Atmospheric Environment (v.41, #28)

The momentum extracted from fluid flow by the underlying surface roughness is important for understanding processes of entrainment, transportation and deposition of sediments. The parameter z 0 is a length scale that characterizes the loss of wind momentum attributable to the roughness elements. However, it is very difficult to estimate accurately and precisely even under carefully controlled conditions in wind tunnels. This limits the use of the parameter over large areas and in particular across scales of roughness, e.g., grain to form scale. This is problematic for studies of wind erosion and dust dispersion which require estimates of aerodynamic resistance over very large areas.A new concept is proposed with the potential to unify the estimates of fluid flow resistance along the continuum of sparse to tightly packed object spacing and across multiple scales. It is based on the creation of shadows by the illumination of roughness elements and the assumption that flow separation is created behind roughness elements on a plane surface as a function of free-stream wind velocity and obstacle height. The concept was implemented using a computer program and validated against a wind tunnel study that estimated z 0 for configurations of spheroids. Various spheroid coverages used in the wind tunnel study were reconstructed using a digital elevation model of the surface simulated by the computer. A strong relationship was established (R 2=0.91) over two orders of magnitude between the shadow area ratio (SAR) and z 0.Fluid drag was shown to be dependent on the arrangement of roughness elements at the surface. The configurations of spheroids were replaced by cylinders of the same basal area and computer simulations of shadow area were repeated. Object shape was evidently important to the overlap of shadow with downstream adjacent obstacles and hence aerodynamic resistance was dependent on object shape. These findings appear to contradict empirical evidence of previous studies.Illumination and shadow of objects on a plane surface appears to adequately represent z 0. Shadow appears to approximate the flow separation behind an obstacle and to represent a wake. The overlap on to downstream adjacent objects of the shadow cast from an upstream object appears to mimic the interference of wakes caused by fluid flow moving around stationary objects with close spacing. There is a compelling argument for the use of SAR as a unifying measure of aerodynamic resistance over the continuum between isolated and tightly packed objects. Furthermore, given elevation data of objects on a plane surface the results show that shadow length is a point-based measure that may be integrated for all points evaluated to provide SAR. The demonstrated angular relationship between illumination and drag (shadow and flow separation) has considerable potential for estimating aerodynamic resistance over multiple scales and for significant investigations of (i) the anisotropic nature of aerodynamic resistance and (ii) its estimation using directional measurements of reflectance and bidirectional reflectance models.
Keywords: Flow separation; Drag; Wake; Aerodynamic resistance; Boundary layer; Roughness length; Shadow; Illumination; Ray casting; Digital elevation model;

In this study, we demonstrate the utility of conditional probability functions (CPFs), potential source contribution functions (PSCFs), and hierarchical clustering analysis (HAC) to identify the source region and transport pathways of hydrocarbons measured at five photochemical assessment monitoring stations (PAMS) near the Houston Ship Channel from June to October 2003. In contrast to scatter plots, which only show the pair-wise correlation of species, commonality in CPF figures shows both correlation and information on the source region of the species in question. In this study, we use over 50 hourly volatile organic compound (VOC) concentrations and surface wind observations to show that VOCs with similar CPF patterns likely have common transport pathways. This was established with the multivariate technique, which uses the hierarchical clustering analysis to define clusters of VOCs having similar CPF patterns. This method revealed that alkenes, and in particular those with geometric isomers such as cis-/trans-2-butene and cis-/trans-2-pentene, have similar CPF patterns and hence, a common area of origin. The alkane isomers often show CPF patterns among themselves, and similarly, aromatic compounds often show similar patterns. We also show how calculated trajectory information can be used in the PSCF analysis to produce a graphic picture that identifies specific geographic areas associated with a given VOC (or other pollutant). The use of these techniques in the chemically and meteorologically complex environment of Houston, Texas, suggests its further utility in other areas with relatively simpler conditions.
Keywords: Conditional probability function (CPF); Potential source contribution function (PSCF); Hierarchical clustering analysis (HAC); Houston; Volatile organic compound (VOC); Source receptor relationship;

A simple network approach to modelling dispersion among large groups of obstacles by David Hamlyn; Trevor Hilderman; Rex Britter (5848-5862).
A simple network approach has been developed to simulate the movement of pollutant within urban areas. The model uses estimates of pollutant exchange obtained from velocity measurements in experiments with various regular obstacle arrays. The transfer of tracer material was modelled using concepts of advection along streets, well-mixed flow properties within street segments and exchange velocities (akin to aerodynamic conductances) across side and top facets of the street segments.The results predicted both the centreline concentration and lateral dispersion of the tracer with reasonable accuracy for a range of packing densities and wind directions. The basic model's concentration predictions were accurate to better than a factor of two in all cases for the region from two obstacle rows behind a source located within the array to around eight rows behind, a range of distances that falls into the so-called “neighbourhood-scale” for dispersion problems. The results supported the use of parameterized rates of exchange between regions of flow as being useful for fast, approximate dispersion modelling. It was thought that the effects of re-entrainment of tracer back into the canopy were of significance, but modelling designed to incorporate these effects did not lead to general improvements to the modelling for these steady-state source experiments.The model's limitations were also investigated. Chief amongst these was that it worked poorly among tall buildings where the well-mixed assumption within street segments was inadequate.
Keywords: Urban canopy; Box model; Exchange velocity; Re-entrainment;

An automated forecast system for ozone in seven Kentucky metropolitan areas has been operational since 2004. The forecast system automatically downloads the required input data twice each day, produces next-day forecasts of metro area peak 8-h average ozone concentration using a computer coded hybrid nonlinear regression (NLR) model, and posts the results on a website. The automated models were similar to previous NLR models, first applied to forecasting ozone in the Louisville metro area. The forecast system operated reliably during the 2004 and 2005 O3 seasons, producing at least one forecast per day better than 99% of the time. The forecast accuracy of the automated system was good. For all 2004 and 2005 forecasts, the mean absolute error was equal to 8.7 ppb, or 15.6% of the overall mean concentration. The overall detection rate of air quality standard exceedences was 56%, and the overall false alarm rate was 42%. In Louisville, the performance of the automated system was comparable to that of expert forecasters using the NLR model as a forecast tool.
Keywords: Air pollution; Air quality forecast; Ground-level ozone; Nonlinear regression;

Assessment of variations in atmospheric PCDD/Fs by Asian dust in Southeastern Korea by Se-Jin Lee; Hyokeun Park; Sung-Deuk Choi; Jae-Min Lee; Yoon-Seok Chang (5876-5886).
Atmospheric concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were measured in southeastern Korea during the spring of 2002. During this period, severe Asian dust events (ADs) occurred throughout Korea. Total suspended particulates (TSP) of ADs (456.8 μg m−3) increased approximately 3.6-fold compared with non-Asian dust events (NADs; 128.5 μg m−3). However, the concentrations of PCDD/Fs (average concentration, 3.34 pg m−3) did not increase as much as TSP; there was not a significant difference in the concentrations of particle-bound PCDD/Fs collected between ADs (2.45 pg m−3) and NADs (2.05 pg m−3). Meanwhile, according to TSP levels, the concentrations during NADs were 2.8-fold higher than ADs (16.73 and 5.98 ng g−1-TSP, respectively). High TSP levels during sand storms without an increase in PCDD/Fs reflected an increase in coarse and accumulation mode particles. Gas/particle partitioning studies revealed the additional inputs of particulate matters to the air during ADs which did not relate with the increase of PCDD/Fs. Furthermore, emissions from ADs may consist of relatively complex atmospheric particles; back trajectories showed air masses moving at low altitudes over Korea, but there were no differences in PCDD/Fs or atmospheric pollutants regardless of air movements. The study area, which is located in southeastern Korea, might be affected by both marine and regional anthropogenic sources, which do not appear to cause clear differences in PCDD/F concentrations or congener profiles between different air trajectories.
Keywords: Asian dust; PCDD/Fs; TSP; Gas/particle partitioning; Back trajectory;

The reactions of the nitrate radical with N,N-dimethylformamide (k 1); N,N-dimethylacetamide (k 2); N,N-dimethylproprionamide (k 3) and 1-methyl-2-pyrrolidinone (k 4), have been investigated using an absolute rate method. Experiments were performed using a laser photolysis technique coupled with UV-Visible absorption detection over the pressure range (100–200)±2 Torr and the temperature range (277–353)±2 K. This study provides the first determination of NO3 rate constant for reactions with four amides over a large temperature range. NO3 radical was produced by photolysis of the gas mixture F2/N2/HNO3/amide at 351 nm and detected at 662 nm where its cross section is well known. Four amides, showing a systematic variation of substitute, have been studied. The Arrhenius expressions (in cm3  molecule−1  s−1) were as follows: k 1 = ( 1.06 × 1 0 - 11 exp ( ( - 1600 ± 300 ) / T ) , k 2 = ( 2.82 × 1 0 - 11 exp ( ( - 1900 ± 200 ) / T ) , k 3 = ( 12.52 × 1 0 - 11 exp ( ( - 2700 ± 300 ) / T ) , k 4 = ( 2.42 × 1 0 - 11 exp ( ( - 1500 ± 100 ) / T ) . The obtained rate coefficients are compared with the reactivity towards the OH radicals. The results are also discussed in terms of the structure–reactivity relationship. In addition, the atmospheric implications are discussed.
Keywords: Nitrate radical; Amide; Kinetics; Cross section; Rate constant; Atmospheric lifetimes;

Monitoring personal, indoor, and outdoor exposures to metals in airborne particulate matter: Risk of contamination during sampling, handling and analysis by Pat E. Rasmussen; Amanda J. Wheeler; Nouri M. Hassan; Alain Filiatreault; Monique Lanouette (5897-5907).
Rigorous sampling and quality assurance protocols are required for the reliable measurement of personal, indoor and outdoor exposures to metals in fine particulate matter (PM2.5). Testing of five co-located replicate air samplers assisted in identifying and quantifying sources of contamination of filters in the laboratory and in the field. A field pilot study was conducted in Windsor, Ont., Canada to ascertain the actual range of metal content that may be obtained on filter samples using low-flow (4 L min−1) 24-h monitoring of personal, indoor and outdoor air. Laboratory filter blanks and NIST certified reference materials were used to assess contamination, instrument performance, accuracy and precision of the metals determination. The results show that there is a high risk of introducing metal contamination during all stages of sampling, handling and analysis, and that sources and magnitude of contamination vary widely from element to element. Due to the very small particle masses collected on low-flow 24-h filter samples (median 0.107 mg for a sample volume of approximately 6 m3) the contribution of metals from contamination commonly exceeds the content of the airborne particles being sampled. Thus, the use of field blanks to ascertain the magnitude and variability of contamination is critical to determine whether or not a given element should be reported. The results of this study were incorporated into standard operating procedures for a large multiyear personal, indoor and outdoor air monitoring campaign in Windsor.
Keywords: Exposure assessment; PM2.5; Metals; Quality assurance; ICP-MS; Gravimetric analysis; Residential environments;

On the variability of Black Smoke and carbonaceous aerosols in the Netherlands by M. Schaap; H.A.C. Denier van der Gon (5908-5920).
The study addresses the characteristics of elemental carbon (EC) and organic carbon (OC) distributions in the Netherlands by using Black Smoke (BS) data in combination with dedicated measurements and modelling. The BS levels indicate a large-scale background concentration over the Netherlands with low spatial variability and a gradient with highest levels (∼9 μg m−3) in the south gradually decreasing to the north-west (∼5.5 μg m−3). The BS concentrations at rural sites in the Netherlands are highly correlated due to common (diffuse) sources and large-scale meteorology. Superimposed on the regional background are the contributions of local/urban sources. Urban and rural BS levels show a distinct variation over the week with minimum levels on Sundays.BS levels do not reflect a real concentration as they are obtained via an optical measurement in combination with an outdated calibration curve to arrive at total suspended particles (TSP). We have found that the relation between BS and EC in the Netherlands is linear and highly correlated but dependent on station type. Application of these relations to the BS time series yields a gradient in the rural background EC concentration from 0.5 μg m−3 in the north to 0.7 μg m−3 in the south of the Netherlands. The relationship between OC and BS appears to be location specific and is determined by the BS–EC relation in combination with a characteristic OC/EC ratio. OC/EC ratios are ∼5 at regional background sites and ∼2 at traffic locations. Minimum OC/EC ratios at the traffic sites reflect the primary OC/EC ratio of traffic. We argue that estimation of secondary organic aerosol by assuming the minimum OC/EC ratio to be a proxy for the primary OC/EC is not allowed since this approach does not account for sources with high OC/EC ratios. Based on European scale modelling and the measured data, we estimate that national sources contribute ∼40–60% to Dutch EC levels.The rather costly and laborious EC measurements provide a better indicator of the carbonaceous fraction in ambient particulate matter (PM) but the cheap BS method may provide valuable information on spatial distribution of EC when used in combination with validation sites to characterise the EC–BS relationship.
Keywords: Black Smoke; Carbonaceous aerosol; Netherlands; Elemental carbon;

Source apportionment of time and size resolved ambient particulate matter measured with a rotating DRUM impactor by Emma Peré-Trepat; Eugene Kim; Pentti Paatero; Philip K. Hopke (5921-5933).
Ambient particulate chemical composition data acquired from samples collected using a three-stage Davis Rotating-drum Universal-size-cut Monitoring (DRUM) impactor in Detroit, MI, between February and April 2002 were analyzed through the application of a three-way factor analysis model. PM2.5 (particulate matter ⩽2.5 μm in aerodynamic diameter) was collected by a DRUM impactor with 3-h time resolution and three size modes (2.5 μm>D p>1.15 μm, 1.15 μm>D p>0.34 μm and 0.34 μm>D p>0.1 μm). A novel three-way factor analysis model was applied to these data where the source profiles are a three-way array of size, composition and source while the contributions are a matrix of sample by source. Nine factors were identified: road salt, industrial (Fe+Zn), cloud processed sulfate, two types of metal works, road dust, local sulfate source, sulfur with dust, and homogeneously formed sulfate. Road salt had high concentrations of Na and Cl. Mixed industrial emissions are characterized by Fe and Zn. The cloud processed sulfate had a high concentration of S in the intermediate size mode. The first metal works represented by Fe in all three size modes and by Zn, Ti, Cu, and Mn. The second included a high concentration of small size particle sulfur with intermediate size Fe, Zn, Al, Si, and Ca. Road dust contained Na, Al, Si, S, K, and Fe in the large size mode. The local and homogeneous sulfate factors show high concentrations of S in the smallest size mode, but different time series behavior in their contributions. Sulfur with dust is characterized by S and a mix of Na, Mg, Al, Si, K, Ca, Ti, and Fe from the medium and large size modes. This study shows that the utilization of time and size resolved DRUM data can assist in the identification of sources and atmospheric processes leading to the observed ambient concentrations.
Keywords: High time resolution; Size distribution; Aerosol; Multilinear engine (ME); Rotating drum impactor (DRUM); Detroit; SXRF;

This paper uses spectral methods to analyze changes in air quality at a single monitoring site in Delhi since 2000. Power spectral density calculations of daily concentration data for particulate matter (PM10), carbon monoxide (CO), oxides of nitrogen (NO x ) and oxides of sulfur (SO x ) reveal the presence of trends and periodic oscillations for all the pollutants. Singular Spectrum Analysis (SSA) is used to decompose daily data into statistically significant non-linear trends, seasonal cycles and other oscillations. Periods of sharp reductions were observed for both SO x and CO concentrations in 2001 and 2002, respectively. NO x concentration trends show a sustained rise from 2000 to 2004, followed by small decline thereafter. PM10 concentration trends remain essentially unchanged over the time period. All pollutants also show strong annual and biannual cycles. The observed trends in CO and NO x likely relate changes in Delhi's vehicular traffic emissions. The sharp drop in both the trend and amplitude of the seasonal cycle of CO coincides with the switch to Compressed Natural Gas (CNG) as a fuel for Delhi's public transport fleet. Observed changes in SO x and PM10 concentrations were most likely caused by sources unrelated to vehicular traffic.
Keywords: New Delhi; Air pollution; Singular Spectrum Analysis; Compressed Natural Gas; Alternative fuels;

Winter-grazing reduces methane uptake by soils of a typical semi-arid steppe in Inner Mongolia, China by Chunyan Liu; Jirko Holst; Nicolas Brüggemann; Klaus Butterbach-Bahl; Zhisheng Yao; Jin Yue; Shenghui Han; Xingguo Han; Julia Krümmelbein; Rainer Horn; Xunhua Zheng (5948-5958).
Steppe ecosystems are regarded as an important sink of atmospheric methane (CH4) and grazing is hypothesized to reduce CH4 uptake. However, firm experimental evidence is required to prove this hypothesis. Using a fully automated, chamber-based measuring system, we conducted continuous high-frequency (at a 3-h interval) measurements of CH4 uptake in a Leymus chinensis steppe, which is a typical grassland ecosystem in Inner Mongolia, China. Two management regimes were investigated: ungrazed since 1999 (UG99) and winter-grazed since 2001 (WG01). Measurements were carried out continuously during the periods of June–September 2004, May–September 2005 and March–June 2006. During all of these periods, significantly lower mean CH4 uptake (±S.E.) at WG01 (28±0.7 μg C m−2  h−1) as compared to UG99 (56±1.0 μg C m−2  h−1) (p<0.01) was found. Total CH4 uptake during the growing seasons (May–September) 2004 and 2005 at WG01 and UG99 was quantified as 1.15 and 2.15 kg C ha−1, respectively. Annual rates of CH4 uptake were approximately 1.91 (WG01) and 3.58 kg C ha−1 (UG99), respectively. These results indicate that winter-grazing of steppe significantly reduced atmospheric CH4 uptake by ca. 47%. The winter-grazing practice may have inhibited CH4 uptake by (a) increasing the likelihood of physiological water stress for CH4-consuming bacteria during dry periods, (b) decreasing gas diffusion into the soil and, (c) reducing the populations of CH4 oxidizing bacteria. These three mechanisms could have collectively or independently facilitated the observed inhibitory effects. Our results suggest that grazing exerts a considerable negative impact on CH4 uptake in semi-arid steppes at regional scales. Notwithstanding, further studies involving year-round, intensive measurements of CH4 uptake are needed.
Keywords: Methane uptake; Steppe; Grazing; Gas diffusion; Moisture;

Keywords: Air pollution modelling; Street canyons; Traffic emissions;

Comparative analysis of organic and elemental carbon concentrations in carbonaceous aerosols in three European cities by M. Viana; W. Maenhaut; H.M. ten Brink; X. Chi; E. Weijers; X. Querol; A. Alastuey; P. Mikuška; Z. Večeřa (5972-5983).
Sampling and analysis of carbonaceous compounds in particulate matter presents a number of difficulties related to artefacts during sampling and to the distinction between organic (OC) and elemental carbon (EC) during analysis. Our study reports on a comparative analysis of OC, EC and WSOC (water-soluble organic carbon) concentrations, as well as sampling artefacts, for PM2.5 aerosol in three European cities (Amsterdam, Barcelona and Ghent) representing Southern and Western European urban environments. Comparability of results was ensured by using a single system for sample analysis from the different sites. OC and EC concentrations were higher in the vicinity of roads, thus having higher levels in Amsterdam (3.9–6.7 and 1.7–1.9 μg m−3, respectively) and Barcelona (3.6–6.9 and 1.5–2.6 μg m−3) than in Ghent (2.7–5.4 and 0.8–1.2 μg m−3). A relatively larger influence of secondary organic aerosols (SOA), as deduced from a larger OC/EC ratio, was observed in Ghent. In absolute sense, WSOC concentrations were similar at the three sites (1.0–2.3 μg m−3). Positive artefacts were higher in Southern (11–16% of the OC concentration in Barcelona) than in Western Europe (5–12% in Amsterdam, 5–7% in Ghent). During special episodes, the contribution of carbonaceous aerosols from non-local sources accounted for 67–69% of the OC concentration in Western Europe, and for 44% in Southern Europe.
Keywords: Sampling artefacts; Denuder; Urban aerosols; Secondary organic carbon;

Mercury concentrations and air/soil fluxes in Wuchuan mercury mining district, Guizhou province, China by Shaofeng Wang; Xinbin Feng; Guangle Qiu; Lihai Shang; Ping Li; Zhongqing Wei (5984-5993).
Wuchuan Hg mine, located in the Circum-Pacific Global Mercuriferous Belt, is one of the important Hg production centers in Guizhou province, China. Soil Hg concentrations in this area are elevated by 2–4 orders of magnitude compared to the national background value in soil which is 0.038 μg g−1. In situ air Hg concentrations and air/soil Hg fluxes were measured at five sampling sites in Wuchuan Hg mining area (WMMA) from 19 to 26 December 2003 and from 18 to 25 December 2004. The results showed that air Hg concentrations were 2–4 orders of magnitude higher than those observed in background areas in Europe and North America due to a large amount of Hg emission from artisanal Hg smelting activities. The average in situ Hg fluxes at site Laohugou, Jiaoyan, Luoxi, Sankeng and Huanglong were −5493, 124, −924, −13 and 140 ng m−2  h−1, respectively. Diurnal pattern of Hg flux was not found and a number of negative Hg fluxes were observed in our sampling campaigns. The correlations between Hg fluxes and meteorological parameters such as solar irradiation, air temperature, soil temperature and relative humidity and air Hg concentrations were investigated. The commonly observed significant correlations between Hg fluxes and meteorological parameters observed in many previous studies were not obtained in WMMA. However, significantly negative correlations between Hg flux and air Hg concentration were observed at all sites. Our study demonstrated that highly elevated air Hg concentrations could suppress Hg emission processes even from Hg-enriched soil. At specific conditions in WMMA, air Hg concentrations play a dominant role in controlling Hg emission from soil.
Keywords: Air/soil Hg exchange; Air Hg concentration; Source; Sink; Guizhou province;

Local and regional anthropogenic influence on PM2.5 elements in Hong Kong by G.S.W. Hagler; M.H. Bergin; L.G. Salmon; J.Z. Yu; E.C.H. Wan; M. Zheng; L.M. Zeng; C.S. Kiang; Y.H. Zhang; J.J. Schauer (5994-6004).
Hong Kong's persistent unhealthy level of fine particulate matter is a current public health challenge, complicated by the city being located in the rapidly industrializing Pearl River Delta Region of China. While the sources of the region's fine particulate matter (PM2.5) are still not well understood, this study provides new source information through ground measurements and statistical analysis of 24 elements associated with particulate matter collected on filters. Field measurements took place over 4 months (October 2002, December 2002, March 2003, and June 2003) at seven sites throughout the Pearl River Delta, with three sites located in Hong Kong and four sites in the neighboring province, Guangdong. The 4-month average element concentrations show significant variation throughout the region, with higher levels of nearly every species seen among the northern Guangdong sites in comparison to Hong Kong. The high correlation (Pearson r>0.8) and similar magnitudes of 11 species (Al, Si, S, K, Ca, Mn, Fe, Zn, Br, Rb, and Pb) at three contrasting sites in Hong Kong indicate that sources external to Hong Kong dominate the regional levels of these elements. Further correlative analysis compared Hong Kong against potential source areas in Guangdong Province (Shenzhen, Zhongshan, and Guangzhou). Moderate correlation of sulfur for all pairings of Hong Kong sites with three Guangdong sites in developed areas (average Pearson r of 0.52–0.94) supports the importance of long-distance transport impacting the region as a whole, although local sources also clearly impact observed concentrations. Varying correlative characteristics for zinc when Hong Kong sites are paired with Shenzhen (average r=0.86), Guangzhou (average r=−0.65) and Zhongshan (average r=0.45) points to a source area located south of Guangzhou and locally impacting Zhongshan. The concentration distribution and correlative characteristics of bromide point to sources located within the Pearl River Delta, but the specific location is yet inconclusive. Uniquely poor correlation of eight species (Al, Si, K, Ca, Mn, Fe, Rb, and Pb) for the pairing of Hong Kong sites with Guangzhou, in addition to the relatively higher concentrations measured at Guangzhou, indicates a significant regional impact due to land development and industrial activities in the Guangzhou vicinity.
Keywords: Pearl River Delta; Elements; PM2.5; Source areas; Correlation;

Primary products of the reactions of gas-phase ozone with anthracene and phenanthrene adsorbed on silica model particles have been investigated. Silica was selected as proxy for mineral atmospheric particles. The particles, coated with anthracene or phenanthrene and placed on a filter, were exposed in a reaction cell to a gaseous ozone flow. Ozone concentration was constant ((6.0±0.6)×1013  molecule cm−3) during the experiments. Anthracene, phenanthrene and their ozonation products were then extracted by focused microwave-assisted extraction or fluid pressurized extraction and analyzed by gas chromatography coupled to mass spectrometry. Anthraquinone and anthrone on the one hand, and 1,1′-biphenyl-2,2′-dicarboxaldehyde on the other hand were identified as the products of anthracene and phenanthrene, respectively and quantified versus time of ozone exposure. This kinetical approach allowed to show that anthraquinone, anthrone and 1,1′-biphenyl-2,2′-dicarboxaldehyde are the primary products of the studied reactions, and to determine their formation yields (respectively, 0.42±0.04, 0.056±0.005 and 1.0±0.4).
Keywords: Polycyclic aromatic hydrocarbons (PAH); Ozonation products; GC/MS analysis; Heterogeneous reactivity;

Nonmethane hydrocarbons (NMHCs) are important precursors of ozone and other photo oxidants. We presented continuous hourly average concentrations of 45 C2–C10 NMHCs measured in urban area of Dallas, USA from 1996 to 2004. Most of the selected compounds are good variables with less noise. The top 10 species with high ozone-generating potential were identified according to their concentrations and reactivities. The ambient concentrations of abundant anthropogenic emission hydrocarbons measured in Dallas were about 2–4 times of the background values measured in the remote areas with adjacent latitude. The time series for anthropogenic emission hydrocarbons showed an obvious seasonal cycle with relatively high concentration in winter and low concentration in summer. The sinusoidal function with a linearly decreasing factor could well fit the time series of NMHCs. The phase of seasonal cycle for the aromatic hydrocarbons of toluene, m/p xylene and o-xylene that might come from both vehicle emission and solvent utilities evaporation was about 1 month earlier than that for alkanes and alkenes that mainly came from vehicle emission. Ambient NMHCs in Dallas decreased with a stable rate during 1996–2004. For most of compounds with high ozone-generating potential, the rate of ambient concentration decrease was higher or much higher than the rate of volatile organic compounds (VOCs) source emission reduction estimated by EPA's National Emission Inventory. On weekdays, the morning hydrocarbon concentration peak was coincident with morning traffic rush time in Dallas. Another concentration peak was delayed to afternoon traffic rush time. The characteristics of VOCs sources, photochemical removal processes and atmospheric dilution could be interpreted by the diurnal variations of benzene/ethylbenzene (B/E), toluene/ethylbenzene (T/E) and xylene/ethylbenzene (X/E). The ratio of VOC/NO x measured in Dallas was substantially smaller than that calculated for USA cities. Ozone formation in Dallas was VOC sensitive.
Keywords: Volatile organic compounds; Reactivity; Seasonal trend; Diurnal variation;

Ambient gaseous phase mercury concentrations (TGM) were measured at three locations in NY State including Potsdam, Stockton, and Sterling from May 2000 to March 2005. Using these data, three hybrid receptor models incorporating backward trajectories were used to identify source areas for TGM. The models used were potential source contribution function (PSCF), residence time weighted concentration (RTWC), and simplified quantitative transport bias analysis (SQTBA). Each model was applied using multi-site measurements to resolve the locations of important mercury sources for New York State.PSCF results showed that southeastern New York, Ohio, Indiana, Tennessee, Louisiana, and Virginia were important TGM source areas for these sites. RTWC identified Canadian sources including the metal production facilities in Ontario and Quebec, but US regional sources including the Ohio River Valley were also resolved. Sources in southeastern NY, Massachusetts, western Pennsylvania, Indiana, and northern Illinois were identified to be significant by SQTBA. The three modeling results were combined to locate the most important probable source locations, and those are Ohio, Indiana, Illinois, and Wisconsin. The Atlantic Ocean was suggested to be a possible source as well.
Keywords: TGM; New York; Trajectory; PSCF; RTWC; SQTBA; Ohio river valley; Atlantic Ocean;

Surface ozone in Yosemite National Park by Joel D. Burley; John D. Ray (6048-6062).
During the summers of 2003 and 2005, surface ozone concentrations were measured with portable ozone monitors at multiple locations in and around Yosemite National Park. The goal of these measurements was to obtain a comprehensive survey of ozone within Yosemite, which will help modelers predict and interpolate ozone concentrations in remote locations and complex terrain. The data from the portable monitors were combined with concurrent and historical data from two long-term monitoring stations located within the park (Turtleback Dome and Merced River) and previous investigations with passive samplers. The results indicate that most sites in Yosemite experience roughly similar ozone concentrations during well-mixed daytime periods, but dissimilar concentrations at night. Locations that are well exposed to the free troposphere during evening hours tend to experience higher (and more variable) nocturnal ozone concentrations, resulting in smaller diurnal variations and higher overall ozone exposures. Locations that are poorly exposed to the free troposphere during nocturnal periods tend to experience very low evening ozone, yielding larger diurnal variations and smaller overall exposures. Ozone concentrations are typically highest for the western and southern portions of the park and lower for the eastern and northern regions, with substantial spatial and temporal variability. Back-trajectory analyses suggest that air with high ozone concentrations at Yosemite often originates in the San Francisco Bay Area and progresses through the Central California Valley before entering the park.
Keywords: Ozone; Yosemite; Portable ozone monitor; HYSPLIT model;

Characterisation of bio-aerosols during dust storm period in N–NW India by Sudesh Yadav; M.S. Chauhan; Anupam Sharma (6063-6073).
Bio-investigations for pollen and spores were performed on dry free-fall dust and PM10 aerosol samples, collected from three different locations separated by a distance of 600 km, situated in dust storm hit region of N–NW India. Presence of pollen of trees namely Prosopis (Prosopis juliflora and Prosopis cinearia), Acacia, Syzygium, Pinus, Cedrus, Holoptelea and shrubs namely Ziziphus, Ricinus, Ephedra and members of Fabaceae, Oleaceae families was recorded but with varying proportions in the samples of different locations. Poaceae, Chenopodiaceae/Amaranthaceae, Caryophyllaceae, Brassicaceae and Cyperaceae (sedges) were some of the herb pollen identified in the samples. Among the fungal spores Nigrospora was seen in almost all samples. Nigrospora is a well known allergen and causes health problems. The concentration of trees and shrubs increases in the windward direction just as the climate changes from hot arid to semiarid. The higher frequency of grasses (Poaceae) or herbs could either be a result of the presence of these herbs in the sampling area and hence the higher production of pollen/spores or due to the resuspension from the exposed surface by the high-intensity winds. But we cannot ascertain the exact process at this stage. The overall similarity in the pollen and spore assemblage in our dust samples indicates a common connection or source(s) to the dust in this region. Presence of the pollen of the species of Himalayan origin in our entire samples strongly point towards a Himalayan connection, could be direct or indirect, to the bioaerosols and hence dust in N–NW India. In order to understand the transport path and processes involved therein, present study needs further extension with more number of samples and with reference to meteorological parameters.
Keywords: Palynology; Pollen; Spores; Dust/Aerosols; Thar Desert;

Hog concentrated animal feeding operations (CAFOs) in North Carolina release ammonia (NH3), hydrogen sulfide, VOCs, and particulate matter to the atmosphere. These operations are located mainly in the NC coastal plain and can create potential health hazards for nearby human populations. Limited work has been performed to measure NH3 at the community level to assess potential human exposure. In an effort to address this issue, a study was designed to measure NH3 levels near hog CAFOs and community locations (i.e. homes and schools) in Eastern NC.NH3 was collected using passive diffusion tubes in triplicate exposed primarily in weekly intervals. Sampling occurred from October 2003 to May 2004 (20 sites) and from July 2004 to October 2004 (23 sites) at varying distances from hog CAFOs in close proximity to homes and schools. Average weekly NH3 levels were measured as mass (μg NH3-N) and converted to concentration (ppb). Mean level of 13.8 ppb near homes and schools (<2 km) was 4–12 times greater than ambient background levels (1–3 ppb), reaching as high as 80 ppb. Exposed sites (<2 km from a hog CAFO) had a mean level of 12.8 ppb which was over 2 times higher than the mean level of 5.5 ppb at less exposed sites (>2 km from a hog CAFO).The study establishes that passive sampling can be effectively used to measure average atmospheric ammonia levels at community locations near hog CAFOs in Eastern NC. The collected data indicate the relative exposure for human populations who live near a hog CAFO. The closer a populace is to the hog CAFO, the more intense the exposure. These results require more validation in the field by comparison to a reference method.
Keywords: Atmospheric ammonia; Passive sampling; Industrial swine operations; Community level; Exposure;

In air quality monitoring studies, continuous sampling is capable of reflecting real time variation of gas levels, however, with a margin of uncertainty related to the response time of the sensor and to the speed of concentration fluctuation. In contrast, grab sampling allows the determination of average gas concentration over the whole sampling period eliminating thus the uncertainties associated with the continuous method. As studies of in-vehicle carbon monoxide (CO) exposure often show rapidly fluctuating CO levels and are increasingly using the continuous electrochemical sensing method, the present activity aims at validating the suitability of the latter method for this monitoring task. For this purpose, an electrochemical CO sensing monitor was used to continuously monitor CO level inside and outside of a vehicle moving in an urban area, and to analyze the content of concomitantly taken grab samples. Trip-average CO levels measured using the two testing methods were compared. For CO levels higher than the instrument detection limit (1 ppm), the observed percent difference between continuous and grab sampling results varied within a fairly acceptable range (0.6–15.4%). The regression of continuous sampling data against grab sampling data revealed an average error of 6.9%, indicating the suitability of the continuous electrochemical method for monitoring in-vehicle and exterior average CO concentration under typical urban traffic conditions.
Keywords: Carbon monoxide; Continuous and grab sampling; Electrochemical analysis;