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Atmospheric Environment (v.45, #36)

Editorial board (pp. i).

Evaluation of near surface ozone in air quality simulations forced by a regional climate model over Europe for the period 1991–2000 by P. Zanis; E. Katragkou; I. Tegoulias; A. Poupkou; D. Melas; P. Huszar; F. Giorgi (pp. 6489-6500).

This study aims to evaluate near surface ozone simulated with the modelling system RegCM3/CAMx against ozone measurements from the EMEP database for the recent decade 1991–2000. The RegCM3/CAMx simulations were performed on a 50 km × 50 km grid over Europe driven either by ERA-40 reanalysis (hereafter referred as ERA simulation) or the global circulation model (GCM) ECHAM5 (hereafter referred as ECHAM simulation). A set of statistical metrics is used for the model evaluation, including temporal correlation coefficient, the ratio of the standard deviations and the bias of simulated versus observed values. Overall, a good agreement is found for both ERA and ECHAM simulations at the majority of the selected EMEP stations in all metrics throughout the year based either on monthly or daily ozone values. Based on these results, it is assessed that the modelling system RegCM3/CAMx is suitable to be used for present and future regional climate-air quality simulations with emphasis on near surface ozone. The ERA simulations reproduce more accurately the observed ozone values in comparison to ECHAM simulations because the meteorology of the ERA experiment is closer to real atmospheric conditions than the GCM based experiment. On a seasonal basis, both ERA and ECHAM simulations exhibit a seasonally dependent bias, with winter and spring ozone values being generally under-estimated by the model and summer and autumn values being slightly overestimated. This seasonally dependent bias is also evident from median and peak midday ozone values. However, the highest observed midday ozone peaks in summer, with values higher than 80 ppbv, could not be captured either by ERA or ECHAM simulations. An analysis of day-time and night-time ERA and ECHAM modelled ozone values shows that CAMx performs better during the day-time.► Evaluation of RegCM3/CAMx simulations against EMEP O₃ measurements for 1991–2000. ► RegCM3/CAMx is driven either by ERA-40 or the global circulation model ECHAM5. ► A good agreement is found for the majority of stations in all evaluation metrics. ► The model performance is considerably better during the day-time than night-time. ► RegCM3/CAMx is suitable for regional climate-air quality simulations regarding O₃.

Keywords: Tropospheric ozone; Regional climate modelling; Air quality modelling; Evaluation; Europe

Vertical distributions of non-methane hydrocarbons and halocarbons in the lower troposphere over northeast China by Likun Xue; Tao Wang; Isobel. J. Simpson; Aijun Ding; Jian Gao; Donald R. Blake; Xuezhong Wang; Wenxing Wang; Hengchi Lei; Dezhen Jin (pp. 6501-6509).

Vertical distributions of air pollutants are crucial for understanding the key processes of atmospheric transport and for evaluating chemical transport models. In this paper, we present measurements of non-methane hydrocarbons (NMHCs) and halocarbons obtained from an intensive aircraft study over northeast (NE) China in summer 2007. Most compounds exhibited a typical negative profile of decreasing mixing ratios with increasing altitude, although the gradients differed with different species. Three regional plumes with enhanced VOC mixing ratios were discerned and characterized. An aged plume transported from the northern part of the densely populated North China Plain (NCP; i.e. Beijing–Tianjin area) showed relatively higher levels of HCFC-22, 1,2-dichloroethane (1,2-DCE) and toluene. In comparison, the plume originating from Korea had higher abundances of CFC-12, tetrachloroethene (C₂Cl₄) and methyl chloride (CH₃Cl), while regional air masses from NE China contained more abundant light alkanes. By comparing these results with the earlier PEM-West B (1994) and TRACE-P (2001) aircraft measurements, continuing declining trends were derived for methyl chloroform (CH₃CCl₃), tetrachloromethane (CCl₄) and C₂Cl₄ over the greater China–northwestern Pacific region, indicating the accomplishment of China in reducing these compounds under the Montreal protocol. However, the study also provided evidence for the continuing emissions of several halocarbons in China in 2007, such as CFCs (mainly from materials in stock) and HCFCs.► Negative vertical distributions of NMHCs and halocarbons. ► Different VOC profiles for three regional plumes. ► Continuing declining trends for CH₃CCl₃, CCl₄, and C₂Cl₄ over China. ► Continuing emissions of selected halocarbons in northeast China in 2007.

Keywords: Non-methane hydrocarbon; Halocarbon; Aircraft study; NE China; Vertical distribution; Regional plume

Variability of dust iron solubility in atmospheric waters: Investigation of the role of oxalate organic complexation by R. Paris; K.V. Desboeufs; E. Journet (pp. 6510-6517).

Atmospheric dust deposition is a major external iron source for remote surface ocean waters. Organic complexation is known to play a role in the dissolution of iron-containing minerals. In this paper, we present our study on the effect of oxalate on dust iron solubility in simulated rainwater. Our results reveal that the solubility of iron carried by analogs of different African dusts varies with the dust source. Our experiments indicate a positive linear correlation between iron solubility and oxalate concentration. Soluble iron (SFe) increases from 0.0025(±0.0005)% to 0.26(±0.01)% of total iron, considering all dust sources and with oxalate concentrations ranging from 0 to 8 μM. These results show that the observed variability of iron solubility in aerosols collected over the Atlantic Ocean is, at least partly, due to an increase in dust iron solubility, with the presence of oxalate complexation, rather than to the presence of more soluble anthropogenic iron. Considering the mineralogical composition of those particles, experiments with pure minerals (hematite, goethite and illite) were performed to study the dissolution process. We found that oxalate promotes the solubility of iron contained in clay and hence confirmed that more than 95% of SFe from soil dust is provided by clay (illite). This experimental work enables us to establish a parameterization of iron solubility in dust as a function of oxalate concentration and based on the individual iron solubility of pure iron-bearing minerals usually present in dust particles. Finally, our results emphasize that oxalate contributes to iron solubility on the same order of magnitude as the acid processes. Organic complexation appears to be a process that increases iron solubility and likely enhances the bioavailability of iron from dust.► Soluble iron deposition is a key factor for phytoplankton growth. ► We study the effect of oxalate complexation on dust iron dissolution in simulated rainwater. ► This atmospheric process explains partly iron solubility variability of collected aerosols. ► The variability is also linked to the sources of dust particles. ► We parameterize the iron solubility as a function of the dust mineralogical composition.

Keywords: Dust; Iron; Solubility; Oxalate; Organic complexation; Mineralogical composition

Variation of low molecular weight organic acids in precipitation and cloudwater at high elevation in South China by Yan Wang; Minghu Sun; Penghui Li; Yuhua Li; Likun Xue; Wenxing Wang (pp. 6518-6525).

To investigate the sources and chemical behaviors of carboxylic acids in Southern China, precipitation and corresponding cloudwater samples were collected in an acid rain-prone area of Mount Heng. The carboxylic acid levels in the samples were measured, and the concentration patterns were evaluated with respect to temporal and seasonal variations. Formic and acetic acids were predominant among the carboxylic acids identified for both precipitation and cloudwater. Most of the organic acids in the precipitation had a clear seasonal pattern, reaching higher levels during the warm season; these higher levels were attributed to the stronger source strength of biogenic emissions during this season. The cloud–fog samples did not display a similar trend. A distinctive diurnal pattern in carboxylic acids was only observed in the precipitation samples during the warm season. In cloud–fog, the ratio of formic to acetic acid differed considerably with time, with these values varying little in the precipitation samples. This result indicates that the organic acids in precipitation originate consistently from primary sources throughout the entire period, while those in cloud are mainly associated with direct emissions in the earlier stage and with secondary sources in the later period.► The diverse wet depositions in southern China were analyzed. ► Organic acids accounted for 16.78% to the total acidity of the precipitation. ► Organic acids in the precipitation had a clear seasonal pattern. ► A distinctive diurnal pattern was observed in precipitation during the warm season. ► The F/ A ratio implied there was a source variation about organic acids in fog–cloud.

Keywords: Carboxylic acids; Mount Heng; Cloud-precipitation; Sources

Aircraft emissions and local air quality impacts from takeoff activities at a large International Airport by Yifang Zhu; Elinor Fanning; Rong Chun Yu; Qunfang Zhang; John R. Froines (pp. 6526-6533).

Real time number concentrations and size distributions of ultrafine particles (UFPs, diameter <100 nm) and time integrated black carbon, PM_2.5 mass, and chemical species were studied at the Los Angeles International Airport (LAX) and a background reference site. At LAX, data were collected at the blast fence (∼140 m from the takeoff position) and five downwind sites up to 600 m from the takeoff runway and upwind of the 405 freeway. Size distributions of UFPs collected at the blast fence site showed very high number concentrations, with the highest numbers found at a particle size of approximately 14 nm. The highest spikes in the time series profile of UFP number concentrations were correlated with individual aircraft takeoff. Measurements indicate a more than 100-fold difference in particle number concentrations between the highest spikes during takeoffs and the lowest concentrations when no takeoff is occurring. Total UFP counts exceeded 10⁷ particles cm⁻³ during some monitored takeoffs. Time averaged concentrations of PM_2.5 mass and two carbonyl compounds, formaldehyde and acrolein, were statistically elevated at the airport site relative to a background reference site. Peaks of 15 nm particles, associated with aircraft takeoffs, that occurred at the blast fence were matched with peaks observed 600 m downwind, with time lags of less than 1 min. The results of this study demonstrate that commercial aircraft at LAX emit large quantities of UFP at the lower end of currently measurable particle size ranges. The observed highly elevated UFP concentrations downwind of LAX associated with aircraft takeoff activities have significant exposure and possible health implications.► UFP, BC, PM_2.5, and chemical species were measured at LAX. ► Aircrafts emit large quantities of UFP at the lower end of measurable size ranges. ► PM_2.5, formaldehyde, and acrolein were statistically elevated at LAX. ► Spikes of UFPs due to takeoff emissions were detected at 600 m downwind of LAX. ► Results from this study have significant exposure and possible health implications.

Keywords: Ultrafine particles; Aircraft emissions; Los Angeles International Airport; Chemical speciation; Takeoff; Emission index

Experimental investigation of outdoor and indoor mean concentrations and concentration fluctuations of pollutants by J.M. Santos; I. Mavroidis; N.C. Reis Jr.; E.C. Pagel (pp. 6534-6545).

Tracer gas was released upwind of a two-compartment complex shaped building under unstable atmospheric conditions. The mean wind direction was normal to or at 45° to the long face of the building. The general patterns of concentration distribution on the building external walls and inside the building were analysed and the influence of natural and mechanical ventilation on indoor concentration distributions was discussed. Mean concentration levels, as well as the concentration fluctuation intensity, were higher on the windward walls of the building, although concentration levels varied along each wall. Concentration fluctuations measured inside the building were lower than those measured outside. Inside the two compartments of the building, the time series of concentrations had a similar general behaviour; however, gas concentrations took approximately 1.5 times longer to reach the mean maximum concentration value at the downwind compartment 02 while they also decreased more rapidly in the upwind compartment 01 after the source was turned off. The highest indoor concentration and concentration fluctuation values were observed at the detectors located close to the windward walls, especially when the building windows were open. Experiments with and without natural ventilation suggested that infiltration and exfiltration of contaminants is much faster when the building windows are open, resulting to higher indoor concentration levels. Furthermore, mechanical ventilation tends to homogenize concentrations and suppress concentration fluctuations, leading to lower maximum concentration values.► Experiments on contaminant dispersion and infiltration from an upwind source. ► Higher mean concentrations and concentration fluctuations near windward wall. ► Lower concentration fluctuations inside the building than outside. ► Natural ventilation resulted to higher indoor maximum mean concentrations. ► Mechanical ventilation resulted to lower indoor maximum mean concentrations.

Keywords: Atmospheric dispersion; Building; Indoor air quality; Infiltration; Outdoor source; Ventilation; Concentration fluctuations

Predicted changes in summertime organic aerosol concentrations due to increased temperatures by Melissa C. Day; Spyros N. Pandis (pp. 6546-6556).

Changes in summertime organic aerosol (OA) concentrations in the Eastern U.S. are investigated for different temperature change scenarios using the chemical transport model PMCAMx-2008. OA is simulated using the volatility basis set approach, assuming that the primary emissions are semi-volatile and that the intermediate volatile and semi-volatile organic compounds are oxidized in the gas phase, resulting in products with lower volatility. For the basic temperature change scenario where biogenic emissions are kept constant, ground-level OA decreases by −0.3% K⁻¹ on average. Increases in the north (+0.1% K⁻¹) and decreases in the south (−0.5% K⁻¹) are predicted. The effect of the uncertain temperature dependence of the aging rate constant is modest, changing the OA by only 0.1% K⁻¹ over the temperature-independent case. For the more realistic scenario in which biogenic OA precursor emissions are allowed to increase with temperature (up to 10% K⁻¹), however, average OA increases by 4.1% K⁻¹, with even higher increases in southern regions. These results suggest that as temperature increases, complicated changes in production, partitioning and chemical aging will take place. Nevertheless, the change in biogenic emissions and subsequent production of biogenic OA is more than an order of magnitude more important than the changes in the rates of chemical and physical atmospheric processes.► Temperature can increase or decrease simulated organic aerosol concentrations. ► With constant emissions, organic aerosol will decrease with increasing temperature. ► Organic aerosol is weakly sensitive to a temperature-dependent aging rate. ► Increasing biogenic emissions with temperature significantly increases aerosol.

Keywords: Climate change; Air quality; Organic aerosol; Volatility basis set; Modeling; PMCAMx

Determination and analysis of PM₁₀ source apportionment during episodes of air pollution in Central Eastern European urban areas: The case of wintertime 2006 by Katarzyna Juda-Rezler; Magdalena Reizer; Jean-Paul Oudinet (pp. 6557-6566).

Source apportionment of air pollution due to particulate matter with an aerodynamic diameter <10 μm (PM₁₀) was investigated in Central Eastern European urban areas. A combination of four methods was developed to distinguish long-range transport (LRT) and regional transport (RT) from local pollution (LP) sources as well as to discern the involvement of traffic or residential sources in LP. Sources of PM₁₀ events of pollution were determined in January 2006 in representative Polish cities using monitored air quality and meteorological data, backward air mass trajectories, correlation and principal component analysis (PCA). Daily patterns of PM₁₀ levels show that several peak episodes were registered in Poland; January 21–30th being the most polluted days. Air mass back-trajectory analysis shows that all cities were under the influence of LRT from North-eastern origins (Russia–Belarus–Ukraine), most were also under LRT from Southern origin (Slovakia, Czech Republic), and northern cities were under national RT influence. PCA analysis shows that ion-sums of secondary inorganic aerosols account for LRT pollution while arsenic and chromium represents markers of RT (industrial) and LP (residential) sources of PM₁₀, respectively. Determination of several ratios (REG/UB, REG/TRAF, TRAF/UB) calculated between PM₁₀ levels measured at regional background (REG); urban background (UB) and traffic (TRAF) monitoring sites shows that, with ratios REG/UB ≥ 0.57, PM₁₀ episodes in both Szczecin and Warsaw bore a marked RT origin. The lower REG/UB ≤ 0.35 in the Southern cities of Cracow and Zabrze indicates that LP was the main contributor to the observed episodes. Only PM₁₀ episodes in Southern-western Poland (Jelenia Góra) were clearly of LP origin as characterized, by the lowest REG/UB ratio (<0.2). The high TRAF/UB ratios obtained for all cities (close to 1) indicate that there was a great uniformity of PM levels on an urban scale owing to the meteorologically stagnant conditions. A high correlation between PM₁₀, NO₂ and CO confirms that traffic emission represented a common and an important LP source of urban pollution in most Polish cities during January 2006. On the other hand PM₁₀ which is also highly correlated with SO₂ in 4 cities out of 6, indicates that coal combustion through domestic heating or industrial activities was also an important LP source of PM₁₀. Finally, extremely unfavourable meteorological conditions caused by the influence of a Siberian high-pressure system were found to be associated with the occurrence of severe PM₁₀ episodes of pollution.► We analysed severe PM₁₀ episodes recorded during January 2006 in Polish cities. ► Applied methodology discerns LRT & regional transports from local PM₁₀ sources. ► Depending on city location, either LRT & regional or local sources dominate. ► Road transport or residential sectors are main local PM₁₀ sources. ► As, Cr, SIA represent industrial, residential & LRT sources of PM₁₀, respectively.

Keywords: Urban particulate air pollution; PM; ₁₀; Trace metals; Source apportionment; Backward trajectories; Poland

Distribution of polychlorinated dibenzo- p-dioxins and dibenzofurans in ambient air of different regions in China by Tong Chen; Xiaodong Li; Jianhua Yan; Shengyong Lu; Kefa Cen (pp. 6567-6575).

Levels of polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs) were determined in fourteen ambient air samples collected in twelve cities of five provinces and one large municipality in China. The PCDD/F concentrations varied from 2.6 to 120 pg m⁻³ (or from 0.04 to 1.93 pg I-TEQ m⁻³). Generally, TCDF was the dominant homologue group and as a rule the homologue concentration of PCDF decreased with rising chlorine substitution number of PCDF. In all cases 2,3,4,7,8-PeCDF was the most important contributor to the I-TEQ value, accounting for 35–57% of the total I-TEQ value. Higher PCDD/F levels in ambient air were found during winter. The highest PCDD/F levels were found in Chengdu, Sichuan Province. In general, the PCDD/F levels in this study were in the same range as in other studies in China.► Profiles of PCDD/F in atmosphere of medium or small cities in China were studied. ► PCDD/F concentrations were investigated and compared with other results. ► Climate and region effect for PCDD/Fs was also illuminated.

Keywords: PCDD/Fs; Ambient air; Homologue profile; Congener profile; China

Simulation of aerosol direct radiative forcing with RAMS-CMAQ in East Asia by Xiao Han; Meigen Zhang; Zhiwei Han; Jinyuan Xin; Xiaohong Liu (pp. 6576-6592).

The air quality modeling system RAMS-CMAQ is developed to assess aerosol direct radiative forcing by linking simulated meteorological parameters and aerosol mass concentration with the aerosol optical properties/radiative transfer module in this study. The module is capable of accounting for important factors that affect aerosol optical properties and radiative effect, such as incident wave length, aerosol size distribution, water uptake, and internal mixture. Subsequently, the modeling system is applied to simulate the temporal and spatial variations in mass burden, optical properties, and direct radiative forcing of diverse aerosols, including sulfate, nitrate, ammonium, black carbon, organic carbon, dust, and sea salt over East Asia throughout 2005. Model performance is fully evaluated using various observational data, including satellite monitoring of MODIS and surface measurements of EANET (Acid Deposition Monitoring Network), AERONET (Aerosol Robotic Network), and CSHNET (Chinese Sun Hazemeter Network). The correlation coefficients of the comparisons of daily average mass concentrations of sulfate, PM2.5, and PM10 between simulations and EANET measurements are 0.70, 0.61, and 0.64, respectively. It is also determined that the modeled aerosol optical depth (AOD) is in congruence with the observed results from the AERONET, the CSHNET, and the MODIS. The model results suggest that the high AOD values ranging from 0.8 to 1.2 are mainly distributed over the Sichuan Basin as well as over central and southeastern China, in East Asia. The aerosol direct radiative forcing patterns generally followed the AOD patterns. The strongest forcing effect ranging from −12 to −8 W m⁻² was mainly distributed over the Sichuan Basin and the eastern China’s coastal regions in the all-sky case at TOA, and the forcing effect ranging from −8 to −4 W m⁻² could be found over entire eastern China, Korea, Japan, East China Sea, and the sea areas of Japan► An aerosol optical properties/radiative transfer module is built in this study. ► This module is incorporated into RAMS-CMAQ modeling system. ► Aerosol direct forcing over East Asia in 2005 is simulated. ► Modeling system has good ability to reproduce aerosol physico-chemical properties.

Keywords: CMAQ; Aerosols; Optical properties; Radiative forcing

Pragmatic estimation of a spatio-temporal air quality model with irregular monitoring data by Paul D. Sampson; Adam A. Szpiro; Lianne Sheppard; Johan Lindström; Joel D. Kaufman (pp. 6593-6606).

Statistical analyses of health effects of air pollution have increasingly used GIS-based covariates for prediction of ambient air quality in “land use” regression models. More recently these spatial regression models have accounted for spatial correlation structure in combining monitoring data with land use covariates. We present a flexible spatio-temporal modeling framework and pragmatic, multi-step estimation procedure that accommodates essentially arbitrary patterns of missing data with respect to an ideally complete space by time matrix of observations on a network of monitoring sites. The methodology incorporates a model for smooth temporal trends with coefficients varying in space according to Partial Least Squares regressions on a large set of geographic covariates and nonstationary modeling of spatio-temporal residuals from these regressions. This work was developed to provide spatial point predictions of PM_2.5 concentrations for the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air) using irregular monitoring data derived from the AQS regulatory monitoring network and supplemental short-time scale monitoring campaigns conducted to better predict intra-urban variation in air quality. We demonstrate the interpretation and accuracy of this methodology in modeling data from 2000 through 2006 in six U.S. metropolitan areas and establish a basis for likelihood-based estimation.► We show air quality monitoring data manifesting temporal trends varying in space. ► We present a hierarchical nonstationary model using land use covariates. ► We demonstrate a multi-step estimation procedure with irregular space-time data. ► Our methodology establishes a basis for formal likelihood based estimation. ► We make predictions of PM_2.5 concentrations for the EPA-funded MESA Air study.

Keywords: Exposure estimation; Hierarchical model; Nonstationary spatial covariance; Partial least squares; Particulate matter; Universal kriging

Analysis of surface and aerosol polarized reflectance for aerosol retrievals from polarized remote sensing in PRD urban region by X. Gu; T. Cheng; D. Xie; Z. Li; T. Yu; H. Chen (pp. 6607-6612).

A precise estimate of polarization induced by surface is crucial for polarized remote sensing dedicated to monitoring aerosol properties over urban area. The accurate knowledge of interaction between surface and aerosol polarized reflectance is essential for accurately achieving aerosol properties. In order to study surface and aerosol polarized reflectance for aerosol retrievals over urban area, a new airborne directional polarimetric camera (DPC) with high spatial resolution (4m at 4000m a.g.l) was developed. The surface polarized reflectance over distinct surface covers of urban area (forest, shrub, and soil) were studied using DPC measurements during a field campaign in the Pearl River Delta (PRD), China. The large variations were found in surface polarized reflectance of distinct urban covers due to surface type variability. For all surface types, the empirical BPDF model cannot describe accurately surface polarized reflectance at all possible illumination and observation geometries. From the quantitatively study of relationship between surface and aerosol polarized contribution to DPC measurements, we show that the polarized contributions of aerosol, which optical properties were defined by ground-based measurements, are much larger than the polarized contribution of surface, and found that the polarized contribution of surface covers increases with decreasing NDVI. The effect of polarization accuracy of measurements on aerosol retrieval was also investigated using DPC measurements, and found that 0.1% polarization accuracy of measurements can be neglected when AOD is retrieved using polarized measurements. Based on the information of effects of polarized reflectance differences between distinct surface covers and polarization accuracy of polarized measurements on retrieved aerosols over urban area, we found that the accuracy of aerosol retrieval over forest covers is higher than other surface types using polarized remote sensing.

Keywords: Surface polarized reflectance; Aerosol properties; Aerosol polarized reflectance; Polarized remote sensing; Pearl River Delta (PRD)

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Atmospheric Environment (v.45, #36)