Atmospheric Environment (v.42, #32)

Seasonal and spatial variations of sources of fine and quasi-ultrafine particulate matter in neighborhoods near the Los Angeles–Long Beach harbor by María Cruz Minguillón; Mohammad Arhami; James J. Schauer; Constantinos Sioutas (7317-7328).
The Los Angeles–Long Beach harbor is the busiest port in the US. Levels of particulate matter (PM) are relatively high in this area, since it is affected by multiple PM sources. A Chemical Mass Balance (CMB) model was applied to speciated chemical measurements of quasi-ultrafine and fine particulate matter from seven different sites. Winter measurements were obtained during a 7-week period between March and May 2007, and summer measurements corresponded to a 6-week period between July and September 2007. Four of the sites were located within the communities of Wilmington and Long Beach, two sites were located at a background area in the harbor of Los Angeles and Long Beach, and one more site was located further downwind, near downtown Los Angeles, representing urban downtown LA, influenced by mostly traffic sources. The samples were analyzed for organic (OC) and elemental (EC) carbon content, organic species, inorganic ions, water soluble and total elements. The sources included in the CMB model were light duty vehicles (LDV), heavy-duty vehicles (HDV), road dust (RD), biomass burning and ship emissions. The model predictions of the LDV and HDV source contributions accounted, on average, for 83% of total fine OC in winter and for 70% in summer, whereas ship emissions’ contribution was lower than 5% of total OC at all sites. In the quasi-ultrafine mode, the vehicular sources accounted for 118% in winter and 103% in summer. Spatial variation of source contributions was not very pronounced with the exception of some specific sites. In terms of total fine PM, vehicular sources together with road dust explain up to 54% of the mass, whereas ship contribution is lower than 5% of total fine PM mass. Our results clearly indicate that, although ship emissions can be significant, PM emissions in the area of the largest US harbor are dominated by vehicular sources.
Keywords: CMB; Harbor; OC; Source apportionment; Long Beach;

Spatial variation of volatile organic compounds in a “Hot Spot” for air pollution by Xianlei Zhu; Zhihua (Tina) Fan; Xiangmei Wu; Qingyu Meng; Sheng-wei Wang; Xiaogang Tang; Pamela Ohman-Strickland; Panos Georgopoulos; Junfeng Zhang; Linda Bonanno; Joann Held; Paul Lioy (7329-7338).
The spatial variations of volatile organic compounds (VOCs) were characterized in the Village of Waterfront South neighborhood (WFS), a “hot spot” for air toxics in Camden, NJ. This was accomplished by conducting “spatial saturation sampling” for 11 VOCs using 3500 OVM passive samplers at 22 sites in WFS and 16 sites in Copewood/Davis Streets (CDS) neighborhood, an urban reference area located ∼1000 m east of the WFS. Sampling durations were 24 and 48 h. For all 3 sampling campaigns (2 in summer and 1 in winter), the spatial variations and median concentrations of toluene, ethylbenzene, and xylenes (TEX) were found significantly higher (p  < 0.05) in WFS than in CDS, where the spatial distributions of these compounds were relatively uniform. The highest concentrations of methyl tert-butyl ether (MTBE) (maximum of 159 μg m−3) were always found at one site close to a car scrapping facility in WFS during each sampling campaign. The spatial variation of benzene in WFS was found to be marginally higher (p  = 0.057) than in CDS during one sampling campaign, but similar in the other two sampling periods. The results obtained from the analyses of correlation among all species and the proximity of sampling site to source indicated that local stationary sources in WFS have significant impact on MTBE and BTEX air pollution in WFS, and both mobile sources and some of the stationary sources in WFS contributed to the ambient levels of these species measured in CDS. The homogenous spatial distributions (%RSD < 24%) and low concentrations of chloroform (0.02–0.23 μg m−3) and carbon tetrachloride (0.45–0.51 μg m−3) indicated no significant local sources in the study areas. Further, results showed that the sampling at the fixed monitoring site may under- or over-estimate air pollutant levels in a “hot spot” area, suggesting that the “spatial saturation sampling” is necessary for conducting accurate assessment of air pollution and personal exposure in a community with a high density of sources.
Keywords: Spatial variation; VOCs; Hot spot; Air toxics; Proximity; Personal exposure; New Jersey;

Dry deposition of acidic air pollutants to tree leaves, determined by a modified leaf-washing technique by Mirai Watanabe; Takejiro Takamatsu; Masami K. Koshikawa; Shigeki Yamamura; Kazuyuki Inubushi (7339-7347).
Dry deposition fluxes (F L) of NO3 and SO4 2− to leaf surfaces were measured for Japanese red pine (Pinus densiflora), Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa), and Japanese white oak (Quercus myrsinaefolia), together with atmospheric concentrations (C L) of NO x (NO + NO2), T-NO3 (gaseous HNO3  + particulate NO3 ) and SO x (gaseous SO2  + particulate SO4 2−) around the leaves in a suburban area of Japan, using a modified leaf-washing technique. F L of NO3 and SO4 2− decreased as follows: pine >> cedar > cypress ≥ oak and pine >> cedar > oak ≥ cypress, respectively. F L of NO3 for all tree species fluctuated synchronously with C L of T-NO3. F L of SO4 2− fluctuated with C L of SO x , but the dominant pollutant deposited (SO2 or SO4 2−) appeared to differ for different tree species. Dry deposition conductance (K L) of T-NO3 and SO x was derived as an F L/C L ratio. Seasonal variations of K L likely reflect the gas/particle ratios of T-NO3 and SO x , which were affected by meteorological conditions such as temperature. Dry deposition velocities (V d) of T-NO3 and SO x were obtained as the mathematical product of annual mean K L and the total leaf surface areas in the forests. The comparison of V d among tree species indicated that the loads of acidic air pollutants were higher to coniferous forests than broad-leaved forest because of the higher K L and/or larger leaf surface areas.
Keywords: Acid deposition; Nitrate; Sulfate; Filter pack; Forest pollution; Nitrogen saturation;

Secondary aerosol formation from the oxidation of toluene by chlorine atoms by Xuyi Cai; Luke D. Ziemba; Robert J. Griffin (7348-7359).
Oxidation of toluene by chlorine atoms (Cl) was studied in a chamber. Secondary organic aerosol (SOA) yields ranged from 3.0 to 7.9% for aerosol concentrations up to 12.0 μg m−3. SOA yields from toluene/Cl reactions and model parameters related to aerosol growth depend on the initial ratio of molecular chlorine to toluene. Data from an Aerodyne quadrupole Aerosol Mass Spectrometer (Q-AMS) indicate that a small fraction of the generated aerosol mass is inorganic chloride (approximately 4%), that inorganic chloride aerosol growth ceases contemporaneously with that of SOA, and that particles are mixed internally. Analysis of Q-AMS spectra indicates predominance of species that traditionally are thought to be representative of SOA but with increased importance of aromatic/ring-retaining products. Mechanistic modeling of the toluene system indicates that final SOA products likely result from the oxidation of quinone type compounds derived via oxidation of the first-generation product benzaldehyde. Zero-dimensional calculations indicate Cl-initiated oxidation could be as important as hydroxyl-radical-initiated oxidation in SOA formation from toluene in early morning in certain coastal or industrialized areas.
Keywords: Chamber studies; Chlorine atom; Modeling studies; Secondary organic aerosol; Toluene;

This study reports comprehensive two-dimensional gas chromatography hyphenated to time-of-flight mass spectrometry detection (GC × GC/TOFMS) for characterisation and identification of components generated by four different types of powdered incense headspace (H/S) and incense smoke. GC × GC/TOFMS allowed simultaneous separation and identification of compounds emitted into the atmosphere as a result of combustion of incense powder. The smoke stream comprised compounds originating from the incense powder, and combustion products such as saturated and unsaturated hydrocarbons, essential oil type compounds, nitromusks, fatty acid methyl esters (FAMEs), polycyclic aromatic hydrocarbons (PAHs, which possibly include oxygenated and nitrated PAH), N-heterocyclics, pyrans and furans, which were detected and tentatively identified by GC × GC/TOFMS. GC × GC-electron capture detector/nitrogen phosphorous detector (ECD/NPD) potentially offers the prospect of providing selective chemical compositional information of incense powder and smoke, such as nitrogen-containing (N-containing) and halogenated compounds. Results of GC×GC-ECD/NPD showed that both incense powder and smoke generated emission of N-containing and halogenated compounds. A significant number of halogenated and N-containing compounds were emitted during the incomplete combustion of incense. However, one further objective of this paper is to demonstrate the capacity of comprehensive two-dimensional gas chromatography coupled to specific and/or selective detectors such as those used in this study (GC × GC-ECD/NPD) for the detection of particular classes of compounds such as N-containing and halogenated compounds at trace level concentrations in complex smoke samples.
Keywords: Incense; Smoke; Comprehensive two-dimensional gas chromatography; GC × GC/TOFMS; ECD; NPD; SPME;

Influence of source–sensor geometry on multi-source emission rate estimates by B.P. Crenna; T.K. Flesch; J.D. Wilson (7373-7383).
Multi-source emission rates inferred from measured concentrations using numerical dispersion models are often extremely sensitive to measurement and model error, rendering them unusable. This sensitivity to error is quantified by the condition number of the matrix of model-derived coefficients relating source strengths to concentrations. Using a dispersion model, we examine the dependence of this condition number on source–sensor geometry, atmospheric conditions, and the amount of concentration data included in the solution. Optimal sensor arrangements are those that measure source emissions (and background concentration, if it is unknown) as independently from each other as possible under the expected range of wind directions and atmospheric stabilities. Although including more concentration measurements can improve the emission inferences, the benefit is highly contingent upon sensor placement. A set of recommendations to minimize sensitivity to error is presented. This includes arranging sensors so that each detects emissions from as few sources as possible; keeping sensors separated, both horizontally and vertically, to benefit from asymmetries in source distribution and surface layer structure; using more measurements in a given calculation, either by adding more sensors or by incorporating data from different times; and using dispersion models to assess condition number and guide sensor placement before and during a field study.
Keywords: Dispersion modeling; Inverse dispersion; Multiple sources; Condition number; Emission rates;

Impact of regional trans-boundary ozone associated with complex terrain on urban air quality by Soon-Hwan Lee; Kyoung-Hee Sung; Hwa-Woon Lee (7384-7396).
In order to clarify the contribution of the trans-boundaries ozone produced in the vicinity of the Daegu metropolitan area in the southeastern part of the Korean Peninsula, several numerical experiments were performed. A fifth-generation Mesoscale Model (MM5) and a Model-3/Community Multiscale Air Quality (CMAQ) model were used to estimate the meteorological wind field and urban air quality, respectively.The topography around the Daegu metropolis is very complicated, with the wind originated within the metropolitan often coupled with that generated over the closely located Busan and Ulsan metropolis. Therefore, the mesoscale wind and ozone distribution patterns in Daegu metropolis are complicated.The contribution of the ozone produced over Busan to the ozone concentration in Daegu increases rapidly at 18 LST, with its maximum contribution reaching 58.1% of the maximum values of the ozone concentration over Daegu. Ozone originating from the Ulsan metropolis is also transported through the east gate of Daegu, with a contribution of 48.1% when measured at Yulha at 18 LST. The trans-boundary ozone from the outside also contributes to the ozone concentration; therefore, the exact concentration of ozone over Daegu cannot be explained from internally produced ozone only. Therefore, trans-boundaries winds and their impact on the ozone concentration should be considered and evaluated to precisely estimate the ozone concentration.
Keywords: Atmospheric modeling; Trans-boundary ozone; Urban air quality; MM5; CMAQ;

Evidence of local emission of organochlorine pesticides in the Tibetan plateau by Jun Li; Tian Lin; Shihua Qi; Gan Zhang; Xiang Liu; Kechang Li (7397-7404).
Organochlorine pesticides (OCPs) including DDTs, HCHs, chlordanes and hexachlorobenzene (HCB) in the atmosphere of Lhasa, the capital city of Tibet, China, were monitored in an attempt to assess their concentration level and potential sources. Twenty air samples collected at two sites in Lhasa between 6 and 11 August 2006 were analyzed for OCPs. The mean concentrations of α-, γ-HCHs, HCB, trans-chlordane (TC), cis-chlordane (CC), p,p′-DDE, p,p′-DDD, o,p′-DDT, and p,p′-DDT were 49, 163, 182, 204, 128, 122, 46, 206, and 114 pg/m3, respectively. The relatively low α-HCH/γ-HCH ratios indicated that lindane is the current source of HCHs in Lhasa. A TC/CC ratio of ≈1.2 was observed for samples with relatively high chlordane concentrations, suggesting a current local use of technical chlordane. The isomer ratios of DDTs also implied present usages of DDT-containing dicofol and technical DDT in the city. Contrary to other OCPs, HCB displayed higher concentrations during nighttime than daytime, indicative of a dominant contribution from local combustion. We conclude that current use and local emissions may be important sources for OCPs in Lhasa and may contribute to OCP contamination in the environment of the populated agricultural Lahsa River basin.
Keywords: Organochlorine pesticides; Atmosphere; Lhasa city; Tibetan plateau;

Growth of nucleation mode particles: Source rates of condensable vapour in a smog chamber by Ari P. Leskinen; Markku Kulmala; Kari E.J. Lehtinen (7405-7411).
We investigated the formation and subsequent growth of organic aerosol particles in laboratory conditions by irradiating a mixture of xylene and nitrogen oxides (NO x ) with UV light in a 6 m3 Teflon chamber. We used different initial hydrocarbon (HC) and NO x concentrations, with mixing ratios of 3.5–30 (28–240 ppmC/ppm), and monitored the changes in particle size distribution in the range of 7–330 nm. We applied the concept of condensation sink to the measured size distribution data in order to estimate the concentration and source rate of condensable vapours in the chamber. We observed the nucleation and Aitken mode growth rate to be 10.6–18.6 nm h−1, which corresponds to a vapour concentration of 1.5–2.4×108  cm−3, from which our deduced estimation for the source rate was 0.2–2.5×107  cm−3 s−1. These vapour source rates are up to four orders of magnitude higher than the atmospheric values observed in Antarctica and other background stations, up to two orders of magnitude higher than at urban areas of Athens and Marseille, up to 13 times higher than at a coastal site and of the same magnitude, within a factor of five, as in New Delhi, a heavily polluted urban area. In the chamber experiments we observed a strong dependence of the source rate of condensable vapours on the initial NO x concentration. This indicates that oxidation processes play an important role in particle formation and subsequent growth.
Keywords: Aerosol formation; Condensation sink; Photooxidation; Smog chamber; Xylene;

How is surface ozone in Europe linked to Asian and North American NO x emissions? by R.G. Derwent; D.S. Stevenson; R.M. Doherty; W.J. Collins; M.G. Sanderson (7412-7422).
Source–receptor relationships linking North American and Asia NO x emissions with surface ozone in Europe have been explored using a global Lagrangian chemistry-transport model. We used the model to perform a set of simulations, each 21 months in duration, which were comprised of a base case and a series of emission perturbation experiments. In each of the perturbation runs, an additional month-long NO x emission pulse from a particular 10° × 10° region was included. Overall, results from 42 different emission regions in both boreal summer and winter were analysed. Shortly after the start of each NO x emission pulse, increased ozone mixing ratios were detected at surface sites across Europe. The extra ozone peaked and then decayed away to leave a small but persistent ozone deficit that persisted throughout the year-long model experiments. The ozone responses varied spatially by over three orders of magnitude, depending on the location of the NO x emission pulses in each continent and on the receptor location within Europe. Source–receptor relationships also varied markedly with season. NO x emissions from lower latitudes, especially in the boreal summer, were found to decrease European ozone, when both the short- and long-term responses were considered. In this study, it has been possible to begin the process of examining the likely influences on ozone levels across Europe resulting from precursor emission controls in North America and Asia and, in turn, their possible impacts on meeting ozone air quality targets over Europe.
Keywords: Source–receptor relationships; Intercontinental transport; Tropospheric ozone; NO x emissions;

Contribution of nitrated polycyclic aromatic hydrocarbons to the mutagenicity of ultrafine particles in the roadside atmosphere by Youhei Kawanaka; Emiko Matsumoto; Ning Wang; Sun-Ja Yun; Kazuhiko Sakamoto (7423-7428).
This is the first report of the quantification of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in ultrafine particles in the roadside atmosphere and their contribution to the direct-acting mutagenicity of ultrafine particles. The detailed size distributions of six nitro-PAHs (2-nitrofluoranthene, 1-nitropyrene, 6-nitrobenzo[a]pyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, and 1,8-dinitropyrene) were measured by highly sensitive gas chromatography–negative ion chemical ionization tandem mass spectrometry. Direct-acting mutagenicity of size-fractionated particulate matter (PM) was determined by the Ames test using Salmonella typhimurium strains TA98 and YG1024. The amounts of nitro-PAHs per unit mass of ultrafine particles (<0.12 μm) were significantly higher than those of accumulation mode particles (0.12–2.1 μm) and of coarse particles (>2.1 μm). Therefore, more than 20% of each nitro-PAH, with the exception of 2-nitrofluoranthene, was observed in the ultrafine particle fraction, although the contribution of ultrafine particles to the total PM mass in the roadside atmosphere was only 2.3%. Also, in both tester strains TA98 and YG1024, the mutagenicity per unit mass of ultrafine particles was significantly higher than those of accumulation mode particles or coarse particles. The contributions of 2-nitrofluoranthene, 1-nitropyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, and 1,8-dinitropyrene to the direct-acting mutagenicity of ultrafine particles were 0.56, 1.5, 0.57, 2.2, and 9.2%, respectively, in the TA98 strain, and 0.54, 1.1, 0.71, 5.0, and 17%, respectively, in the YG1024 strain, while the contribution of 6-nitrobenzo[a]pyrene was less than 0.01% in both strains. 1,8-Dinitropyrene was the largest contributor to the mutagenicity not only of ultrafine particles but also of accumulation mode particles in both strains. Only five nitro-PAHs accounted for as much as 14 and 24% of the direct-acting mutagenicity of ultrafine particles in the roadside atmosphere in the TA98 strain and the YG1024 strain, respectively. This result indicated that nitro-PAHs, especially 1,8-dinitropyrene, were important contributors to the high direct-acting mutagenicity of ultrafine particles in the roadside atmosphere.
Keywords: Nitrated polycyclic aromatic hydrocarbons; Size distribution; Ultrafine particle; Mutagenicity; Roadside atmosphere;

Atmospheric mercury accumulation and washoff processes on impervious urban surfaces by Chris S. Eckley; Brian Branfireun; Miriam Diamond; Peter C. Van Metre; Frank Heitmuller (7429-7438).
The deposition and transport of mercury (Hg) has been studied extensively in rural environments but is less understood in urbanized catchments, where elevated atmospheric Hg concentrations and impervious surfaces may efficiently deliver Hg to waterways in stormwater runoff. We determined the rate at which atmospheric Hg accumulates on windows, identified the importance of washoff in removing accumulated Hg, and measured atmospheric Hg concentrations to help understand the relationship between deposition and surface accumulation. The main study location was Toronto, Ontario. Similar samples were also collected from Austin, Texas for comparison of Hg accumulation between cities. Windows provided a good sampling surface because they are ubiquitous in urban environments and are easy to clean/blank allowing the assessment of contemporary Hg accumulation. Hg Accumulation rates were spatially variable ranging from 0.82 to 2.7 ng m−2  d−1 in Toronto and showed similar variability in Austin. The highest accumulation rate in Toronto was at the city center and was 5× higher than the rural comparison site (0.58 ng m−2  d−1). The atmospheric total gaseous mercury (TGM) concentrations were less than 2× higher between the rural and urban locations (1.7 ± 0.3 and 2.7 ± 1.1 ng m−3, respectively). The atmospheric particulate bound fraction (HgP), however, was more than 3× higher between the rural and urban sites, which may have contributed to the higher urban Hg accumulation rates. Windows exposed to precipitation had 73 ± 9% lower accumulation rates than windows sheltered from precipitation. Runoff collected from simulated rain events confirmed that most Hg accumulated on windows was easily removed and that most of the Hg in washoff was HgP. Our results indicate that the Hg flux from urban catchments will respond rapidly to changes in atmospheric concentrations due to the mobilization of the majority of the surface accumulated Hg during precipitation events.
Keywords: Mercury; Urban; Deposition; Washoff;

The secondary organic aerosol (SOA) module in PMCAMx, a three-dimensional chemical transport model, has been updated based on laboratory results from recent smog chamber experiments. A new modeling framework is used based on the SOA volatility basis-set approach instead of the two-product approach used in existing models. The different scenarios are simulated for July 2001, and the predicted organic aerosol (OA) concentrations are compared to the available ambient measurements from the EPA Speciation Trends Network (STN) and the Interagency Monitoring of Protected Visual Environments (IMPROVE). The base-case OA simulation slightly overpredicts the ambient measured OA concentrations at the rural IMPROVE monitoring sites with a bias of 0.33 μg m−3. Compared to the urban STN sites, the base-case scenario still underpredicts the observed OA concentrations but is performing significantly better than the two-product module in PMCAMx compared to observations. The contribution of biogenic and anthropogenic SOA to the predicted organic aerosol concentrations and the potential role of chemical aging are investigated. The higher yields of SOA from anthropogenic precursors reported in the most recent studies improve the model performance in urban areas.
Keywords: SOA; VOC; Volatility basis set; PMCAMx; Air quality;

Influence of atmospheric ozone, PM10 and meteorological factors on the concentration of airborne pollen and fungal spores by S.I.V. Sousa; F.G. Martins; M.C. Pereira; M.C.M. Alvim-Ferraz; H. Ribeiro; M. Oliveira; I. Abreu (7452-7464).
The increase of allergenic symptoms has been associated with air contaminants such as ozone, particulate matter, pollen and fungal spores. Considering the potential relevance of crossed effects of non-biological pollutants and airborne pollens and fungal spores on allergy worsening, the aim of this work was to evaluate the influence of non-biological pollutants and meteorological parameters on the concentrations of pollen and fungal spores using linear correlations and multiple linear regressions. For that, the seasonal variation of ozone, particulate matter with an equivalent aerodynamic diameter smaller than 10 μm, pollen and fungal spores were assessed and statistical correlations were analysed between those parameters. The data were collected through 2003–2005 in Porto, Portugal. The linear correlations showed that ozone and particulate matter had no significant influence on the concentration of pollen and fungal spores. On the contrary, when using multiple linear regressions those parameters showed to have some influence on the biological pollutants, although results were different depending on the year analysed. Among the meteorological parameters analysed, temperature was the one that most influenced the pollen and fungal spores airborne concentrations, both when using linear and multiple linear correlations. Relative humidity also showed to have some influence on the fungal spore dispersion when multiple linear regressions were used. Nevertheless, the conclusions for each pollen and fungal spore were different depending on the analysed period, which means that the correlations identified as statistically significant may not be, even so, consistent enough. Furthermore, the comparison of the results here presented with those obtained by other authors for only one period should be made carefully.
Keywords: Air pollutants; Meteorological parameters; Biological pollutants; Linear correlation; Multiple linear correlations;

Road-transport emission projections to 2020 in European urban environments by Marina Kousoulidou; Leonidas Ntziachristos; Giorgos Mellios; Zissis Samaras (7465-7475).
Road-transport emissions were projected to 2020 using the TREMOVE model to estimate the vehicle stock mix over EU15 and three new European member states (Czech Republic, Hungary, and Poland). The COPERT model was used to estimate the exhaust emissions of NO x , NO2 and PM2.5. Non-exhaust (tyre and break wear) PM2.5 and PM10 were also calculated. Emissions were projected following current legislation (CLE) measures and a scenario representing maximum feasible technical reductions (MFR). Projections to 2020 showed that CLE will bring 89, 25 and 50% reductions in NO x from gasoline passenger cars (GPCs), diesel passenger cars (DPCs) and heavy duty vehicles (HDVs), respectively, over 2000 levels, when comparing average emissions on a per vehicle-km basis. The corresponding reductions in the MFR scenario were 91, 53 and 67%, respectively. Despite these significant reductions, NO2 emissions do not seem to be effectively controlled for DPCs due to the increased NO2/NO x ratio of new and expected aftertreatment systems. Moreover, there is an almost 9-fold increase of NO2 emissions from mopeds, as they gradually shift to stoichiometric mixtures, four-stroke combustion and use of catalysts in the exhaust. Following CLE, PM exhaust and non-exhaust emissions will decrease on a per vehicle-km basis by 61% for DPCs and 63% for HDVs. Reductions by MFR over the reference year are estimated in the order of 77% and 65% for DPCs and HDVs, respectively. However, the increasing share of non-exhaust sources to the total PM emissions may hamper the effectiveness of exhaust control measures in meeting future urban air-quality standards.
Keywords: Exhaust emissions; Emission projection; NO x ; NO2; PM;

Hydrogen sulfide (H2S) in urban ambient air by K. Kourtidis; A. Kelesis; M. Petrakakis (7476-7482).
Despite indications of high hydrogen sulfide levels in some urban environments, only sparse measurements have been reported in the literature. Here we present one full year of hydrogen sulfide measurements in an urban traffic site in the city of Thessaloniki, Greece. In this 1-million-population city the H2S concentrations were surprisingly high, with a mean annual concentration of 8 μg m−3 and wintertime mean monthly concentrations up to 20 μg m−3 (12.9 ppb). Daily mean concentrations in the winter were up to 30 μg m−3 (19.3 ppb), while hourly concentrations were up to 54 μg m−3 (34.8 ppb). During calm (wind velocity < 0.5 m s−1) conditions, mainly encountered during night-time hours, hourly values of H2S were highly correlated with those of CO (r 2  = 0.75) and SO2 (r 2  = 0.70), pointing to a common traffic source from catalytic converters. Annual mean concentrations are above the WHO recommendation for odor annoyance; hence, H2S might play a role to the malodorous episodes that the city occasionally experiences. The high ambient H2S levels might also be relevant to the implementation of preservation efforts for outdoor marble and limestone historical monuments that have been targeting SO2 emissions as an atmospheric acidity source, since the measurements presented here suggest that about 19% of the annual sulfur (SO2  + H2S) emissions in Thessaloniki are in the form of H2S.
Keywords: Air pollution; Sulfur; Odor;

Weekday and weekend ambient aerosol samples were collected from the city centre of Cairo, namely “Ramsis” during the summer season of the year 2006, and have been analyzed for water-soluble ionic species. The average concentrations of the total suspended particulate matter (TSP) and their water-soluble components were higher during weekdays than on weekends, indicating that the decreased traffic density on weekends leads to a decrease in the levels of the TSP and their water-soluble ionic species. The average concentrations of the TSP were 454 μg m−3 on weekdays and 298 μg m−3 on weekends. The weekday/weekend concentration ratios were 1.52 for TSP, 1.27 for SO4 2−, 1.64 for Cl, 1.54 for NO3 , 1.17 for NH4 +, 1.67 for Ca2+, 1.83 for Na+, 1.75 for K+ and 1.73 for Mg2+. City centre of Cairo has high levels of the TSP and their water-soluble ionic species compared with many polluted cities in the world. Among all of the measured water-soluble components, SO4 2− was the most abundant species followed by Ca2+ on weekdays and weekends. The average mass ratios of NO3 /SO4 2− in the TSP were 0.41 on weekdays and 0.34 on weekends, suggesting that the stationary source emissions were more predominant. The NH4 +/SO4 2− molar ratios and its relation with the concentrations of TSP and Ca2+ during the weekdays and weekends indicate that the chemical form of sulfate and ammonium in aerosol particles varies with TSP and Ca2+ levels. At high TSP and Ca2+ levels, and NH4 +/SO4 2− molar ratios less than one, SO4 2− in aerosol particles may be present as CaSO4 and (NH4)2SO4·CaSO4·2H2O, whereas it is expected to be present as (NH4)2SO4, (NH4)2SO4·CaSO4·2H2O and CaSO4 at low levels of TSP and Ca2+, and NH4 +/SO4 2− molar ratios between 1 and 2. The mean pH values of the TSP were 7.65 on weekdays and 6.97 on weekends, indicating that aerosol particles brought a large amount of crustal species, and might alleviate the tendency of acidification. The relationships between the concentrations of acidic components (NO3 and SO4 2−) and basic components (NH4 +, Ca2+ and Mg2+) on weekdays and weekends indicate that the acidity of aerosol particles is neutralized. Ca2+ and NH4 + are the most dominant neutralization substances in Cairo atmosphere.
Keywords: Aerosol; Water-soluble ions; Chemical characteristics; Weekend effect; Sources; Cairo;

Atmospheric trace metal concentrations at Norwegian background sites during 25 years and its relation to European emissions by Torunn Berg; Wenche Aas; Jozef Pacyna; Hilde T. Uggerud; Marit Vadset (7494-7501).
A comprehensive time trend analysis for a 25-years data set on trace metal concentrations from Norwegian monitoring stations have been carried out. At the Birkenes station, one of the stations with longest data record and located at a region in Southern Norway which is mostly affected by atmospheric long-range transport, the reductions have been 97%, 95% and 70% for, respectively, Pb, Cd and Zn in precipitation in the period 1980–2005. Changes in pollution levels are mainly due to changes in emission data and transboundary pollution. A comparison of the changes in monitoring data with changes in the anthropogenic emissions for Europe and Norway have therefore been carried out especially for Pb and Cd.
Keywords: Trace metal; Precipitation; Air; Emission; Trend; Norway; Europe;

Impacts of noise barriers on near-road air quality by R. Baldauf; E. Thoma; A. Khlystov; V. Isakov; G. Bowker; T. Long; R. Snow (7502-7507).
Numerous health studies conducted worldwide suggest an increase in the occurrence of adverse health effects for populations living, working, or going to school near large roadways. A study was designed to assess traffic emission impacts on air quality near a heavily traveled highway. The portion of highway studied included a section of open field and a section with a noise barrier adjacent to the road. In addition, the section containing the noise barrier included a portion with vegetation in the vicinity of the barrier. Thus, this field study provided an opportunity to evaluate near-road air quality with no barriers, with a noise barrier only, and with a noise barrier and vegetation adjacent to the road. Pollutants measured under these scenarios included carbon monoxide (CO) and particulate matter (PM).Measurements showed the effects of a noise barrier on near-road air quality. The presence of this structure often led to pollutant concentration reductions behind the barrier during meteorological conditions with winds directionally from the road. CO and PM number concentrations generally decreased between 15 and 50% behind the barrier. However, conditions occurred when pollutant concentrations were greater behind the barrier than when no barrier was present. These results imply that the presence of a noise barrier can lead to higher pollutant concentrations on the road during certain wind conditions. In addition, the study results suggested that the presence of mature trees in addition to the barrier further lowered PM number concentrations.
Keywords: Motor vehicle emissions; Noise barriers; Near-road; Particulate matter; Carbon monoxide;

Implications of the chemical transformation of Asian outflow aerosols for the long-range transport of inorganic nitrogen species by Charles C.-K. Chou; C.T. Lee; C.S. Yuan; W.C. Hsu; C.-Y. Lin; S.-C. Hsu; S.C. Liu (7508-7519).
To improve our understanding of the chemical characteristics of aerosols transported from the Asian continent to the western North Pacific, an aerosol observation network has been established in Taiwan. From the measurements made during 2003–2005, it was found that the aerosol concentrations in the continental outflows were much higher than those of remote areas, evidently due to the long-range transport of air pollutants and dust from the Asian continent. Analysis on the chemical compositions of aerosols revealed that the Asian outflow aerosols underwent chemical transformation and, consequently, became more abundant in ammonium and nitrate when they mixed with air pollutants originating from Taiwan. The NH4 +/SO4 2− ratio in fine aerosols (PM2.5) increased from 1.55 at the Cape Fuguei, the northern tip of Taiwan, to 2.30 at Penghu, in the middle of the Taiwan Strait. The increased NH4 +/SO4 2− ratio implied that the acidity of the sulfate aerosols in Asian outflows was totally neutralized by ammonia as the aerosols traveled through the North Taiwan and its vicinity. In addition, the analysis indicated that the chlorine deficiency of sea salt aerosols was higher at the southern stations than at the Cape Fuguei. The chlorine deficiency was attributed to the heterogeneous reaction of NaCl and HNO3(g), which means that the oxidation of SO2 in sea spray droplets was inhibited. Moreover, uptake of secondary acids by the dust particles was observed. The results of this study suggested that the Asian outflow aerosols are important carriers of gaseous inorganic nitrogen species, particularly nitric acid and ammonia, in this region. Hence the atmospheric deposition of soluble inorganic nitrogen could become enhanced in the northern South China Sea, which is downwind of Taiwan during the periods of Asian winter monsoons.
Keywords: Asian outflows; Composition of aerosols; Chlorine deficiency; Inorganic nitrogen transport;

Opposing behaviour of organic compounds at interfaces by Galal Elmanfe; Abdelhaq Acharid; Mireille Privat (7520-7529).
Despite its extremely weak adsorption at the water/silica interface, carbofuran can, however, induce the coadsorption of metallic salts like lead nitrate, for example; by way of consequence its adsorption is enhanced. At the water/atmosphere interface, carbofuran adsorption is far more important than at the water–silica interface, whereas ionic adsorption remains smaller despite its enhancement by coadsorption. After comparison of the data obtained by a depletion method in the case of the solid/liquid interface and by tensiometry for the atmosphere/liquid interface, we tried to find a relationship between both from kinetic measurements of adsorbent desorption from a silica surface. Indeed, desorption from soil particles may feed surface adsorption, bubbling and entail the formation of polluted aerosols. In this study, the concentration conditions were close to the environmental ones. A model based on the Wagner–Onsager–Samaras' views of ionic interfaces positively accounts for the opposite behaviour of the systems according to the surface under study. This report shows that these facts have to be thoroughly considered in order to make a relevant assessment of environmental issues.
Keywords: Coadsorption; Organics and ionic solution surfaces; Silica; Atmosphere; Onsager–Samaras' model;

Chemical composition of atmospheric aerosols during the 2003 summer intense forest fire period by C.A. Pio; M. Legrand; C.A. Alves; T. Oliveira; J. Afonso; A. Caseiro; H. Puxbaum; A. Sanchez-Ochoa; A. Gelencsér (7530-7543).
In Portugal, during summer 2003, unusually large forested areas (>300,000 ha) were destroyed by fire, emitting pollutants to the atmosphere. During this period, aerosol samples were collected in the Aveiro region, and analysed for total mass and a set of inorganic and organic compounds, including tracers of biomass burning. Comparisons of aerosol size distributions, levels of particulate mass and chemical aerosol composition between heavily smoke-impacted periods and the rest of the summer permit to evaluate the contribution of forest fires to the regional aerosol load. The absolute and relative variability of the particulate inorganic and organic constituents were used to evaluate the importance of wildfires as emission sources responsible for the presence of compounds such as molecular tracers in the summer atmosphere. From organic carbon to levoglucosan or to potassium ratios it was estimated that 40–55% of primary organic carbon could be attributed to wood smoke. The large fraction of secondary organic carbon suggested that forest fires may strongly contribute to gas-to-particle processes. It was found a better correlation of organic carbon with potassium than with levoglucosan, indicating that, during more complete combustive processes, potassium is possibly a more reasonable biomass burning tracer.
Keywords: Atmospheric aerosols; Portugal; Forest fires; Levoglucosan; Potassium; Monosugars; Polyols; Diacids;

Nighttime chemistry in the Houston urban plume by Menachem Luria; Ralph J. Valente; Solomon Bairai; William J. Parkhurst; Roger L. Tanner (7544-7552).
A late afternoon polluted air parcel transported from the Houston metropolitan area was monitored by an instrumented aircraft throughout the night of 21–22 July, 2005. Sampling was conducted during three flight segments over several downwind areas that were identified by a controllable meteorological balloon released from the Houston area at sundown. Samples were taken for approximately 2 h over each area. Using carbon monoxide as a tracer of the urban plume, it was revealed that the dilution inside the plume was relatively small. Ozone levels of up to 120 ppb were found in the plume at the furthest downwind distance, some 250 km northwest of Houston, with plume transport in the direction of the Dallas metropolitan area. The data further suggest that the nighttime conversion of NO x to NO z was very rapid, with complete (∼100%) conversion by the end of the night. At two locations the urban plume mixed with fresh emissions from power plants. At these sampling points ∼50% of the NO y had already been converted to NO z , thus indicating very rapid oxidation at night.
Keywords: Urban plume; Nighttime photochemistry; Ozone production efficiency; Aircraft measurements;

The size- and time-resolved composition of aerosols from a sub-Arctic boreal forest prescribed burn by Catherine F. Cahill; Thomas A. Cahill; Kevin D. Perry (7553-7559).
Aerosols from wildfires are the primary aerosols in the Arctic atmosphere during the summer months. These aerosols occur in large, increasing quantities and impact the sensitive radiative balance in the Arctic. FROSTFIRE, a controlled burn in a Long-Term Ecological Research Area 50 km north of Fairbanks, Alaska, was designed to quantify the impacts of wildfire on sub-Arctic boreal forest ecosystems in permafrost regions. However, it provided a unique opportunity to examine smoke aerosols collected in the middle of a sub-Arctic boreal forest fire. A battery-powered eight-stage aerosol impactor (i.e. a Davis Rotating-drum Unit for Monitoring), mounted at the top of a 10 m meteorological tower in the burn zone, collected size- and time-resolved aerosol samples with 19.45 min resolution for 24 h during the burn. The samples underwent Proton Induced X-ray Emission (PIXE) and Proton Elastic Scattering Analysis (PESA) to determine the sizes and elemental compositions of the collected aerosols. Throughout the fire, the smoke reaching the sampler was strongly monodisperse with most of the aerosol mass in the optically active 0.56–1.15 μm in aerodynamic diameter size range. Fine organics comprised almost all of the mass in this optically active size range and the concentrations of the organics were high throughout the sampling period. However, unlike the fine organics, the potassium concentrations in the smoke decreased exponentially during the sampling period as the fire progressed from an active flaming to a smoldering behavior. The major findings from this field experiment are the dramatic differences in aerosol composition as a function of fire type (i.e. smoldering or active flaming) and that the largest emission of organics occurs during the smoldering phase, unaccompanied by the potassium emissions often used as a smoke tracer. These results agree with recent laboratory experiments.
Keywords: Impactor; Wildfire; Alaska; Arctic; Smoke;