Atmospheric Environment (v.51, #C)

Ozone production from wildfires: A critical review by Daniel A. Jaffe; Nicole L. Wigder (1-10).
Tropospheric ozone (O3) negatively impacts human health and ecosystems, and is a greenhouse gas. Wildfires are a source of tropospheric O3, and studies show that wildfires are increasing in North America. In this study, we present a critical review of O3 production from wildfires focusing on three key topics: the influence of wildfire emissions on O3 production; the influence of photochemistry on wildfire O3 production; and regulatory issues associated with wildfire O3 production in the United States. Observations of ΔO3/ΔCO range from approximately −0.1 to 0.9, and are caused by the interplay of numerous factors including fire emissions, efficiency of combustion, chemical and photochemical reactions, aerosol effects on chemistry and radiation, and local and downwind meteorological patterns. Using average ΔO3/ΔCO ratios for major biomes, we estimate global wildfires produce approximately 170 Tg of O3 per year, which is 3.5% of all global tropospheric O3 production. Areas of uncertainty in wildfire O3 production include the net effect of aerosols on chemical and photochemical reactions within a fire plume, the impact of oxygenated volatile organic compounds and nitrous acid on O3 production, and the interplay of variables that lead to extreme ΔO3/ΔCO values. Because wildfire frequencies are likely increasing and have been shown to contribute to elevated O3 at air quality monitoring sites, it is important to better understand the emissions, photochemistry and impacts of these fires.► Wildfires produce approximately 170 Tg of O3 globally per year. ► Observations of ΔO3/ΔCO in fire plumes range from approximately −0.1 to 0.9. ► O3 production depends on fire emissions, photochemical reactions, meteorology and aerosol effects. ► Wildfires can contribute to exceedances of the ozone air quality standard.
Keywords: Ozone production; Wildfires; Air quality impacts; Ozone exceedances; Ozone photochemistry; Fire emissions;

Characterization of aerosol acidity at a high mountain site in central eastern China by Yang Zhou; Likun Xue; Tao Wang; Xiaomei Gao; Zhe Wang; Xinfeng Wang; Jiamin Zhang; Qingzhu Zhang; Wenxing Wang (11-20).
Aerosol acidity plays an important role in the formation of secondary organic aerosols. In the present study, strong and aerosol acidity properties of PM2.5 were evaluated based on the highly time-resolved measurements of PM2.5 ionic compositions obtained at the highest mountain site in central eastern China in spring and summer of 2007. Overall, PM2.5 was weakly acidic at Mt. Tai with 57.2% and 81.3% of the observations being acidic aerosols in spring and summer, respectively. Strong and aerosol acidities showed higher levels in summer (mean ± stand deviation: 142.65 ± 115.23 and 35.27 ± 30.88 nmol m−3) and lower concentrations in spring (64.82 ± 75.07 and 25.25 ± 32.23 nmol m−3). Aerosol pH exhibited an opposite seasonal trend with less acidic aerosols in summer compared to the aerosols in spring due to high water content in the particles in summer. Strong acidity showed a well-defined diurnal profile with a broad peak during the daytime, while aerosol acidity was at relatively low level in the daytime. The effects of ambient RH and atmospheric aging on the acidities of PM2.5 were examined. Aerosol water content facilitated the release of free H+ in the aerosol droplet via hydrolysis processes of bisulphate and acidic aerosols were often associated with more processed air masses. Several cases with formation and accumulation of secondary organic aerosols occurring were investigated. The results indicated that the increase of secondary organic aerosols was probably due to effects of acidity promotion and aqueous phase formation. This is the first attempt to investigate aerosol acidity based on high resolution measurements of aerosol ions in central eastern China.► Hourly data of water-soluble ions in PM2.5 was used to evaluate the aerosol acidity. ► PM2.5 was weakly acidic at Mt. Tai, with higher acidities in summer than in spring. ► Secondary organic aerosol formation events were investigated in more detail. ► Aerosol acidity promoted the serious secondary aerosol pollution at Mt. Tai. ► Aqueous phase reactions enhanced the secondary aerosol formation.
Keywords: Semi-continuous measurements; Aerosol acidity; AIM-II; Mt. Tai; PM2.5; Secondary organic aerosol formation;

Black carbon aerosol characterization in a coastal city in South China using a single particle soot photometer by Xiao-Feng Huang; Tian-Le Sun; Li-Wu Zeng; Guang-He Yu; Sheng-Ji Luan (21-28).
Black carbon (BC) is the dominant light-absorbing aerosol component in the atmosphere and plays an important role in atmospheric pollution and climate change. The light-absorbing properties of BC rely on particle size, shape, composition, as well as the BC mixing state with other aerosol components, thus more thorough exploration of BC aerosol characteristics is critical in understanding its atmospheric sources and effects. In this study, a newly-developed Single Particle Soot Photometer (SP2) was deployed in Shenzhen, China, for continuous BC measurements to obtain the important information about size distribution and mixing state of BC under severe air pollution conditions of China. The mean BC mass concentrations were found to be 6.0 and 4.1 μg m−3 at an urban site (UT) in the fall and winter, respectively, while it is much lower (2.6 μg m−3) at a rural site (BG) in the fall. The mass size distributions of BC in volume equivalent diameter (VED) at the three sites showed a similar lognormal pattern, with the peak diameter at BG (222 nm) slightly larger than at the UT (210 nm) site. As to mixing state, the average percentage of internally mixed BC at the UT site was detected to be 40% and 46% in the fall and winter, respectively, while that at the BG site in the fall was only a slightly higher (47%), which implies that fresh local fossil fuel combustions were still significant at this rural site. The analysis of extremely high BC concentrations (>20 μg m−3) at UT indicates that they were a complex of comparable contributions from both local fresh emissions and regional transport under unfavorable meteorology. Other characteristics of BC aerosol and their influencing factors in Shenzhen were also discussed.► A newly-developed single particle soot photometer was deployed in Shenzhen, China. ► Size distribution and mixing state of black carbon aerosol were measured on-line. ► Black carbon aerosol showed features of both local emissions and regional transport.
Keywords: Single Particle Soot Photometer (SP2); Black carbon (BC); Size distribution; Mixing state;

Risk of lower respiratory diseases was significantly correlated with levels of monthly average concentration of SO2; NO2 and association rules have high lifts. In view of Lanzhou’s special geographical location, taking into account the impact of different seasons, especially for the winter, the relations between air pollutants and the respiratory disease deserve further study. In this study the monthly average concentration of SO2, NO2, PM10 and the monthly number of people who in hospital because of lower respiratory disease from January 2001 to December 2005 are grouped equidistant and considered as the terms of transactions. Then based on the relational algebraic theory we employed the optimization relation association rule to mine the association rules of the transactions. Based on the association rules revealing the effects of air pollutants on the lower respiratory disease, we forecast the number of person who suffered from lower respiratory disease by the group method of data handling (GMDH) to reveal the risk and give a consultation to the hospital in Xigu District, the most seriously polluted district in Lanzhou. The data and analysis indicate that individuals may be susceptible to the short-term effects of pollution and thus suffer from lower respiratory diseases and this effect presents seasonal.► Extract the association rules between lower respiratory diseases and the level of air pollution. ► Association rules extracted by data mining can be a supplementation of the causal analysis. ► The group method of data handling network gives a perspective of the lower respiratory diseases.
Keywords: Lower respiratory diseases; Association rules; ORAR; GMDH; Air pollution; Lanzhou;

Characteristics of water-soluble ions and carbon in fine and coarse particles collected near an open burning site by Chih-Chung Lin; Kuo-Lin Huang; Jen-Hsiung Tsai; Wen-Jhy Lee; Shui-Jen Chen; Shao-Kai Lin (39-45).
This study investigates the chemical characteristics of particles that were collected from the open burning of wax apple agricultural waste, and evaluates the impact of such burning on regional air quality. The water-soluble ions, elemental carbon (EC), and organic carbon (OC) in fine (D p ≤ 2.5 μm) and coarse (2.5 < D p ≤ 10 μm) particles were collected using a micro-orifice uniform deposition impactor (MOUDI) and two Dichot samplers. The average PM2.5/PM10 ratio during open burning (0.90) was higher than those both before and after burning (0.57 and 0.55, respectively). The particle distributions before and during burning were bi-modal and uni-modal, respectively. During the open burning, the OC or K+ content markedly increased; however, that of secondary aerosol ( NH 4 + , NO 3 − and SO 4 2 − ) decreased. The Na+/Cl molar ratios of fine particles before, after, and during the open burning 0.40, 0.18, and 0.24, respectively; however, the corresponding (Na+ + K+)/Cl molar ratios were 0.74, 0.99, and 0.39, respectively. OC, K+ and Cl were quite abundant in the open burning of agricultural waste (wax apple), and the OC/Na+, K+/Na+, and Cl/Na+ (mass) ratios in fine particles (318, 10.2, and 10.5, respectively) may be used as reference indexes associated with the open burning of wax apple waste.► We evaluate aerosol water-soluble ions and carbons near an open burning site. ► During the open burning, the OC and K+ contents markedly increase. ► K+/Na+ and Cl/Na+ ratios may be used as indexes associated with the open burning.
Keywords: Biomass combustion; Particle size distribution; Agricultural waste; Smoke aerosol;

Fugitive pollutant sources from the oil and gas industry are typically quite difficult to find within industrial plants and refineries, yet they are a significant contributor of global greenhouse gas emissions. A novel approach for locating fugitive emission sources using computationally efficient trajectory statistical methods (TSM) has been investigated in detailed proof-of-concept simulations. Four TSMs were examined in a variety of source emissions scenarios developed using transient CFD simulations on the simplified geometry of an actual gas plant: potential source contribution function (PSCF), concentration weighted trajectory (CWT), residence time weighted concentration (RTWC), and quantitative transport bias analysis (QTBA). Quantitative comparisons were made using a correlation measure based on search area from the source(s). PSCF, CWT and RTWC could all distinguish areas near major sources from the surroundings. QTBA successfully located sources in only some cases, even when provided with a large data set. RTWC, given sufficient domain trajectory coverage, distinguished source areas best, but otherwise could produce false source predictions. Using RTWC in conjunction with CWT could overcome this issue as well as reduce sensitivity to noise in the data. The results demonstrate that TSMs are a promising approach for identifying fugitive emissions sources within complex facility geometries.► Trajectory statistical methods can identify fugitive emissions sources. ► Test data from CFD model of wind and gas release over simplified gas plant geometry. ► Among several TSMs, RTWC was best, but could give false sources with poor data. ► Algorithms could be made relatively insensitive to concentration measurement noise. ► RTWC used in conjunction with CWT is a promising approach.
Keywords: Fugitive emissions; Trajectory statistical methods; Source location; Backward trajectories;

We apply a three-dimensional prognostic model, namely TAPM, consisting of coupled meteorological and air pollution modules to simulate the turbulence and short-range dispersion (about 0.5 km) of a near-surface tracer release measured during the 1974 Idaho Falls experiment in light-wind stable conditions. We find that the model substantially underestimates the concentration data. An examination of the near-surface turbulence levels reveals that the modelled vertical turbulence is similar in magnitude to the data but the horizontal component is seriously underestimated. We investigate the latter through a comparison of the boundary condition for the turbulent kinetic energy (TKE) in the model with turbulence data from the U.K. Met Office’s Cardington site, and propose a semi-empirical modification to the TKE boundary condition that accounts for the observed horizontal meandering of the air not represented in the model. This modification increases the modelled horizontal turbulence for the Idaho Falls case, in accordance with the observations, but leads to a further underestimation of the observed concentrations. We attribute this underestimation to the inadequacy of vertical resolution in the model in resolving the concentration gradients near the ground. It is not feasible to simply increase the vertical model resolution near the surface, and instead we derive an analytical scheme based on a mass-balance approach that corrects the modelled concentrations at the lowest model level for such gradients. A remarkable improvement in the predicted concentrations is obtained following the application of the derived correction factor. This factor can be easily incorporated in a typical model for point sources and is valid for all stabilities. Lastly, it is clear that more research is required on horizontal flow meandering and its incorporation in prognostic models.► A prognostic model, TAPM, is applied to dispersion in light-wind stable conditions. ► The model underestimates observed concentrations and horizontal turbulence. ► A modification to the turbulent kinetic energy boundary condition is proposed. ► A new analytical scheme resolves concentrations below the first model level. ► A remarkable improvement in the predicted concentrations is obtained.
Keywords: Calm winds; Cardington data; Horizontal meandering; Idaho Falls experiment; Mesoscale modelling; Model resolution; Stable boundary layer; TAPM;

As part of an extensive modeling effort on the air–soil-groundwater transport pathway of perfluorooctanoic acid (PFOA), this study was designed to compare the performance of different air dispersion modeling systems (AERMOD vs. ISCST3), and different approaches to handling incomplete meteorological data using a data set with substantial soil measurements and a well characterized point source for air emissions. Two of the most commonly used EPA air dispersion models, AERMOD and ISCST3, were linked with the EPA vadose zone model PRZM-3. Predicted deposition rates from the air dispersion model were used as input values for the vadose zone model to estimate soil concentrations of PFOA at different depths. We applied 34 years of meteorological data including hourly surface measurements from Parkersburg Airport and 5 years of onsite wind direction and speed to the air dispersion models. We compared offsite measured soil concentrations to predictions made for the corresponding sampling depths, focusing on soil rather than air measurements because the offsite soil samples were less likely to be influenced by short-term variability in emission rates and meteorological conditions. PFOA concentrations in surface soil (0–30 cm depth) were under-predicted and those in subsurface soil (>30 cm depth) were over-predicted compared to observed concentrations by both linked air and vadose zone model. Overall, the simulated values from the linked modeling system were positively correlated with those observed in surface soil (Spearman’s rho, R sp  = 0.59–0.70) and subsurface soil (R sp  = 0.46–0.48). This approach provides a useful modeling scheme for similar exposure and risk analyses where the air–soil-groundwater transport is a primary contamination pathway.► We link air models with a soil model to understand an air–soil transport pathway. ► Predicted PFOA soil concentrations were compared to observed concentrations. ► The simulated values were positively correlated with observed values. ► ISCST3 predicts surface soil concentration better than AERMOD with Parkersburg data.
Keywords: Perfluorooctanoic acid; Air dispersion modeling; Vadose zone modeling; Meteorological data;

We evaluated global and regional aerosol optical depth (AOD) trends in view of aerosol (precursor) emission changes between 2000 and 2009. We used AOD data products from MODIS, MISR and AERONET and emission estimates from the EMEP, REAS and IPCC inventories. The trends in global monthly AOD of MODIS (L3), MISR (L3) and AERONET (L2) are significantly negative over Europe and North America, whereas over South and East Asia they are mostly positive. The calculated 2000–2009 trends from the monthly L3 products correspond well with the more detailed daily MODIS L2 AODs for three selected regions (Central Mediterranean, North-East America and East Asia). Furthermore, daily and monthly AERONET L2 AOD trends agree well. The trends in AOD are compared to estimated emission changes of SO2, NOx, NH3 and black carbon. We associate the downward trends in AOD over Europe and North America with decreasing emissions of SO2, NOx and other pollutants. Over East Asia the MODIS L2 trends are generally positive, consistent with increasing pollutant emissions by fossil energy use and growing industrial and urban activities. It appears that SO2 emission changes dominate the AOD trends, although especially in Asia NOx emissions may become increasingly important. Our results suggest that solar brightening due to decreasing SO2 emissions and the resulting downward AOD trends over Europe may have weakened in the 2000s compared to the 1990s.► AOD trends by MODIS, MISR, AERONET are negative over Europe and North America. ► Over South and East Asia AOD trends are positive. ► Increasing/decreasing AOD trends are related to increasing/decreasing of pollutants. ► AOD trends from the MODIS monthly L3 products correspond well with MODIS L2. ► Daily and monthly AERONET Level 2 AOD trends agree well.
Keywords: AOD trends MODIS; MISR; AERONET; Emission pollutants;

Odor, gaseous and PM10 emissions from small scale combustion of wood types indigenous to Central Europe by Magdalena Kistler; Christoph Schmidl; Emmanuel Padouvas; Heinrich Giebl; Johann Lohninger; Reinhard Ellinger; Heidi Bauer; Hans Puxbaum (86-93).
In this study, we investigated the emissions, including odor, from log wood stoves, burning wood types indigenous to mid-European countries such as Austria, Czech Republic, Hungary, Slovak Republic, Slovenia, Switzerland, as well as Baden-Württemberg and Bavaria (Germany) and South Tyrol (Italy). The investigations were performed with a modern, certified, 8 kW, manually fired log wood stove, and the results were compared to emissions from a modern 9 kW pellet stove. The examined wood types were deciduous species: black locust, black poplar, European hornbeam, European beech, pedunculate oak (also known as “common oak”), sessile oak, turkey oak and conifers: Austrian black pine, European larch, Norway spruce, Scots pine, silver fir, as well as hardwood briquettes. In addition, “garden biomass” such as pine cones, pine needles and dry leaves were burnt in the log wood stove. The pellet stove was fired with softwood pellets.The composite average emission rates for log wood and briquettes were 2030 mg MJ−1 for CO; 89 mg MJ−1 for NOx, 311 mg MJ−1 for CxHy, 67 mg MJ−1 for particulate matter PM10 and average odor concentration was at 2430 OU m−3. CO, CxHy and PM10 emissions from pellets combustion were lower by factors of 10, 13 and 3, while considering NOx – comparable to the log wood emissions. Odor from pellets combustion was not detectable. CxHy and PM10 emissions from garden biomass (needles and leaves) burning were 10 times higher than for log wood, while CO and NOx rise only slightly. Odor levels ranged from not detectable (pellets) to around 19,000 OU m−3 (dry leaves). The odor concentration correlated with CO, CxHy and PM10. For log wood combustion average odor ranged from 536 OU m−3 for hornbeam to 5217 OU m−3 for fir, indicating a considerable influence of the wood type on odor concentration.► Study reports emissions from burning of 12 wood types and pellets in modern stoves. ► We examine CO, hydrocarbons (CxHy), PM10 and odor. ► Emissions show high inter-species variability. ► Odor from wood burning is PM10 and CxHy related and is formed mostly during smoldering. ► Pellets burning in an automatically operated stove does not cause odor.
Keywords: Wood smoke; Odor; Biomass combustion; Particulate emissions; Pellet stove; Log wood stove;

Chemical and size characterization of particles emitted from the burning of coal and wood in rural households in Guizhou, China by Hefeng Zhang; Shuxiao Wang; Jiming Hao; Lin Wan; Jingkun Jiang; Min Zhang; Heidi E.S. Mestl; Line W.H. Alnes; Kristin Aunan; Abdel Wahid Mellouki (94-99).
Field measurements were conducted to determine indoor air particulate pollutant emissions from the burning of coal and wood, two major household fuels, in rural households in Guizhou, China. Chemical composition, particle mass and particle size distribution as well as number concentration were measured in this study. Chemical composition analysis indicates that the carbonaceous particle is dominant in the PM2.5 mass, accounting for about 41% for wood and 55% for coal. The OC/EC ratio was 10.8 for wood and 7.6 for coal. Most of the water-soluble ions were found in the 0.4–2.1 μm size fractions and dominated by ammonium and sulfate. Particle mass concentrations inversely correlate with particle total number concentrations during the sampling period. Obvious differences were observed in the evolution of particle number concentrations and size distributions between coal combustion and wood burning. Particles emitted from coal combustion were characterized by unimodal size distribution, with average peak values ranging from 70.3 to 75.7 nm during the flaming stage of the burning cycle. Particles from wood burning were characterized by a transition from a bimodal size distribution to a unimodal distribution during the same period. Average peak values in the bimodal mode were 10–20 nm (nucleation mode) and 40–50 nm (Aitken mode), whereas the average peak value in the unimodal mode was about 63 nm.Display Omitted► Measurements were conducted to characterize indoor particle emissions in China. ► Chemical analysis showed that carbonaceous particle is dominant in the PM2.5 mass. ► Reverse trend was observed between mass and number concentrations. ► Evolution of particle size distributions were observed during the flaming stage.
Keywords: Wood burning; Coal combustion; Chemical composition; Mass concentration; Number concentration; Size distribution;

Weekday related anthropogenic aerosol emissions have been suggested to affect regional climate via indirect aerosol effects. I studied the variability of potential cloud condensation nuclei using measurements of number size distributions of Cloud Condensation Nuclei (CCN)-sized aerosol particles and CCNs measured at several European regional background stations, located at a wide variety of environments. With notably rare exceptions, there were no statistically significant difference between concentrations on different weekdays. I further analysed the concentration time-series of four long-period datasets in Germany and Finland with wavelet analysis. Outside of urban areas, very little weekday-connected variability was found. The lack of 7-day variability outside of cities is in contrast of earlier studies in this field, which used mostly particle mass as the representative measure of aerosol concentration. A time-scale and variability analysis showed that PM10 and PM2.5 are more sensitive for the weekly variation than CCN-sized particles. Using mass-based variations as a proxy for short-term variations of CCN particle numbers can thus overestimate the weekend effect for these particles. The results of this study do not support aerosol indirect effects from 50 to 500 nm diameter particles as a major contributor on potential weekday connected variations in European meteorology.► The weekly variation of cloud condensation nuclei sized aerosol concentrations was studied. ► No clear signal of weekly variation in the number of CCN was found in the European background air. ► Time-scale analysis shows that most mass-based measurements overestimate the weekly variability of CCNs. ► Using PM or optical measurements to evaluate the short-term variability of NCCN is not recommended. ► The indirect aerosol effects are not likely to cause weekly variation in European background.
Keywords: Cloud condensation nuclei; Weekend effect; Aerosol number concentration; Wavelet analysis; Time-scale analysis;

PAH volatilization following application of coal-tar-based pavement sealant by Peter C. Van Metre; Michael S. Majewski; Barbara J. Mahler; William T. Foreman; Christopher L. Braun; Jennifer T. Wilson; Teresa L. Burbank (108-115).
Coal-tar-based pavement sealants, a major source of PAHs to urban water bodies, have recently been identified as a source of volatile PAHs to the atmosphere. We tracked the volatilization of PAHs for 1 year after application of a coal-tar-based pavement sealant by measuring gas-phase PAH concentrations above the pavement surface and solid-phase PAH concentrations in sealant scraped from the surface. Gas-phase concentrations at two heights (0.03 and 1.28 m) and wind speed were used to estimate volatilization flux. The sum of the concentrations of eight frequently detected PAHs (ΣPAH8) in the 0.03-m sample 1.6 h after application (297,000 ng m−3) was about 5000 times greater than that previously reported for the same height above unsealed parking lots (66 ng m−3). Flux at 1.6 h after application was estimated at 45,000 μg m−2 h−1 and decreased rapidly during the 45 days after application to 160 μg m−2 h−1. Loss of PAHs from the adhered sealant also was rapid, with about a 50% decrease in solid-phase ΣPAH8 concentration over the 45 days after application. There was general agreement, given the uncertainties, in the estimated mass of ΣPAH8 lost to the atmosphere on the basis of air sampling (2–3 g m−2) and adhered sealant sampling (6 g m−2) during the first 16 days after application, translating to a loss to the atmosphere of one-quarter to one-half of the PAHs in the sealcoat product. Combining the estimated mass of ΣPAH8 released to the atmosphere with a national-use estimate of coal-tar-based sealant suggests that PAH emissions from new coal-tar-based sealcoat applications each year (∼1000 Mg) are larger than annual vehicle emissions of PAHs for the United States.Display Omitted► Greatly elevated PAH concentrations in air occur soon after sealant application. ► PAH fluxes and concentrations in air decrease rapidly after application. ► Rapid changes in PAH fluxes coincide with rapid losses from the sealant surface. ► Total PAH emissions during initial drying probably exceed annual vehicle emissions.
Keywords: PAHs; Emissions; Atmosphere; Sealcoat; Coal-tar;

The impact of ultrafine particles (diameters <100 nm) on human health has been addressed in many toxicological studies. It is therefore important to assess relevant respiratory exposure of the population. In this paper, aerosol number-size distribution was measured with 1 s time resolution, in a street canyon, in proximity to traffic, with the purpose of studying the fast evolution of UFP doses deposited in the respiratory system. Close to the traffic, nucleation particle concentrations increase within few seconds and decrease in tens of seconds. As a consequence, the exposure pattern, near to traffic, may be represented as a sequence of short-term peak exposures. The number of UFPs deposited for each tidal volume of air inhaled (instant UFP doses) rapidly reaches level of 107 particles, with maximum values for the alveolar interstitial region. For the correct estimate of short-term exposures, in scenarios involving proximity to traffic, it is therefore crucial to rely on aerosol measurements with a time resolution able to trace the fast evolution of aerosol from vehicle exhausts. When traffic levels drop, spike values of instant UFP doses are comparatively less frequent and the maxima of their size distributions shift from 10 to 20 nm (nucleation particles) to greater diameter (up to about 60 nm).Display Omitted► Traffic aerosol evolves within few seconds, for the formation of nucleation particles and tens of seconds for their removal. ► Close to vehicular exhausts, the respiratory exposure may be represented by a sequence of short-term high peak exposures. ► To estimate such brief exposures, measurement time resolution should be in the time scale of few tens of seconds. ► UFP respiratory doses were calculated with 1 and 0.03 Hz aerosol data, in a downtown area close to traffic. ► Differences between the two data-sets, in terms of number of UFPs deposited for each respiratory act, are discussed.
Keywords: Ultra fine particles; Fast evolution; Respiratory exposure; Peak exposures; Regional deposition;

Predicting reaction rate constants of ozone with organic compounds from radical structures by Xinliang Yu; Bing Yi; Xueye Wang; Jianfang Chen (124-130).
The reaction rate constants of ozone with organic compounds in the atmosphere were predicted by a quantitative structure–activity relationship (QSAR) model. Density functional theory (DFT) calculations, for the first time, were carried out on the radicals from organic compounds, at the UB3LYP level of theory with 6-31G(d) basis set. A set of quantum chemical descriptors calculated from the radicals, the energy of the highest occupied molecular orbital of beta spin states (E βHOMO), the molecular average polarizability (α), and the total energy (E T), were used to build the general QSAR model for aliphatic compounds, applying the genetic algorithm (GA) technique and support vector machine (SVM) regression. The root mean square errors (RMSE) are 0.680 for the training set (68 compounds), 0.777 for the validation set (36 compounds) and 0.709 for the test set (35 compounds). Investigated results indicate that the SVM model given here has good predictivity for aliphatic compounds.Three quantum chemical descriptors derived from the radicals of corresponding chemicals by DFT/UB3LYP level of theory can be well used to predict reaction rate constants of ozone with 139 aliphatic compounds in the atmosphere.Display Omitted► A new SVM model was developed for ozone reaction rate constants k O 3 . ► Molecular descriptors were calculated from the radicals. ► Only three descriptors were used in the SVM model. ► Calculating descriptors from radicals is feasible.
Keywords: DFT; Ozone; QSAR; Quantum chemical descriptors; Radicals; Rate constant;

The uncertainty in particle size distribution retrievals is analyzed theoretically and numerically when using aerosol optical depth (AOD) data affected by three distinct error-inducing effects. Specifically, circumsolar radiation (CS), optical mass (OM), and solar disk’s brightness distribution (BD) effects are taken into consideration here. Because of these effects, the theoretical AOD is affected by an error, ∂AOD, that consequently translates into errors in the determined (apparent) particle size distribution (PSD). Through comparison of the apparent and the true size distributions, the relative error, ∂PSD, is calculated here as a function of particle radius for various instrument’s fields of view (aperture) and solar zenith angles. It is shown that, in general, the CS effect overestimates the number of submicron-sized particles, and that the significance of this effect increases with the aperture. In case of maritime aerosols, the CS effect may also lead to an underestimation of the number concentration of large micron-sized particles. The BD and OM effects become important, and possibly predominant, when AOD is low. Assuming large particles dominate in the atmosphere, the BD effect tends to underestimate the concentration of the smallest aerosol particles. In general, the PSD(apparent)/PSD(true) ratio is affected by the CS effect equally over all particle sizes. The relative errors in PSD are typically smaller than 40–60%, but can exceptionally exceed 100%, which means that the apparent PSD may then be twice as large as the true PSD. This extreme situation typically occurs with maritime aerosols under elevated humidity conditions. Recent instruments tend to be designed with smaller apertures than ever before, which lower the CS-induced errors to an acceptable level in most cases.► The uncertainty in particle size distribution retrievals is analyzed theoretically. ► Circumsolar, optical mass, and brightness distribution effects are considered. ► If unaccounted for, these effects yield errors in retrieved aerosol optical depth. ► The retrieved size distribution of maritime aerosols is particularly affected. ► Results show the effects of photometer field of view, zenith angle and humidity.
Keywords: Aerosol size distribution depth; Circumsolar radiation; Light scattering; Sunphotometry; Radiometry;

Study of PCBs and PBDEs in King George Island, Antarctica, using PUF passive air sampling by Yingming Li; Dawei Geng; Fubin Liu; Thanh Wang; Pu Wang; Qinghua Zhang; Guibin Jiang (140-145).
Polyurethane foam (PUF)-disk based passive air samplers were deployed in King George Island, Antarctica, during the austral summer of 2009–2010, to investigate levels, distributions and potential sources of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Antarctic air. The atmospheric levels of ∑ indicator PCBs and ∑14 PBDEs ranged from 1.66 to 6.50 pg m−3 and from 0.67 to 2.98 pg m−3, respectively. PCBs homologue profiles were dominated by di-PCBs, tri-PCBs and tetra-PCBs, whereas BDE-17 and BDE-28 were the predominant congeners of PBDEs, which could be explained by long-range atmospheric transport processes. However, the sampling sites close to the Antarctic research stations showed higher atmospheric concentrations of PCBs and PBDEs than the other sites, reflecting potential local sources from the Antarctic research stations. The non-Aroclor congener PCB-11 was found in all the air samples, with air concentrations of 3.60–31.4 pg m−3 (average 15.2 pg m−3). Comparison between the results derived from PUF-disk passive air sampling and high-volume air sampling validates the feasibility of using the passive air samplers in Antarctic air. To our knowledge, this study is the first employment of PUF-disk based passive air samplers in Antarctic atmosphere.► PUF-based passive air sampling was conducted in King George Island, Antarctica. ► Atmospheric levels of ∑ indicator PCBs ranged from 1.66 to 6.50 pg m−3. ► The air concentrations of ∑ PBDEs ranged from 0.67 to 2.98 pg m−3. ► LRAT and local sources from research stations were suspected as main sources. ► This study demonstrates the feasibility of using PUF samplers in Antarctic air.
Keywords: Antarctica; PUF-disk passive air sampling; PCBs; PBDEs; PCB-11;

Sulfur dioxide and nitrogen oxides form two of largest contributors to PM2.5 in Europe; ammonium sulfate ((NH4)2SO4) and ammonium nitrate (NH4NO3). In-situ observations of many chemical components are rather sparse, and thus neither can accurately characterize the distribution of pollutants nor predict the effectiveness of emission control. Understanding (and controlling) the formation regimes for these components is important for the achievement of the reduction objectives established in the European legislation for PM2.5 (20% of PM2.5 triennial for the mean of urban background levels between 2018 and 2020). For this purpose, the present work uses the CALIOPE high-resolution air quality modeling system (12 km × 12 km, 1 h) to investigate the formation of SIA (SO4 2−, NO3 and NH4 +, which involve an important part of PM) and their gaseous precursors (SO2, HNO3 and NH3) over Europe during the year 2004. The CALIOPE system performs well at estimating SIAs when compared to the measurements from EMEP monitoring network, but errors are larger for gaseous precursors. NH3 is underestimated in the warmest months, HNO3 tends to be overestimated in the summer months, and SO2 appears to be systematically overestimated. The temporal treatment of ammonia emission is a probable source of uncertainty in the model representation of SIA. Furthermore, we discuss the annual pattern for each inorganic aerosol and gas precursor species over Europe estimated with the EMEP data and CALIOPE outputs, comparing the performance with other European studies. Spatial distribution of key indicators is used to characterize chemical regimes and understand the sensitivity of SIA components to their emission precursors. Results indicate that SO4 2− is not usually fully neutralized to ammonium sulfate in ambient measurements and is usually fully neutralized in model estimates. CALIOPE and EMEP observations agree that the continental regions in Europe tend to be HNO3-limited for nitrate formation. Regulatory strategies in such regions should focus on reductions in NO x (NO + NO2) rather than NH3 to control ammonium nitrate. This work assesses how well the CALIOPE system reproduces the spatial and temporal variability of SIAs and their gaseous precursors over Europe and complements the measurement findings.► Regional evaluation of the CALIOPE system for SIA and precursors. ► Regional evaluation against measurements and other European studies. ► Uncertainties in current European chemical transport models. ► Assessing SIA formation in Europe through modeling and measuring techniques.
Keywords: Air quality; Model evaluation; Aerosol precursors; Geochemistry; Sulfate; Nitrate; Ammonia;

Sectoral and geographical contributions to summertime continental United States (CONUS) black carbon spatial distributions by Min Huang; Gregory R. Carmichael; Sarika Kulkarni; David G. Streets; Zifeng Lu; Qiang Zhang; R. Bradley Pierce; Yutaka Kondo; Jose L. Jimenez; Michael J. Cubison; Bruce Anderson; Armin Wisthaler (165-174).
The sectoral and regional contributions from northern hemisphere anthropogenic and biomass burning emission sectors to black carbon (BC) distributions over the continental United States (CONUS) in summer 2008 are studied using the Sulfur Transport and dEposition Model (STEM). North American (NA) emissions heavily (>70% of total emissions) affect the BC levels from the surface to ∼5 km, while non-NA plumes compose more than half of the BC above ∼5 km. Among all sectors, NA and non-NA biomass burning, NA transportation and non-NA residential emissions are the major contributors. The sectoral contributions vary among ten regions defined by the US Environmental Protection Agency (EPA): NA anthropogenic emissions enhance northeastern US BC levels; biomass burning strongly impacts northern California and southeastern US; and the influence of extra-regional plumes is largest in the northwestern US but extends to eastern US. The mean contribution from non-NA sources to US surface BC is ∼0.05 μg m−3, with a maximum value of ∼0.11 μg m−3 in the northwestern US. The non-NA contributions to column BC are higher than to surface BC, ranging from 30% to 80%, depending on region. EPA region 8 is most sensitive to extra-regional BC, partially explaining the observed increasing BC trend there during the past decades associated with the increasing Asian BC emissions. Measurements from the June 24 DC-8 flight during the ARCTAS-CARB field campaign show that BC/(organic matter + nitrate + sulfate) mass ratios fairly well represent BC's warming potential over southern California, which can be approximated by BC/(organic matter + sulfate) and BC/sulfate for plumes affected and unaffected by fires, respectively. The responses of BC/(organic matter + sulfate) and BC/sulfate to removing each emission sector are further discussed, indicating that mitigating NA transportation emissions has the highest potential for regional air quality and climate co-benefits.► Source contributions to summertime CONUS BC distributions vary among EPA regions. ► Ratios of BC/cooling aerosols can be used to represent plume warming potentials. ► EPA Region 10 receives highest amount of extra-regional BC. ► EPA Region 8 is most sensitive to extra-regional BC.
Keywords: Black carbon; Sectoral and geographical contributions; Warming potential;

Advection of aerosols from adjoining continental regions into the Bay of Bengal (BoB) is considered important in view of its potential aerosol radiative impacts on Indian summer monsoon and the mesoscale weather. Though several reports are available on the features of Aerosol Optical Depth (AOD) over BoB region based on cruise as well as satellite data, day to day variability over the oceanic regions due to day to day variability at the aerosol source regions and advection pathways is yet incomplete. In this article results on a systematic investigation carried out on the AOD vis-a-vis the advection pathways indicate that the day to day variability in AOD could possibly be reflected as spatial variation when short period cruise measurements are made. A statistical analysis of the short period variations using W-ICARB cruise data and the MODIS satellite data for the whole winter 2008–09 show that in 65% of the case, the airmass pathways have the potential of inducing large day to day variability in AOD with 79% of the cases over eastern BoB affected by east Asian airmass, 98% of the cases over western BoB affected by airmass pathways from the Indian region, while the southern BoB is mostly affected by the east Asian aerosol transport, which is significant in altering the mean AOD features over the regions. Long term assessment using MODIS data for the period 2005–2010 indicate that there is a steady increase in AOD over the western BoB during 2005–2010, while it is more or less stable over southern BoB.► Regional short term perturbations in AOD over BoB are studied statistically. ► Advection from the India is inducing 98% perturbations over western BoB. ► East Asian advection is causing 84% perturbations in southern BoB. ► Major advection is from IGB over west BoB in winter and East Asia in other seasons. ► Increasing trend in AOD over western BoB from 2005 to 2010 is observed.
Keywords: Aerosols; Bay of Bengal; Advection;

Comparative study of aerosol and cloud detected by CALIPSO and OMI by Zhong Chen; Omar Torres; M. Patrick McCormick; William Smith; Changwoo Ahn (187-195).
Aerosol and cloud play important roles in the atmosphere and climate system. Accurately detecting their presence, altitude, and properties using satellite radiance measurements is a very important task. This paper presents a comparative analysis of the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Level 2 Vertical Feature Mask (VFM) product with the Ozone Monitoring Instrument (OMI) UV Aerosol Index (UVAI) and reflectivity datasets for a full year of 2007 from regional to global scales. Based on CALIPSO and OMI observations, the vertical and horizontal extent of clouds and aerosols are determined and effects of aerosol type, load and cloud fraction on aerosol identification are discussed. It was found that the spatial–temporal correlation found between CALIPSO and OMI observations, is strongly dependent on aerosol types and cloud contamination. CALIPSO is more sensitivity to cloud and often misidentifies aerosol as cloud, while some small scale aerosol layers as well as some pollution aerosols are unidentified by OMI UVAI. Large differences in aerosol distribution patterns between CALIPSO and OMI are observed, especially for the smoke and pollution aerosol dominated areas. In addition, the results found a significant correlation between CALIPSO lidar 1064 nm backscatter and the OMI UVAI over the study regions.► Capabilities of CALIPSO and OMI to detect aerosol and cloud. ► Large differences in aerosol distribution patterns between CALIPSO and OMI. ► Relationship between the CALIPSO measured 1064 nm backscatter and the OMI derived UVAI. ► Satellite’s horizontal coverage, resolution and vertical information.
Keywords: Aerosol; Satellite measurements; Comparative analysis;

Atmospheric polycyclic aromatic hydrocarbon profiles and sources in pine needles and particulate matter in Dayton, Ohio, USA by Timothy A. Tomashuk; Triet M. Truong; Madhavi Mantha; Audrey E. McGowin (196-202).
Polycyclic aromatic hydrocarbons (PAHs) were measured in pine needles (passive sampling) and on high-volume particulate matter (PM) filters (active sampling) over a period of eight to ten months at two separate sites in the Dayton, Ohio, USA metropolitan area: Moraine and Yellow Springs. Total PAH concentrations for PM ranged from 77.4 μg g−1 to 837 μg g−1 (dry wt.) at both sites with high molecular weight PAHs being the predominant form that tended to be higher in concentration during the colder months. Total PAH concentrations for pine needles varied by tree species and location. With an average concentration of 4187 ng g−1, Austrian pine (Pinus nigra) needles in Moraine ranged from 2543 ng g−1to 6111 ng g−1 (dry wt.) with the lowest and highest concentrations occurring in October and August, respectively. The amount of phenanthrene was extremely high for August, 4200 ± 112, which could have resulted from the close proximity of the tree to the parking lot at a firehouse. White pine (Pinus strobus) needles in Yellow Springs had an average concentration of 384 ng g−1and ranged from 127 ng g−1 to 589 ng g−1 (dry wt.) with September and November, respectively, having the lowest and highest PAH concentrations. The 2- and 3-ring PAHs were the predominant form in P. nigra, while the 4-ring PAHs predominated in P. strobus. Total PAH concentrations in P. nigra were an order of magnitude greater than for P. strobus. A bivariate plot of BaA/(BaA + Chry) versus Flt(Flt + Pyr) allowed the PM and pine needle data to be included in the same source analysis and indicated sources of PM at both sites were biomass and/or coal combustion. This plot also suggested PAHs in Yellow Springs P. strobus originated from petroleum combustion sources, whereas PAHs in Moraine P. nigra originated from petroleum combustion with some sources more aged or remote.► Simultaneous active and passive sampling for atmospheric PAHs at two locations over ten months. ► Particulate matter and pine needles collected different fractions of PAHs from the atmosphere. ► PAH profiles of two pine species were dissimilar. ► Bivariant plots of isomeric ratios showed that active and passive sampling were complementary. ► Known industrial and municipal activities coincided with conclusions from the bivariant plots.
Keywords: Pine needles; PAHs; Particulate matter; Passive sampling; Biomonitor; Source apportionment;

Towards improved bottom-up inventories of methane from the European land surface by Dennis Grunwald; Ann-Catrin Fender; Stefan Erasmi; Hermann F. Jungkunst (203-211).
Forests and wetlands are generally seen as opposites in the methane cycle of terrestrial ecosystems. Wetlands are sources for atmospheric methane and forest soils sinks. However, this greenhouse gas is also emitted by wet forest soils, which is commonly disregarded due to lacking information on their spatial distribution. Here, we estimated the potential bias made for the European methane budget of terrestrial ecosystems when neglecting wet forest ecosystems but including rice paddies and latest estimates for lakes. We appointed distinct annual methane rates for individual land use types based on a literature survey and weighted them according to their European area. This was performed separately for four major ecozones (cold, temperate, continental and Mediterranean). Three approaches were applied: (1) the mean values for forests and wetlands were calculated in three different scenarios, (2) assuming that boreal needle-leaved evergreen forest with a low tree cover (<40%) is predominately forested wetland (3) assuming different shares of wet forest ecosystems in individual forest areas. For the net balance 2.8 Tg CH4–C a−1 were calculated which includes emissions from rice paddies (0.2 Tg CH4–C a−1) and from lakes (2.5 Tg CH4–C a−1). The different approaches for the net balances that included wet forest ecosystems mainly ranged between 4.6 and 6.7 Tg CH4–C a−1. The results suggest that wet forest ecosystems are approximately as important as wetlands for the European methane balance. European bottom-up inventories are improved best by more accurate mapping of wetlands both within and outside forests and more flux data for lakes and continental wetlands.► Ways of improving bottom-up inventories of methane source or sink ecosystems shown. ► Plausible range for the net European ecosystem methane balance given. ► Wet forest soils likely to be as important as wetlands as methane sources. ► Methane release from wetlands of continental Europe potentially crucial – data utterly needed. ► Precise determination of the area of methane sources is the key to improvements.
Keywords: GHG inventory; Spatial modeling; Upscaling; Hydromorphic soils; Continental scale; Land use;

Regional ozone and particulate matter (PM) pollution have a strong dependence on prevailing meteorological conditions. The occurrence of favorable conditions on a regional scale may be influenced by concurrent large scale climatic events like El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). These events evolve over inter-annual and decadal timescales and may result in variability of seasonal/annual frequency of air pollution episodes. The scarcity of measurements of criteria pollutants, especially ozone and PM, limits the scope of observing the influence of climate variability in the past few decades on regional pollution levels. To identify these trends, the frequency of occurrence of conducive conditions during the summer (ozone) and winter (PM2.5) seasons are first obtained for the period 1950–2008. The identified days are subsequently utilized in a generalized linear modeling (GLM) framework to identify the effects of ENSO and PDO on the occurrence of exceedence conducive days. To demonstrate the applicability of the developed methodology, we study the influence of ENSO and PDO on summer ozone and winter PM2.5 pollution at 6 non-attainment regions in the United States.► We identify the frequency of occurrence of exceedance conducive conditions during past 6 decades. ► Ozone and PM2.5 regional air pollution is studied at 6 non-attainment areas in the United States. ► We quantify ENSO and PDO influence on regional air quality using generalized linear models. ► Large scale climate variability was found to have regionally varying influence on ozone and PM2.5 pollution.
Keywords: ENSO; PDO; Air quality; Exceedance conducive (EC); Generalized Linear Models (GLM);

Performance of a microenviromental model for estimating personal NO2 exposure in children by Anna Mölter; Sarah Lindley; Frank de Vocht; Raymond Agius; Gina Kerry; Katy Johnson; Mike Ashmore; Andrew Terry; Sani Dimitroulopoulou; Angela Simpson (225-233).
A common problem in epidemiological studies on air pollution is exposure misclassification, because investigators often assume exposure is equivalent to outdoor concentrations at participants’ homes or at the nearest urban monitor.The aims of this study were: (1) to develop a new microenvironmental exposure model (MEEM), combining time-activity data with modelled outdoor and indoor NO2 concentrations; (2) to evaluate MEEM against data collected with Ogawa™ personal samplers (OPS); (3) to compare its performance against datasets typically used in epidemiological studies.Schoolchildren wore a personal NO2 sampler, kept a time-activity diary and completed a questionnaire. This information was used by MEEM to estimate individuals’ exposures. These were then compared against concentrations measured by OPS, modelled outdoor concentrations at the children’s home (HOME) and concentrations measured at the nearest urban monitoring station (NUM).The mean exposure predicted by MEEM (mean = 19.6 μg m³) was slightly lower than the mean exposure measured by OPS (mean = 20.4 μg m³). The normalised mean bias factor (0.01) and normalised mean absolute error factor (0.25) suggested good agreement. In contrast, the HOME (mean = 31.2 μg m³) and NUM (mean = 28.6 μg m³) methods overpredicted exposure and showed systematic errors.The results indicate that personal exposure can be modelled by MEEM with an acceptable level of agreement, while methods such as HOME and NUM show a poorer performance.► A novel microenvironmental model (MEEM) was developed. ► MEEM combines children’s time-activity data with indoor and outdoor air pollution. ► NO2 exposures predicted by MEEM were compared against personal measurements. ► MEEM predicted personal NO2 exposure with a good level of agreement. ► MEEM performed better than an outdoor model and urban monitoring stations.
Keywords: Exposure; Schoolchildren; Microenvironments; Modelling; Personal samplers; NO2;

Forest fires release significant amounts of trace gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently reduce air quality and visibility, even far away from emission sources. In 2005, an arson forest fire burned nearly 700 ha near Lançon-de-Provence, southeast France. This paper explores the impact of this Mediterranean fire on the atmospheric dynamics and chemistry downwind of the burning region. The fire smoke plume was observed by the MODIS-AQUA instrument several kilometres downwind of the burning area out of the Mediterranean coast. Signatures of the fire plume on air pollutants were measured at surface stations in southeastern France by the air quality network AtmoPACA. Ground-based measurements revealed unusually high concentrations of aerosols and a well marked depletion of ozone concentrations on the day of the fire. The Lançon-de-Provence fire propagation was successfully simulated by the semi-physical fire spread model ForeFire. ForeFire provided the burnt area at high temporal and spatial resolutions. The burnt areas were scaled to compute the fire heat and water vapour fluxes in the three-dimensional meso-scale non-hydrostatic meteorological model MesoNH. The simulated fire plume kept confined in the boundary layer with high values of turbulent kinetic energy. The plume was advected several kilometres downwind of the ignition area by the Mistral winds in accordance with the MODIS and AtmoPACA observations. The vertical plume development was found to be more sensitive to the sensible heat flux than to the fire released moisture. The burnt area information is also used to compute emissions of a fire aerosol-like tracer and gaseous pollutants, using emission factors for Mediterranean vegetation. The coupled model simulated high concentrations of the fire aerosol-like tracer downwind of the burning zone at the right timing compared to ground-based measurements. A chemical reaction mechanism was coupled on-line to the MesoNH model to account for gaseous chemistry evolution in the fire plume. High levels of ozone precursors (NO x , CO) were simulated in the smoke plume which led to the depletion of ozone levels above and downwind of the burning zone. This depletion of ozone was indeed observed at ground-based stations but with a higher impact than simulated. The difference may be explained by the simplified design of the model with no anthropogenic sources and no interaction of the smoke aerosols with the photolysis rates. Ozone production was modelled tens of kilometres downwind of the ignition zone out of the coast.► We investigate the impact on gaseous air pollutants downwind of a Mediterranean wildfire. ► We use the “off-line” coupling between an atmospheric model and a fire spread model. ► The plume rise is more sensitive to the sensible heat flux released by the fire. ► High concentrations in ozone precursors are simulated close and downwind of the fire. ► The depletion of ozone is reproduced in the smoke plume near and downwind of the fire.
Keywords: Mediterranean region; Off-line coupled model; Fire spread; Injection height; Smoke plume pollutants;

Characterization of summer organic and inorganic aerosols in Beijing, China with an Aerosol Chemical Speciation Monitor by Yele Sun; Zifa Wang; Huabin Dong; Ting Yang; Jie Li; Xiaole Pan; Ping Chen; John T. Jayne (250-259).
An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was first deployed in Beijing, China for characterization of summer organic and inorganic aerosols. The non-refractory submicron aerosol (NR-PM1) species, i.e., organics, sulfate, nitrate, ammonium, and chloride were measured in situ at a time resolution of ∼15 min from 26 June to 28 August, 2011. The total NR-PM1 measured by the ACSM agrees well with the PM2.5 measured by a Tapered Element Oscillating Microbalance (TEOM). The average total NR-PM1 mass for the entire study is 50 ± 30 μg m−3 with the organics being the major fraction, accounting for 40% on average. High concentration and mass fraction of nitrate were frequently observed in summer in Beijing, likely due to the high humidity and excess gaseous ammonia that facilitate the transformation of HNO3 to ammonium nitrate particles. Nitrate appears to play an important role in leading to the high particulate matter (PM) pollution since its contribution increases significantly as a function of aerosol mass loadings. Positive matrix factorization (PMF) of ACSM organic aerosol (OA) shows that the oxygenated OA (OOA) – a surrogate of secondary OA dominates OA composition throughout the day, on average accounting for 64%, while the hydrocarbon-like OA (HOA) shows a large increase at meal times due to the local cooking emissions. Our results suggest that high PM pollution in Beijing associated with stagnant conditions and southern air masses is characterized by the high contribution of secondary inorganic species and OOA from regional scale, whereas the aerosol particles during the clean events are mainly contributed by the local emissions with organics and HOA being the dominant contribution.► An Aerosol Chemical Speciation Monitor was first deployed in Beijing, China. ► High concentration of nitrate was frequently observed in summer in Beijing. ► PMF analysis of ACSM OA mass spectra identified OOA and HOA. ► High PM pollution is primarily associated with secondary organic/inorganic species.
Keywords: ACSM; Particulate matter; Organic aerosol; Sources; Beijing;

Quantitative estimation of excess mortality for drivers and passengers exposed to particulate matters in long-distance buses by Chia-Pin Chio; Yi-Hsien Cheng; Min-Pei Ling; Szu-Chieh Chen; Chung-Min Liao (260-267).
The purpose of this study was to estimate quantitatively the excess mortality for driver/passenger in long-distance buses in terms of long driving time and inhaled particulate matters (PMs) concentrations. This study used an area under the curve (AUC) approach integrating the driving time and a predicted single pulsed PM concentration to estimate the fluctuating PM exposures in long-distance buses. Different peak functions were used to fit a unique fluctuating PM dataset adopted from previous study in Taiwan. We showed that gamma distribution had a best-fitting performance with the minimum values of coefficient of variation (CV) for PM2.5 and PM10 of 2.9% and 11.7%. The results also indicated that the predicted CV values for PM2.5 (5.3%) and PM10 (14.0%) from fitted normal distributions were also agreeable compared with the original dataset. The results indicated that the PM2.5-associated excess mortality estimates ranged from 0.64 to 1.04 and 4103–6833 individuals per 105 population for passengers under short-term and drivers under long-term PM exposures. Moreover, the interquartile ranges of the excess mortality estimate in the proposed model were 2.5–5.6 times less than that in the original dataset. We concluded that our AUC-based model may successfully reduce the variations in PM exposure estimates, and thereby provide more accurate values for improving risk estimation of future excess mortality attributable to traffic-related air pollutants.► AUC approach can estimate fluctuating PM exposure in long-distance buses. ► AUC model could reduce the variations in PM exposure estimates. ► Drivers had 1000-fold higher than passengers of PM2.5-associated excess mortality.
Keywords: Particulate matter; Long-distance bus; Driver; Passenger; Excess mortality;

This paper presents the first large-eddy simulation (LES) study of transfer and dispersion of a scalar released from a rough urban facet, either the street surface, the upstream-wall, or the downstream-wall, under the thermo-dynamical conditions of either the upstream-wall or the downstream-wall, plus the roof, heated by solar radiation. The boundary condition of a constant value is adopted for the scalars on the rough urban facets and a wall function is proposed for the scalars.The LES results demonstrate that dispersion inside the street canyon possesses distinctive characteristics for two conditions: the assisting condition in which the thermal-driven flow has the same direction as that of the wind-driven vortex and the opposing condition in which the thermal-driven flow has the opposite direction as that of the wind-driven vortex. For the street-released scalar under the opposing condition, the concentration fluctuations relative to the mean concentration can reach 50% and in general they are much larger than those for the assisting cases which are in the range of 25–30%. The exchange velocity of a scalar between the street canyon air and the urban boundary layer (UBL), w C B ( c ) , is one order of magnitude larger than the exchange velocity between a facet and the urban boundary layer, UBL, w 0 B ( c ) , indicating quantitatively that the resistance to the transfer of a facet-released scalar is dominated by the near-facet processes. As the temperature difference between the wall and the UBL, ΔT, increases, the total resistance to street canyon ventilation becomes more dominated by the near-facet resistance. The assisting conditions are favourable to ventilating the scalars from both walls, whereas the opposing conditions are only favourable to the ventilation of the downstream-wall released scalar. In the range of ΔT tested in this study, the exchange velocity, w C B ( c ) , linearly increases with ΔT and can be well parameterised. For the assisting cases, the advective (or dispersive) flux dominates the turbulent flux in most part of the canyon and the partition between the two alters dramatically across the roof level with turbulent processes dominating above the roof level. This study also suggests that for the street-released scalar, the resistance between the bottom canyon and the upper canyon is significant compared with the one between the upper canyon and the UBL. It is therefore necessary to adopt a two-box model in order to reasonably model such a case. The results of this study provide the guidance of improving the parameterisation schemes of transfer and dispersion for street canyons which currently do not consider the influence of wall heating.► Various wall heating settings significantly affect ventilation of street canyons. ► Resistance to transfer of a facet scalar is dominated by the near-facet processes. ► The venting velocity and exchange velocity linearly increase with wall heating. ► Transfer of a scalar on a heated wall is much faster than that for a non-heated wall. ► Relative concentration fluctuations can reach 50% if windward wall is heated.
Keywords: Urban street canyon; Large-eddy simulation; Wall heating; Dispersion; Passive scalars;

Use of electronic nose and GC-MS in detection and monitoring some VOC by M. Delgado-Rodríguez; M. Ruiz-Montoya; I. Giraldez; R. López; E. Madejón; M.J. Díaz (278-285).
The aim of this study was to evaluate the use of an electronic nose (e-nose) as on-line, rapid method to quantify the MSW composting gases. Changes in selected VOCs (limonene, β-pinene, 2-butanone, undecane, toluene and dimethyl disulfide) during composting were studied and quantified by means of two different analytical methods (GC-MS and e-nose). The results of this study indicate that it is possible to differentiate and quantify the main gases emitted during Municipal Solid Waste- Legume Trimming Residues composting using an electronic nose equipped with 10 Metal Oxide Sensors. The electronic nose was able to detect a clear difference in volatile compounds profile of emitted gases in composting, using Principal Component Analysis (PCA) analysis. PCA successfully reduced the data sets from the sensors to two principal components, which accounted for 74.5%, 68.8% and 62.8% of the total variance by using patterns for initial, thermophilic and mesophilic composting phases respectively.► We compared two analytical methods in MSW composting (GC-MS and e-nose). ► The higher emissions of VOCs happened at the early stages of the composting. ► Using an e-nose it is possible to differentiate and quantify the main gases emitted.
Keywords: MSW; Composting gases; VOC; E-nose; GC-MS;

This paper presents measurements of the single-particle composition of ice nuclei (IN) in downtown Toronto, Canada, made at 239 ± 1 K, 134 ± 2% relative humidity with respect to ice (RHi). IN were activated within the University of Toronto Continuous-Flow Diffusion Chamber (UT-CFDC), separated from background aerosol using a pumped counterflow virtual impactor (PCVI), and analyzed using a dual-polarity single-particle mass spectrometer (ATOFMS). To account for particles leaked by the PCVI, the ratio of particles observed at high RHi to low RHi was calculated. This ratio was greater than unity for EC (elemental carbon), BB (biomass burning) and dust particles, however only the increase in EC was statistically significant (1σ level) due to a low number of detected particles. The remaining particle categories were: metal-rich organic carbon (M/OC), potassium-rich OC (K/OC), OC potentially mixed with EC (OC/EC) and “other”, none of which were enhanced in number at high RHi. To complement the direct PCVI observations and enhance the number of spectra available, a second study was performed where particle composition and IN concentrations (CIN) were measured in parallel. IN concentrations were regressed against the same categories as above, and dust, BB and EC particles were identified as the best predictors of CIN. Consistency between these two methods provides increased confidence in their individual results and encourages additional study of these potential IN.► A CFDC–CVI–SPMS system measured mass spectra of individual urban ice nuclei (IN). ► The CFDC–CVI–SPMS system measured EC as IN at 238 K and 134% RHi (1σ CL). ► A separate regression study compared IN concentrations to aerosol surface area. ► The regression highlighted EC, dust and BB as potential IN.
Keywords: ATOFMS; CVI; IN; Ice nuclei; Ice nucleation; Single-particle mass spectrometry;

The removal of ultrafine particles (UFP) by vegetation is now receiving significant attention given their role in cloud physics, human health and respiratory related diseases. Vegetation is known to be a sink for UFP, prompting interest in their collection efficiency. A number of models have tackled the UFP collection efficiency of an isolated leaf or a flat surface; however, up-scaling these theories to the ecosystem level has resisted complete theoretical treatment. To progress on a narrower scope of this problem, simultaneous experimental and theoretical investigations are carried out at the “intermediate” branch scale. Such a scale retains the large number of leaves and their interaction with the flow without the heterogeneities and added geometric complexities encountered within ecosystems. The experiments focused on the collection efficiencies of UFP in the size range 12.6–102 nm for pine and juniper branches in a wind tunnel facility. Scanning mobility particle sizers were used to measure the concentration of each diameter class of UFP upstream and downstream of the vegetation branches thereby allowing the determination of the UFP vegetation collection efficiencies. The UFP vegetation collection efficiency was measured at different wind speeds (0.3–1.5 m s−1), packing density (i.e. volume fraction of leaf or needle fibers; 0.017 and 0.040 for pine and 0.037, 0.055 for juniper), and branch orientations. These measurements were then used to investigate the performance of a proposed analytical model that predicts the branch-scale collection efficiency using conventional canopy properties such as the drag coefficient and leaf area density. Despite the numerous simplifications employed, the proposed analytical model agreed with the wind tunnel measurements mostly to within 20%. This analytical tractability can benefit future air quality and climate models incorporating UFP.► Two Peclet numbers were derived to explain the UFP collection efficiency of canopies. ► The two Peclet numbers are described from conventional flow and canopy properties. ► Analytical predictions and wind tunnel measurements agree to within 20%. ► Model parameters bounded between gases and particles with larger than UFP diameters.
Keywords: Analytical model; Canopy turbulence; Dry deposition; Size-dependent removal efficiency; Ultrafine aerosol; Wind tunnel;

Impact of meteorology on air quality modeling over the Po valley in northern Italy by D. Pernigotti; E. Georgieva; P. Thunis; B. Bessagnet (303-310).
A series of sensitivity tests has been performed using both a mesoscale meteorological model (MM5) and a chemical transport model (CHIMERE) to better understand the reasons why all models underestimate particulate matter concentrations in the Po valley in winter. Different options are explored to nudge meteorological observations from regulatory networks into MM5 in order to improve model performances, especially during the low wind speed regimes frequently present in this area. The sensitivity of the CHIMERE modeled particulate matter concentrations to these different meteorological inputs are then evaluated for the January 2005 time period. A further analysis of the CHIMERE model results revealed the need of improving the parametrization of the in-cloud scavenging and vertical diffusivity schemes; such modifications are relevant especially when the model is applied under mist, fog and low stratus conditions, which frequently occur in the Po valley during winter. The sensitivity of modeled particulate matter concentrations to turbulence parameters, wind, temperature and cloud liquid water content in one of the most polluted and complex areas in Europe is finally discussed.► Meteorological observations nudging on MM5-CHIMERE chain. ► Wind speed reduced up to 1 m s−1; temperature reduced causing more fog. ► CHIMERE PM unrealistic in-cloud processes switched off. ► Nudged MM5-CHIMERE increases modeled PM up to 20 μg m−3, 50%.
Keywords: MM5; Nudging; Wind; CHIMERE; PM10; Scavenging;

Observation of elevated air pollutant concentrations in a residential neighborhood of Los Angeles California using a mobile platform by Shishan Hu; Suzanne E. Paulson; Scott Fruin; Kathleen Kozawa; Steve Mara; Arthur M. Winer (311-319).
We observed elevated air pollutant concentrations, especially of ultrafine particles (UFP), black carbon (BC) and NO, across the residential neighborhood of the Boyle Heights Community (BH) of Los Angeles, California. Using an electric vehicle mobile platform equipped with fast response instruments, real-time air pollutant concentrations were measured in BH in spring and summer of 2008. Pollutant concentrations varied significantly in the two seasons, on different days, and by time of day, with an overall average UFP concentration in the residential areas of ∼33 000 cm−3. The averaged UFP, BC, and NO concentrations measured on Soto St, a major surface street in BH, were 57 000 cm−3, 5.1 μg m−3, and 67 ppb, respectively. Concentrations of UFP across the residential areas in BH were nearly uniform spatially, in contrast to other areas in the greater metropolitan area of Los Angeles where UFP concentrations exhibit strong gradients downwind of roadways. We attribute this “UFP cloud” to high traffic volumes, including heavy duty diesel trucks on the freeways which surround and traverse BH, and substantial numbers of high-emitting vehicles (HEVs) on the surface streets traversing BH. Additionally, the high density of stop signs and lights and short block lengths, requiring frequent accelerations of vehicles, may contribute. The data also support a role for photochemical production of UFP in the afternoon. UFP concentration peaks (5 s average) of up to 9 million particles cm−3 were also observed immediately behind HEVs when they accelerated from stop lights in the BH neighborhood and areas immediately adjacent. Although encounters with HEV during mornings accounted for only about 6% and 17% of time spent monitoring residential areas and major surface streets, HEV contributed to about 28% and 53% of total ultrafine particles measured on the route, respectively. The observation of elevated pollutant concentrations across the Boyle Heights community highlights how multiple factors combine to create high pollutant levels, and has important human exposure assessment implications, including the potential utility of our data as inputs to epidemiological studies.► We monitored primary pollutants throughout in a low income Los Angeles neighborhood. ► Multiple factors lead to elevated ultrafine particles in residential areas. ► High traffic density, many high emitters and ubiquitous stop signs all contribute. ► Photochemical production appears to elevate ultrafine particles in the afternoon.
Keywords: Vehicle emissions; Mobile platform; Exposure assessment; Ultrafine particle; Freeway; New particle formation; Boyle Heights;

The rapid increase of the vehicle population makes the transport sector a significant contributor to China’s BC emissions. In this study, we developed an inventory to estimate emissions, reductions, and projections of BC from on-road vehicles. Total emissions of on-road vehicles were 15.0 Gg in 1990 and 64.0 Gg in 2009. Diesel vehicles were the biggest contributor, emitting 83%–95% of total emissions. Results of provincial-level analysis showed that Guangdong, Shandong, and Hebei had higher emissions than other provinces. Emission standards introduced by the government to reduce particulate matter (PM) resulted in decreased BC emissions. Total reductions were up to 375.8 Gg in the period of 1999–2009, equivalent to 270 Tg CO2 (100-year). Projections show that emissions continue to decline from 2010 but start to increase from 2015 under a BAU scenario. If EURO V/VI emission standards are implemented, emissions will decline steadily until 2025. Further reductions of BC can be achieved by using biodiesel and low-sulfur fuels.Display Omitted► We developed an inventory to estimate emissions, reductions, and projections of BC from on-road vehicles. ► We determined the BC reductions co-benefit from PM emission standards. ► Projections were made under BAU and EURO V/VI. ► Biodiesel and low-sulfur fuels were considered.
Keywords: Black carbon; On-road vehicles; Emission inventory; Projection; China;

Automated closed-chamber measurements of methane fluxes from intact leaves and trunk of Japanese cypress by Kenshi Takahashi; Yoshiko Kosugi; Akito Kanazawa; Ayaka Sakabe (329-332).
Continuous in situ measurements of methane (CH4) fluxes from intact leaves and trunk of Japanese cypress (Chamaecyparis obtusa Sieb. et Zucc) were conducted in a temperate forest from August 2009 to August 2010. An automated closed-chamber system, which was used to evaluate CO2 exchange between the atmosphere and forest ecosystems, was coupled to a laser-based instrument to monitor CH4 concentrations. Temporal changes in CH4 concentrations from the foliage and trunk were measured at one-second intervals during chamber closure to determine CH4 fluxes between the leaf and trunk surfaces and the atmosphere. While recent studies have suggested that some plants emit CH4 under aerobic conditions, emission or uptake of CH4 in detectable amounts with our experimental system, by intact leaves or the trunk of C. obtusa, was not significantly observed throughout the measurement period.► We present long-term measurements of methane fluxes from intact leaves and trunks of Japanese cypress in a temperate forest. ► No evidence for significant emission or uptake of CH4 by intact leaves and trunk was observed. ► Seasonal changes in the flux distributions were not detected.
Keywords: Methane; Plant emission; Aerobic conditions; Laser-based technique; Chamber method;

New Directions: Toward a community emissions approach by Gregory J. Frost; Stefan R. Falke; Claire Granier; Terry Keating; Jean-François Lamarque; Megan L. Melamed; Paulette Middleton; Gabrielle Pétron; Steven J. Smith (333-334).
Keywords: Emissions; Science-policy; Air quality; Climate; Community approach;