Atmospheric Environment (v.42, #7)

Indoor pollutants emitted by office equipment: A review of reported data and information needs by Hugo Destaillats; Randy L. Maddalena; Brett C. Singer; Alfred T. Hodgson; Thomas E. McKone (1371-1388).
Computers, printers, copier machines and other electronic equipment are a common part of the home and office environments. However, human exposure to potentially harmful pollutants emitted from office equipment has not been systematically evaluated, and is currently not well understood. In this review, we summarize available information on emission rates and/or indoor concentrations of various pollutants that are related to office equipment use, briefly describe experimental methods used to characterize emissions and identify critical research needs in this field. The office equipment evaluated in this review includes computers (desktops and notebooks), printers (laser, ink-jet and all-in-one machines) and photocopy machines. We summarize reported emission rates for the following pollutant groups: volatile organic chemicals (VOCs), ozone, particulate matter and several semivolatile organic chemicals (SVOCs). The latter includes phthalate esters, brominated flame retardants, organophosphate flame retardants, and polycyclic aromatic hydrocarbons (PAHs). We also review studies reporting airborne concentrations in indoor environments (offices, residences, schools, electronics recycling plants) where office equipment was present and deemed to be a significant contributor to the total pollutant burden. We find that for some pollutants, such as organophosphate flame retardants, the link between office-equipment emissions and indoor air concentrations is relatively well established. However, indoor VOCs, ozone, PAHs and phthalate esters can originate from a variety of sources, and their source apportionment is less straightforward. We then observe that personal exposures may be significantly larger than those estimated through average pollutant indoor concentrations, due to proximity of users to the sources over extended periods of time. Finally, we observe that the magnitude of emissions, the link from emissions to personal exposure, the toxicological significance of the chemicals emitted, and the costs and impacts of alternate materials should all be considered in order to evaluate potential importance of human exposures and health risks.
Keywords: Polybrominated diphenyl ethers (PBDEs); Indoor aerosols; Polycyclic aromatic hydrocarbons (PAHs); Volatile organic compounds; Ozone; Particulate matter; Phthalate esters; Laser printers; Plasticizers;

Regionality and particularity of a survey site from the viewpoint of the SO2 and SO4 2− concentrations in ambient air in a 250-km×250-km region of Japan by Masahide Aikawa; Takatoshi Hiraki; Makiko Yamagami; Masaru Kitase; Yoshinori Nishikawa; Itsushi Uno (1389-1398).
We reviewed the data on the atmospheric SO2 and SO4 2− concentrations measured in a survey conducted by the Japan Environmental Laboratories Association (JELA). The data collected in the Tokai–Kinki–Hokuriku branch, which covers a 250-km×250-km region, were reviewed as one of the activities of the Tokai–Kinki–Hokuriku branch. The atmospheric SO2 and SO4 2− concentrations were measured using the four-stage filter-pack method. The data collected for 3 years (Campaign III by JELA) were reviewed. The SO2 concentration was affected by the eruption episode of the Miyakejima Volcano. In contrast, the SO4 2− concentration (annual mean in 1999: 35.0 nmol m−3) was scarcely affected by the eruption episode. The SO4 2− concentration level was within or slightly higher than the level of the European Monitoring Evaluation Program (EMEP) (lower than 30 nmol m−3) and that of mid-latitude North America. The particularity of the site would be potentially clarified by the relationship of the SO4 2−/(SO2+SO4 2−) ratio with the SO2 concentration and the correlation with the results of the Community Multi-scale Air Quality (CMAQ). The peculiar pattern of the monthly variation of the SO2 concentration clarified the particularity of the site, which was deeply associated to the spatial relationship with an express highway with heavy traffic and the wind rose.
Keywords: Filter pack; Sulfate; Sulfur dioxide; Tokai–Kinki–Hokuriku branch; Japan Environmental Laboratories Association (JELA);

Equilibrium partial pressures of trifluoroacetic acid ( P CF 3 C ( O ) OH ) over aqueous trifluoroacetic acid test solutions were determined at 278.15, 288.15, and 298.15 K. The concentration of undissociated trifluoroacetic acid ( C CF 3 C ( O ) OH ) in each test solution was determined by means of attenuated total reflection IR spectroscopy and window factor analysis. From the linear relationship between P CF 3 C ( O ) OH and C CF 3 C ( O ) OH , the Henry's law constant of trifluoroacetic acid (K H) at 298.15 K was determined to be 5800±700 mol dm−3  atm−1 and K H at temperature T in K was determined to be K H=5780 exp[−4120×(1/298.15−1/T)] in mol dm−3  atm−1. The K H value at 298.15 K was 0.65 times the reported value [Bowden, D.J., Clegg, S.L., Brimblecombe, P., 1996. The Henry's law constant of trifluoroacetic acid and its partitioning into liquid water in the atmosphere. Chemosphere 32, 405–420] for pK a=0.47 and it was equal to that for pK a=0.2.
Keywords: Gas-to-water partition; Ion pairs; ATR-IR; Window factor analysis;

Airborne particulate matter (PM) in the PM10, PM2.5 and PM1.0 size fractions has been sampled at three sites within the UK West Midlands, i.e. BROS (roadside), BCCS (urban background) and CPSS (rural). Daily samples were analysed for organic (OC) and elemental carbon (EC) using a technique involving optical pyrolysis correction. The results show a strong roadside to urban to rural gradient in EC, but little if any gradient in OC. The concentrations are consistent with a regional background which contributes most of the OC concentration at all sites, upon which is superimposed a locally generated aerosol with high EC/OC content consistent with that of road traffic emissions. This explains not only the roadside increment above the urban background, but also the urban background above rural concentrations. Estimation of secondary and primary OC concentrations using the EC tracer method reveals a strong seasonality in primary OC paralleling that of EC with higher winter than summer levels, but a much smaller seasonal pattern in secondary OC, with higher average concentrations in winter than summer. A number of explanations for this apparent behaviour are explored, but no firm conclusions are reached. Similarities between the seasonal cycles of secondary OC and nitrate are suggestive of long-range transport and temperature (through semi-volatility) having a major influence on secondary OC concentrations.
Keywords: Elemental carbon; Organic carbon; Carbonaceous aerosol; Secondary organic aerosol;

Long-term trend of visibility and its characterizations in the Pearl River Delta (PRD) region, China by Xuejiao Deng; Xuexi Tie; Dui Wu; Xiuji Zhou; Xueyan Bi; Hanbo Tan; Fei Li; Chenglin Jiang (1424-1435).
This paper suggests that the rapid increase in urbanization and human activities has important impacts on visibility in the Pearl River Delta (PRD) region. A long-term trend of visibility in Guangzhou (one of the largest cities in PRD) shows that between 1954 and 2006, there is a rapid change in visibility. Between 1954 and 1972, low visibility has the smallest occurrence (less than a few days per year). Between 1972 and 1980, the visibility condition is within a transition period, and the occurrence of low visibility increases rapidly. Between 1980 and 2006, the occurrence of low visibility remains very high (150 days year−1), suggesting that the city of Guangzhou is often under low-visibility conditions since the 1980s. In order to understand the causes of the low visibility in Guangzhou, we analyze physical and chemical characterizations of a low-visibility event occurring between 15 and 29 November 2005. The analysis suggests that high concentration of aerosol particles is a major cause for the low visibility. The threshold aerosol concentration that is corresponding to the low visibility (<10 km) is about 120 μg m−3. Further analysis indicates that the relationship between aerosol concentrations and visibility appears in a non-linearity correlation. When aerosol concentrations are very high (above 120 μg m−3), the change in visibility is not sensitive to aerosol concentration. By contrast, when aerosol concentrations are <120 μg m−3, the change in visibility is very sensitive to aerosol concentrations. This study also shows that absorbing aerosol particles (such as element carbon (EC)) play important roles in the reduction of visibility. In most cases, the extremely low visibility (<2 km) is often resulted from high EC concentrations (above 15 μg m−3). In averaged condition, small scattering aerosol particles (<1 μm in radius) have the largest contribution to the reduction of visibility (about 70%). By contrast, large scattering particles have the smallest contribution to the reduction of visibility. This analysis implies that the persistent low visibility is mainly resulted from small aerosol particles, including both scattering and absorbing particles. In order to improve the visibility in the Guangzhou region, the reduction of small particle emissions is urgently needed. This study suggests that there are two important steps to improve the visibility in Guangzhou. First, the aerosol concentration should be reduced to less than the threshold value (120 μg m−3). Second, a further decrease in aerosols from its threshold value will lead to a significant improvement in visibility due to the non-linearity relationship between aerosol and visibility.
Keywords: Aerosols; Long-term trend of visibility; Scattering and absorbing particles; Guangzhou;

Nitrogen inputs and isotopes in precipitation in the North China Plain by Y. Zhang; X.J. Liu; A. Fangmeier; K.T.W. Goulding; F.S. Zhang (1436-1448).
Nitrogen (N) deposition in the North China Plain (NCP), an intensive agricultural region undergoing rapid economic development in China, has not been well documented until now. In a 4-year study, using a deposition network (11 sites), we analyzed bulk and wet-only deposition, and the isotopic composition (δ 15N) of ammonium and nitrate in precipitation in the NCP. Annual bulk deposition of inorganic N averaged 27 kg N ha−1 (ranging from 15 to 50 kg N ha−1) across sites and years, but with very large variation in both space and time. Bulk and wet deposition of inorganic N were significantly higher at sites in the Beijing area compared with that at rural sites in the NCP, implying more air N pollution around Beijing. Although there was a wide seasonal variation of δ 15N for NH4-N (−12.7‰ to +12.9‰) and NO3-N (−10.0‰ to +20.7‰) in precipitation across the sites in the NCP, a significant difference in the mean isotopic composition of NH4-N and NO3-N was measured in precipitation samples from two suburban sites (Dongbeiwang, DBW; Campus experimental farm, CEF) in Beijing (+0.45±4.39‰ for NH4-N and +4.23±4.34‰ for NO3-N on average) compared to two rural sites (Quzhou, QZ; Wuqiao, WQ) in Hebei (−2.8±4.06‰ for NH4-N and −1.19±3.74‰ for NO3-N on average). Both deposition flux and isotopic composition of inorganic N in precipitation suggest that N deposition is most probably influenced by multiple pollution sources in the urban area around Beijing area, while it is mainly derived from local agricultural sources of reactive N species at rural areas of the NCP.
Keywords: Nitrogen deposition; Precipitation; Ammonium; Nitrate; Stable isotopes; Fractionation;

Partitioning of phthalates among the gas phase, airborne particles and settled dust in indoor environments by Charles J. Weschler; Tunga Salthammer; Hermann Fromme (1449-1460).
A critical evaluation of human exposure to phthalate esters in indoor environments requires the determination of their distribution among the gas phase, airborne particles and settled dust. If sorption from the gas phase is the dominant mechanism whereby a given phthalate is associated with both airborne particles and settled dust, there should be a predictable relationship between its particle and dust concentrations. The present paper tests this for six phthalate esters (DMP, DEP, DnBP, DiBP, BBzP and DEHP) that have been measured in both the air and the settled dust of 30 Berlin apartments. The particle concentration, C Particle, of a given phthalate was calculated from its total airborne concentration and the concentration of airborne particles (PM4). This required knowledge of the particle–gas partition coefficient, K p, which was estimated from either the saturation vapor pressure (p s) or the octanol/air partition coefficient (K OA). For each phthalate in each apartment, the ratio of its particle concentration to its dust concentration (C Particle/C Dust) was calculated. The median values of this ratio were within an order of magnitude of one another for five of the phthalate esters despite the fact that their vapor pressures span four orders of magnitude. This indicates that measurements of phthalate ester concentrations in settled dust can provide an estimate of their concentration in airborne particles. When the latter information is coupled with measurements of airborne particle concentrations, the gas-phase concentrations of phthalates can also be estimated and, subsequently, the contribution of each of these compartments to indoor phthalate exposures.
Keywords: Phthalates; Gas–particle partitioning; Settled dust; Vapor pressure; Octanol/air partition coefficient;

Impact of transport of sulfur dioxide from the Asian continent on the air quality over Korea during May 2005 by Chulkyu Lee; Andreas Richter; Hanlim Lee; Young J. Kim; John P. Burrows; Young G. Lee; Byeong C. Choi (1461-1475).
The East Asian countries have been affected by atmospheric gaseous pollutants (in particular SO2) transported from the Asian continent as well as Asian dust storms. For investigation of the impact of these anthropogenic trace gases on local air quality in Korea, ground-based measurements using a Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) system and in situ gas analyzers as well as synoptic meteorological data and scattered sunlight spectra obtained by the satellite-borne instrument, Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) launched on board of Environmental Satellite (ENVISAT) in March 2002, were utilized to retrieve SO2 and trace its transport from the Asian continent to Korea in May 2005. The ground-based measurements were carried out in the region of interest, at Korea Global Watch Observatory (KGAWO) in Korea. Plumes of high SO2 over Chinese industrial areas and their transport to the Korean peninsula were observed in SCIAMACHY data in the period of 21–26 May 2005. Highly increased SO2 was measured by the MAX-DOAS system and in situ gas analyzer in the period of 27–29 May 2005 at KGAWO. These observations are supported by the meteorological results that the air-masses picking up these high SO2 plumes while passing over the Chinese industrial and metropolitan areas were transported to the Korean peninsula. The tropospheric SO2 VCDs over these Chinese industrial and metropolitan areas ranged up to 1.4×1017  mol cm−2 in SCIAMACHY data. These SO2 plumes resulted in increased SO2 surface levels of up to 7.8 ppbv (measured by an in situ gas analyzer) at KGAWO.
Keywords: Anthropogenic SO2; Air pollutant transport; UV spectroscopy; DOAS;

Secondary organic aerosol (SOA) is a substantial component of total atmospheric organic particulate matter, but little is known about the composition of SOA formed through cloud processing. We conducted aqueous phase photo-oxidation experiments of methylglyoxal and hydroxyl radical to simulate cloud processing. In addition to predicted organic acid monomers, oligomer formation from methylglyoxal–hydroxyl radical reactions was detected by electrospray ionization mass spectrometry (ESI-MS). The chemical composition of the oligomers and the mechanism of their formation were investigated by ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and LCQ DUO ion trap mass spectrometry (ESI-MS-MS). Reaction products included 415 compounds detected in the mass range 245–800 Da and the elemental composition of all 415 compounds were determined by ultra-high resolution FT-ICR MS. The ratio of total organic molecular weight per organic carbon weight (OM:OC) of the oligomers (1.0–2.5) was lower than the OM:OC of the organic acid monomers (2.3–3.8) formed, suggesting that the oligomers are less hygroscopic than the organic acid monomers formed from methylglyoxal–hydroxyl radical reaction. The OM:OC of the oligomers (average=2.0) is consistent with that of aged atmospheric aerosols and atmospheric humic-like substances (HULIS). A mechanism is proposed in which the organic acid monomers formed through hydroxyl radical reactions oligomerize through esterification. The mechanism is supported by the existence of series of oligomers identified by elemental composition from FT-ICR MS and ion fragmentation patterns from ESI-MS-MS. Each oligomer series starts with an organic acid monomer formed from hydroxyl radical oxidation, and increases in molecular weight and total oxygen content through esterification with a hydroxy acid (C3H6O3) resulting in multiple additions of 72.02113 Da (C3H4O2) to the parent organic acid monomer. Methylglyoxal is a water-soluble product of both gas phase biogenic (i.e., isoprene) and anthropogenic (i.e., aromatics, alkenes) hydrocarbon oxidation. The varied and multiple sources of methylglyoxal increase the potential for these low volatility cloud processing products (e.g., oxalic acid and oligomers) to significantly contribute to SOA. Aqueous phase oligomer formation investigated here and aerosol phase oligomer formation appear to be more similar than previously realized, which may simplify the incorporation of oligomers into atmospheric SOA models.
Keywords: Methylglyoxal; Oligomers; Cloud processing; FT-ICR MS; SOA; Isoprene;

Spatial accuracy of a simplified disaggregation method for traffic emissions applied in seven mid-sized Chilean cities by Margarita Ossés de Eicker; Rainer Zah; Rubén Triviño; Hans Hurni (1491-1502).
The spatial accuracy of top-down traffic emission inventory maps obtained with a simplified disaggregation method based on street density was assessed in seven mid-sized Chilean cities. Each top-down emission inventory map was compared against a reference, namely a more accurate bottom-up emission inventory map from the same study area. The comparison was carried out using a combination of numerical indicators and visual interpretation. Statistically significant differences were found between the seven cities with regard to the spatial accuracy of their top-down emission inventory maps. In compact cities with a simple street network and a single center, a good accuracy of the spatial distribution of emissions was achieved with correlation values>0.8 with respect to the bottom-up emission inventory of reference. In contrast, the simplified disaggregation method is not suitable for complex cities consisting of interconnected nuclei, resulting in correlation values<0.5. Although top-down disaggregation of traffic emissions generally exhibits low accuracy, the accuracy is significantly higher in compact cities and might be further improved by applying a correction factor for the city center. Therefore, the method can be used by local environmental authorities in cities with limited resources and with little knowledge on the pollution situation to get an overview on the spatial distribution of the emissions generated by traffic activities.
Keywords: Emission inventory map; Traffic; Spatial accuracy; Top-down emission inventory; Latin America;

Seasonality of major aerosol species and their transformations in Cairo megacity by Olivier Favez; Hélène Cachier; Jean Sciare; Stéphane C. Alfaro; Tarek M. El-Araby; Maha A. Harhash; Magdy M. Abdelwahab (1503-1516).
Bulk aerosols sampled on a weekly basis at two Cairo (Egypt) urban sites from January 2003 to May 2006 were analysed for their chemical composition of major aerosol species (elemental carbon, water soluble/insoluble organic carbon, nitrate, sulphate, ammonium, chloride, sodium and calcium). Data subsequently obtained constitute one of the longest and more detailed dataset related to Cairo aerosols, and offer the opportunity to investigate seasonal trends. Dust aerosols (derived from calcium measurements) displayed maximum concentrations in spring and winter, due to frequent dust storms, but also high background concentration levels (∼50 μg m−3) all year long. Within these particles, about 40% on average of Ca2+ was found to be associated with SO4 2−, NO3 and/or Cl, pointing out “dust anthropization” processes and their subsequent climatic impact on a regional scale. Seasonal variations of non-dust aerosols, equally distributed between carbonaceous aerosols and ions, were also observed, with concentrations of the order of 100 μg m−3 in autumn and winter, and of 60 μg m−3 in spring and summer. High concentration levels of non-sea-salt chloride (up to 15 μg m−3 on a monthly basis), likely of industrial origin, were observed in autumn and winter. During the autumn “Black Cloud” event, biomass burning aerosols originating from rice straw burning in the Nile Delta have shown to account for 12%, 35% and 50% of Cairo EC, WIOC and WSOC mass concentrations, respectively. Finally, relatively low WSOC/OC ratios (∼1/3) were obtained all the year long, calling for more investigation on the water-solubility of organic aerosols originating from the burning of agricultural waste, and on that of secondary organic aerosols formed in dry urban atmospheres.
Keywords: Aerosol chemical composition; Dust material; Biomass burning; Water soluble organic carbon; Greater Cairo;

Aerosol deposition and origin in French mountains estimated with soil inventories of 210Pb and artificial radionuclides by Gaël Le Roux; Laurent Pourcelot; Olivier Masson; Céline Duffa; Françoise Vray; Philippe Renaud (1517-1524).
Radionuclide inventories were measured in soils from different French mountainous areas: Chaîne des Puys (Massif Central), Eastern Corsica, Jura, Montagne Noire, Savoie, Vosges and Rhine Valley. 210Pb soil inventories were used to estimate long-term (>75 yr) deposition of submicron aerosols. Whereas 210Pb total deposition is explained partly by wet deposition, as demonstrated by increase of 210Pb inventory with annual rainfall; a part of 210Pb in the soils of higher altitude is caused by orographic depositions. Using measurements of radionuclides coming from nuclear aerial weapon tests (137Cs and Pu isotopes), we were able to estimate the origin of aerosols deposited in high-altitude sites and to confirm the importance of occult deposition and feeder–seeder mechanism. Using a simple mass balance model, we estimate that occult deposition and feeder–seeder mechanisms account to more than 50% of total deposition of 210Pb and associated submicron aerosols in French altitude sites.
Keywords: Atmospheric deposition; 210Pb; 137Cs; Pu isotopes; Mountain environment; Orographic deposition;

Influences of relative humidity and particle chemical composition on aerosol scattering properties during the 2006 PRD campaign by Xingang Liu; Yafang Cheng; Yuanhang Zhang; Jinsang Jung; Nobuo Sugimoto; Shih-Yu Chang; Young J. Kim; Shaojia Fan; Limin Zeng (1525-1536).
In situ measurements of the physical, chemical, and optical properties of aerosols were carried out in Guangzhou city, China, from 1 to 31 July 2006 during the Pearl River Delta (PRD) Campaign. The light extinction coefficient of the ambient atmosphere, the aerosol scattering coefficient under dry conditions, the aerosol absorption coefficient under ambient conditions, NO2 concentration, and relative humidity (RH) were measured by transmissionmeter, an integrating nephelometer, a multi-angle absorption photometer (MAAP), a NO X analyzer, and an automatic meteorological station, respectively. Meanwhile, the molecular scattering coefficient was calculated by the Rayleigh scattering function using the US Standard Atmosphere. A method to calculate the aerosol hygroscopic growth factor f(RH), defined as the ratio of the aerosol scattering coefficient under a wet condition to that under a dry condition (40% RH), is proposed based on these optical parameters. The mean and standard deviation aerosol hygroscopic growth factors at 80% RH (f(RH)=80%) in Ganzhou were 2.04±0.28, 2.29±0.28, and 2.68±0.59 for urban aerosols, mixed aerosols, and marine aerosols, respectively, with the air mass classification being based on the air mass source region. The relationship between f(RH) and RH is fitted by empirical equations and the fitting parameters are calculated. The relationships between f(RH)=80% and total carbon mass fraction (TCF) in PM2.5, the water-soluble mass fraction (WSF) in PM10, and the sea-salt aerosol mass fraction (SSF) in PM10 reveal that the hygroscopic properties of the observed aerosol have a good positive correlation with the WSF and SSF, but have a negative correlation with the TCF.
Keywords: Hygroscopic growth factor; Carbonaceous aerosols; Sea salt; PRD campaign;

The present study attempts to provide an insight into the chaotic nature of air pollutants by applying the recent developments in the field of nonlinear dynamics. The Volterra–Wiener–Korenberg (VWK) series approach by Barahona and Poon [1996. Detection of nonlinear dynamics in short, noisy time series. Nature 381, 215–217] has been used to investigate the nonlinearity of O3, NO, NO2 and CO time series at two urban stations, namely—Hohenpeissenberg and Jungfraujoch. Nonlinearity has been detected in NO2 and CO time series at both the stations. The numerical titration technique [Poon, C., Barahona, M., 2001. Titration of chaos with added noise. Proceedings of the National Academy of Sciences 98, 7107–7112] reveals that the dynamics of NO2 and CO are indeed governed by deterministic chaos. Cao's method [Cao, L., 1997. Practical method for determining the minimum embedding dimension of a scalar time series. Physica D 110, 43–50] to determine the minimum embedding dimension further reveals that probably the dynamics of both NO2 and CO time series are manifestations of high-dimensional chaos. It is interesting to note that similar chaotic characteristic of NO2 and CO time series have been observed at both the sites indicating a possible universality in their chaotic nature in the ambient urban environment.
Keywords: Nonlinearity; Chaos; Numerical titration; Minimum embedding dimension;

Characterising exposure to PM aerosols for an epidemiological study by M. Viana; X. Querol; A. Alastuey; F. Ballester; S. Llop; A. Esplugues; R. Fernández-Patier; S. García dos Santos; M.D. Herce (1552-1568).
Recent health studies evidence that epidemiological studies must be combined with accurate analyses of the physico-chemical properties of the particles, and vice versa, in order to determine the effects of atmospheric PM on human health. The present study focuses on the chemical characterisation of PM10 and PM2.5 aerosols, with the aim to characterise the exposure to this pollutant of the pregnant women in a cohort study in Valencia, Spain. PM sampling was carried out during five campaigns (1 month by trimester) between 2004 and 2005, when the women in the study were pregnant. Four sites were selected, representing a gradient of urban, metropolitan, suburban and rural environments. The study includes the determination of PM levels, major and trace elements, and 15 polycyclic aromatic hydrocarbons (PAHs). The results evidenced a marked gradient regarding PM levels from urban to rural sites, which was also observed for anthropogenic PM components (OM+EC, NO3 , Fe, SO4 2−, NO3 , NH4 +) but not for elements of mineral origin (Al2O3, Ca, K, Mg). PAH levels were similar or slightly higher that those reported for other Spanish sites but lower than in Europe. Findings show that the relationship between exposure to PM and adverse health effects cannot be determined only by the study of PM levels; other parameters such as chemical and physical properties of the aerosols must also be taken into account. Results also allow evaluating the adequacy of central monitor measurements as proxies for actual exposure to local emissions (e.g., vehicular emissions), which are known to vary considerably with distance to the source. The sampling strategy used in this study, devised jointly by PM monitoring and epidemiology specialists could be considered a guideline for the design of air quality monitoring studies aimed at epidemiological analysis.
Keywords: Atmospheric aerosols; Exposure; PAHs; PM10; PM2.5 speciation;

Influence of basements, garages, and common hallways on indoor residential volatile organic compound concentrations by Robin E. Dodson; Jonathan I. Levy; John D. Spengler; James P. Shine; Deborah H. Bennett (1569-1581).
Concentrations of many volatile organic compounds (VOCs) are often higher inside residences than outdoors as a result of sources or activities within the residences. These sources can be located directly in the living space of the home or in areas associated with the home such as an attached garage, basement, or common apartment hallway. To characterize the contributions from these areas to indoor residential concentrations, VOC concentrations were measured inside, outside, and, if present, in the attached garage, basement, or common hallway of an apartment of 55 residences in the Boston area, most over two seasons, as part of the Boston Exposure Assessment in Microenvironments (BEAM) Study. Of the 55 residences in the study, 11 had attached garages and basements, 24 had only basements, 10 other residences had common apartment hallways, and the remaining 10 were treated as single compartment residences. Concentrations in the garage were up to 5–10 times higher at the median than indoor concentrations for mobile source pollutants including benzene, toluene, ethylbenzene, and xylenes. Basement/indoor concentration ratios were significantly >1 for methylene chloride, ethylbenzene, m,p-xylene, and o-xylene, and summer ratios tended to be higher than winter ratios. Approximately, 20–40% of the indoor concentration for compounds associated with gasoline sources, such as methyl t-butyl ether (MTBE), benzene, toluene, ethylbenzene, and xylenes, can be attributed to an attached garage at the residence, with garages laterally attached to the first floor of the home having a larger impact. At the median, basements contributed to approximately 10–20% of the estimated indoor concentrations. For apartments, approximately 5–10% of the estimated indoor concentrations confer with air from the hallway. Contributions of these secondary zones to concentrations in the living area of a home were calculated using concentration and airflow estimates. Our findings illustrate the potential significance of these non-living spaces from an exposure perspective and suggest potentially effective mitigation measures.
Keywords: Attached garages; Basements; Apartment; Mass-balance model;

Regional precipitation mercury trends in the eastern USA, 1998–2005: Declines in the Northeast and Midwest, no trend in the Southeast by Thomas J. Butler; Mark D. Cohen; Françoise M. Vermeylen; Gene E. Likens; David Schmeltz; Richard S. Artz (1582-1592).
Mercury emissions in the USA declined between the 1990s and the beginning of this decade, largely due to the closure of municipal and medical waste incinerators. Declines in emissions have been greater in the Northeastern (NE) than the Midwestern (MW), and Southeastern (SE) regions of the eastern USA. During this time, global emissions of mercury have declined in Europe but have not declined in Asia and Africa. We have examined the patterns and trends in annual volume-weighted mean precipitation concentration for 33 Mercury Deposition Network (MDN) sites in the eastern USA, for the period 1998–2005. Individual linear regressions indicate that, 11 of 12 sites in the NE and all nine sites in the MW show declining patterns in mercury concentration, but only nine of these 21 sites show statistically significant downward trends (p<0.10). For the SE, seven of 12 sites show a decreasing pattern, but only two sites show significant downward trends (p<0.10). Random coefficient models were used to test the trends in mercury concentration for each of the three regions as a whole. These results for the NE and the MW are statistically significant (p<0.01), and show annual declines of −1.70±0.51% (S.E.) per year, and −3.52±0.74% per year for the NE and MW, respectively. The SE region as a whole shows no significant trend in mercury concentration during the same period. Different mercury transformation and deposition processes in the SE may account for these results. A comprehensive mercury emissions record was not available for the same 1998–2005 time period as the precipitation concentration analysis. Therefore, while the empirical relation between changing regional mercury emissions and changing precipitation mercury concentrations is suggestive, it cannot be confidently assessed at this time.
Keywords: Mercury wet deposition; Mercury emissions; Mercury precipitation concentration;

Evaluation of emissions and air quality in megacities by B.R. Gurjar; T.M. Butler; M.G. Lawrence; J. Lelieveld (1593-1606).
Several concepts and indicators exist to measure and rank urban areas in terms of their socio-economic, infrastructural, and environment-related parameters. The World Bank regularly publishes the World Development Indicators (WDI), and the United Nations reports the City Development Index (CDI) and also ranks megacities on the basis of their population size. Here, we evaluate and rank megacities in terms of their trace gas and particle emissions and ambient air quality. Besides ranking the megacities according to their surface area and population density, we evaluate them based on carbon monoxide (CO) emissions per capita, per year, and per unit surface area. Further, we rank the megacities according to ambient atmospheric concentrations of criteria pollutants, notably total suspended particles (TSP), sulfur dioxide (SO2), and nitrogen dioxide (NO2). We propose a multi-pollutant index (MPI) considering the combined level of the three criteria pollutants (i.e., TSP, SO2, and NO2) in view of the World Health Organization (WHO) Guidelines for Air Quality. Of 18 megacities considered here 5 classify as having “fair” air quality, and 13 as “poor”. The megacities with the highest MPI, Dhaka, Beijing, Cairo, and Karachi, most urgently need reduction of air pollution.
Keywords: Megacity; Emissions; Urban air pollution; Air quality index; Environmental Kuznets curve;

Characterization of the atmospheric electrical environment near a corona ion-emitting source by F.O. J-Fatokun; E.R. Jayaratne; L. Morawska; R. Rachman; D. Birtwhistle; K. Mengersen (1607-1616).
Presence of high concentrations of corona ions in any air environment cause changes in the earth's natural dc e-field; while their interaction with airborne aerosols produce charged particles. The charged particles and ions are dispersed by wind, and depending on the prevailing meteorology, their presence can be observed several hundreds of metres from the ion source. This paper presents a study characterizing the electrical environment of a strong substantially constant source of corona ions (a high voltage electricity substation).Results of the study showed that corona ion and particle charge concentrations as well as their associated effect on the vertical dc e-field perturbations decreased with distance from the emitting source. Mean particle charge concentration in the air environment of the ion-emitting source (−1750±745 ions cm−3) was three times higher than that of an urban outdoor air and 17 times that of a mechanically ventilated room. Statistical investigation of possible associations between parameters showed strong associations (R 2=74%, p<0.05) between particle charge and ion concentration; and 54% correlation between particle charge and magnitude of the vertical dc e-field (mean value of −285±51 V m−1). Although a source of ambient electrical charge, the electricity substation was not a significant generator of aerosol particles within the size range (0.02–1 μm) examined in this study.
Keywords: Ambient aerosol; Charged particle; Corona discharge; High voltage; Transmission substation;

Modality in ambient particle size distributions and its potential as a basis for developing air quality regulation by Lidia Morawska; Diane U. Keogh; Stephen B. Thomas; Kerrie Mengersen (1617-1628).
Current ambient air quality standards are mass-based and restricted to PM2.5 and PM10 fractions. The major contribution to both PM2.5 and PM10 fractions is from particles belonging to the coarse mode and generated by mechanical processes. These standards are thus unable to effectively control particle concentrations from combustion sources, such as motor vehicles and power plants, which tend to emit very small particles that are almost entirely respirable and in the submicron range, and dominate the nucleation and accumulation modes, which contribute much less to particle mass concentration.The aim of this work was to examine whether PM1 and PM10 would be a more effective combination of mass standards than PM2.5 (dominant in the nucleation and accumulation modes) and PM10 (dominant in the coarse mode) in controlling combustion-related ambient particles, as well as those originating from mechanical processes. First, a large body of data on particle size distributions in a range of environments in South East Queensland, Australia, was analysed, with an aim of identifying the relation between modality in the distributions and sources of particles belonging to different modes. The analyses included a matrix of the following elements: particle volume and number distributions, type of environment and locations of the modes in the range of PM1, PM2.5 and PM10 fractions. Second, with the same aim, 600 published modal location values relating to number, surface area, volume and mass size distributions for a range of environments worldwide were analysed. The analysis identified a clear and distinct separation between the location of the modes for a substantial number of environments worldwide and particle metrics, which suggests that modality in particle size distributions may be a parameter that has potential to be used in the development of PM1 air quality guidelines and standards. Based on these analyses, implications for choosing different mass standards for airborne particulate matter are discussed in the paper.
Keywords: Modality of particle distribution; Ambient aerosol; PM1; PM2.5; PM10; Air quality regulation;

Emissions of aerosol from biomass burning in northern Australia are globally significant, yet existing estimates of their magnitude are essentially unconstrained by observation. This two-part series (see Part II by Luhar et al. [2008. Biomass burning emissions over northern Australia constrained by aerosol measurements: II—Model validation, and impacts on air quality and radiative forcing. Atmospheric Environment, submitted for publication] seeks to address this by first formulating a scheme to determine the emissions from the Top End region of the Northern Territory during the 2004 burning season at a high temporal and spatial resolution (1 h, 1 km). The emissions are then validated using a meteorological and transport model called TAPM coupled with a variety of field measurements. The high resolution not only enables validation against various meteorological and aerosol data sets, but also allows prediction of local air quality events. Essential inputs to the emission calculations are satellite-based measurements of fire scars, yielding burnt areas, and hotspots, providing timing information on daily basis. It is shown that hotspots without associated fire scars must be taken into account in order to produce credible aerosol fields. Prediction of emissions at hourly time resolution is enabled by assigning a diurnal variation based on a McArthur fire danger meter. The total carbon emission for the 2004 season is computed to be 67.6 Tg, in remarkable agreement with the bulk estimate of 64.3 Tg derived for the Australian National Greenhouse Gas Inventory, and comparable to the figure of 57.0 Tg determined from the Global Fire Emissions Database (GFEDv2). The total PM2.5 (particulate matter with an aerodynamic diameter of 2.5 μm or less) emission is computed to be 0.67 Tg. The transport modelling shows that emissions leaving the study region are largely advected to the west over the Timor Sea towards the Indonesian archipelago from April to September, shifting to the south-west during October–November where they enhance the aerosol loading over Western Australia.
Keywords: Bushfire emissions; Fire scars; Hotspots; TAPM; MODIS data; Aerosol loading; Air quality in northern territory; Top End;

Biomass burning emissions over northern Australia constrained by aerosol measurements: II—Model validation, and impacts on air quality and radiative forcing by Ashok K. Luhar; Ross M. Mitchell; C.P. (Mick) Meyer; Yi Qin; Susan Campbell; John L. Gras; David Parry (1647-1664).
Keywords: Bushfire emissions; TAPM; Aerosol optical depth; MODIS data; Air quality modelling; Air quality in Northern Territory; Atmospheric radiative transfer; Radiative forcing efficiency;