Atmospheric Environment (v.43, #18)

Sulfur is an extremely motile and vital element in the Earth's biogeochemical environment, one whose active redox chemistry maintains small reservoirs in the atmosphere and biosphere yet large fluxes through both. Essential for life, intimately linked to the climate state, and an important component of air quality, sulfur and its transport and processing in the atmosphere have been the subject of active research for several decades. This review article describes the current state of our understanding of the atmospheric sulfur cycle, focusing on the marine atmospheric boundary layer, with the aim of identifying the largest roots of uncertainty that most inhibit accurate simulation of sulfur cycling in the atmosphere. An overview of the emissions by phytoplankton and shipping, dispersion and entrainment in the marine boundary layer, and chemical processing by aerosols, clouds, and dry deposition is presented. Analysis of 20 contemporary modeling studies suggests that the greatest ambiguity in global sulfur cycling derives from (in descending order) wet deposition of aerosol sulfate, dry deposition of sulfur dioxide to the Earth's surface, and the heterogeneous oxidation of SO2 in aerosols and clouds.
Keywords: Sulfur cycle; Atmospheric chemistry; Marine boundary layer; Heterogeneous oxidation;

Errors in representing regional acid deposition with spatially sparse monitoring: Case studies of the eastern US using model predictions by Joseph E. Sickles; Douglas S. Shadwick; J. Vasu Kilaru; Jeffrey W. Grimm (2855-2861).
The current study uses case studies of model-predicted regional precipitation and wet ion deposition over 5-year periods to estimate errors in corresponding regional values derived from the means of site-specific values within regions of interest located in the eastern US. The mean of model-predicted site-specific values for sites within each region was found generally to overestimate the corresponding model-predicted regional wet ion deposition. On an annual basis across four regions in the eastern US, these overestimates of regional wet ion deposition were typically between 5 and 25% and may be more exaggerated for individual seasons. Corresponding overestimates of regional precipitation were typically <5%, but may be more exaggerated for individual seasons. Period-to-period relative changes determined from the mean of site-based model-predicted wet deposition for the current regional ensembles of sites generally estimated larger beneficial effects of pollutant emissions reductions in comparison to changes based on model-predicted regional wet deposition. On an annual basis site-based relative changes were generally biased low compared to regional relative changes: differences were typically <7%, but they may also be more exaggerated for individual seasons. Spatial heterogeneities of the wet ion deposition fields with respect to the sparse monitoring site locations prevented the monitoring sites considered in the current study from providing regionally representative results. Monitoring site locations considered in the current study over-represent the geographical areas subject to both high emissions and high wet ion deposition and under-represent the geographical areas subject to low emissions and low wet deposition. Since the current case studies consider only those eastern US site locations that have supported concurrent wet and dry deposition monitoring, similar errors may be expected for dry and total deposition using results from the same monitoring site locations. Current case study results illustrate the approximate range of potential errors and suggest caution when inferring regional acid deposition from a network of sparse monitoring sites.
Keywords: Spatial representation; Deposition; Sulfate; Nitrate; Ammonium; Hydrogen ion; Precipitation;

Near roadway concentrations of organic source markers by David A. Olson; Stephen R. McDow (2862-2867).
Concentrations of elemental carbon (EC), organic carbon (OC), and 33 organic source markers (12 alkanes, 18 polycyclic aromatic hydrocarbons and ketones, and 3 hopanes) are reported near a highway in Raleigh, NC with an annual average daily traffic count of approximately 125,000 vehicles. Daily samples (24-h) were collected at two locations, one approximately 10 m and the other 275 m perpendicular from the road. Concentrations of OC were similar between near (mean = 7.6 μg m−3) and far (8.0 μg m−3) locations, but concentrations of most organic species at the near site were between 1.5 and 2 times higher than those at the far site.
Keywords: Organic source markers; Source apportionment; Hopanes; Polycyclic aromatic hydrocarbons (PAHs); Traffic;

Characterization of the Khamaseen (spring) dust in Jordan by Abdulkader M. Abed; Mustafa Al Kuisi; Hani Abul Khair (2868-2876).
During the spring each year, the Eastern Mediterranean is affected by Khamaseen dust cyclones sourced from the North African Sahara. In order to characterize Khamaseen dust in Jordan, we collected dust from ten localities during the spring of 2006. The collected dust was analyzed for grain size, mineralogy, and chemical composition. The dust is predominantly aluminosilicates (clay minerals and feldspars), quartz and carbonates with minor amounts of phosphate. The particles are mostly subrounded to subangular and generally between 5 and 20 μm in size. The majority of the elements analyzed have a natural abundance and distribution. However, several elements such as As, Cd, Cr, Cu, Pb, Se and Zn have higher than natural abundances due to anthropogenic enrichment by various enrichment factors. The analyzed dust samples are chemically homogenous, indicating a similar provenance and good mixing by the Khamaseen winds. The rare earth elements patterns are similar to those of the upper continental crust composition and average shale. Total amount of dust deposited on Jordan during the spring of 2006 is around 0.3 million tons.
Keywords: Khamaseen; Dust; Mineralogy; Geochemistry; Provenance; Jordan;

On-road comparison of a portable emission measurement system with a mobile reference laboratory for a heavy-duty diesel vehicle by K.C. Johnson; T.D. Durbin; D.R. Cocker; W.J. Miller; D.K. Bishnu; H. Maldonado; N. Moynahan; C. Ensfield; C.A. Laroo (2877-2883).
On-road comparisons were made between a mobile emissions laboratory (MEL) meeting federal standards and a portable emissions measurement system (PEMS). These comparisons were made over different conditions; including road grade, vibration, altitude, electric fields, and humidity with the PEMS mounted inside and outside of the tractor's cab. Brake-specific emissions were calculated to explore error differences between the MEL and PEMS during the Not-To-Exceed (NTE) engine operating zone. The PEMS brake-specific NOx (bsNOx) NTE emissions were biased high relative to the MEL and, in general, were about 8% of the 2007 in-use NTE NO x standard of 2.68 g kW−1 h−1 (2.0 g hp−1 h−1). The bsCO2 emissions for the PEMS were also consistently biased high relative to the MEL, with an average deviation of +4% ± 2%. NMHC and CO emissions were very low and typically less than 1% of the NTE threshold. This research was part of a comprehensive program to determine the “allowance” when PEMS are used for in-use compliance testing of heavy-duty diesel vehicles (HDDVs).
Keywords: PEMS; On-road; In-use; Heavy-duty diesel; Semtech DS; Not-to-exceed (NTE);

Ethnicity, housing and personal factors as determinants of VOC exposures by Jennifer C. D'Souza; Chunrong Jia; Bhrarmar Mukherjee; Stuart Batterman (2884-2892).
Previous studies investigating effects of personal, demographic, housing and other factors on exposures to volatile organic compounds (VOC) have focused on mean or median exposures, and generally not the high exposures that are of great interest. This paper identifies determinants of personal VOC exposures on a quantile-specific basis using a nationally representative sample. The NHANES 1999–2000 VOC dataset was merged with personal, demographic, housing, smoking and occupation variables. Bivariate analyses tested for differences in geometric means and quantiles across levels of potential exposure determinants. Multivariate sample-weighted ordinary least-squares (OLS) and quantile regression (QR) models were then used to adjust for covariates. We identify a number of exposure determinants, most of which varied by exposure quantile. The most striking finding was the much higher exposures experienced by Hispanics and Blacks for aromatic VOCs (BTEX: benzene, toluene, ethylbenzene and xylenes), methyl tert-butyl ether (MTBE), and 1,4-dichlorobenzene (DCB). Exposure to gasoline, paints or glues, and having a machine-related occupation also were associated with extremely high BTEX and MTBE exposures. Additional determinants included the presence of attached garages and open windows, which affected exposures of BTEX (especially at lower quantiles) and MTBE (especially at higher quantiles). Smoking also increased BTEX exposures. DCB was associated with air freshener use, and PERC with dry-cleaned clothing. After adjusting for demographic, personal and housing factors, age and gender were not significant predictors of exposure. The use of QR in conjunction with OLS yields a more complete picture of exposure determinants, and identifies subpopulations and heterogeneous exposure groups in which some individuals experience very elevated exposures and which are not well represented by changes in the mean. The high exposures of Hispanics and Blacks are perplexing and disturbing, and they warrant further investigation.
Keywords: Benzene; Chloroform; Distributions; Exposure; Minority; NHANES; Quantile regression; Volatile organic compounds;

Seasonal and diurnal variations of ambient PM2.5 concentration in urban and rural environments in Beijing by Xiujuan Zhao; Xiaoling Zhang; Xiaofeng Xu; Jing Xu; Wei Meng; Weiwei Pu (2893-2900).
Three years of measurement of PM2.5 with 5-min time resolution was conducted from 2005 to 2007 in urban and rural environments in Beijing to study the seasonal and diurnal variations in PM2.5 concentration. Pronounced seasonal variation was observed in the urban area, with the highest concentrations typically observed in the winter and the lowest concentrations generally found in the summer. In the rural area, the maximum in PM2.5 concentration usually appeared during the spring, followed by a second maximum in the summer, while the minimum generally occurred in the winter. Significant diurnal variations in PM2.5 concentration were observed in both urban and rural areas. In the urban area, the PM2.5 concentration displays a bimodal pattern, with peaks between 7:00 and 8:00 a.m. and between 7:00 and 11:00 p.m. The minimum generally appears around noon. The morning peak is attributed to enhanced anthropogenic activity during rush hours. The decreases of boundary layer height and wind speed in the afternoon companying with increased source activity during the afternoon rush hour result in the highest PM2.5 concentration during evening hours. In the rural area, the PM2.5 concentration shows a unimodal pattern with a significant peak between 5:00 and 11:00 p.m.The seasonal and diurnal variations in PM2.5 concentration in the urban area are mostly dominated by the seasonal and diurnal variability of boundary layer and source emissions. The year-to-year variability of rainfall also has an important influence on the seasonal variation of PM2.5 in the urban area. The seasonal and diurnal wind patterns are more important factors for PM2.5 variation in the rural area. Southerly winds carry pollutants emitted in southern urban areas northward and significantly enhance the PM2.5 concentration level in the rural area.
Keywords: PM2.5 concentration; Seasonal variation; Diurnal variation; Beijing area;

Organic aerosol source apportionment from highly time-resolved molecular composition measurements by Matthew A. Dreyfus; Kouame Adou; Steven M. Zucker; Murray V. Johnston (2901-2910).
Organic molecular composition measurements with 3.5 min time resolution were performed with the photoionization aerosol mass spectrometer (PIAMS) over an 18-day period in October–November 2007 in Wilmington, Delaware, USA. Mass spectra were obtained for a total of 6244 time periods, and the signal intensities of 60 specific m/z ratios corresponding to key organic molecular species were modeled by positive matrix factorization (PMF). Six factors were identified that could be tentatively linked to specific sources (diesel exhaust, car emissions/road dust, meat cooking) or types of compounds (alkanes/alkanoic acids, phthalates, PAHs). Owing to the inherent high time resolution of PIAMS, the temporal (diurnal) and wind direction dependencies of these factors could be examined in detail to assess the impacts of point sources and atmospheric processes. Time-resolved EC/OC and gas-phase data (O3, NOx, CO) were also obtained during the measurement period to help distinguish primary (POC) and secondary (SOC) organic carbon. The total organic carbon (TOC) concentration averaged 2.6 μg m−3 during the measurement period and most (>90%) was classified as primary. Of this, approximately one-third could be assigned as combustion POC and the other two-thirds as non-combustion POC. The PMF results were combined with EC/OC data for source apportionment. The diesel and car/road dust factors together represented about two-thirds of TOC, while the alkane/alkanoic acid and meat cooking factors contributed most of the remaining one-third. The phthalate and PAH factors contributed very little, only a few percent of the total. The diesel factor correlated most strongly to combustion POC, while the sum of the remaining factors correlated well with non-combustion POC.
Keywords: Organic carbon; Source apportionment; Receptor modeling; Photoionization aerosol mass spectrometer; Urban aerosol;

Ionic composition of TSP and PM2.5 during dust storms and air pollution episodes at Xi'an, China by Zhenxing Shen; Junji Cao; Richard Arimoto; Zhiwei Han; Renjian Zhang; Yuemei Han; Suixin Liu; Tomoaki Okuda; Shunsuke Nakao; Shigeru Tanaka (2911-2918).
TSP and PM2.5 samples were collected at Xi'an, China during dust storms (DSs) and several types of pollution events, including haze, biomass burning, and firework displays. Aerosol mass concentrations were up to 2 times higher during the particulate matter (PM) events than on normal days (NDs), and all types of PM led to decreased visibility. Water-soluble ions (Na+, NH4 +, K+, Mg2+, Ca2+, F, Cl, NO3 , and SO4 2−). were major aerosol components during the pollution episodes, but their concentrations were lower during DSs. NH4 +, K+, F, Cl, NO3 , and SO4 2− were more abundant in PM2.5 than TSP but the opposite was true for Mg2+ and Ca2+. PM collected on hazy days was enriched with secondary species (NH4 +, NO3 , and SO4 2) while PM from straw combustion showed high K+ and Cl. Firework displays caused increases in K+ and also enrichments of NO3 relative to SO4 2−. During DSs, the concentrations of secondary aerosol components were low, but Ca2+ was abundant. Ion balance calculations indicate that PM from haze and straw combustion was acidic while the DSs samples were alkaline and the fireworks' PM was close to neutral. Ion ratios (SO4 2−/K+, NO3 /SO4 2−, and Cl/K+) proved effective as indicators for different pollution episodes.
Keywords: TSP; PM2.5; Water-soluble ions; Pollution episodes;

Temporal processes that contribute to nonlinearity in vegetation responses to ozone exposure and dose by Robert L. Heath; Allen S. Lefohn; Robert C. Musselman (2919-2928).
Ozone interacts with plant tissue through distinct temporal processes. Sequentially, plants are exposed to ambient O3 that (1) moves through the leaf boundary layer, (2) is taken up into plant tissue primarily through stomata, and (3) undergoes chemical interaction within plant tissue, first by initiating alterations and then as part of plant detoxification and repair. In this paper, we discuss the linkage of the temporal variability of apoplastic ascorbate with the diurnal variability of defense mechanisms in plants and compare this variability with daily maximum O3 concentration and diurnal uptake and entry of O3 into the plant through stomata. We describe the quantitative evidence on temporal variability in concentration and uptake and find that the time incidence for maximum defense does not necessarily match diurnal patterns for maximum O3 concentration or maximum uptake. We suggest that the observed out-of-phase association of the diurnal patterns for the above three processes produces a nonlinear relationship that results in a greater response from the higher hourly average O3 concentrations than from the lower or mid-level values. The fact that these out-of-phase processes affect the relationship between O3 exposure/dose and vegetation effects ultimately impact the ability of flux-based indices to predict vegetation effects accurately for purposes of standard setting and critical levels. Based on the quantitative aspect of temporal variability identified in this paper, we suggest that the inclusion of a diurnal pattern for detoxification in effective flux-based models would improve the predictive characteristics of the models. While much of the current information has been obtained using high O3 exposures, future research results derived from laboratory biochemical experiments that use short but elevated O3 exposures should be combined with experimental results that use ambient-type exposures over longer periods of time. It is anticipated that improved understanding will come from future research focused on diurnal variability in plant defense mechanisms and their relationship to the diurnal variability in ambient O3 concentration and stomatal conductance. This should result in more reliable O3 exposure standards and critical levels.
Keywords: Air quality standards; Ascorbate; Defense mechanisms; Flux; Repair; Uptake;

The methods of positive matrix factorization–chemical mass balance and principal component analysis/multiple linear regression–chemical mass balance were studied in this paper, for combined source apportionment. Due to the high similarity among the source profiles, several problems would raised when only one receptor model was applied. For example, the collinearity problem would result in the negative contributions when applying CMB model; certain sources would not to be separated out when applying PCA or PMF model. In this study, PCA/MLR–CMB model and PMF–CMB were attempted to resolve the problem, where the combined models were applied to study the synthetic and ambient datasets. In synthetic dataset, there were seven sources (six actual sources from real world, and one unknown source). The results obtained by the combined models show that the combined source apportionment technique is feasible. In addition, an ambient dataset from a northern city in China was analyzed by PCA/MLR–CMB model and PMF–CMB model, and these two models got the similar results. The results show that coal combustion contributed the largest fraction to the total mass.
Keywords: Combined source apportionment; Original receptor; Secondary receptor;

The effect of a woodstove changeout on ambient levels of PM2.5 and chemical tracers for woodsmoke in Libby, Montana by Megan A. Bergauff; Tony J. Ward; Curtis W. Noonan; Christopher P. Palmer (2938-2943).
Residential woodstoves are the single largest source of PM2.5 in Libby, MT, resulting in the community being designated as a nonattainment area for PM2.5. Beginning in 2005, a community-wide woodstove changeout program was implemented that replaced nearly 1200 old stoves with EPA-certified units. In an effort to track the reduction of woodsmoke particles throughout the program, ambient PM2.5 samples were collected before, during, and after the changeout. These samples were analyzed for seven selected woodsmoke tracers, including vanillin, acetovanillone, guaiacol, 4-ethylguaiacol (methoxyphenols), levoglucosan (sugar anhydride), abietic acid, and dehydroabietic acid (resin acids). Results of the changeout showed that PM2.5 levels decreased by 20% during the changeout period, while levels of the seven chosen tracer compounds gave variable responses. Levoglucosan levels decreased by 50% while both resin acids increased after the changeout, suggesting a change in the chemistry of the particles. No trend was observed in the levels of methoxyphenols as a group over the changeout period. The results suggest that the concentrations of woodsmoke related PM2.5 in the Libby airshed have decreased; however, the chemistry of the emitted particles also changed when old woodstoves were replaced with new EPA-certified stoves.
Keywords: Particulate matter; Chemical tracers; Levoglucosan; Woodstove changeout; Residential combustion;

Assessment of the relationship between total suspended particles and the response of two biological indicators transplanted to an urban area in central Argentina by H.A. Carreras; J.H. Rodriguez; C.M. González; E.D. Wannaz; F. Garcia Ferreyra; C.A. Perez; M.L. Pignata (2944-2949).
Samples of the vascular plant Tradescantia pallida and the lichen Usnea amblyoclada were exposed from October 2004 to April 2005 in three sites with different local sources of air pollution in Córdoba city, Argentina. Simultaneous determinations of the ambient levels of total suspended particles were made for each site. Young inflorescenses of T. pallida were collected in November, February and April and the frequency of micronuclei was determined on early tetrads of pollen mother cells. Physiological parameters and the elemental composition of lichen thalli were measured from samples exposed and replaced every month. Significant differences among sampling sites were observed in the frequency of micronuclei measured in T. pallida as well as in many physiological parameters and elements accumulated in lichen thalli. The mass of particulate material as well as the concentration of Ca, Mn, Cu, Zn and Sr was significantly different in different sampling sites, too. These results suggest that in situ biomonitoring using both higher plants and lichens may be of use to characterize air pollution in areas devoid of instrumental monitoring techniques or where it is necessary to explore the distribution of air contaminants at a microscale.
Keywords: In situ biomonitoring; Usnea amblyoclada; Tradescantia pallida; Total suspended particles; Multielemental composition;

Metals emitted from heavy-duty diesel vehicles equipped with advanced PM and NOX emission controls by Shaohua Hu; Jorn D. Herner; Martin Shafer; William Robertson; James J. Schauer; Harry Dwyer; John Collins; Tao Huai; Alberto Ayala (2950-2959).
Emission factors for elemental metals were determined from several heavy-duty diesel vehicles (HDDV) of 1998–2007 vintage, operating with advanced PM and/or NOX emissions control retrofits on a heavy-duty chassis dynamometer, under steady state cruise, transient, and idle conditions. The emission control retrofits included diesel particulate filters (DPF): catalyzed and uncatalyzed, passive and active prototype vanadium- or zeolite-based selective catalytic reduction (SCR) systems, and a catalyzed DPF fitted on a hybrid diesel electric drive vehicle. The prototype SCR systems in combination with DPF retrofits are of particular interest because they represent the expected emissions controls for compliance with PM and NOX regulations in 2010. PM samples from a full-exhaust dilution tunnel were collected on bulk filters, and on a Personal Cascade Impactor Sampler (PCIS) for total and water-soluble elemental analysis. All the DPFs significantly reduced emissions of total trace elements (>85% and >95% for cruise and for the Urban Dynamometer Driving Schedule (UDDS), respectively). However, we observed differences in the post-retrofit metals emissions due to driving cycle effects (i.e., exhaust temperature) and type of retrofit. In general, the metals emissions over cruise conditions (which leads to higher exhaust temperatures) were substantially different from the emissions over a transient cycle or while idling. For instance, during cruise, we observed higher levels of platinum (1.1 ± 0.6–4.2 ± 3.6 ng km−1) for most of the retrofit-equipped vehicle tests compared to the baseline configuration (0.3 ± 0.1 ng km−1). The vanadium-based DPF + SCR vehicle during cruise operation exhibited emissions of vanadium (562 ± 265 ng km−1) and titanium (5841 ± 3050 ng km−1), suggesting the possible release of actual SCR wash-coat (V2O5/TiO2) from the catalyst under the higher temperatures characteristic of cruise operation. The vanadium emissions exhibited a bi-modal mass size distribution, with modes at <0.25 μm and 1.0–2.5 μm size ranges for the vanadium-based SCR system. For the DPF + SCR systems, a greater fraction of the metal emissions from the zeolite-based system is water-soluble compared to emissions from the vanadium-based system.
Keywords: Metals; Aftertreatment system; Diesel particulate filter; DPF; Selective catalytic reduction; SCR; Heavy-duty diesel vehicles; HDDV; Water-soluble metals;

A mobile platform was outfitted with real-time instruments to spatially characterize pollution concentrations in communities adjacent to the Ports of Los Angeles and Long Beach, communities heavily impacted by emissions related to dieselized goods movement, with the highest localized air pollution impacts due to heavy-duty diesel trucks (HDDT). Measurements were conducted in the winter and summer of 2007 on fixed routes driven both morning and afternoon. Diesel-related pollutant concentrations such as black carbon, nitric oxide, ultrafine particles, and particle-bound polycyclic aromatic hydrocarbons were frequently elevated two to five times within 150 m downwind of freeways (compared to more than 150 m) and up to two times within 150 m downwind of arterial roads with significant amounts of diesel traffic. While wind direction was the dominant factor associated with downwind impacts, steady and consistent wind direction was not required to produce; high impacts were observed when a given area was downwind of a major roadway for any significant fraction of time. This suggests elevated pollution impacts downwind of freeways and of busy arterials are continuously occurring on one side of the road or the other, depending on wind direction. The diesel truck traffic in the area studied was high, with more than 2000 trucks per peak hour on the freeway and two- to six-hundred trucks per hour on the arterial roads studied. These results suggest that similarly-frequent impacts occur throughout urban areas in rough proportion to diesel truck traffic fractions. Thus, persons living or working near and downwind of busy roadways can have several-fold higher exposures to diesel vehicle-related pollution than would be predicted by ambient measurements in non-impacted locations.
Keywords: Mobile monitoring; Freeway; Diesel vehicles; Black carbon; Ultrafine particles;

Possible change in Asian dust source suggested by atmospheric anthropogenic radionuclides during the 2000s by Yasuhito Igarashi; Yayoi Inomata; Michio Aoyama; Katsumi Hirose; Hiroshi Takahashi; Yoshihiro Shinoda; Nobuo Sugimoto; Atsushi Shimizu; Masaru Chiba (2971-2980).
Decades-long monitoring of anthropogenic radionuclides in the atmospheric deposition in Tsukuba, Japan suggests not only the substantial impacts of the Asian dust (Kosa) on the deposition but also the possible change of the Kosa source region, especially during springs of the 2000s. In order to know more about such change, 4 single wet deposition events occurred in the spring of 2007 were scrutinized. The largest anthropogenic radionuclides wet deposition was supplied by the April 2–4 event. It brought several tens % of the monthly depositions (April 2007) of the dust (residue) mass (4.5 g m−2) and anthropogenic radionulides (90Sr: 16, 137Cs: 97 and Pu: 3 mBq m−2). None of the events observed fulfilled both criteria of the specific activities and 90Sr/137Cs activity ratio to the Tsukuba soil; they did not exhibit local soil dust signature. The Kosa events in fact have extensive impacts on the atmospheric environment over Japan in spring season. Considering the elevated specific activities as well as greater 137Cs/90Sr activity ratio in the deposited dust, it is hypothesized that the dust source areas in Asian continent would be shifting from the arid zone to the desert-steppe zone suffering from desertification during the 2000s. This type of the Kosa may be called as the ‘new-regime Kosa’. Chemical observation in the far downwind region of the Kosa dust could allow us to know possible shift in the source regions.
Keywords: Asian dust; Atmospheric deposition; Anthropogenic radionuclides; Climate change;

Flow and dispersion in street intersections by L. Soulhac; V. Garbero; P. Salizzoni; P. Mejean; R.J. Perkins (2981-2996).
Street intersections play an important role in determining pollutant concentrations in the urban canopy – vehicle emissions often increase in the vicinity of road intersections, and the complex flow patterns that occur within the intersection determine the pollutant fluxes into adjoining streets and into the atmosphere. Operational models for urban air quality therefore need to take account of the particular characteristics of street intersections. We have performed an experimental and numerical investigation of flow and dispersion mechanisms within an urban intersection, and on the basis of our observations and results, we have developed a new operational model for pollutant exchanges in the intersection, which takes account of the non-uniformity of the pollutant fluxes entering and leaving the intersection. The intersection is created by two streets of square cross-section, crossing orthogonally; concentrations were measured by releasing a neutrally buoyant tracer gas from a line source located in one of the streets. As a general result, the numerical simulations agree well with the measurements made in the wind tunnel experiments, except for the case of ground-level concentrations, where the computed concentrations far from the axis of the line source are significantly lower than the measured values. In the first part of the study we investigate the influence of an intersection on the velocity and concentration fields in the adjoining streets; we show that the immediate influence of the intersection extends within the adjoining streets, to a distance of the order of the characteristic size of the streets. A large recirculating vortex is formed at the entrance to the cross-wind streets, and this determines the exchange of pollutants between the streets and the intersection. For some wind directions the average velocity in the street segment between intersections is the same as that which occurs in an infinitely long street with the same wind, but for other angles the average velocity in the finite-length street is significantly lower. The average concentration along a finite-length street is significantly different from that observed in an infinitely long street. In the second part of the study we investigate how the pollutant fluxes in the incoming streets are redistributed amongst the outgoing streets. An analysis of the mean streamlines shows that the flows remain relatively planar, with little variation over the vertical, and we have exploited this result to develop a simple operational model for the redistribution of pollutant fluxes within the intersection. This model has been further adapted to take account of the influence of fluctuations in wind direction over typical averaging periods. The resulting model is used in the street network model SIRANE.
Keywords: Street canyon; Street intersection; Urban air pollution; Dispersion models;

Characterization of odor released during handling of swine slurry: Part I. Relationship between odorants and perceived odor concentrations by V. Blanes-Vidal; M.N. Hansen; A.P.S. Adamsen; A. Feilberg; S.O. Petersen; B.B. Jensen (2997-3005).
Odor emission from livestock production systems is a major nuisance in many rural areas. This study aimed at determining the major airborne chemical compounds responsible for the unpleasant odor perceived in swine facilities during slurry handling, and at proposing predictive models of odor concentration (OC) based on the concentrations of specific odorants in the air. A multivariate data analysis strategy involving principal components analysis and multiple linear regressions was implemented to analyze the relationships between concentration of 35 gases (measured by GC/MS or gas detection tubes), and the overall OC perceived by sensory analysis. The study compiled data on the concentration of odor and odorants, measured in the headspace of 24 unstored and stored slurry samples collected from three different types of production units on 8 commercial swine farms. Among all the measured constituents, OC was found to have the highest correlation with the sulfur containing compounds (i.e. hydrogen sulfide, dimethylsulfide, dimethyldisulfide, dimethyltrisulfide). The concentration of hydrogen sulfide accounted for 68% of the variation in OC above the stirred slurry samples. The highest concentrations of volatile organic compounds were observed for phenols and indoles, which made a significant contribution to the overall OC when the slurry was fresh. The contribution of ammonia to the OC was only significant in the absence of hydrogen sulfide. The precision of predictive models of OC based on the concentration of specific odorants in the air was satisfactory (R 2 between 0.66 and 0.89). Hence, this study suggests that monitoring of specific odor compounds released from agitated swine slurry can be used to predict the concentration of odor perceived close to the source (e.g. at storage units), allowing the assessment of odor nuisance potentials.
Keywords: Odor; Odorants; Principal components analysis (PCA); Slurry;

The quality of rural life can be affected by offensive odors released from animal buildings and storage units. The objectives of this study were to compare the concentrations of odor and odorants above different types of stirred swine slurry to analyze the relationships between concentrations of odor (and odorants) and physicochemical characteristics of the slurry (i.e. pH, temperature, dry matter, volatile solids, and concentration of 22 chemical compounds); and to propose predictive models for the odor concentration (OC) based on these physicochemical characteristics (solely and in combination with concentrations of specific odorants in the air above the slurries). The study comprised data on concentrations of odor and odorants in the air above slurry samples (fresh and/or stored) collected from production units with farrowing sows, finishing swines, or weaning pigs at eight swine operations (N  = 48). OC measured in the air above stirred swine slurry samples were not significantly different among production types or storage times. The physicochemical characteristics of the slurries were not useful for predicting OC or concentrations of hydrogen sulfide (or organic sulfides) above the slurry, but were related to concentrations of other emitted gases such as phenols and indoles (r 2  = 0.65–0.79, p  <0.05), ammonia (r 2  = 0.86, p  < 0.05) and carboxylic acids (r 2  = 0.23–0.59, p  <0.05). There was good precision of predictive models of OC based on selected slurry characteristics (i.e. pH, dry matter, nitrogen content, sulfur content or concentrations of individual aromatic compounds and carboxylic acids) together with concentrations of specific odorants in the air (e.g. hydrogen sulfide) (r 2 between 0.70 and 0.92). This study suggests that predictive models could be useful for evaluating odor nuisance potentials of swine slurry during handling.
Keywords: Composition; Model; Odor; Principal components analysis (PCA); Slurry;

The photochemical oxidation and dispersion of reduced sulfur compounds (RSCs: H2S, CH3SH, DMS, CS2, and DMDS) emitted from anthropogenic (A) and natural (N) sources were evaluated based on a numerical modeling approach. The anthropogenic emission concentrations of RSCs were measured from several sampling sites at the Donghae landfill (D-LF) (i.e., source type A) in South Korea during a series of field campaigns (May through December 2004). The emissions of natural RSCs in a coastal study area near the D-LF (i.e., source type N) were estimated from sea surface DMS concentrations and transfer velocity during the same study period. These emission data were then used as input to the CALPUFF dispersion model, revised with 34 chemical reactions for RSCs. A significant fraction of sulfur dioxide (SO2) was produced photochemically during the summer (about 34% of total SO2 concentrations) followed by fall (21%), spring (15%), and winter (5%). Photochemical production of SO2 was dominated by H2S (about 55% of total contributions) and DMS (24%). The largest impact of RSCs from source type A on SO2 concentrations occurred around the D-LF during summer. The total SO2 concentrations produced from source type N around the D-LF during the summer (a mean SO2 concentration of 7.4 ppbv) were significantly higher than those (≤0.3 ppbv) during the other seasons. This may be because of the high RSC and SO2 emissions and their photochemistry along with the wind convergence.
Keywords: Photochemical oxidation; Dispersion; H2S; DMS; SO2; CALPUFF; Donghae landfill;

Spatial variability of sulfur dioxide and sulfate over complex terrain in East Tennessee, USA by LaToya Myles; Ronald J. Dobosy; Tilden P. Meyers; William R. Pendergrass (3024-3028).
In 2004 and 2005, the East Tennessee Ozone Study (ETOS) enhanced its regional measurement program with annular denuder systems to quantify sulfur dioxide (SO2) and PM2.5 sulfate (SO4 2−) at five sampling sites that were representative of the complex terrain and physiographic features of East Tennessee. Intersite spatial variability was more defined for SO2 than for SO4 2−, which showed a fairly uniform structure in both daytime and nighttime measurements. Pollution roses indicated that two sites may have been influenced by the proximity of SO2 emission sources. The data suggest that SO2 is affected by nearby sources in the study area while the sources of SO4 2− are regionally distributed.
Keywords: ETOS; Sulfur dioxide; Sulfate; Pollution roses;

A photochemical reactor for studies of atmospheric chemistry by E.J.K. Nilsson; C. Eskebjerg; M.S. Johnson (3029-3033).
A photochemical reactor for studies of atmospheric kinetics and spectroscopy has been built at the Copenhagen Center for Atmospheric Research. The reactor consists of a vacuum FTIR spectrometer coupled to a 100 L quartz cylinder by multipass optics mounted on electropolished stainless steel end flanges, surrounded by UV-A, UV-C and broadband sun lamps in a temperature-controlled housing. The combination of a quartz vessel and UV-C lamps allows higher concentrations of O(1D) and OH than can be generated by similar chambers. The reactor is able to produce radical concentrations of ca. 8 × 1011 cm−3 for OH, 3 × 106 cm−3 for O(1D), 3.3 × 1010 cm−3 for O(3P) and 1.6 × 1012 cm−3 for Cl. The reactor can be operated at pressures from 10−3 to 103 mbar and temperatures from 240 to 330 K. As a test of the system we have studied the reaction CHCl3 + Cl using the relative rate technique and find kCHCl3+Cl/kCH4+Cl = 1.03 ± 0.11, in good agreement with the accepted value.
Keywords: Smog chamber; Photochemical reactor; Relative rate; Infrared spectroscopy; Atmospheric chemistry; Hydroxyl radical;