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Atmospheric Environment (v.43, #6)

Editorial board (pp. i).

Receptor modeling of source apportionment of Hong Kong aerosols and the implication of urban and regional contribution by H. Guo; A.J. Ding; K.L. So; G. Ayoko; Y.S. Li; W.T. Hung (pp. 1159-1169).

Understanding the spatial–temporal variations of source apportionment of PM_2.5 is critical to the effective control of particulate pollution. In this study, two one-year studies of PM_2.5 composition were conducted at three contrasting sites in Hong Kong from November 2000 to October 2001, and from November 2004 to October 2005, respectively. A receptor model, principal component analysis (PCA) with absolute principal component scores (APCS) technique, was applied to the PM_2.5 data for the identification and quantification of pollution sources at the rural, urban and roadside sites. The receptor modeling results identified that the major sources of PM_2.5 in Hong Kong were vehicular emissions/road erosion, secondary sulfate, residual oil combustion, soil suspension and sea salt regardless of sampling sites and sampling periods. The secondary sulfate aerosols made the most significant contribution to the PM_2.5 composition at the rural (HT) (44±3%, mean±1 σ standard error) and urban (TW) (28±2%) sites, followed by vehicular emission (20±3% for HT and 23±4% for TW) and residual oil combustion (17±2% for HT and 19±1% for TW). However, at the roadside site (MK), vehicular emissions especially diesel vehicle emissions were the major source of PM_2.5 composition (33±1% for diesel vehicle plus 18±2% for other vehicles), followed by secondary sulfate aerosols (24±1%). We found that the contribution of residual oil combustion at both urban and rural sites was much higher than that at the roadside site (2±0.4%), perhaps due to the marine vessel activities of the container terminal near the urban site and close distance of pathway for the marine vessels to the rural site. The large contribution of secondary sulfate aerosols at all the three sites reflected the wide influence of regional pollution. With regard to the temporal trend, the contributions of vehicular emission and secondary sulfate to PM_2.5 showed higher autumn and winter values and lower summer levels at all the sites, particularly for the background site, suggesting that the seasonal variation of source apportionment in Hong Kong was mainly affected by the synoptic meteorological conditions and the long-range transport. Analysis of annual patterns indicated that the contribution of vehicular emission at the roadside was significantly reduced from 2000/01 to 2004/05 ( p<0.05, two-tail), especially the diesel vehicular emission ( p<0.001, two-tail). This is likely attributed to the implementation of the vehicular emission control programs with the tightening of diesel fuel contents and vehicular emission standards over these years by the Hong Kong government. In contrast, the contribution of secondary sulfate was remarkably increased from 2001 to 2005 ( p<0.001, two-tail), indicating a significant growth in regional sulfate pollution over the years.

Keywords: Source apportionment; PCA/APCS; PM; _2.5; Receptor modeling; PRD; Hong Kong; Long-range transport

Laboratory and field investigations of particulate and carbon monoxide emissions from traditional and improved cookstoves by Christoph A. Roden; Tami C. Bond; Stuart Conway; Anibal Benjamin Osorto Pinel; Nordica MacCarty; Dean Still (pp. 1170-1181).

We implemented a program in which emission characterization is enabled through collaborations between academic, US and international non-governmental entities that focus on evaluation, dissemination, and in-use testing, of improved cookstoves. This effort resulted in a study of field and laboratory emissions from traditional and improved biofuel cookstoves. We found that field measured particulate emissions of actual cooking average three times those measured during simulated cooking in the laboratory. Emission factors are highly dependent on the care and skill of the operator and the resulting combustion; these do not appear to be accurately reproduced in laboratory settings. The single scattering albedo (SSA) of the emissions was very low in both lab and field measurements, averaging about 0.3 for lab tests and around 0.5 for field tests, indicating that the primary particles are climate warming. Over the course of three summers in Honduras, we measured field emissions from traditional cookstoves, relatively new improved cookstoves, and “broken-in” improved cookstoves. We found that well-designed improved cookstoves can significantly reduce PM and CO emission factors below traditional cookstoves. For improved stoves, the presence of a chimney generally resulted in lower emission factors but left the SSA unaffected. Traditional cookstoves had an average PM emission factor of 8.2gkg⁻¹ – significantly larger than previous studies. Particulate emission factors for improved cookstoves without and with chimneys averaged about 6.6gkg⁻¹ and 4.5gkg⁻¹, respectively. The elemental carbon (EC) fraction of PM varied significantly between individual tests, but averaged about 25% for each of the categories.

Keywords: Biofuel emissions; Cookstoves; Emission factors; Particulate matter; Elemental carbon; Organic carbon

Transforming meadows into free surface water wetlands: Impact of increased nitrate and carbon loading on greenhouse gas production by Johanna Stadmark; Anne-Gret Seifert; Lars Leonardson (pp. 1182-1188).

In a laboratory study we investigated 1) the potential production of nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) and 2) the effect of nitrate (NO₃⁻) and anaerobic N₂O development on CH₄ production in sediment from a recently recreated free surface water wetland (FSWW) and in soil from an adjacent meadow. We designed an experiment where production of greenhouse gases was registered at the time of maximum net development of N₂O. We made additions of biodegradable carbon (glucose) and/or NO₃⁻ to sediment and soil slurries and incubated them at four temperatures (4, 13, 20, 28 °C). Gas production from both substrates was positively correlated with temperature. We also found that the sediment produced more N₂O than the soil. N₂O production in sediment was NO₃⁻ limited, whereas in soil carbon availability was lower and only combined additions of NO₃⁻ and glucose supported increased N₂O development. CH₄ production was generally low and did not differ between soil and sediment. Nor did glucose addition increase CH₄ rates. The results suggest that neither soil nor sediment environment did support development of methanogenic populations. There were no clear effects of NO₃⁻ on CH₄ production. However, the highest records of CH₄ were found in incubations with low N₂O production, which indicates that N₂O might be toxic to methanogens. In summary, our study showed that transforming meadows into FSWWs implies a risk of increased N₂O emissions. This does not seem to be valid for CH₄. However, since N₂O is almost always produced wherever NO₃⁻ is denitrified, increased N₂O production in wetlands leads to reduced rates in downstream environments. Hence, we conclude that when balancing NO₃⁻ retention and global warming aspects, we find no reason to discourage future creation or restoration of wetlands.

Keywords: Nitrous oxide; Methane; Wetland; Nitrate; Glucose

Impact of large scale circulation on European summer surface ozone and consequences for modelling forecast by S. Szopa; G. Foret; L. Menut; A. Cozic (pp. 1189-1195).

In this study, we investigate the benefit for European ozone simulation of using day-to-day varying chemical boundary conditions produced by a global chemical weather forecast platform instead of climatological monthly means at the frontiers of a regional model. We performed two simulations over Europe using the regional (0.5×0.5°) CHIMERE CTM forced by global scale simulations based on the LMDz-INCA CTM. For summer 2005, ozone differences exceeding 20ppb can be punctually found between these two simulations in the borders of the domain. The mean of the differences ranges between 0 and 3ppb beyond 15° of the frontiers of the regional model.Correlations with ground-based ozone measurements at more than 400 stations are slightly increased by the use of daily boundary conditions. The simulation of the temporal variability is significantly enhanced in particular for the daily means and daily maxima. As expected, the gain is higher at the borders of the regional domain.The change of percentile distribution shows that the net impact of high temporal resolution boundary conditions is not of major concern for surface ozone peaks which are mainly due to local photochemistry. The use of daily boundary conditions is however necessary to correctly simulate concentrations in the 20–35ppb range which are of crucial interest for human and vegetation exposure effects.

Keywords: Global and regional modelling; Air quality forecast; Ozone

Source analysis of high particulate matter days in Hong Kong by Xiao-Feng Huang; Jian Zhen Yu; Zibing Yuan; Alexis K.H. Lau; Peter K.K. Louie (pp. 1196-1203).

This study identifies major contributing sources of high particulate matter (PM) days in Hong Kong and conducive meteorological conditions leading to high PM. The PM₁₀ chemical composition of 3393 ambient samples collected at ten monitoring stations in Hong Kong during 1998–2005 were used as input for positive matrix factorization (PMF) modeling to identify and quantify the aerosol sources in Hong Kong. Days with PM₁₀ levels exceeding 56μgm⁻³, the average plus one standard deviation of the mass concentration of all samples, are defined as high PM days. A total of 401 samples fell in the high PM category during the study period. Biomass burning, secondary sulfate and secondary nitrate were found to be the major contributors leading to high PM, responsible for 68–73% of PM₁₀ mass on high PM days. The contributions by these sources on high PM days were 140–180% higher than their respective average concentration contributions. These sources were identified to be regional sources on the grounds of little spatial variation in their concentrations among the monitoring stations and a temporal pattern of higher in the winter and lower in the summer. Sampling days of high PM in 2004 and 2005 were individually examined for weather charts and regional surface wind maps. Weak high pressures over mainland China were the most important synoptic event leading to high PM days in the fall and winter, while typhoon episodes were responsible for most summer cases. Approximately 80% of the high PM days were in the fall and winter months (September–February). Almost all the high PM days were associated with northwesterly, northerly or northeasterly regional transport. Anthropogenic primary sources (coal combustion, vehicular exhaust, and residue oil combustion) showed the highest contributions associated with northwesterly wind, indicating the strong influence of the more urbanized areas to the northwest of Hong Kong in the Pearl River Delta region.

Keywords: Chinese aerosols; Sulfate; Source apportionment; Episodic analysis; Regional transport; Secondary aerosols

The impact of spatial correlation and incommensurability on model evaluation by Jenise L. Swall; Kristen M. Foley (pp. 1204-1217).

Standard evaluations of air quality models rely heavily on a direct comparison of monitoring data matched with the model output for the grid cell containing the monitor's location. While such techniques may be adequate for some applications, conclusions are limited by such factors as the sparseness of the available observations (limiting the number of grid cells at which the model can be evaluated) and the incommensurability between volume-averages and pointwise observations. We examine several sets of simulations to illustrate the effect of incommensurability in a variety of cases distinguished by the type and extent of spatial correlation present. Block kriging, a statistical method which can be used to address the issue, is then demonstrated using the simulations. Lastly, we apply this method to actual data and discuss the practical importance of understanding the impact of spatial correlation structure and incommensurability.

Keywords: Block kriging; Air quality modeling; Spatial interpolation; Statistical simulation

Regional contributions to airborne particulate matter in central California during a severe pollution episode by Qi Ying; Michael Kleeman (pp. 1218-1228).

The externally-mixed source-oriented UCD/CIT air quality model was applied to determine the significance of inter-regional transport for primary and secondary particulate matter (PM) in California's Central Valley during a severe wintertime PM pollution episode from December 15, 2000 to January 7, 2001. The gases and primary PM emitted from eight different geographical sub-regions were tracked separately in a model simulation that included transport, physical and chemical transformation and deposition processes. The model results directly predict the contribution that each sub-region makes to PM concentrations throughout the entire model domain. The boundary layer was relatively stagnant during the simulated 3-week air quality episode, and no consistent transport pattern for primary PM was predicted. Several significant inter-regional transport events were identified that each lasted a few days. Each of these inter-regional events was characterized by transport of gas-phase precursors of nitrate that combined with local emissions of ammonia to produce particulate nitrate. Nitrate already in the particle phase was not transported efficiently due to higher dry deposition rates for particles relative to gas-phase nitrogen oxides. The distinctive pattern of transport for nitrate precursors reflects the relatively long timescales required to convert NO_x emissions to nitrate during winter conditions characterized by low temperatures, weak photolysis rates, and low oxidant concentrations. The equilibrium partitioning of nitrate and ammonia to the particle phase is relatively fast once the nitrate has been produced. The most-likely transport distance for nitrate during the current episode varied from 130–140km for the northern portion of the Central Valley to 50–60km in the southern portion of the Central Valley. Sub-regions further south in the Valley have smaller transport distances because of slower wind speeds and the greater abundance of ammonia in these areas, leading to faster conversion of gas-phase reactive nitrogen into particulate nitrate, which has a higher dry deposition rate than the gas-phase species. The most-likely transport distance for primary organic compounds (OC) was found to be less than that for nitrate, varying from 50 to 60km for the northern portion of the Valley to 20–30km for southern portion of the Valley. Overall, 68% of the particulate nitrate formed in the most polluted sub-regions of the Central Valley originates from emissions in those same sub-regions. Local emissions controls should therefore provide an effective strategy to reduce airborne particulate matter concentrations to acceptable levels.

Keywords: Source-oriented model; Inter-regional transport; Ammonium nitrate; Transport distance; CRPAQS

Ultrafine particles near a major roadway in Raleigh, North Carolina: Downwind attenuation and correlation with traffic-related pollutants by G.S.W. Hagler; R.W. Baldauf; E.D. Thoma; T.R. Long; R.F. Snow; J.S. Kinsey; L. Oudejans; B.K. Gullett (pp. 1229-1234).

Ultrafine particles (UFPs, diameter<100nm) and co-emitted pollutants from traffic are a potential health threat to nearby populations. During summertime in Raleigh, North Carolina, UFPs were simultaneously measured upwind and downwind of a major roadway using a spatial matrix of five portable industrial hygiene samplers (measuring total counts of 20–1000nm particles). While the upper sampling range of the portable samplers extends past the defined “ultrafine” upper limit (100nm), the 20–1000nm number counts had high correlation (Pearson R=0.7–0.9) with UFPs (10–70nm) measured by a co-located research-grade analyzer and thus appear to be driven by the ultrafine range. Highest UFP concentrations were observed during weekday morning work commutes, with levels at 20m downwind from the road nearly fivefold higher than at an upwind station. A strong downwind spatial gradient was observed, linearly approximated over the first 100m as an 8% drop in UFP counts per 10m distance. This result agreed well with UFP spatial gradients estimated from past studies (ranging 5–12% drop per 10m). Linear regression of other vehicle-related air pollutants measured in near real-time (10-min averages) against UFPs yielded moderate to high correlation with benzene ( R²=0.76), toluene ( R²=0.49), carbon monoxide ( R²=0.74), nitric oxide ( R²=0.80), and black carbon ( R²=0.65). Overall, these results support the notion that near-road levels of UFPs are heavily influenced by traffic emissions and correlate with other vehicle-produced pollutants, including certain air toxics.

Keywords: Ultrafine particles; Air toxics; Carbon monoxide; Traffic emissions; Gradient

Aerosol number size distributions within the exhaust plume of a diesel and a gasoline passenger car under on-road conditions and determination of emission factors by B. Wehner; U. Uhrner; S. von Löwis; M. Zallinger; A. Wiedensohler (pp. 1235-1245).

A new setup has been developed and built to measure number size distributions of exhaust particles and thermodynamic parameters under real traffic conditions. Measurements have been performed using a diesel and a gasoline passenger car driving with different speeds and engine conditions. Significant number of nucleation mode particles was found only during high load conditions, i.e. high car and engine speeds behind the diesel car. The number concentration of soot mode particles varied within a factor of two for different engine conditions while the concentration of nucleation mode particles varied up to two orders of magnitude. The results show that roadside measurements are still quite different from those behind the tailpipe. Beside dilution transformation processes within the first meter behind the tailpipe also play an important role, such as nucleation and growth. Emission factors were calculated and compared with those obtained by other studies. Emission factors for particles larger than 25nm (primary emissions) varied within 1.1×10¹⁴km⁻¹ and 2.7×10¹⁴km⁻¹ for the diesel car and between 0.6×10¹²km⁻¹ and 3.5×10¹²km⁻¹ for the gasoline car. The advantage of these measurements is the exhaust dilution under atmospheric conditions and the size-resolved measurement technique to divide into primary emitted and secondary formed particles.

Keywords: Traffic emission; Number size distribution; Emission factor

Spatial surrogates for the disaggregation of CORINAIR emission inventories by Joachim Maes; Jo Vliegen; Karen Van de Vel; Stijn Janssen; Felix Deutsch; Koen De Ridder; Clemens Mensink (pp. 1246-1254).

CORINAIR atmospheric emission inventories are frequently used input data for air quality models with a domain situated in Europe. In CORINAIR emission inventories, sources are broken down over 11 major source categories. This paper presents spatial surrogates for the disaggregation of CORINAIR atmospheric emission inventories for input of air pollutants and particulate matter to grid or polygon based air quality model domains inside Europe. The basis for the disaggregation model was the CLC2000 land cover data to which statistical weights were added. Weights were population census data for residential emissions, employment statistics for agricultural and industrial area emissions, livestock statistics for ammonia emissions and annual aircraft movements for emissions realized by air transport. Additional road and off-road network information was used to disaggregate emissions realized by traffic. A comparison of top down produced emission estimates with spatially resolved national emission data for The Netherlands and the United Kingdom gave confidence in the present spatial surrogates as a tool for the top down production of atmospheric emission maps. Explained variance at a spatial resolution of 5km was >70% for CO, NMVOC and NO_x, >60% for PM10 and almost 50% for SO₂.

Keywords: Atmospheric emissions; CORINE land cover; EMEP; SNAP; Spatial disaggregation

Long-range transport episodes of fine particles in southern Finland during 1999–2007 by Jarkko V. Niemi; Sanna Saarikoski; Minna Aurela; Heikki Tervahattu; Risto Hillamo; Douglas L. Westphal; Päivi Aarnio; Tarja Koskentalo; Ulla Makkonen; Hanna Vehkamäki; Markku Kulmala (pp. 1255-1264).

The frequency, strength and sources of long-range transport (LRT) episodes of fine particles (PM_2.5) were studied in southern Finland using air quality monitoring results, backward air mass trajectories, remote sensing of fire hot spots, transport and dispersion modelling of smoke and chemical analysis of particle samples (black carbon, monosaccharide anhydrides, oxalate, succinate, malonate, SO₄²⁻, NO₃⁻, K⁺ and NH₄⁺). At an urban background site in Helsinki, the daily WHO guideline value (24-h PM_2.5 mean 25 μg m⁻³) was exceeded during 1–7 LRT episodes per year in 1999–2007. The 24-h mean maximum concentrations varied between 25 and 49 μg m⁻³ during the episodes, which was 3–6 times higher than the local mean concentration (8.7 μg m⁻³) in 1999–2007. The highest particle concentrations (max. 1-h mean 163 μg m⁻³) and the longest episodes (max. 9 days) were mainly caused by the emissions from open biomass burning, especially during springs and late-summers in 2002 and 2006. During the period 2001–2007, the satellite remote sensing of active fire hot spots and transport and dispersion modelling of smoke indicated that approximately half of the episodes were caused partly by the emissions from wildfires and/or agricultural waste burning in fields in Eastern Europe, especially in Russia, Belarus and Ukraine. Other episodes were mainly caused by the LRT of ordinary anthropogenic pollutants, e.g. from energy production, traffic, industry and wood combustion. During those ‘other episodes’, air masses also arrived from Eastern Europe, including Poland. The highest concentrations of biomass-burning tracers, such as monosaccharide anhydrides (levoglucosan + mannosan + galactosan) and K⁺, were observed during open biomass-burning episodes, but quite high values were also measured during some winter episodes due to wood combustion emissions. Our results indicate that open biomass burning in Eastern Europe causes high fine particle concentration peaks in large areas of Europe almost every year.

Keywords: Long-range transport; Fine particles; Open biomass burning; Chemical tracers; Satellite remote sensing

Zn isotope study of atmospheric emissions and dry depositions within a 5 km radius of a Pb–Zn refinery by Nadine Mattielli; Jérôme C.J. Petit; Karine Deboudt; Pascal Flament; Esperanza Perdrix; Aurélien Taillez; Juliette Rimetz-Planchon; Dominique Weis (pp. 1265-1272).

The present paper examines the use of zinc isotopes as tracers of atmospheric sources and focuses on the potential fractionation of Zn isotopes through anthropogenic processes. In order to do so, Zn isotopic ratios are measured in enriched ores and airborne particles associated with pyrometallurgical activities of one of the major Pb–Zn refineries in France. Supporting the isotopic investigation, this paper also compares morphological and chemical characteristics of Zn particles collected on dry deposition plates (“environmental samples”) placed within a 5km radius of the smelter, with those of Zn particles collected inside the plant (“process samples”), i.e. dust collected from the main exhaust system of the plant. To ensure a constant isotopic “supply”, the refinery processed a specific set of ores during the sampling campaigns, as agreed with the executive staff of the plant. Enriched ores and dust produced by the successive Zn extraction steps show strong isotope fractionation (from −0.66 to +0.22‰) mainly related to evaporation processes within the blast furnaces. Dust from the main chimney displays a δ⁶⁶Zn value of −0.67‰. Application of the Rayleigh equation to evaluate the fractionation factor associated with the Zn vapor produced after a free evaporation gives a range of α_ore/vapor from 1.0004 to 1.0008. The dry deposits, collected on plates downwind of the refinery, display δ⁶⁶Zn variations of up to +0.7‰. However, it is to be noted that between 190 and 1250m from the main chimney of the refinery, the dry deposits show a high level of large (>10μm) Zn, S, Fe and O bearing aggregates characterized by positive δ⁶⁶Zn values (+0.02 to +0.19‰). These airborne particles probably derive from the re-suspension of slag heaps and local emissions from the working-units. In contrast, from 1720 to 4560m, the dry deposits are comprised of small (PM10) particles, including spherical Zn-bearing aggregates, showing negative δ⁶⁶Zn values (−0.52 to −0.02‰). Our results suggest that the source of the distal dry fallouts is the main chimney plume, whose light Zn isotopic signature they preserve. Based on Zn isotopic analysis in combination with morphological and chemical characteristics of airborne particles, the present study suggests the traceability of smelter dusts by Zn isotopes.

Keywords: Zn isotopes; Lead–zinc refinery/smelter; Aerosol; PM10; MC-ICP-MS

Hydrocarbon emissions speciation in diesel and biodiesel exhausts by Francisco Payri; Vicente R. Bermúdez; Bernardo Tormos; Waldemar G. Linares (pp. 1273-1279).

Diesel engine emissions are composed of a long list of organic compounds, ranging from C₂ to C₁₂₊, and coming from the hydrocarbons partially oxidized in combustion or produced by pyrolisis. Many of these are considered as ozone precursors in the atmosphere, since they can interact with nitrogen oxides to produce ozone under atmospheric conditions in the presence of sunlight. In addition to problematic ozone production, Brookes, P., and Duncan, M. [1971. Carcinogenic hydrocarbons and human cells in culture. Nature.] and Heywood, J. [1988. Internal Combustion Engine Fundamentals.Mc Graw-Hill, ISBN 0-07-1000499-8.] determined that the polycyclic aromatic hydrocarbons present in exhaust gases are dangerous to human health, being highly carcinogenic.The aim of this study was to identify by means of gas chromatography the amount of each hydrocarbon species present in the exhaust gases of diesel engines operating with different biodiesel blends. The levels of reactive and non-reactive hydrocarbons present in diesel engine exhaust gases powered by different biodiesel fuel blends were also analyzed.Detailed speciation revealed a drastic change in the nature and quantity of semi-volatile compounds when biodiesel fuels are employed, the most affected being the aromatic compounds. Both aromatic and oxygenated aromatic compounds were found in biodiesel exhaust. Finally, the conservation of species for off-side analysis and the possible influence of engine operating conditions on the chemical characterization of the semi-volatile compound phase are discussed.The use of oxygenated fuel blends shows a reduction in the Engine-Out emissions of total hydrocarbons. But the potential of the hydrocarbon emissions is more dependent on the compositions of these hydrocarbons in the Engine-Out, to the quantity; a large percent of hydrocarbons existing in the exhaust, when biodiesel blends are used, are partially burned hydrocarbons, and are interesting as they have the maximum reactivity, but with the use of pure biodiesel and diesel, the most hydrocarbons are from unburned fuel and they have a less reactivity. The best composition in the fuel, for the control of the hydrocarbon emissions reactivity, needs to be a fuel with high-saturated fatty acid content.

Keywords: Hydrocarbon speciation; Biodiesel; Diesel; Gas chromatography; Semi-volatile compounds

Recent trends of persistent organic pollutants in air in central Europe - Air monitoring in combination with air mass trajectory statistics as a tool to study the effectivity of regional chemical policy by A. Dvorská; G. Lammel; I. Holoubek (pp. 1280-1287).

We use air mass back trajectory analysis of persistent organic pollutant (POP) levels monitored at a regional background site, Košetice, Czech Republic, as a tool to study the effectiveness of emission reduction measures taken in the last decade in the region. The representativity of the chosen trajectory starting height for air sampling near ground was ensured by excluding trajectories starting at time of inversions lower than their starting height. As the relevant pollutant sources are exclusively located in the atmospheric boundary layer, trajectory segments above this layer were also excluded from the analysis. We used a linear time weight to account for the influence of dispersion and deposition on trace components abundances and to quantify the ground source loading, a continuous measure for the influence of surface emissions. Hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs), DDT, and two time periods, the years 1997–1999 and 2004–2006, were studied. The pollutant levels transported to Košetice decreased for all substances except HCB. Except for lindane seasonal emissions were insignificant. Increasing emissions of HCB were at least partly linked to the 2002 floods in the Danube basin. Major emissions of 1997–1999 which decreased significantly were in France (lindane), western Poland, Hungary and northern ex-Yugoslavia (technical HCH), and the Czech Republic (DDT). Emissions remaining in 2004–2006 include HCB and DDT in the northern Czech Republic, HCB and PCBs in Germany. Besides changes in emission strength meteorological factors influence the level of transported pollutant concentrations. The prevailing air flow pattern limits the geographic coverage of this analysis to central Europe and parts of western Europe. However, no POP monitoring stations exist in areas suitable for a possible extension of the study area.

Keywords: Persistent organic pollutants; Air mass trajectories statistics; Quantitative evaluation; Chemical policy; Emissions

Identification of sources affecting fog formation using receptor modeling approaches and inventory estimates of sectoral emissions by Bhavin Mehta; Chandra Venkataraman; Mani Bhushan; Sachchida Nand Tripathi (pp. 1288-1295).

Positive matrix factorization (PMF) was used to identify factors affecting fog formation in Kanpur during the ISRO-GBP land campaign-II (LC-II) in December 2004. PMF predicted factors were validated by contrasting the emission strength of sources in the foggy and clear periods, using a combination of potential source contribution function (PSCF) analysis and quantitative emission inventory information. A time series aerosol chemical data set of 29 days and 12 species was decomposed to identify 4-factors: Secondary species, Biomass burning, Dust and Sea salt. PMF predicted particle mass with a satisfactory goodness-of-fit (slope of 0.83±0.17 and R² of 0.8), and strong species within 11–12% relative standard deviation. Mean contributions of anthropogenic factors were significantly higher during the foggy period for secondary species (2.9±0.3) and biomass burning (1.2±0.09) compared to the clear period. Local sources contributing to aerosols that mediated fog events at Kanpur, based on emissions in a 200km×200km area around Kanpur city were thermal power plants and transportation (SO₂) and biofuel combustion (BC and OM). Regional scale sources influencing emissions during the foggy period, in probable source regions identified by PSCF included thermal power plants, transportation, brick kilns and biofuel combustion. While biofuel combustion and transportation are distributed area sources, individual point sources include coal-fired thermal power plants located in Aligarh, Delhi, Ghaziabad, Jhansi, Kanpur, Rae Bareli and Rupnagar and brick kilns located in Allahabad, Agra, Farrukhabad, Ghaziabad, Kanpur, Ludhiana, Lucknow and Rae Bareli. Additionally, in the foggy period, large areas of probable source regions lay outside India, implying the significance of aerosol incursion from outside India.

Keywords: Positive matrix factorization (PMF); Potential source contribution function (PSCF); Kanpur (80°22′E, 26°26′N); Thermal power plants; Brick kilns; Biofuel combustion

State of mixture of atmospheric submicrometer black carbon particles and its effect on particulate light absorption by Hiroaki Naoe; Shuichi Hasegawa; Jost Heintzenberg; Kikuo Okada; Akihiro Uchiyama; Yuji Zaizen; Eriko Kobayashi; Akihiro Yamazaki (pp. 1296-1301).

The state of mixture of light-absorbing carbonaceous particles was investigated in relation to light absorption properties using electron microscopic examinations, black carbon (BC) analyses of quartz filter by thermal/optical reflectance (TOR) method, measurements with two continuous light-absorbing photometers at a suburban site of Tsukuba, about 60 km northeast of Tokyo. The volume fraction of water-soluble material ( ɛ) in individual particles is important for assessing particulate light-absorbing and/or scattering of atmospheric aerosols. The values of ɛ in BC particles were evaluated by electron micrographs before and after dialysis (extraction) of water-soluble material. The mass absorption coefficient (MAC in units of m²g⁻¹) tended to increase with increasing the average ɛ in BC particles with the radius range of 0.05–0.5 μm. Thus, our results indicate that coatings of water-soluble material around BC particles can enhance the absorption of solar radiation. Moreover, the single scattering albedo (SSA) will increase because a large amount of coating material will scatter more light.

Keywords: Mass absorption coefficient; Black carbon; Electron microscope; Light absorption

Large-scale aircraft observations of ultra-fine and fine particle concentrations in the remote Siberian troposphere: New particle formation studies by Jean-Daniel Paris; Mikhail Yu. Arshinov; Philippe Ciais; Boris D. Belan; Philippe Nédélec (pp. 1302-1309).

Ultra-fine particle number concentrations were measured over Siberia during two large-scale airborne measurement campaigns in April and September 2006. During both campaigns, an aircraft flew between Novosibirsk and Yakutsk, collecting every 200km vertical profiles up to 7km. This dataset was completed by 5years of monthly profiles above Novosibirsk. Particle number concentration was measured in the size ranges 3–70 and 70–200nm, along with other tracers. Free troposphere (FT) particle concentrations (N_3–200) varied between 60 and 460cm⁻³, inferior to boundary layer concentrations (100–7000cm⁻³). In April, high concentrations of ∼500cm⁻³ were observed in a polluted air mass recently uplifted at 5–6km altitude over eastern Siberia, with no sign of significant new particle formation. In September, particle concentrations decreased with altitude, but with a steeper gradient in N_70–200 compared to N_3–70, the latter accounting for 90% of the total particle concentration in the free troposphere at 6–7km altitude. Because ultra-fine particles presumably have short lifetimes, these observed particles could have been formed in situ in the clean Siberian atmosphere. Two cases of possible nucleation with high concentration and N_3–70/N_70–200 ratios are reported for the September campaign, in the upper troposphere and in cloud outflow in the mid-troposphere. In the seasonal analysis, a FT N_3–70 maximum is found in July–August between 6 and 7km altitude, with N_3–70 accounting for ∼90% of N_3–200 supporting the hypothesis of in situ formation in the FT. A secondary FT maximum of N_3–70 was identified later in autumn. In the boundary layer, seasonally maximum N_3–70 concentrations were found over Novosibirsk in May and September, but not in summer, possibly due to scavenging by precipitations and a large condensational sink from biomass burning aerosols. Our dataset has a limited size resolution and no speciation capability; more investigation is thus required to understand the conditions leading to in situ nucleation processes in the Siberian air shed.

Keywords: New particle formation; Aerosol; Nucleation; Remote free troposphere; Concentration; Airborne campaign; Siberia; Russia; Continental

Surface ozone background in the United States: Canadian and Mexican pollution influences by Huiqun Wang; Daniel J. Jacob; Philippe Le Sager; David G. Streets; Rokjin J. Park; Alice B. Gilliland; A. van Donkelaar (pp. 1310-1319).

We use a global chemical transport model (GEOS-Chem) with 1°×1° horizontal resolution to quantify the effects of anthropogenic emissions from Canada, Mexico, and outside North America on daily maximum 8-hour average ozone concentrations in US surface air. Simulations for summer 2001 indicate mean North American and US background concentrations of 26±8ppb and 30±8ppb, as obtained by eliminating anthropogenic emissions in North America vs. in the US only. The US background never exceeds 60ppb in the model. The Canadian and Mexican pollution enhancement averages 3±4ppb in the US in summer but can be occasionally much higher in downwind regions of the northeast and southwest, peaking at 33ppb in upstate New York (on a day with 75ppb total ozone) and 18ppb in southern California (on a day with 68ppb total ozone). The model is successful in reproducing the observed variability of ozone in these regions, including the occurrence and magnitude of high-ozone episodes influenced by transboundary pollution. We find that exceedances of the 75ppb US air quality standard in eastern Michigan, western New York, New Jersey, and southern California are often associated with Canadian and Mexican pollution enhancements in excess of 10ppb. Sensitivity simulations with 2020 emission projections suggest that Canadian pollution influence in the Northeast US will become comparable in magnitude to that from domestic power plants.

Keywords: Background ozone; Surface ozone; Air quality standard; Chemical transport model; Global model

Seasonal characteristics of chemically apportioned aerosol optical properties at Seoul and Gosan, Korea by Sihye Lee; Young Sung Ghim; Sang-Woo Kim; Soon-Chang Yoon (pp. 1320-1328).

Seasonal variations of aerosol optical properties in Seoul (polluted urban site) and Gosan (coastal background site), Korea, with an emphasis on the relative humidity were investigated using ground-based aerosol measurements and optical model calculations. The mass fraction of elemental carbon was 9–20%, but the optical contribution of these particles to light extinction was higher, up to 33–55% in Seoul. In Gosan, the contribution of non-sea-salt water-soluble aerosols on extinction was 81–93% due to the high mass fraction of these particles. Based on daily MODIS datasets, our analysis showed that the aerosol optical depths at Seoul and Gosan were highest in spring due to the influence of dust particles. The aerosol water content at Gosan, calculated using a thermodynamic equilibrium model, was higher than that at Seoul; this was attributed to the high relative humidity and high fraction of water-soluble aerosols at Gosan. At Seoul, despite abundant water vapors in summer, the possibility of hygroscopic growth of water-soluble aerosols was not more significant than that at Gosan.

Keywords: Aerosol optical properties; Aerosol water content; Relative humidity; Gosan; Seoul

Assimilating concentration observations for transport and dispersion modeling in a meandering wind field by Sue Ellen Haupt; Anke Beyer-Lout; Kerrie J. Long; George S. Young (pp. 1329-1338).

Assimilating concentration data into an atmospheric transport and dispersion model can provide information to improve downwind concentration forecasts. The forecast model is typically a one-way coupled set of equations: the meteorological equations impact the concentration, but the concentration does not generally affect the meteorological field. Thus, indirect methods of using concentration data to influence the meteorological variables are required. The problem studied here involves a simple wind field forcing Gaussian dispersion. Two methods of assimilating concentration data to infer the wind direction are demonstrated. The first method is Lagrangian in nature and treats the puff as an entity using feature extraction coupled with nudging. The second method is an Eulerian field approach akin to traditional variational approaches, but minimizes the error by using a genetic algorithm (GA) to directly optimize the match between observations and predictions. Both methods show success at inferring the wind field. The GA-variational method, however, is more accurate but requires more computational time. Dynamic assimilation of a continuous release modeled by a Gaussian plume is also demonstrated using the genetic algorithm approach.

Keywords: Data assimilation; Dispersion modeling; Genetic algorithm; Gaussian puff; Gaussian plume

Atmospheric deposition of nitrogen emitted in the Metropolitan Area of Buenos Aires to coastal waters of de la Plata River by Andrea L. Pineda Rojas; Laura E. Venegas (pp. 1339-1348).

The Metropolitan Area of Buenos Aires (MABA) is the third mega-city in Latin America. Atmospheric N emitted in the area deposits to coastal waters of de la Plata River. This study describes the parameterizations included in DAUMOD-RD (v.3) model to evaluate concentrations of nitrogen compounds (nitrogen dioxide, gaseous nitric acid and nitrate aerosol) and their total (dry and wet) deposition to a water surface. This model is applied to area sources and CALPUFF model to point sources of NO_x in the MABA. The models are run for 3years of hourly meteorological data, with a spatial resolution of 1km². Mean annual deposition is 69, 728kg-Nyear⁻¹ over 2 339km² of river. Dry deposition contributions of N-NO₂, N-HNO₃ and N-NO₃⁻ to this value are 44%, 22% and 20%, respectively. Wet deposition of N-HNO₃ and N-NO₃⁻ represents 3% and 11% of total annual value, respectively. This very low contribution results from the rare occurrence of rainy hours with wind blowing from the city to the river. Monthly dry deposition flux estimated for coastal waters of MABA varies between 7 and 13kg-Nkm⁻²month⁻¹. These results are comparable to values reported for other coastal zones in the world.

Keywords: Atmospheric dispersion modelling; Atmospheric deposition; Oxidized nitrogen compounds; Urban area; Coastal waters

Composition and yields of secondary organic aerosol formed from OH radical-initiated reactions of linear alkenes in the presence of NO _x: Modeling and measurements by Aiko Matsunaga; Kenneth S. Docherty; Yong B. Lim; Paul J. Ziemann (pp. 1349-1357).

The products and mechanism of secondary organic aerosol (SOA) formation from the OH radical-initiated reactions of linear alkenes in the presence of NO _x were investigated in an environmental chamber. The SOA consisted primarily of products formed through reactions initiated by OH radical addition to the CC double bond, including β-hydroxynitrates and dihydroxynitrates, as well as cyclic hemiacetals, dihydrofurans, and dimers formed from particle-phase reactions of dihydroxycarbonyls. 1,4-Hydroxynitrates formed through reactions initiated by H-atom abstraction also appeared to contribute. Product yields and OH radical and alkoxy radical rate constants taken from the literature or calculated using structure–reactivity methods were used to develop a quantitative chemical mechanism for these reactions. SOA yields were then calculated using this mechanism with gas-particle partitioning theory and estimated product vapor pressures for comparison with measured values. Calculated and measured SOA yields agreed very well at high carbon numbers when semi-volatile products were primarily in the particle phase, but diverged with decreasing carbon number to a degree that depended on the model treatment of dihydroxycarbonyls, which appeared to undergo reversible reactions in the particle phase. The results indicate that the chemical mechanism developed here provides an accurate representation of the gas-phase chemistry, but the utility of the SOA model depends on the partitioning regime. The results also demonstrate some of the advantages of studying simple aerosol-forming reactions in which the majority of products can be identified and quantified, in this case leading to insights into both gas- and particle-phase chemistry.

Keywords: Secondary organic aerosol; OH radical; Modeling; Particle-phase chemistry; Reaction mechanism; Hydrocarbon oxidation; Oligomers

Increase in springtime tropospheric ozone at a mountainous site in Japan for the period 1998–2006 by Hiroshi Tanimoto (pp. 1358-1363).

The trend of tropospheric ozone from 1998 to 2006 was examined based on continuous measurements made at a site on Mt. Happo, Japan. We focused our study on springtime ozone, to coincide with the East Asian continental outflow that dominates the lower tropospheric ozone over Japan during this season. The observed increase of ∼1ppbvyr⁻¹ in the mean ozone level was statistically significant. We also found that the probability distribution of the springtime ozone mixing ratios was substantially modified, with the ozone mixing ratios greatly increasing at the upper end of the probability distribution. This increase has been particularly large since 2003, with larger increases occurring at the higher percentiles. The number of high-ozone days doubled during 2003–2006 compared to 1999–2002. One of the very likely explanations is the enhancement of regional ozone pollution due to rapidly increasing anthropogenic emissions from East Asia.

Keywords: Ozone; Trend; East Asia; Mt. Happo

Two daily smoke maxima in eighteenth century London air by R. Giles Harrison (pp. 1364-1366).

Varied electrostatics experiments followed Benjamin Franklin's pioneering atmospheric investigations. In Knightsbridge, Central London, John Read (1726–1814) installed a sensing rod in the upper part of his house and, using a pith ball electrometer and Franklin chimes, monitored atmospheric electricity from 1789 to 1791. Atmospheric electricity is sensitive to weather and smoke pollution. In calm weather conditions, Read observed two daily electrification maxima in moderate weather, around 9 am and 7 pm. This is likely to represent a double diurnal cycle in urban smoke. Before the motor car and steam railways, one source of the double maximum smoke pattern was the daily routine of fire lighting for domestic heating.

Keywords: Air pollution; Atmospheric electricity; Potential gradient; Smoke proxy; Black carbon

A highly resolved anion-exchange chromatographic method for determination of saccharidic tracers for biomass combustion and primary bio-particles in atmospheric aerosol by Yoshiteru Iinuma; Guenter Engling; Hans Puxbaum; Hartmut Herrmann (pp. 1367-1371).

An improved high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) method is developed and validated for simultaneous determination of atmospherically relevant sugar alcohols, monosaccharides, and monosaccharide anhydrides. The improved method enables the separation of levoglucosan and arabitol which were not or insufficiently separated by the previous HPAEC–PAD methods. Reproducibility of the method was tested for both standard solutions and atmospheric aerosol samples. The peak area relative standard deviation (RSD%) of standard solutions were found to be lower than 1.5% for consecutive analyses ( n=3) and lower than 4% for day to day variation ( n=9). The peak area RSD% of atmospheric samples with typical European wintertime monosaccharide concentrations ( n=9) was found to be similar to that of standard solutions. Limits of detection ranged from 0.002mgL⁻¹ for inositol to 0.08mgL⁻¹ for fructose. The developed method offers a simple, reliable and cost effective determination of atmospheric tracers for biomass combustion and for selected bio-aerosol components at sub-nanogram per cubic-meter-air concentration levels for routine analysis.

Keywords: Atmospheric aerosols; Sugars; Anhydrosugars; Levoglucosan; Arabitol; Biomass burning

On the efficiency of impingers with fritted nozzle tip for collection of ultrafine particles by B. Miljevic; R.L. Modini; S.E. Bottle; Z.D. Ristovski (pp. 1372-1376).

The aim of this study was to determine the collection efficiency of ultrafine particles into an impinger fitted with a fritted nozzle tip as a means to increase contact surface area between the aerosol and the liquid. The influence of liquid sampling volume, frit porosity and the nature of the sampling liquid was explored and it was shown that all impact on the collection efficiency of particles smaller than 220nm. Obtained values for overall collection efficiency were substantially higher (∼30–95%) than have been previously reported, mainly due to the high deposition of particles in the fritted nozzle tip, especially in case of finer porosity frits and smaller particles. Values for the capture efficiency of the solvent alone ranged from 20 to 45%, depending on the type and the volume of solvent. Additionally, our results show that airstream dispersion into bubbles improves particle trapping by the liquid and that there is a difference in collection efficiencies based on the nature and volume of the solvent used.

Keywords: Impinger; Fritted nozzle; Ultrafine particles; Collection efficiency

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Atmospheric Environment (v.43, #6)