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Atmospheric Environment (v.45, #14)

Editorial board (pp. i).

Application of14C analyses to source apportionment of carbonaceous PM2.5 in the UK by Mathew R. Heal; Philip Naysmith; Gordon T. Cook; Sheng Xu; Teresa Raventós Duran; Roy M. Harrison (pp. 2341-2348).
Determination of the radiocarbon (14C) content of airborne particulate matter yields insight into the proportion of the carbonaceous material derived from fossil and contemporary carbon sources. Daily samples of PM2.5 were collected by high-volume sampler at an urban background site in Birmingham, UK, and the fraction of14C in both the total carbon, and in the organic and elemental carbon fractions, determined by two-stage combustion to CO2, graphitisation and quantification by accelerator mass spectrometry. OC and EC content was also determined by Sunset Analyzer. The mean fraction contemporary TC in the PM2.5 samples was 0.50 (range 0.27–0.66, n=26). There was no seasonality to the data, but there was a positive trend between fraction contemporary TC and magnitude of SOC/TC ratio and for the high values of these two parameters to be associated with air-mass back trajectories arriving in Birmingham from over land. Using a five-compartment mass balance model on fraction contemporary carbon in OC and EC, the following average source apportionment for the TC in these PM2.5 samples was derived: 27% fossil EC; 20% fossil OC; 2% biomass EC; 10% biomass OC; and 41% biogenic OC. The latter category will comprise, in addition to BVOC-derived SOC, other non-combustion contemporary carbon sources such as biological particles, vegetative detritus, humic material and tyre wear. The proportion of total PM2.5 at this location estimated to derive from BVOC-derived secondary organic aerosol was 9–29%. The findings from this work are consistent with those from elsewhere in Europe and support the conclusion of a significant and ubiquitous contribution from non-fossil biogenic sources to the carbon in terrestrial aerosol.► Carbon-14 used to apportion fossil and contemporary carbon in samples of PM2.5. ► Mean fraction contemporary total carbon in 26 samples ∼0.50 (range 0.27–0.66). ► Overall: 27% fossil EC; 20% fossil OC; 2% biomass EC; 10% biomass OC; 41% biogenic OC. ► Ubiquitous contribution from non-fossil sources to the carbon in terrestrial aerosol. ► Biogenic SOA contribution exceeds fossil SOA.

Keywords: PM; 2.5; Particulate mater; Carbon-14; BVOC; SOA; Source apportionment


Hygroscopicity and evaporation of ammonium chloride and ammonium nitrate: Relative humidity and size effects on the growth factor by Dawei Hu; Jianmin Chen; Xingnan Ye; Ling Li; Xin Yang (pp. 2349-2355).
The hygroscopicity and evaporation of ammonium chloride and ammonium nitrate in the size range of 40–200 nm are investigated from 20% to 86% RH using a self-assembled hygroscopic tandem differential mobility analyzer (H-TDMA) system. The hygroscopicity of 100 nm (NH4)2SO4 is also measured for comparison. The measured hygroscopic growth factors (GFs) of (NH4)2SO4 agree well with the theoretical Köhler curve. Great discrepancies between the measured GFs and the theoretical values are observed for NH4Cl and NH4NO3 due to their volatile properties. The evaporation of NH4Cl below the deliquescence RH (DRH) is significantly promoted while RH increases. Similar trend is also observed for NH4NO3 particle less than 50 nm. The proposed mechanism suggests that the increase of RH alters the chemical equilibrium among NH4X(s) (X represents Cl− or NO3−), NH3(g) and HX(g), i.e.,NH4X(s)⇆NH3+HX(g), by converting NH3(g) and HX(g) into NH3·nH2O and HX·nH2O, which accelerates the evaporation of NH4X(s). When RH is higher than the DRH, the GFs of NH4X increase with initial particle size ( D0) throughout the investigated size range. In this study, the iso-GF curves are also drawn to illustrate the effects of D0 and RH on the GFs. Different from (NH4)2SO4, NaCl, Na2SO4 and NaNO3, the GFs of NH4X are more sensitive to D0 than RH due to the unique volatility of NH4Cl and NH4NO3 particles.► The effect of particle size on the hygrocopicity of NH4NO3 and NH4Cl is discussed. ► The effect of RH on the evaporation of NH4NO3 and NH4Cl is investigated. ► The evaporation of NH4Cl is significantly promoted while RH increases below the DRH. ► The hygroscopic growth factor of NH4Cl and NH4NO3 is more sensitive to D0 than RH.

Keywords: Hygroscopicity; Evaporation; Ammonium chloride; Ammonium nitrate; H-TDMA


Seasonality in the latitudinal distributions of NMHCs over Bay of Bengal by L.K. Sahu; S. Lal; S. Venkataramani (pp. 2356-2366).
Surface level measurements of light non-methane hydrocarbons (C2–C4 NMHCs) were conducted during summer and winter monsoon campaigns over Bay of Bengal (BOB). The mixing ratios of major NMHCs during winter monsoon were significantly higher compared to summer monsoon. During both seasons, the distributions of NMHCs show clear north–south decreasing gradients over open oceanic region of BOB. During the summer (winter) monsoons, the latitudinal gradients of ethane, propane and acetylene were 29±3 (136±4)pptvdeg−1, 14±2 (46±8)pptvdeg−1 and 14±4 (148±10)pptvdeg−1, respectively over open oceanic region of BOB. For measurements during summer monsoon, the latitudinal gradients in the mixing ratios of NMHCs were caused by the transport of pollutants from peninsular India to the northern BOB and flow of cleaner marine air over southern BOB. On the other hand, the gradients in the mixing ratios of NMHCs during winter monsoon are due to the dilution and photochemical loss towards the southern BOB. In both seasons, no such clear latitudinal trends were observed along the east coast of India. The measurements along the coastal tracks were influenced by stagnant flow and photochemically aged air which also lacks clear north–south directionality. Alkenes show opposite seasonality to that of major NMHCs as the mixing ratios of both ethene and propene during summer monsoon were higher than the winter values. In addition, the distributions of alkenes also show significant heterogeneity, however, no clear latitudinal trends can be seen during both seasons. The investigations of wind and ocean color parameters suggest substantial emissions of alkenes from surface sea waters which also support the seasonality of these species over BOB.► Seasonality in the latitudinal distribution of C2–C4 NMHCs over Bay of Bengal. ► Role of transport and photochemical oxidation in latitudinal gradients of NMHCs. ► Impact of oceanic emissions on the distributions of alkenes.

Keywords: Bay of Bengal; Transport; NMHCs; Latitude; Ocean


Space-borne and ground observations of the characteristics of CO pollution in Beijing, 2000–2010 by Lingjun Li; Yang Liu (pp. 2367-2372).
Both the long-term and short-term variability of carbon monoxide (CO) pollution in Beijing metropolitan area, China are studied with 11 years of MOPITT observations and 10 years of ground measurements. The impact of the 2008 Beijing Olympic Games on regional air quality is also examined. MOPITT CO columns exhibit different temporal patterns from ground CO concentration measurements. MOPITT CO column in August has gradually increased from 2000 to 2007, even though ground level CO concentrations have significantly decreased due to continued local air pollution control effort. Both CO columns and ground CO concentrations were reduced due to strict albeit temporary emissions control measures from July to September 2008 to support the Beijing Olympic Games. However, the reduction of total CO columns (∼13%) was less pronounced than ground CO concentration (∼44%), indicating that local emission control effort was partially offset by the continuously deteriorating regional air quality. In addition, MOPITT CO mixing ratio profiles indicate a significant regional pattern at higher altitudes. CO total columns after 2008 show an overall increasing trend, in contrast to the decreasing trend observed in ground measurements.► MOPITT CO column seasonal pattern differs from ground CO concentrations in Beijing. ► MOPITT CO column in August has increased from 2000 to 2007, even though ground CO concentrations have significantly decreased in Beijing. ► Emission control measures caused 44% reduction in ground CO concentrations and 13% reduction in CO column during the Beijing 2008 Olympic Games. ► CO total columns show an overall increasing trend, in contrast to the decreasing trend in ground observations.

Keywords: MOPITT; CO; Beijing; Northern China; Olympic Games; Air pollution control


Adsorption of water vapor on MgCl2 × 6H2O salt surface by Yuri Bedjanian; Ekaterina Loukhovitskaya (pp. 2373-2378).
The adsorption of water vapor on dry solid films of MgCl2 × 6H2O salt was studied as a function of partial pressure of water over the temperature range 240–340 K using a flow reactor coupled to a modulated molecular beam mass spectrometer. The uptake of water was found to be completely reversible. The adsorption data are well described by a Freundlich isotherm with the heterogeneity parameter close to 0.5. The isosteric enthalpy of adsorption was found to be –(44.7 ± 1.2) kJ mol−1, independent of the salt surface coverage in the range (0.8–30) × 1015 molecule cm−2. An empirical equation is proposed for the amount of water adsorbed on MgCl2 × 6H2O as a function of relative humidity. Uptake of H2O on MgCl2 × 6H2O is observed to be much higher than on NaCl indicating that the amount of surface adsorbed water on mixed salts will be drastically dependent on the salt sample composition. The observed results support previous considerations that under atmospheric conditions sea salt particles are probably enveloped by a MgCl2 × 6H2O brine.► The adsorption of water vapor on dry solid films of MgCl2 × 6H2O salt was studied. ► The uptake of water was found to be completely reversible. ► The adsorption data are well described by a Freundlich isotherm with the heterogeneity parameter close to 0.5. ► The isosteric enthalpy of adsorption was found to be –(44.7 ± 1.2) kJ mol−1. ► The amount of surface adsorbed water on mixed salts is drastically dependent on the salt sample composition.

Keywords: Water; Salt; MgCl; 2;  × 6H; 2; O; Uptake; Adsorption isotherm


Factors affecting the surface radiation trends over China between 1960 and 2000 by Chenghai Wang; Zhifu Zhang; Wenshou Tian (pp. 2379-2385).
In this paper, the surface solar radiation data from 1960 to 2000 gathered from 40 weather stations over China were reexamined, and the relationship of long-term trends of the solar radiation and climate factors were analyzed. The results indicate that the surface solar radiation in most regions of China begins to increase after 1990. Decreases in cirrus and cirrostratus clouds, which account for a larger percentage of the total cloud amount over China, have an important contribution to the increasing trend of the surface solar radiation. Further examination of the surface water vapor changes reveals that the surface solar radiation negatively correlates with the near surface water vapor in most region of China, and this negative correlation is more pronounced in higher latitudes of China where the atmosphere is compared to regions in southern China.► Alto-clouds have a large impact on surface solar radiation trends over China. ► Aerosols are not the main factor affecting solar radiation trends over China. ► The surface solar radiation negatively correlates with water vapor in dry regions.

Keywords: Cirrus and cirrostratus cloud; Trend of radiation; Climatic variations


Polybrominated diphenyl ethers (PBDEs) in indoor dust and human hair by Yuan Kang; Hong Sheng Wang; Kwai Chung Cheung; Ming Hung Wong (pp. 2386-2393).
In the present study, settled workplace dust ( n=55) from commercial offices, secondary schools, shopping malls, hospitals, electronic factories and manufacturing plants in Hong Kong and settled home dust ( n=23) from Hong Kong, Shenzhen and Guangzhou, around the Pearl River Delta were collected. Chemical analyses showed that the total PBDEs in workplace dust ranged from 397 to 40,236ngg−1, with the dust samples from electronic factories having the highest levels (2122–40,236ngg−1), and dust from homes ranging from 685 to 18,385ngg−1. The most abundant BDE congeners found were BDE-209 in both workplace dust and home dust, followed by BDE-99 and BDE-47. No significant correlations were observed between total PBDE concentrations in home dust and the age or the house ( p>0.05), concentrations of BDE-99+BDE-47 and the number of furniture containing foam ( p>0.05), and concentrations of BDE-209 and the number of electronic appliances ( p>0.05). BDE-47, -99, -100 and -183 were found in most of the hair samples collected from occupants of these homes with BDE-47 being the dominant congener (0.86–5.24ngg−1). The BDE-183 concentration in home dust was significantly correlated with that in human hair ( r=0.55, p<0.05, n=18). Risk assessment indicated that daily intake of PBDEs for children via non-dietary ingestion of dust (101–404ngday−1) was higher than that via food consumption (77–190ngday−1).► BDE-47 was found as the dominant congener in most of the hair samples. ► BDE-183 concentration in house dust was significantly correlated with that in human hair. ► Indoor dust is more important than food for PBDEs exposure in HK, as found elsewhere.

Keywords: Dust; Pearl River Delta; PBDEs; Hair


A spatial-temporal regression model to predict daily outdoor residential PAH concentrations in an epidemiologic study in Fresno, CA by Elizabeth M. Noth; S. Katharine Hammond; Gregory S. Biging; Ira B. Tager (pp. 2394-2403).
Polycyclic aromatic hydrocarbons (PAHs) are generated as a byproduct of combustion, and are associated with respiratory symptoms and increased risk of asthma attacks.To assign daily, outdoor exposures to participants in the Fresno Asthmatic Children’s Environment Study (FACES) using land use regression models for the sum of 4-, 5- and 6-ring PAHs (PAH456).PAH data were collected daily at the EPA Supersite in Fresno, CA from 10/2000 through 2/2007. From 2/2002 to 2/2003, intensive air pollution sampling was conducted at 83 homes of participants in the FACES study. These measurement data were combined with meteorological data, source data, and other spatial variables to form a land use regression model to assign daily exposure at all FACES homes for all years of the study (2001–2008).The model for daily, outdoor residential PAH456 concentrations accounted for 80% of the between-home variability and 18% of the within-home variability. Both temporal and spatial variables were significant in the model. Traffic characteristics and home heating fuel were the main spatial explanatory variables.Because spatial and temporal distributions of PAHs vary on an intra-urban scale, the location of the child’s home within the urban setting plays an important role in the level of exposure that each child has to PAHs.► Daily ambient PAHs were measured in Fresno, CA both centrally and residentially. ► The data were modeled in a land use regression model using mixed effects. ► The model accounted for 80% of between-home variability in residential PAHs. ► The model accounted for 18% of within-home variability in residential PAHs. ► Daily outdoor residential exposure to PAHs is variable within Fresno, CA.

Keywords: Air pollution; Exposure assessment; Polycyclic aromatic hydrocarbons; Traffic; Land use regression; Spatial modelingAbbreviations; DEP; Diesel exhaust particles; EPA; United States Environmental Protection Agency; FACES; Fresno Asthmatic Children’s Environment Study; FL; Fuel loading factor for agricultural burning; HI; Home intensive; IARC; International Agency for Research on Cancer; LUR; Land use regression; PAH; Polycyclic aromatic hydrocarbons; PAH456; Sum of the PAHs with 4-, 5-, or 6-rings; SJVUAPCD; San Joaquin Valley Unified Air Pollution Control District


Volatile organic compounds in pesticide formulations: Methods to estimate ozone formation potential by Mazyar Zeinali; Laura L. McConnell; Cathleen J. Hapeman; Anh Nguyen; Walter F. Schmidt; Cody J. Howard (pp. 2404-2412).
The environmental fate and toxicity of active ingredients in pesticide formulations has been investigated for many decades, but relatively little research has been conducted on the fate of pesticide co-formulants or inerts. Some co-formulants are volatile organic compounds (VOCs) and can contribute to ground-level ozone pollution. Effective product assessment methods are required to reduce emissions of the most reactive VOCs. Six emulsifiable concentrate pesticide products were characterized for percent VOC by thermogravimetric analysis (TGA) and gas chromatography–mass spectrometry (GC–MS). TGA estimates exceeded GC–MS by 10–50% in all but one product, indicating that for some products a fraction of active ingredient is released during TGA or that VOC contribution was underestimated by GC–MS. VOC profiles were examined using TGA–Fourier transform infrared (FTIR) evolved gas analysis and were compared to GC–MS results. The TGA–FTIR method worked best for products with the simplest and most volatile formulations, but could be developed into an effective product screening tool. An ozone formation potential ( OFP) for each product was calculated using the chemical composition from GC–MS and published maximum incremental reactivity ( MIR) values. OFP values ranged from 0.1 to 3.1 g ozone g−1 product. A 24-h VOC emission simulation was developed for each product assuming a constant emission rate calculated from an equation relating maximum flux rate to vapor pressure. Results indicate 100% VOC loss for some products within a few hours, while other products containing less volatile components will remain in the field for several days after application. An alternate method to calculate a product OFP was investigated utilizing the fraction of the total mass of each chemical emitted at the end of the 24-h simulation. The ideal assessment approach will include: 1) unambiguous chemical composition information; 2) flexible simulation models to estimate emissions under different management practices; and 3) accurate reactivity predictions.► Pesticide products can contain volatile and reactive co-formulants. ► Reliable methods are needed to predict which products contribute to ozone pollution. ► Available methods to estimate ozone formation potential were tested on six products. ► Best results combined analysis with GC–MS and maximum incremental reactivity (MIR). ► Improved simulation models are needed to incorporate management practice effects.

Keywords: Ozone formation potential; Pesticide; Volatile organic compounds; Thermogravimetric analysis; Agriculture


Correction methods for statistical models in tropospheric ozone forecasting by J.C.M. Pires; F.G. Martins (pp. 2413-2417).
This study proposes two methods to enhance the performance of statistical models for prediction tropospheric ozone concentrations. The first method corrects the statistical model based on the average daily profile of the model errors in training set. The second method estimates the model error by making the analogy with three basic modes of feedback control: proportional, integral and derivative. These correction methods were tested with multiple linear regression (MLR) and artificial neural networks (ANN) for prediction of hourly average tropospheric ozone (O3) concentrations.The inputs of the models were the hourly average concentrations of sulphur dioxide (SO2), carbon monoxide (CO), nitrogen oxide (NO), nitrogen dioxide (NO2) and O3, and some meteorological variables (temperature – T; relative humidity – RH; and wind speed – WS) measured 24 h before. The analysed period was from May to June 2003 divided in training and test periods.ANN presented slightly better performance than MLR model for prediction of O3 concentrations. Both models presented improvements with the proposed correction methods. The first method achieved the highest improvements with ANN model. However, the second method was the one that obtained the best predictions of hourly average O3 concentrations with the correction of MLR model.► The model errors were estimated by making the analogy with feedback control. ► The value of R2 increased 115% for MLR and 105% for ANN with the correction method. ► MLR overperformed ANN in prediction of tropospheric O3 concentrations.

Keywords: Tropospheric ozone; Air pollution modelling; Multiple linear regression; Artificial neural network; Correction methods


Two-year observations of fine carbonaceous particles in variable sampling intervals by Fumo Yang; Lin Huang; Sangeeta Sharma; Jeffrey R. Brook; Wendy Zhang; Shao-Meng Li; Jihua Tan (pp. 2418-2426).
Daily to weekly integrated PM2.5 samples were collected consecutively from August 2005 through November 2007 at Egbert, a rural site in southern Ontario with two collocated samplers to characterize temporal variations of organic and elemental carbon (OC and EC) concentrations and to review the effects of different sampling intervals on their respective concentrations. OC and EC concentrations from both samplers had reasonable agreements for the samples with identical sampling intervals, whereas for the samples with different sampling intervals, they did not coincide. Considering sampling artifacts, analytical challenges and highly varied daily concentrations, it is suggested and would be advantageous to adopt the weekly integrated sampling strategy other than 24-h sampling on selected days for long-term trend studies on ambient carbonaceous PM. Both OC and EC concentrations varied seasonally by factors of 2.4 and their concentrations in warm seasons (May–October) were higher than those in cold seasons (November–April). Greater fluctuations were also found in warm seasons during the study period. Weekly concentrations of carbonaceous species at Egbert and urban Toronto show similar temporal variations and small urban excess during the one-year parallel sampling period, indicating a relatively large regional contribution from transport instead of local emissions to the paired urban–rural sites. The continental background level of total carbon mass (TCM) in PM2.5 in southern Ontario, constrained by surface air mass directions and back trajectories, was estimated to be 0.5 μg m−3. It is likely that the elevated OC level during the warm season in 2007 compared with those in 2006 was due to more smog days in 2007.► Weekly sampling yields more representative mean OC–EC levels on a long-term basis. ► The elevated warm-season carbonaceous levels were accompanied with more smog days. ► There is a relatively larger regional influence on OC–EC levels in south Ontario. ► The continental background level of total carbon in southern Ontario is 0.5 μg m−3.

Keywords: Carbonaceous species; Fine particles; Temporal variations; Variable sampling intervals; Continental background level; Rural southern Ontario


Effect of rain scavenging on altitudinal distribution of soluble gaseous pollutants in the atmosphere by Tov Elperin; Andrew Fominykh; Boris Krasovitov; Alexander Vikhansky (pp. 2427-2433).
We suggest a one-dimensional model of rain scavenging of moderately soluble gaseous pollutants in the atmosphere. It is shown that below-cloud gas scavenging is determined by non-stationary convective diffusion equation with the effective Peclet number. The obtained equation was analyzed numerically in the case of log-normal droplet size distribution. Calculations of scavenging coefficient and the rates of precipitation scavenging are performed for wet removal of ammonia (NH3) and sulfur dioxide (SO2) from the atmosphere. It is shown that scavenging coefficient is non-stationary and height-dependent. It is found also that the scavenging coefficient strongly depends on initial concentration distribution of soluble gaseous pollutants in the atmosphere. It is demonstrated that in the case of linear distribution of the initial concentration of gaseous pollutants whereby the initial concentration of gaseous pollutants decreases with altitude, the scavenging coefficient increases with height in the beginning of rainfall. At the later stage of the rain scavenging coefficient decreases with height in the upper below-cloud layers of the atmosphere.► Scavenging coefficient of soluble trace gases by rain depends on time and height. ► Scavenging coefficient at the ground increases with time. ► Below-cloud scavenging coefficient near the cloud decreases with time. ► Scavenging front propagates with wash-down velocity and is smeared by diffusion. ► Scavenging coefficient depends on the initial vertical distribution of trace gas.

Keywords: Soluble gaseous pollutants; Altitudinal distribution; Rain scavenging; Gas absorption; Scavenging coefficient


Daily patterns of the multi-modal structure of the particle number size distribution in Milan, Italy by G. Lonati; M. Crippa; V. Gianelle; R. Van Dingenen (pp. 2434-2442).
Aerosol number concentration and size distributions in the 10–20,000nm size range were measured using a Differential Mobility Particle Sizer (DMPS) and an Optical Particle Counter (OPC) at an urban background site. Daily patterns of the total particle (TP), ultrafine (UFP,D p<100nm) and submicron (SMP, 100p<1000nm) fine particle concentration are analysed both on seasonal (cold and warm season) and weekly (weekdays and weekends) basis. TP number concentrations are in the orders of 104cm−3, with UFPs and SMPs accounting for 80% and 20%, respectively; the contribution of supermicron particles to TP number is negligible. The multi-modal structure of particle number size distributions (NSD) is investigated by fitting a multi-lognormal model to the observed size distributions in the submicron size range, where almost 100% of the TPs fall. Three lognormal components (1 located in the Aitken mode size range and 2 in the accumulation mode range) are usually present in the fitted model and the corresponding modal parameters and their daily pattern have been estimated. The Aitken mode particles increase simultaneously with primary traffic emissions, peaking on the morning rush hour and dominating the NSD still during the afternoon and on the evening rush hour. The smaller accumulation mode particles are influenced by the condensation and coagulation processes induced by the daily patterns of the boundary layer and of ambient temperature, becoming more and more important from the evening rush hour throughout the night and providing the largest contribution to TP number at late night.► Seasonal and day-of-the-week features of particle number size distribution (NSD). ► Original procedure for multi-lognormal model fitting to the observed NSD. ► Daily time-resolved description of the multimodal behaviour of the NSD. ► Influence of traffic emission on particle NSD at an urban background site.

Keywords: Multi-modal size distribution; Number concentration; Fine particles; Ultrafine particles; Urban areas


Volatility of secondary organic aerosol from the ozonolysis of monoterpenes by Byong-Hyoek Lee; Jeffrey R. Pierce; Gabriella J. Engelhart; Spyros N. Pandis (pp. 2443-2452).
The volatility of secondary organic aerosol (SOA) produced from the ozonolysis of α-pinene, β-pinene, and limonene, at low and intermediate RH, and at low and high NOx conditions was investigated using a thermodenuder (TD). More than 90% of the α-pinene and β-pinene SOA volume (for 200nm particles) and approximately 75% of the limonene SOA evaporated at 70°C for a centerline residence time of approximately 16s in the heated zone. Practically all the SOA in all systems evaporated at approximately 90°C. The relative humidity during the formation of SOA had a small effect on its volatility (changes in the evaporated fraction were less than 10%). NOx concentrations had a significant impact on the volatility of α-pinene and β-pinene SOA (reductions of the evaporated fraction by approximately 30%), but a negligible effect on the volatility of limonene SOA. High NOx levels resulted in more volatile SOA than low NOx conditions due to the presence of relatively volatile nitrate containing species at high NOx.The behavior of the SOA in the thermodenuder can be reproduced using an aerosol dynamics model based on the volatility basis-set approach and SOA yield parameters derived in previous smog chamber studies if appropriate values of the mass accommodation coefficient and heat of vaporization (Δ Hvap) are chosen. Use of either a very low effective accommodation coefficient (0.002–0.01) and a heat of vaporization depending on the saturation concentration, or an effective accommodation coefficient of 0.05 for the initial stages of the evaporation and 1 afterward, with a low volatility-independent value of the Δ Hvap, is needed for the simulation of the SOA evaporation.► All the SOA from monoterpene ozonolysis evaporates after 16s at temperatures less than 90°C. ► The α- and β-pinene SOA formed at high NOx conditions is more volatile. ► The formation relative humidity has a small effect on volatility. ► The results are consistent with the volatility basis-set parameters. ► There are significant mass transfer limitations in the evaporation of biogenic SOA.

Keywords: Secondary organic aerosol; Biogenic aerosol; Volatility; Thermodenuder


Impact of boundary-layer anticyclonic weather system on regional air quality by Peng Wei; Shuiyuan Cheng; Jianbing Li; Fuqing Su (pp. 2453-2463).
Based on a Lagrangian particle dispersion model FLEXPART 3-D in conjunction with a Weather Research and Forecasting (WRF) model, this study analyzed the synoptic patterns of the three sections (i.e. front, center, and rear) of a slow-moving anticyclonic weather system that took place during April 22–30, 2002 in northern China. The impacts of anticyclone on regional air quality were also revealed through simulating the transport trajectories of PM10 particles in the anticyclone. The findings indicate that PM10 pollutant transport process within the anticyclone showed the following characteristics: (a) the frontal pressure field played a strong role in removing pollutants from a high concentration zone located before the front, (b) the central part of anticyclone with an evident isobaric pressure field tended to create a pollutant accumulation process, and (c) the rear of the anticyclone system with a southerly warmer advection in the pressure gradient zone formed a stable channel for transporting pollutants. By using air pressure data and PM10 concentration measurements, the quantitative relationship between pressure variability and PM10 variation in different sections of the anticyclone was established. A linear relationship was assumed between PM10 variation per unit area in the mixing layer and pressure variation within a time interval, and different sections of the anticyclone were associated with different linear regression equations. A parameter called PM10 variation rate was then put forward, which could be easily applied for regional air pollution control and management.► A FLEXPART-WRF model was used to analyze the synoptic patterns of an anticyclone. ► The transport trajectories of PM10 particles in the anticyclone were simulated. ► The relationship between air pressure and PM10 variation in anticyclone was established. ► A parameter called PM10 variation rate was put forward for air pollution control.

Keywords: Air pollution; Anticyclone; FLEXPART model; PM; 10; WRF model
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