HM emissions. Improved quantification is required to assess the importance of land management as a source of these pollutants in comparison with other sectors and, if appropriate, to determine the potential for mitigation.► Major emission sources of NH3, N2O and CH4 from land management are accounted. ► The importance of land management for NOx, NMVOC and PM emissions is less certain. ► Emissions of organic nitrogen and their role in the atmosphere is poorly understood. ► Better quantification of the uncertainty in pollutant emission estimates is needed.
Keywords: Atmospheric pollutants; Land management; Uncertainties; Inventories;

The sources of dry-deposited trace elements (As, Cd, Cr, Cu, Mn, Ni, Pb, Sb and V) and the factors controlling their dry deposition fluxes were investigated on the basis of two-year observations (April 2004–March 2006) at a site on the Asian-continent side of Japan, which has been strongly affected by air pollutants from the Asian continent. Dry deposition sampling was conducted using a water surface sampler connected to a wet-only precipitation sampler. The dry deposition of As, Cd, Pb and Sb showed a small contribution to atmospheric deposition (0.25–0.44 as ratios of annual dry/wet deposition fluxes). Moreover, the dry deposition fluxes of those elements increased negligibly during the period when their atmospheric particulate matter (PM) concentrations increased owing to transport from the Asian continent. Thus, the dry deposition of As, Cd, Pb and Sb from the Asian continent was not significant, because their overall dry deposition velocities are relatively low (mostly <1 cm s−1). Conversely, the annual dry deposition fluxes of Cr, Cu and Ni exceeded their annual wet deposition fluxes (2.5–12.4 as ratios of annual dry/wet deposition fluxes). Those overall dry deposition velocities were much higher (3.2–9.7 cm s−1), and the crustal enrichment factors (EFs) frequently exceeded ten. These results suggest that the dry deposition of Cr, Cu and Ni is dominated by considerably coarse particles from local anthropogenic sources. For Mn and V, the dry and wet depositions contributed almost equally to the annual deposition fluxes. Their monthly dry deposition fluxes correlated significantly with that of Al (P < 0.001), and the EFs were close to unity, suggesting a large contribution of background soil to their dry deposition. The dry deposition fluxes of all the trace elements were dependent not on their atmospheric PM concentrations but on their overall dry deposition velocities. The particle size distributions of the elements in the atmosphere are likely the most important factor controlling their dry deposition fluxes on the Asian-continent side of Japan and, consequently, the relative contribution of the dry/wet deposition fluxes.► Dry deposition fluxes of trace elements were measured using a water surface sampler. ► Dry deposition fluxes of trace elements depend on their dry deposition velocities. ► Dry deposition of trace elements is dominated by coarse particles from local sources.
Keywords: Long-range transport of air pollutants; Kosa event; Dry deposition velocity; Enrichment factor; Wet deposition;

Response of ozone and nitrate to stationary source NO x emission reductions in the eastern USA by Thomas J. Butler; Francoise M. Vermeylen; Melissa Rury; Gene E. Likens; Brian Lee; George E. Bowker; Lance McCluney (1084-1094).
This study is an assessment of the impact of reduced stationary source NO x emissions on ground-level concentrations of ozone (O3) and dry-NO3 (HNO3(g) + NO3 (p)) in the eastern United States (EUS). Total anthropogenic NO x and VOC emissions have declined 32% and 20%, respectively, from 1997 to 2005 in the 20 eastern states participating in a NO x Budget Trading Program (NBP). Annual and ozone season (OS) NO x emissions from electric generating units (EGUs) have declined 48% and 66%, respectively, in the EUS.From 1997–1999 to 2006–2008 measured decline in meteorologically adjusted (met-adj) daily maximum 8-h (dm8h) O3, has been 8 ppb or 14% for the EUS during the May–September OS, with the largest declines occurring in the highest concentration category (99th percentile). Random coefficient models, with NBP and Acid Rain Program (ARP) regulated NO x emissions as the independent variable, show highly significant relations (p ≤ 0.0001) to dm8h O3 for 1997–2008 during the OS. Regional declines within the EUS range from 11% to 16%. The patterns of the O3 trends are in general agreement with other recent studies. Rural and urban sites both show similar levels of decline from pre- to post-NBP periods.Dry-NO3 during the OS shows a substantial decline from 3.1 to 1.8 μg NO3 m−3. Random coefficient models show regional results ranging from 32% to 39% declines, and measured results show a 35–46% decline in dry-NO3 from 1997–1999 to 2006–2008. These results suggest that regulating NO x emissions has been highly effective in reducing both ozone and dry-NO3 concentrations during the OS.Overall, a 32% reduction in total annual anthropogenic NO x emissions from 1997 to 2005 has been accompanied by a 7–8 ppb, or 12–13% decline in OS dm8h O3 concentration, and a 34% decline in dry-NO3 concentration in the 20-state NBP region. Model results indicate a 50% further reduction in NBP regulated NO x emissions will reduce O3 concentrations an additional 3–5% and dry-NO3 concentrations by 13–16%.► NBP and ARP NO x emissions have declined 70% from 1997 to 2008 in the Eastern US during O3 season. ► At the same time, daytime ozone in the Eastern US has declined 8 ppb or 14%. ► Dry-NO3 (particulate NO3 + HNO3(g)) has declined from 3.1 to 1.8 μg NO3 m−3. ► Both Dry-NO3 and daytime ozone are highly correlated to the NO x emission declines. ► Strong relations between O3 and NO x emissions exist for both rural and urban sites in the Eastern US.
Keywords: Ozone trends; Nitrate trends; NO x emissions; Random coefficient models; Nitrogen Budget trading program; NBP;

Effect of ammonium-based, non-sulfate fertilizers on CH4 emissions from a paddy field with a typical Chinese water management regime by Haibo Dong; Zhisheng Yao; Xunhua Zheng; Baoling Mei; Baohua Xie; Rui Wang; Jia Deng; Feng Cui; Jianguo Zhu (1095-1101).
The effects of ammonium-based, non-sulfate fertilizers, such as urea and/or ammonium phosphate (NH4H2PO4), on methane (CH4) emissions from paddy rice fields deserve attention, as they are being used increasingly for rice cultivation. A four-year field campaign was conducted in the Yangtze River Delta from 2004 to 2007 to assess the effects of different application rates of urea plus NH4H2PO4 on the CH4 emissions from a paddy rice field. The experimental field was under a typical Chinese water regime that follows a flooding-midseason drainage-reflooding-moist irrigation mode. Over the course of four years, the mean cumulative CH4 emissions during the rice seasons were 221, 136 and 112 kg C ha−1 for nitrogen addition rates of 0, 150 and 250 kg N ha−1, respectively. Compared to the treatment without nitrogen amendments, the 150 kg N ha−1 decreased the CH4 emissions by 6–59% (P  < 0.01 in one year, but not statistically significant in the others). When the addition rate was further increased to 250 kg N ha−1, the CH4 emissions were significantly reduced by 35–53% (P  < 0.01) compared to the no-nitrogen treatment. Thus, an addition rate of 250 kg N ha−1, which has been commonly adopted in the delta region in the past two decades, can be regarded as an effective management measure as regards increasing rice yields while reducing CH4 emissions. Considering that doses of ammonium-based, non-sulfate fertilizers higher than 250 kg N ha−1 currently are, and most likely will continue to be, commonly applied for paddy rice cultivation in the Yangtze River Delta and other parts of China, the inhibitory effects on CH4 emissions from rice production are expected to be pronounced at the regional scale. However, further studies are required to provide more concrete evidence about this issue. Moreover, further research is needed to determine whether N management measures are also effective in view of net greenhouse gas fluxes (including CH4, nitrous oxide, ammonia emissions, nitrate leaching and N loss from denitrification).► Emissions of CH4 showed high interannual variations. ► CH4 emission on average decreased with increasing N application rate. ► Ammonium-based, non-sulfate fertilizers enhanced rice yield and environmental merit.
Keywords: Methane; Paddy field; Nitrogen fertilizer; Intermittent irrigation;

Tree bark suber-included particles: A long-term accumulation site for elements of atmospheric origin by Mickaël Catinon; Sophie Ayrault; Lorenzo Spadini; Omar Boudouma; Juliette Asta; Michel Tissut; Patrick Ravanel (1102-1109).
The deposition of atmospheric elements on and into the bark of 4-year-old Fraxinus excelsior L. was studied. The elemental composition of the suber tissue was established through ICP-MS analysis and the presence of solid mineral particles included in this suber was established and described through SEM-EDX. Fractionation of the suber elements mixture was obtained after ashing at 550 °C through successive water (C fraction) and HNO3 2 M (D fraction) extraction, leading to an insoluble residue mainly composed of the solid mineral particles (E fraction). The triplicated % weight of C, D and E were respectively 34.4 ± 2.7, 64.8 ± 2.7 and 0.8 ± 0.1% of the suber ashes weight. The main component of C was K, of D was Ca. Noticeable amounts of Mg were also observed in D. The E fraction, composed of insoluble particles, was mostly constituted of geogenic products, with elements such as Si, Al, K, Mg, representing primary minerals. E also contained Ca3(PO4)2 and concentrated the main part of Pb and Fe. Moreover, The SEM-EDX analysis evidenced that this fraction also concentrated several types of fly ashes of industrial origin. The study of the distribution between C, D and E was analysed through ICP-MS with respect to their origin. The origin of the elements found in such bark was either geogenic (clay, micas, quartz…), anthropogenic or biogenic (for instance large amounts of solid Ca organic salts having a storage role). As opposed to the E fraction, the C fraction, mainly composed of highly soluble K+ is characteristic of a biological pool of plant origin. In fraction D, the very high amount of Ca++ corresponds to two different origins: biological or acid soluble minerals such as calcite. Furthermore, the D fraction contains the most part of pollutants of anthropic origin such as Zn, Cu, Ni, Co, Cd. As a whole, the fractionation procedure of the suber samples allows to separate elements as a function of their origin but also gives valuable information on distribution and speciation of trace elements.► Minerals of atmospheric origins can integrate tree suber. ► Fractionation of suber ashes gave first H2O solution (mostly K+, Na+). ► A HNO3 pH 2.5 solution contained most of the anthropogenic elements. ► In the remaining particles were geogenic components and anthropogenic fly ashes. ► In old trees, this fraction is able to represent an archive over several decades.
Keywords: Bark; Air pollution; Fly ashes; SEM-EDX; Fractionation; Fraxinus excelsior;

Effect of wastewater discharge on greenhouse gas fluxes from mangrove soils by G.C. Chen; N.F.Y. Tam; Y.S. Wong; Y. Ye (1110-1115).
The effects of wastewater on atmospheric fluxes of three greenhouse gases, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) from mangrove soils were investigated, and the differences among shrimp pond wastewater (SP), livestock wastewater (LS) and municipal (S) sewage were compared. The gas emissions from mangrove soils were significantly enhanced after wastewater irrigation and the highest emission of N2O and CO2 were obtained from SP. High N2O emission was also found in S treatment, where fluxes varied from 13.42 to 16.78 μmol m−2 h−1, but the CH4 and CO2 fluxes were as low as the control irrigated with tap water. Results of soil analyses indicated that the high N2O emissions from mangrove soils receiving SP and S treatments were attributed to the denitrification and nitrification processes, respectively. The highest CH4 flux was recorded in LS treatment (186.14–762.40 μmol m−2 h−1), which also had the highest CO2 flux. The fluxes measured during the non-irrigation period were lower than those measured 4 h after irrigation.► Wastewater discharge significantly increased greenhouse gas fluxes from soil. ► Shrimp pond wastewater (SP) induced the highest N2O flux due to denitrification. ► Nitrification was the main mechanism for N2O flux in municipal sewage treatment. ► Livestock wastewater treatment had low N2O as the control but highest CH4 flux. ► SP had high organic matter content but the CH4 flux was as low as the control.
Keywords: Denitrification; Mangrove; Methane; Nitrification; Nitrous oxide;

Source contributions to carbonaceous aerosol concentrations in Korea by Jaein I. Jeong; Rokjin J. Park; Jung-Hun Woo; Young-Ji Han; Seung-Muk Yi (1116-1125).
We estimated the source contributions to carbonaceous aerosol concentration in Korea on the basis of Intercontinental Chemical Transport Experiment Phase B (INTEX-B) anthropogenic emissions and satellite-derived biomass burning emissions by using a nested version of GEOS-Chem with a spatial resolution of 0.5° × 0.667° for the period March 2006–February 2007. First, we evaluated the model by comparing the simulated and observed aerosol concentrations at East Asia Network (EANET) sites and at a site in Korea. The results indicate that the model reproduces the variability and magnitudes of the observed SO4 2−, NO3 , and NH4 + concentrations in Korea and those of the observed PM10 concentrations in East Asia. However, the organic carbon (OC) and black carbon (BC) aerosol concentrations estimated by the model are lower than those observed in Korea by a factor of 2, especially in winter. This underestimation is likely due to extremely low domestic anthropogenic emissions and lack in seasonal variation. Source adjustments using a simple fitting and the Emission Database for Global Atmospheric Research (EDGAR) monthly allocation factors for seasonal variation yield significantly improved model results (R 2 increased from 0.58 to 0.84), which can then be used to estimate the source contributions to the OC and BC concentrations in Korea. We found that domestic anthropogenic emissions are the most important factors, contributing 74% (9% from fossil fuels and 65% from biofuels) and 78% (42% from fossil fuels and 36% from biofuels) to the OC and BC concentrations, respectively, on an annual mean basis in Korea. The trans-boundary transport of Chinese sources is another important factor, contributing 13% and 20% to the OC and BC concentrations, respectively. The contributions of wildfires and biogenic sources to the annual mean carbonaceous aerosol concentration in Korea are relatively small (4% and 6%, respectively).► The domestic anthropogenic emissions are found to be most important, contributing 74% (9% by fossil fuel and 65% by biofuel) and 78% (42% by fossil fuel and 36% by biofuel) to OC and BC concentrations, respectively, on an annual mean basis in Korea. ► Trans-boundary transport of Chinese sources is also an important factor contributing 13% and 20% to OC and BC. ► Contributions of wildfires and biogenic sources are relatively small, 4% and 6% to annual mean carbonaceous aerosol concentrations in Korea.
Keywords: Chemical transport model; Source contribution; Carbonaceous aerosol; Anthropogenic emission;

Modeling secondary organic aerosol using a dynamic partitioning approach incorporating particle aqueous-phase chemistry by Harshal M. Parikh; Annmarie G. Carlton; William Vizuete; Richard M. Kamens (1126-1137).
Current air quality model (AQM) systems use either an Odum-type two-product or a volatility basis set (VBS) approach to predict secondary organic aerosol (SOA) formation from toluene oxidation. For the SOA module in AQM systems, the stoichiometric and partitioning coefficients used in both these approaches are typically developed from laboratory studies conducted in a single chamber, under a limited set of conditions (e.g., low humidity and initial (NH4)2SO4 seed), and with an implicit assumption of instantaneous thermodynamic equilibrium. In this study, we evaluated independent toluene laboratory studies that include experiments with different combinations of initial toluene, NOx, non-SOA-forming hydrocarbon mixture, initial seed type, and humidity. When evaluated against this observational data set both the Odum-type and VBS approaches fail to predict observed SOA when tested under dry conditions, in the presence of the hydrocarbon mixture, and with low initial seed mass, regardless of seed type. For wet experiments, predictions of temporal trends in aerosol mass growth from both approaches are inconsistent with observations; this is especially true earlier in the day under high humidity conditions. Based on these findings, a new SOA mechanism is developed that includes: 1) gas-phase reaction of semi-volatile products and a dynamic partitioning approach with accommodation coefficient as the principal transport parameter, 2) an additional pathway of SOA formation due to uptake of polar species into the particle aqueous-phase. The new mechanism improves predicted SOA mass reproducing observations from all experiments. Since these changes were made exclusively to existing algorithms in SOA modules, minimal modifications would be required to update air quality models to utilize this approach.► Smog chamber evaluation of SOA modules used in current air quality models. ► Development of new generalized SOA module for air quality models. ► Dominant aqueous phase SOA formation from toluene oxidation in high humidity. ► Kinetic and mass-transfer limitation to partitioning in particle organic phase.
Keywords: Secondary organic aerosol; Toluene; Glyoxal uptake; Thermodynamic equilibrium; Dynamic partitioning;

Measurements of carbon dioxide in an Oregon metropolitan region by Andrew Rice; Gregory Bostrom (1138-1144).
Ambient concentrations of atmospheric carbon dioxide (CO2) are reported for the Portland, Oregon (USA) metropolitan region for the late July through December, 2009 period. Three stationary locations were established: a downtown location on the campus of Portland State University; a residential site in southeast Portland; and a rural station on Sauvie Island, located ∼30 km northwest of Portland in the Columbia River Gorge. Continuous measurements of CO2 at each site average 403–408 ppm and show considerable variability at each site (360–610 ppm) due to CO2 sources, sinks and meteorological variability. Within this variability, a marked 20–30 ppm diurnal cycle is observed due to photosynthetic activity and variations in the planetary boundary layer. In-city CO2 concentrations are on average enhanced by 5–6 ppm over the Sauvie Island site during upgorge wind conditions, a difference which is greatest in the afternoon. Measurements of the 13C/12C ratio of CO2 in downtown Portland are significantly depleted in 13C relative to 12C compared with background air and suggest that regional CO2 is dominated by petroleum sources (75–80%). High degrees of relationship between CO2 variability and primary air pollutants CO and NO (r 2 = 0.80 and 0.77), measured by the Oregon Department of Environmental Quality at the Southeast Portland location, corroborate this finding and illustrate the importance of traffic emissions on elevated ambient CO2 concentrations.► We study carbon dioxide in the Portland, Oregon metropolitan region. ► In-city concentrations are enhanced by 5–6 ppm on average above an upwind site. ► Carbon isotopic composition is depleted due to regional fossil sources. ► Correlations with primary pollutants indicate traffic emissions as large source. ► Isotopic composition indicates that petroleum is 75–80% of the total.
Keywords: Carbon dioxide; Urban carbon budget; Urban area; Greenhouse gas emission; Traffic emission; Portland;

Air quality trends and potential health effects – Development of an aggregate risk index by Pierre Sicard; Olivia Lesne; Nicolas Alexandre; Antoine Mangin; Rémy Collomp (1145-1153).
The “Provence Alpes Côte d’Azur” (PACA) region, in the South East of France, is one of Europe’s regions most influenced by the atmospheric pollution. During the last 15 years, the industrial emissions decrease caused an evolution of the atmospheric pollution nature. Nowadays, atmospheric pollution is more and more influenced by the road traffic, the dominating pollution source in urban zones for the PACA region. Combined with this intense road traffic, the strong hot season of the Mediterranean climate contributes to the region bad air quality; it is known to be one of the worse in Europe. The recognized air pollution effects over public health include increased risk of hospital admissions and mortality by respiratory or cardiovascular diseases. The combination of these serious pollution related health hazards with senior and children vulnerabilities leads to serious sanitary concerns. Over the 1990–2005 period, we obtained, using the non-parametric Mann–Kendall test from annual mortality dataset (CépiDC), decreasing trends for Asthma (−5.00% year−1), Cardiovascular (−0.73% year−1), Ischemic (−0.69% year−1) and cerebrovascular diseases (−3.10% year−1). However, for “Other heart diseases” (+0.10% year−1) and “Respiratory” (+0.10% year−1) an increase was observed. The development of an adequate tool to understand impacts of pollution levels is of utmost importance. Different pollutants have different health endpoints, information may be lost through the use of a single index consequently, in this study we present the modified formula of air quality index, based on Cairncross’s concept the Aggregate Risk Index (ARI). ARI is based on the relative risk of the well-established increased daily mortality, or morbidity, enabling an assessment of additive effects of short-term exposure to the main air pollutants: PM2.5, PM10, SO2, O3 and NO2 in order to account for the reality of the multiple exposures impacts of chemical agents. The ARI, developed per pathology, takes into account the possible adverse effects associated with the coexistence of all pollutants. This index will enable to communicate the health risks associated, from modelled or monitored pollutant concentrations, to the general population. The second step will consist in the construction of a prediction model of this sanitary index.► We examine changes in pollution level time series and mortality occurrences. ► We discuss possible interpretations for the observed trends. ► We discuss plausible air quality impacts on human health. ► We develop a tool to allow an assessment of additive effects of air pollutants and associated risks.
Keywords: Aggregate risk index; Air quality; PACA region; Relative risk; Mortality; Trends;

Traffic and emission simulation in China based on statistical methodology by Huan Liu; Kebin He; Matthew Barth (1154-1161).
To better understand how the traffic control can affect vehicle emissions, a novel TRaffic And Vehicle Emission Linkage (TRAVEL) approach was developed based on local traffic activity and emission data. This approach consists of a two-stage mapping from general traffic information to traffic flow patterns, and then to the aggregated emission rates. 39 traffic flow patterns and corresponding emission rates for light-duty and heavy-duty vehicles considering emission standards classification are generated. As a case study, vehicle activity and emissions during the Beijing Olympics were simulated and compared to BAU scenario. Approximately 42–65% of the gaseous pollutants and 24% of the particle pollutants from cars, taxies and buses were reduced. These results are validated by traffic and air quality monitoring data during the Olympics, as well as other emission inventory studies. This approach improves the ability to fast predict emission variation from traffic control measurements in several typical Chinese cities. Comments related to application of this approach with both advantages and limitations are included.► Approach developed in this research improves the ability to fast predict emission variation from traffic control measurements. ► The TRAVEL could expand current understanding of how traffic volume and road type impact emission factors and total emissions on freeway, arterial and residential roads in China cities. ► The TRAVEL also improves the temporal and spatial resolution of inventories into 1 hr and street level. ► These results are validated by traffic and air quality monitoring data during the Olympics, as well as other emission inventory studies.
Keywords: Traffic flow; Vehicle emission; Simulation; Olympic case;

Impact of California’s air pollution laws on black carbon and their implications for direct radiative forcing by Ranjit Bahadur; Yan Feng; Lynn M. Russell; V. Ramanathan (1162-1167).
We examine the temporal and the spatial trends in the concentrations of black carbon (BC) – recorded by the IMPROVE monitoring network for the past 20 years – in California. Annual average BC concentrations in California have decreased by about 50% from 0.46 μg m−3 in 1989 to 0.24 μ gm−3 in 2008 compared to the corresponding reductions in diesel BC emissions (also about 50%) from a peak of 0.013 Tg Yr−1 in 1990 to 0.006 Tg Yr−1 by 2008. We attribute the observed negative trends to the reduction in vehicular emissions due to stringent statewide regulations. Our conclusion that the reduction in diesel emissions is a primary cause of the observed BC reduction is also substantiated by a significant decrease in the ratio of BC to non-BC aerosols. The absorption efficiency of aerosols at visible wavelengths – determined from the observed scattering coefficient and the observed BC – also decreased by about 50% leading to a model-inferred negative direct radiative forcing (a cooling effect) of −1.4 W m−2 (±60%) over California.► Annual average BC concentrations decreased by about 50% from 0.46 μg m−3 in 1989 to 0.24 μg m−3 in 2008 in California. ► A reduction in diesel BC emissions from a peak of 0.013 Tg Yr−1 in 1990, to 0.006 Tg Yr−1 by 2008 is also observed. ► No long-term trend in the concentrations of scattering aerosols (nitrate, sulfate, and organic carbon) in this period. ► The negative trend in BC is attributed to statewide regulations on vehicular and non-vehicular diesel exhaust. ► That the reduction in absorption efficiency of aerosols at visible wavelengths has led a cooling effect of −1.4 W m−2 over California.
Keywords: Black carbon; Radiative forcing; Diesel emission control;

Observation of carbon and oxygen isotopic compositions of CO2 at an urban site in Nagoya using Mid-IR laser absorption spectroscopy by R. Wada; J.K. Pearce; T. Nakayama; Y. Matsumi; T. Hiyama; G. Inoue; T. Shibata (1168-1174).
We report the application of Mid-IR laser spectroscopy to differentiation of CO2 sources. High-frequency isotopic CO2 measurements (δ13C and δ18O) in urban air in Nagoya allow for the contributions of anthropogenic and biogenic CO2 sources to be differentiated. The laser spectroscopic method, using a Mid-IR quantum cascade laser, provides us with the advantage of higher temporal resolution of the data compared to traditional isotope ratio mass spectroscopy. The relative contribution of CO2 sources in Nagoya was found to be roughly 0.42, 0.33 and 0.25 for natural combustion, gasoline combustion and biogenic respiration in the spring, but with large short-term (hourly) variations dependent on wind direction, and long-term variations dependent on heating demand and biological seasonality.► Mid-IR laser spectroscopy was applied for differentiation of CO2 sources in urban air. ► High-frequency isotopic CO2 measurements (δ13C and δ18O) were performed. ► Relative contribution of CO2 sources showed short-term and seasonal variations. ► Relative contribution of CO2 sources changed in different atmospheric conditions. ► A quantum cascade laser was used for the Mid-IR laser spectroscopy.
Keywords: Atmospheric CO2; Carbon isotope; Oxygen isotope; Laser spectroscopy; CO2 source;

Sources of excess urban carbonaceous aerosol in the Pearl River Delta Region, China by Mei Zheng; Fu Wang; G.S.W. Hagler; Ximei Hou; Michael Bergin; Yuan Cheng; L.G. Salmon; James J. Schauer; Peter K.K. Louie; Limin Zeng; Yuanhang Zhang (1175-1182).
Carbonaceous aerosol is one of the important constituents of fine particulate matter (PM2.5) in southern China, including the Pearl River Delta (PRD) region and Hong Kong (HK). During the study period (October and December of 2002, and March and June of 2003), the monthly average organic carbon (OC) ranged from 3.52 to 7.87 μg m−3 in Hong Kong and 4.14–20.19 μg m−3 in the PRD from simultaneous measurements at three sites in HK and four sites in the PRD. Compared to the PRD, the spatial distribution of carbonaceous aerosol in Hong Kong was relatively homogeneous. Sources contributing to excess OC in the PRD were examined, which is the difference between OC concentrations measured at the PRD sites to the average level in Hong Kong. Eight primary sources contributing to excess OC were identified with chemical mass balance modeling in a combination with molecular markers analyzed by gas chromatography/mass spectrometry. Excess OC at Guangzhou, the capital city of Guangdong province, was consistently high, ranging from 9.77 to 13.6 μg m−3. Four primary sources including gasoline engine exhaust, diesel engine exhaust, biomass burning, and coal combustion accounted for more than 50% of excess OC in the PRD, especially in December (up to 76%). Mobile source emissions alone can contribute about 30% of excess OC. The unexplained or other excess OC was the highest at the rural site, but in general less than 20% at other sites. The coal combustion source contribution was unique in that it exhibited relatively homogeneous spatial distribution, indicating it was still an important source of carbonaceous aerosol in the PRD (17% of excess OC) during the study period. This analysis revealed that primary emissions are important sources of excess OC in the PRD and there is a need to reduce the emissions of mobile sources, biomass burning, and coal combustion in order to improve air quality in southern China.
Keywords: Organic carbon; Source apportionment; Molecular markers; Chemical mass balance; The Pearl River Delta;

In our previous study, exceptionally high concentrations of nitrate (24-h average of up to 42 μg m−3) were found in ammonium-deficient samples of PM2.5 during summer 2005 near Beijing and Shanghai. The formation of such high levels of nitrate in ammonium-poor PM2.5 cannot be explained by the homogeneous gas-phase reaction mechanism involving ammonia and nitric acid. Hence, we postulated that high levels of nitrate were formed via the heterogeneous hydrolysis of N2O5. In the present study, we further examine the formation of nitrate using hourly measurements of sulfate and nitrate and a multiphase chemistry box model (RACM + CAPRAM). Enhancements of nitrate and the NO3 /NOy ratio were observed at nighttime when sulfate and NOy concentrations remained relatively stable. These enhancements and a concomitant shift in the size of the nitrate concentration peak to a bin larger than that of sulfate peak suggested the possibility that nitrate was formed on pre-existing sulfate aerosol surfaces. A multiphase chemistry box model was set up to simulate the observed enhancement of nitrate at nighttime. The model was constrained by the measured concentrations of sulfate, nitrate, ammonium and O3 and NOy, and estimated acidity and aerosol water content using a thermodynamic model (AIM). Assuming an NO2/NOy ratio in the range of 0.2–0.4 for Beijing and 0.4–0.6 for Shanghai, the model results suggest that the heterogeneous hydrolysis of N2O5 contributed 50%–100% of the nighttime enhancement of nitrate concentration. Sensitivity analysis shows that increasing the aerosol water content significantly favors the partitioning of nitrate in the aerosol phase that was formed via the hydrolysis of N2O5 at nighttime.
Keywords: Nighttime nitrate chemistry; Reaction probability of N2O5; China; Heterogeneous hydrolysis of N2O5;

The main objective of this study was to investigate the causes as well as the temporal and spatial dynamics of ozone pollution during three high ozone episodes in the northeastern Mediterranean Basin using surface measurements and WRF/Chem model simulations. The simulation results revealed that the analyzed episodes were mainly caused by the impact of accumulation of pollution rich in ozone over the northern Adriatic. Two mechanisms were simulated: (1) the accumulated pollutants occasionally encroaching and retreating, impacting the coastal areas; and (2) broad advection impacting areas further inland in the northeastern Mediterranean Basin including Slovenia. The simulations also show that in some specific conditions the elevated ozone levels over continental Slovenia can be separated from the direct Mediterranean influences by the Alpine-Dinaric mountain ridge. The simulations show a trend of underestimating maximum and overestimating minimum ozone concentrations, but the overall statistics agree fairly well with the statistics of the measured ozone concentrations.► The study focuses on origin of ozone pollution during three high concentration episodes. ► Characteristics of the accumulation and advection phases of ozone are identified. ► Ozone-rich layers accumulated over the Adriatic Sea and coastal regions during the episodes. ► The accumulated pollution was advected inland by the southwesterly flows.
Keywords: Mediterranean ozone; Adriatic Sea; Air quality; Complex topography;

Understanding how the leaf area density (a(z)) and its depth integrated value, the leaf area index (LAI), modify dry deposition velocities (V d) of aerosol particles within the canopy sub-layer is needed for progressing on a plethora of aerosol related problems in climate change, air quality, and ecosystem service evaluation. Here, the interplay between a(z) (and LAI) of tall and densely forested canopies, the flow dynamics, and V d are explored via model calculations. A multi-layer size-resolving deposition model (hereafter referred to as MLM) is coupled to a second-order closure model (WS77), which are then used to explore a subset of the manifold of a(z) and LAI variations and their concomitant effects on the relationship between V d and particle diameter (d p). The combined MLM-WS77 calculations are evaluated against V d measurements collected above a Scots pine stand in Hyytiälä (southern Finland) in which a(z) was experimentally manipulated via forest thinning. Three key findings are derived from these model calculations: (1) at a given LAI, a near-constant a(z) yields the lowest V d for a given d p class, (2) when the foliage is concentrated in the upper layers of the canopy, increasing LAI predictably increases V d at a given d p, though some saturation occurs thereafter, but (3) suppressing turbo-phoresis leads to an opposite conclusion, decrease of V d with LAI increase, for a d p class between 0.5 and 5 μm. Comparison between the combined MLM-WS77 calculations and a recently proposed pipe-flow analogy formulation that includes turbo-phoresis are also presented.
Keywords: Aerosol particle dry-deposition; Canopy turbulence; Forest thinning; Higher order closure; Leaf area density; Turbo-phoresis;

The advantages of the original form of the predictive expression for the gas/particle partition constant K p (m3  μg−1) are considered. The expression K p,i for compound i contains p L , i o , ζ i and MW ¯ . These are the pure-compound liquid vapor pressure, the mole-fraction-scale activity coefficient in the absorbing particulate matter (PM) phase, and the mean molecular weight (g mol−1) of the absorbing phase. Algorithms are available for predicting ζ i values in mixtures of organic compounds and water as they are affected by energetic and entropic effects; Flory–Huggins Theory provides a convenient way to examine the entropic effects of the presence of high MW compounds on the ζ i values of lower MW compounds. In the exposition of their volatility basis set (VBS) approach for modeling organic aerosol condensation, Donahue et al. (2006, Environ. Sci. Technol., 40, 2635–2643, Supplementary Material) argued that the need to consider MW ¯ values can be avoided by switching from the mole fraction scale to a mass fraction scale and accompanying C i ∗ values that incorporate mass-fraction-scale activity coefficient values ζ i ′ . In practice however, the VBS approach usually ignores both activity and MW ¯ corrections by setting ζ i ′ = 1 . (An equation for ζ i ′ is developed here in the event that modeling with ζ i ′ ≠ 1 becomes of interest.) Regardless of the advantages of the prediction equation for K p,i , there will undoubtedly be circumstances when MW ¯ and ζ i values become inaccessible, as for aged organic particulate matter in which a large mass fraction of the absorbing PM of is of indeterminable molecular nature. In such cases, “prediction” of K p,i values may only be possible by means of empirical correlation of log K p,i vs. log p L , i o for the PM type of interest.► Thermodynamic derivation of traditional gas/particle partitioning constant K p is reviewed. ► Varying thermodynamics of absorbing phase most easily considered in K p approach. ► This includes the effects of varying mean molecular weight and activity coefficients.
Keywords: Organic particulate matter; OPM; Secondary organic aerosol; SOA; Absorption model; Mole-fraction; Accretion products; Oligomers; Flory–Huggins;

Assessing in near real time the impact of the April 2010 Eyjafjallajökull ash plume on air quality by Augustin Colette; Olivier Favez; Frédérik Meleux; Laura Chiappini; Martial Haeffelin; Yohann Morille; Laure Malherbe; Arnaud Papin; Bertrand Bessagnet; Laurent Menut; Eva Leoz; Laurence Rouïl (1217-1221).
The eruption of the Eyjafjallajökull in April 2010 led to the injection in the troposphere of an important quantity of volcanic ash whose advection towards densely populated areas raised serious concerns regarding potential impacts on air quality. Here we investigate to what extent air quality in France was altered using exclusively quantitative data that was available in near real-time. We rely on a combination of atmospheric dispersion modelling, ground-based remote sensing, and chemical characterization of airborne particles. One week after the onset of the eruption we were able to conclude that the Eyjafjallajökull ash plume was locally responsible for an increase of up to 30 ± 10 μg m−3 of total PM10 (particulate matter finer than 10 μm) that reached 65 μg m-3 on 18 and 19 April 2010. The methodology presented in this letter offers promising perspectives in terms of emergency response strategy when facing such unforeseen atmospheric dispersion events.
Keywords: Air quality; Eyjafjallajökull; Long range transport; Lidar remote sensing; Chemistry transport modelling;