Atmospheric Environment (v.44, #10)

We present a comprehensive one-year data set on water-soluble ionic species ( Na + , NH 4 + , K + , Mg 2 + , Ca 2 + , Cl − , NO 3 − , SO 4 2 − , and HCO 3 − ) in PM2.5 (fine) and PM10–2.5 (coarse) aerosols from a high-altitude site (Mt. Abu, 24.6 °N, 72.7 °E, 1680 m asl) in high-dust region of western India. The water-soluble ionic composition (WSIC) varied from 1.0 to 19.5 μg m−3 in the fine mode and constitutes 50, 39 and 31% of the aerosol mass during winter, summer and monsoon respectively, with dominant contribution from SO4 2−, NH4 + and HCO3 . Furthermore, a two-fold increase in the abundances of nss-SO4 2− and NH4 + and their co-variability during wintertime, relative to high-dust conditions in summer, suggest dominance of anthropogenic sources and long-range transport of combustion products (biomass burning and fossil-fuel emissions) from northern India. In the coarse mode, WSIC ranged from 0.1 to 24.8 μg m−3 and its contribution to aerosol mass was consistently low (annual average = 21%) with predominance of Ca2+ and HCO3 , indicating contribution from carbonate rich mineral dust. The nss-SO4 2−/NO3 mass ratio exhibits extreme variability during winter, with values ranging from 2.7 to 101 in PM2.5 and 0.001 to 2.7 in coarse (PM10–2.5) mode. The relatively high abundance of nitrate in the coarse mode, during all seasons, indicates its association with mineral dust. The temporal variability is further evident from significantly lower aerosol mass and WSIC during the SW-monsoon (July–Sept) due to efficient washout. The chemical data set also documents near quantitative neutralization of acidic species (NO3 and SO4 2−) by NH4 + in PM2.5 and mineral dust in PM10–2.5, thus, representing a dominant atmospheric chemical transformation process occurring in the high-dust semi-arid region.
Keywords: Aerosol chemistry; Mineral dust; Acid uptake;

Wet deposition of mercury within the vicinity of a cement plant before and during cement plant maintenance by Sarah E. Rothenberg; Lester McKee; Alicia Gilbreath; Donald Yee; Mike Connor; Xuewu Fu (1255-1262).
Hg species (total mercury, methylmercury, reactive mercury) in precipitation were investigated in the vicinity of the Lehigh Hanson Permanente Cement Plant in the San Francisco Bay Area, CA., USA. Precipitation was collected weekly between November 29, 2007 and March 20, 2008, which included the period in February and March 2008 when cement production was minimized during annual plant maintenance. When the cement plant was operational, the volume weighted mean (VWM) and wet depositional flux for total Hg (HgT) were 6.7 and 5.8 times higher, respectively, compared to a control site located 3.5 km east of the cement plant. In February and March, when cement plant operations were minimized, levels were approximately equal at both sites (the ratio for both parameters was 1.1). Due to the close proximity between the two sites, meteorological conditions (e.g., precipitation levels, wind direction) were similar, and therefore higher VWM HgT levels and HgT deposition likely reflected increased Hg emissions from the cement plant. Methylmercury (MeHg) and reactive Hg (Hg(II)) were also measured; compared to the control site, the VWM for MeHg was lower at the cement plant (the ratio = 0.75) and the VWM for Hg(II) was slightly higher (ratio = 1.2), which indicated the cement plant was not likely a significant source of these Hg species to the watershed.
Keywords: Mercury; Precipitation; Cement plant; Flux; Methylmercury;

Evidence for short-range transport of atmospheric mercury to a rural, inland site by Sarah E. Rothenberg; Lester McKee; Alicia Gilbreath; Donald Yee; Mike Connor; Xuewu Fu (1263-1273).
Atmospheric mercury (Hg) species, including gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate-bound mercury (Hgp), were monitored near three sites, including a cement plant (monitored in 2007 and 2008), an urban site and a rural site (both monitored in 2005 and 2008). Although the cement plant was a significant source of Hg emissions (for 2008, GEM: 2.20 ± 1.39 ng m−3, RGM: 25.2 ± 52.8 pg m−3, Hgp 80.8 ± 283 pg m−3), average GEM levels and daytime average dry depositional RGM flux were highest at the rural site, when all three sites were monitored sequentially in 2008 (rural site, GEM: 2.37 ± 1.26 ng m−3, daytime RGM flux: 29 ± 40 ng m−2 day−1). Photochemical conversion of GEM was not the primary RGM source, as highest net RGM gains (75.9 pg m−3, 99.0 pg m−3, 149 m−3) occurred within 3.0–5.3 h, while the theoretical time required was 14–23 h. Instead, simultaneous peaks in RGM, Hgp, ozone (O3), nitrogen oxides, and sulfur dioxide in the late afternoon suggested short-range transport of RGM from the urban center to the rural site. The rural site was located more inland, where the average water vapor mixing ratio was lower compared to the other two sites (in 2008, rural: 5.6 ± 1.4 g kg−1, urban: 9.0 ± 1.1 g kg−1, cement plant: 8.3 ± 2.2 g kg−1). Together, these findings suggested short-range transport of O3 from an urban area contributed to higher RGM deposition at the rural site, while drier conditions helped sustain elevated RGM levels. Results suggested less urbanized environments may be equally or perhaps more impacted by industrial atmospheric Hg emissions, compared to the urban areas from where Hg emissions originated.
Keywords: Atmospheric mercury; Flux; Diurnal; Ozone;

The link between the African Monsoon systems and aerosol loading in Africa is studied using multi-year satellite observations of UV-absorbing aerosols and rain gauge measurements.The main aerosol types occurring over Africa are desert dust and biomass burning aerosols, which are UV-absorbing. The abundance of these aerosols over Africa is characterised in this paper using residues and Absorbing Aerosol Index (AAI) data from Global Ozone Monitoring Experiment (GOME) on board ERS-2 and SCanning Imaging Absorption SpectroMeter for Atmospheric ChartograpHY (SCIAMACHY) on board Envisat.Time series of regionally averaged residues from 1995 to 2008 show the seasonal variations of aerosols in Africa. Zonally averaged daily residues over Africa are related to monthly mean precipitation data and show monsoon-controlled atmospheric aerosol loadings. A distinction is made between the West African Monsoon (WAM) and the East African Monsoon (EAM), which have different dynamics, mainly due to the asymmetric distribution of land masses around the equator in the west. The seasonal variation of the aerosol distribution is clearly linked to the seasonal cycle of the monsoonal wet and dry periods in both studied areas.The residue distribution over Africa shows two distinct modes, one associated with dry periods and one with wet periods. During dry periods the residue varies freely, due to aerosol emissions from deserts and biomass burning events. During wet periods the residue depends linearly on the amount of precipitation, due to scavenging of aerosols and the prevention of aerosol emissions from the wet surface. This is most clear over east Africa, where the sources and sinks of atmospheric aerosols are controlled directly by the local climate, i.e. monsoonal precipitation. Here, the wet mode has a mean residue of −1.4 and the dry mode has a mean residue of −0.3. During the wet modes a reduction of one residue unit for every 160 mm monthly averaged precipitation was found. Shielding effects due to cloud cover may also play a role in the reduction of the residue during wet periods.A possible influence of aerosols on the monsoon, via aerosol direct and indirect effects, is plausible, but cannot directly be deduced from these data.
Keywords: Absorbing aerosols; Remote sensing; African monsoon; Precipitation;

Natural chloroform emissions from the blanket peat bogs in the vicinity of Mace Head, Ireland over a 14-year period by P.G. Simmonds; R.G. Derwent; A.J. Manning; S. O'Doherty; G. Spain (1284-1291).
Simultaneous chloroform (CHCl3) emission and ozone (O3) deposition are regularly observed under nocturnal inversions during the summer months from and to the peat bogs in the vicinity of the Mace Head Atmospheric Research Station, Connemara, Co Galway, Ireland. Emissions were estimated using the nocturnal box model applied to routine atmospheric observations collected over a 14-year period from 1995 to 2008. Strict criteria were applied in the selection of events of low wind speed, under a stable night-time inversion layer in baseline air conditions, with no transport from Europe. The mean peatland CHCl3 flux was 2.91 μg m−2 h−1 with highly variable fluxes ranging from 0.44 to 12.94 μg m−2 h−1. These fluxes are generally larger than those reported previously for similar biomes and if representative would make a significant contribution to the global estimated source of CHCl3. Fluxes were not strongly correlated with either atmospheric temperature or the level of precipitation. Over the 14-year period there appears to have been a small increase in overall CHCl3 emissions, although we stress that the nocturnal box model has a number of limitations and assumptions which should be taken into account.
Keywords: Chloroform (CHCl3); Peatland emissions; Nocturnal box model; Mace Head;

Aerosol (total suspended particulate) samples collected at three diverse locations (urban-commercial, semi-urban and rural-agricultural) in Patiala, India were analyzed for loss on ignition (LOI) and organic tarry matter (OTM) content in ambient air during crop residue burning (CRB) episodes and non-crop residue burning (NCRB) months in 2006–2007. Results showed high levels of LOI and OTM during wheat and rice crop residue-burning periods at all the sites. Higher levels were obtained during rice crop residue-burning period as compared to the wheat residue-burning period. At semi-urban site, LOI varied between 53 ± 36 μg m−3 and 257 ± 14 μg m−3 constituting 38–78% (w/w) part of the aerosols whereas levels of OTM varied between 0.98 ± 0.11 μg m−3 and 7.93 ± 2.76 μg m−3 comprising 0.42–3.28% (w/w) fraction. At rural-agricultural area site, levels of LOI varied between 86 ± 40 μg m−3 and 293 ± 70 μg m−3 comprising 27–84% (w/w), whereas OTM levels varied between 1.31 ± 0.64 μg m−3 and 10.09 ± 6.56 μg m−3 constituting 0.83–2.42% (w/w) fraction of the aerosols. At urban-cum-commercial site, levels of LOI and OTM varied between 48 ± 23 μg m−3 and 281 ± 152 μg m−3 and 2.53 ± 1.23 μg m−3 and 17.40 ± 8.50 μg m−3, constituting 24–62% (w/w) part of the aerosols, respectively. Results also indicated that OTM and LOI were integral parts of aerosols and their concentrations were influenced by the crop residue burning practices with incorporated effect of vehicular activities in Patiala.
Keywords: Aerosol; Loss on ignition; Crop residue burning; Organic tarry matter; Combustible matter;

Validation of in-situ measurements of volatile organic compounds through flask sampling and gas chromatography/mass spectrometry analysis by Chih-Chung Chang; Chang-Feng OuYang; Chieh-Heng Wang; Sen-Wei Chiang; Jia-Lin Wang (1301-1307).
Continuous monitoring of ambient non-methane hydrocarbons (NMHCs) by automated gas chromatographs equipped with flame ionization detection (termed in-situ GC/FID) with hourly data resolution was instated in ozone non-attainment areas throughout Taiwan. Performance of these on-site in-situ GCs was validated by manual flask sampling, as well as by in-lab gas chromatography/mass spectrometry (GC/MS) analysis. More than 50 VOCs from C2 to C11 were analyzed by both methods. Ninety flask samples were collected in series near an in-situ GC monitoring station in order to closely compare with the in-situ measurements. Both time-series and scatter plots from the two methods are displayed and discussed. It was found that over-simplified, un-humidified single-point calibration leading to surface loss was responsible for the bias in the in-situ method, resulting in greater error in accuracy as VOC volatility decreased. Although this over-estimate of the concentrations was found across all target VOCs, both methods were able to consistently capture the variability of ambient VOCs, with R 2 values greater than 0.9 for most of the major VOCs.
Keywords: Inter-comparison; Non-methane hydrocarbons (NMHCs); Photochemical assessment monitoring stations (PAMS);

A European aerosol phenomenology – 3: Physical and chemical characteristics of particulate matter from 60 rural, urban, and kerbside sites across Europe by J.-P. Putaud; R. Van Dingenen; A. Alastuey; H. Bauer; W. Birmili; J. Cyrys; H. Flentje; S. Fuzzi; R. Gehrig; H.C. Hansson; R.M. Harrison; H. Herrmann; R. Hitzenberger; C. Hüglin; A.M. Jones; A. Kasper-Giebl; G. Kiss; A. Kousa; T.A.J. Kuhlbusch; G. Löschau; W. Maenhaut; A. Molnar; T. Moreno; J. Pekkanen; C. Perrino; M. Pitz; H. Puxbaum; X. Querol; S. Rodriguez; I. Salma; J. Schwarz; J. Smolik; J. Schneider; G. Spindler; H. ten Brink; J. Tursic; M. Viana; A. Wiedensohler; F. Raes (1308-1320).
This paper synthesizes data on aerosol (particulate matter, PM) physical and chemical characteristics, which were obtained over the past decade in aerosol research and monitoring activities at more than 60 natural background, rural, near-city, urban, and kerbside sites across Europe. The data include simultaneously measured PM10 and/or PM2.5 mass on the one hand, and aerosol particle number concentrations or PM chemistry on the other hand. The aerosol data presented in our previous works () were updated and merged to those collected in the framework of the EU supported European Cooperation in the field of Scientific and Technical action COST633 (Particulate matter: Properties related to health effects). A number of conclusions from our previous studies were confirmed. There is no single ratio between PM2.5 and PM10 mass concentrations valid for all sites, although fairly constant ratios ranging from 0.5 to 0.9 are observed at most individual sites. There is no general correlation between PM mass and particle number concentrations, although particle number concentrations increase with PM2.5 levels at most sites. The main constituents of both PM10 and PM2.5 are generally organic matter, sulfate and nitrate. Mineral dust can also be a major constituent of PM10 at kerbside sites and in Southern Europe. There is a clear decreasing gradient in SO4 2− and NO3 contribution to PM10 when moving from rural to urban to kerbside sites. In contrast, the total carbon/PM10 ratio increases from rural to kerbside sites. Some new conclusions were also drawn from this work: the ratio between ultrafine particle and total particle number concentration decreases with PM2.5 concentration at all sites but one, and significant gradients in PM chemistry are observed when moving from Northwestern, to Southern to Central Europe. Compiling an even larger number of data sets would have further increased the significance of our conclusions, but collecting all the aerosol data sets obtained also through research projects remains a tedious task.
Keywords: Aerosol; Chemical composition; Number concentration; PM10; PM2.5;

An efficient approach of aerosol thermodynamic equilibrium predictions by the HDMR method by Yu Cheng; Dong Liang; Wenqia Wang; Sunling Gong; Min Xue (1321-1330).
In this paper, we develop a new and efficient approach for high dimensional atmospheric aerosol thermodynamic equilibrium predictions. The multi-phase and multi-component aerosol thermodynamic input–output systems are solved by the high dimensional model representation (HDMR) method combining with the moving multiple cut points. The developed approach improves the accuracy of numerical simulations for the general high dimensional input–output systems compared with the standard cut-HDMR method. It can simulate efficiently the atmospheric aerosol thermodynamic equilibrium problems in a large range of aerosol concentrations from 10−10 to 10−6 mol m−3. Numerical experiments show that the approach has great computational efficiency and the CPU-time of the approach is much less than that of ISORROPIA. The method does excellent performance in predicting high dimensional aerosol thermodynamic components as well as particulate matters (PMs).
Keywords: Atmospheric prediction; Aerosol thermodynamic equilibrium; Efficient approach; HDMR; Moving cut points;

The UCD/CIT air quality model with the Caltech Atmospheric Chemistry Mechanism (CACM) was used to predict source contributions to secondary organic aerosol (SOA) formation in the San Joaquin Valley (SJV) from December 15, 2000 to January 7, 2001. The predicted 24-day average SOA concentration had a maximum value of 4.26 μg m−3 50 km southwest of Fresno. Predicted SOA concentrations at Fresno, Angiola, and Bakersfield were 2.46 μg m−3, 1.68 μg m−3, and 2.28 μg m−3, respectively, accounting for 6%, 37%, and 4% of the total predicted organic aerosol. The average SOA concentration across the entire SJV was 1.35 μg m−3, which accounts for approximately 20% of the total predicted organic aerosol. Averaged over the entire SJV, the major SOA sources were solvent use (28% of SOA), catalyst gasoline engines (25% of SOA), wood smoke (16% of SOA), non-catalyst gasoline engines (13% of SOA), and other anthropogenic sources (11% of SOA). Diesel engines were predicted to only account for approximately 2% of the total SOA formation in the SJV because they emit a small amount of volatile organic compounds relative to other sources. In terms of SOA precursors within the SJV, long-chain alkanes were predicted to be the largest SOA contributor, followed by aromatic compounds. The current study identifies the major known contributors to the SOA burden during a winter pollution episode in the SJV, with further enhancements possible as additional formation pathways are discovered.
Keywords: CACM; CRPAQS; Secondary organic aerosol; Source apportionment; UCD/CIT air quality model;

In order to make projections for future air-quality levels, a robust methodology is needed that succeeds in reconstructing present-day air-quality levels. At present, climate projections for meteorological variables are available from Atmospheric-Ocean Coupled Global Climate Models (AOGCMs) but the temporal and spatial resolution is insufficient for air-quality assessment. Therefore, a variety of methods are tested in this paper in their ability to hindcast maximum 8 hourly levels of O3 and daily mean PM10 from observed meteorological data. The methods are based on a multiple linear regression technique combined with the automated Lamb weather classification. Moreover, we studied whether the above-mentioned multiple regression analysis still holds when driven by operational ECMWF (European Center for Medium-Range Weather Forecast) meteorological data. The main results show that a weather type classification prior to the regression analysis is superior to a simple linear regression approach. In contrast to PM10 downscaling, seasonal characteristics should be taken into account during the downscaling of O3 time series. Apart from a lower explained variance due to intrinsic limitations of the regression approach itself, a lower variability of the meteorological predictors (resolution effect) and model deficiencies, this synoptic-regression-based tool is generally able to reproduce the relevant statistical properties of the observed O3 distributions important in terms of European air quality Directives and air quality mitigation strategies. For PM10, the situation is different as the approach using only meteorology data was found to be insufficient to explain the observed PM10 variability using the meteorological variables considered in this study.
Keywords: Statistical downscaling; Stepwise multiple linear regression; Synoptic Lamb weather types; O3 and PM10 hindcast; European air quality Directives; Horizontal resolution;

Using the synoptic-regression based approach developed in Part I of this research, this study estimates future maximum 8 hourly mean O3 levels (m8hO3) using three future SRES (Special Report on Emission) scenarios for a rural background area situated in The Netherlands. The statistical downscaling tool was used to downscale the Atmospheric–Ocean Coupled General Circulation Model (AOGCM) ECHAM5-MPI/OM for the present-day 20 Century (20C) control run (1991–2000) and the future SRES scenarios A2, A1B and B1 for two periods (2051–2060 and 2091–2100). First, the statistical downscaling tool is evaluated in terms of downscaled m8hO3 levels for the present-day climate, using a long record of observed m8hO3 concentrations. It was found that a bias correction is needed and this bias correction is then further used to estimate future m8hO3 concentrations. Under the various SRES scenarios, the overall mean m8hO3 increases with 2.5–6.5 and 6.1–10.9 μg m−3, for the 2051–2060 and 2091–2100 period respectively, which is about 20% of the present-day 10-year average. This effect is enhanced when considering the summer season only, with a range of increase between the different future scenarios of 5.4–12.5 μg m−3 and 13.4–26 μg m−3 (for 2051–2060 and 2091–2100 respectively) against a present-day summer average of 73.5 μg m−3. An increase in maximum temperature and shortwave radiation, associated with a decrease in cloud cover under the various future scenarios are the main drivers of ozone increase. A comparison with August 2003 shows the physical plausibility of our results and reflects that the extreme summer of 2003 might show a close resemblance to future European summers in terms of m8hO3 and meteorological characteristics.
Keywords: Synoptic-regression based statistical downscaling; Objective Lamb weather types; Future O3 levels; ECHAM5-MPI/OM;