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Atmospheric Environment (v.42, #24)

Editorial board (pp. i).

Long-range transport of acidifying substances in East Asia—Part I by Meiyun Lin; Taikan Oki; Tracey Holloway; David G. Streets; Magnus Bengtsson; Shinjiro Kanae (pp. 5939-5955).

This study has conducted a comprehensive model evaluation to help identify major uncertainties of regional air quality model in predicting long-range transport and deposition of acidifying substances in East Asia. Annual predictions of the Community Multiscale Air Quality (CMAQ) model are carried out at two horizontal scales: an 81km domain over East Asia and a 27km domain over Northeast Asia. The model successfully reproduces the magnitudes and diurnal variations of SO₂ mixing ratios at most sites of the Acid Deposition Monitoring Network in East Asia (EANET). Through the comparison with tropospheric NO₂ columns from the Global Ozone Monitoring Experiment (GOME), the model is shown to be able to capture major spatial and seasonal variations of NO₂ observed from space over East Asia. Regarding the magnitudes, however, CMAQ underpredicts the GOME retrieval over industrial area of eastern China in March and December, and over the remote western China in July. Primary reasons for the discrepancy over eastern China are the uncertainties both in emission inventory and in the GOME retrieval in wintertime. For the wet season the soil-biogenic NO emission estimates need to be reviewed regarding the intensity and timing of fertilizer applications, and the magnitude of rain-induced pulsing. The sensitivities of predicted NO₂ columns,NOx mixing ratios, and wet nitrate deposition to 50% increase ofNOx emissions are studied. Due to the underpredictions ofNOx and also to the uncertainty in modeled precipitation and nitrate formation, CMAQ has a tendency to underpredict annual wet deposition loads of nitrate observed by the EANET network.

Keywords: Nitrogen oxides; Satellite data; Acid deposition; Multiscale; East Asia

Long-range transport of acidifying substances in East Asia—Part II by Meiyun Lin; Taikan Oki; Magnus Bengtsson; Shinjiro Kanae; Tracey Holloway; D.G. David G. Streets (pp. 5956-5967).

Region-to-grid source–receptor (S/R) relationships are established for sulfur and reactive nitrogen deposition in East Asia, using the Eulerian-type Community Multiscale Air Quality (CMAQ) model with emission and meteorology data for 2001. We proposed a source region attribution methodology by analyzing the non-linear responses of the CMAQ model to emission changes. Sensitivity simulations were conducted where emissions of SO₂,NOx, and primary particles from a source region were reduced by 25%. The difference between the base and sensitivity simulations was multiplied by a factor of four, and then defined as the contribution from that source region. The transboundary influence exhibits strong seasonal variation and generally peaks during the dry seasons. Long-range transport from eastern China contributes a significant percentage (>20%) of anthropogenic reactive nitrogen as well as sulfur deposition in East Asia. At the same time, northwestern China receives approximately 35% of its sulfur load and 45% of its nitrogen load from foreign emissions. Sulfur emissions from Miyakejima and other volcanoes contribute approximately 50% of the sulfur load in Japan in 2001. Sulfur inflows from regions outside the study domain, which is attributed by using boundary conditions derived from the MOZART global atmospheric chemistry model, are pronounced (10–40%) over most parts of Asia. Compared with previous studies using simple Lagrangian models, our results indicate higher influence from long-range transport. The estimated S/R relationships are believed to be more realistic since they include global influence as well as internal interactions among different parts of China.

Keywords: Sulfur; Reactive nitrogen; Eulerian models; Source–receptor relationships; East Asia

Mercury deposition/accumulation rates in the vicinity of a lead smelter as recorded by a peat deposit by V. Vojtěch Ettler; T. Navratil Tomáš Navrátil; Mihaljevic Martin Mihaljevič; Jan Rohovec; Milan Zuna; O. Sebek Ondřej Šebek; Ladislav Strnad; Hojdova Maria Hojdová (pp. 5968-5977).

Mercury (Hg) concentration profiles and historical accumulation rates were determined in three²¹⁰Pb-dated cores from a peat deposit in the vicinity of a lead (Pb) smelter at Příbram, Czech Republic. The Hg concentrations in peat samples ranged from 66 to 701μgkg⁻¹. Cumulative Hg inventories from each core (for the past ∼150yr) varied by a factor of 1.4 (13.6–18.5mgHgm⁻²), indicating variations of net Hg accumulation rate within the peat deposit. Historical changes in vegetation cover (leading to variable interception by trees) are probably responsible for this variation in space and time. The uncorrected Hg accumulation rates peaked between the 1960s and 1980s (up to 226μgm⁻²yr⁻¹). Recent findings show that Hg records from peat tend to overestimate historical levels of Hg deposition. Therefore we used the mass loss compensation factor (MLCF) to normalize Hg accumulation rates. These corrected Hg accumulation rates were significantly lower (maximum 129μgm⁻²yr⁻¹) and better corresponded to changes in historical smelter emissions, which were highest in the 1960s. The agreement between the corrected Hg accumulation rates in the uppermost peat sections (2–38μgm⁻²yr⁻¹) and biomonitoring of atmospheric deposition by mosses in several recent years (4.7–34.4μgm⁻²yr⁻¹) shows the usefulness of MLCF application on Hg accumulation in peat archives. However, the MLCF correction was unsuitable for Pb. The recent Pb deposition rates obtained by an independent biomonitoring study using mosses (0.5–127mgm⁻²yr⁻¹) were better correlated with net Pb accumulation rates recorded in peat (7–145mgm⁻²yr⁻¹) than with corrected rates obtained by the MLCF approach (1–28mgm⁻²yr⁻¹).

Keywords: Mercury; Deposition; Pb smelter; Historical record; Peat deposit

Particle concentrations in data centers by Arman Shehabi; Arpad Horvath; William Tschudi; Ashok J. Gadgil; William W Nazaroff (pp. 5978-5990).

Cooling buildings with large airflow rates of outside air when temperatures are favorable is an established energy-saving measure. In data centers, this strategy is not widely used, owing to concerns that it would cause increased indoor levels of particles of outdoor origin, which could damage electronic equipment. However, environmental conditions typical of data centers and the associated potential for equipment failure are not well characterized. This study presents the first published measurements of particle concentrations in operating data centers. Indoor and outdoor particle measurements were taken at eight different sites in northern California for particulate matter 0.3–5.0μm in diameter. One of the data centers has an energy-efficient design that employs outside air for cooling, while the rest use conventional cooling methods. Ratios of measured particle concentrations in the conventional data centers to the corresponding outside concentrations were significantly lower than those typically found in office or residential buildings. Estimates using a material-balance model match well with empirical results, indicating that the dominant particle sources and losses have been identified. Measurements taken at the more energy-efficient site show nearly an order of magnitude increase in particle concentration when ventilation rates were high. The model indicates that this increase may be even higher when including particles smaller than the monitoring-equipment size limitation. Even with the increases, the measured particle concentrations are still below concentration limits recommended in industry standards.

Keywords: Data center; Indoor air quality; Particulate matter; Equipment reliability; Energy efficiency; Filtration

Coupled infrared extinction spectra and size distribution measurements for several non-clay components of mineral dust aerosol (quartz, calcite, and dolomite) by Paula K. Hudson; Mark A. Young; Paul D. Kleiber; Vicki H. Grassian (pp. 5991-5999).

Simultaneous size distributions and Fourier transform infrared (FTIR) extinction spectra have been measured for several representative components of mineral dust aerosol (quartz, calcite, and dolomite) in the fine particle size mode ( D=0.1–1μm). Optical constants drawn from the published literature have been used in combination with the experimentally determined size distributions to simulate the extinction spectra. In general, Mie theory does not accurately reproduce the peak position or band shape for the prominent IR resonance features in the 800–1600cm⁻¹ spectral range. The resonance peaks in the Mie simulation are consistently blue shifted relative to the experimental spectra by ∼20–50cm⁻¹. Spectral simulations, derived from a simple Rayleigh-based analytic theory for a “continuous distribution of ellipsoids” particle shape model, better reproduce the experimental spectra, despite the fact that the Rayleigh approximation is not strictly satisfied in these experiments. These results differ from our previous studies of particle shape effects in silicate clay mineral dust aerosols where a disk-shaped model for the particles was found to be more appropriate.

Keywords: Mineral dust; Infrared extinction; Mie theory; Remote sensing

Estimate of initial isoprene contribution to ozone formation potential in Beijing, China by Xin Xie; Min Shao; Ying Liu; Sihua Lu; C.-C. Chih-Chung Chang; Z.-M. Zhong-Ming Chen (pp. 6000-6010).

Volatile organic compounds (VOCs) are important precursors of tropospheric ozone formation. Isoprene contributions to ozone formation by using ambient mixing ratios are generally underestimated because of rapid chemical losses. In this study, ambient mixing ratios of major VOC species were continuously measured at Peking university (PKU) and YUFA, urban and sub-urban sites in Beijing, the city that will host 2008 Olympic Games. The observed mixing ratios of methyl vinyl ketone (MVK), methacrolein (MACR) and isoprene were used to derive the mixing ratios of initial isoprene, which means the ambient isoprene level before it undergoes any photochemical reaction with OH radicals. The average mixing ratios of initial isoprene were 3.3±1.6 and 2.9±1.5ppbv at PKU and YUFA sites, respectively. The percentages of initial isoprene in total initial VOCs were 10.8% at PKU site and 11.4% at YUFA site, in reasonable agreement with the isoprene contribution in total VOC emissions as derived from source inventories. Maximum increment reactivity (MIR) was used to evaluate the ozone formation potential (OFP) for major VOC species. The OFP for initial isoprene accounted for 23% of the total OFPs for all measured species, compared to 11% using ambient mixing ratios of isoprene at PKU site. Similarly, at YUFA site, the ambient measured isoprene and initial isoprene contributed 10% and 22%, respectively, to the OFPs for total measured VOCs. It seems that isoprene has similar contribution to ozone formation at both sites in Beijing city.

Keywords: Initial isoprene; Chemical loss; MIR; VOCs

Using the optical properties of aerosols from the AERONET database to calculate surface solar UV-B irradiance in Córdoba, Argentina: Comparison with measurements by Georgina C. Andrada; Gustavo G. Palancar; Beatriz M. Toselli (pp. 6011-6019).

The main purpose of this study was to perform an evaluation of the particles’ optical parameters’ influence on surface solar UV-B (280–315nm) irradiance in Córdoba, Argentina. To achieve this objective UV-B irradiance dataset, AERONET (AErosol RObotic NETwork) database, and TUV (Tropospheric Ultraviolet and Visible) model were used to analyze the effects of aerosols on surface irradiance on cloudless days during specific days of winter and spring of the period 1999–2006. Together with a direct observer, total irradiance (300–3000nm) measurements were used as an ancillary tool to verify the cloudless condition. Every year, during this period, important reductions in surface irradiance are observed due to the aerosol load. Aerosols were incorporated in the model through the aerosol optical depth at 340nm, the asymmetry parameter at 440nm, and the single scattering albedo at 440nm, all of them provided by AERONET Córdoba-CETT site. These factors vary from near to zero up to 1.4, from 0.56 up to 0.83 and from 0.43 up to 0.99, respectively. The behaviors of these factors along the year are analyzed considering the meteorology of Córdoba. When AERONET data are included in the TUV model they allow an accurate simulation of the UV-B irradiance, making the agreement with the experimental measurements substantially better. Only a small differences (±2%) remains, which can be attributed to diverse factors. As the AERONET site is 20km away from the irradiance measurement site, these results show the regional character of the aerosols in Córdoba, although small contributions of urban aerosols are not discarded. An episode of high aerosol and pollutants laden due to fires in the surrounding hills is briefly analyzed. A set of additional studies are needed to describe comprehensively the characteristics and behavior of the Córdoba aerosols. Some of them are being already carried out.

Keywords: Aerosol optical properties; Córdoba; Radiative transfer model

Background ozone levels of air entering the west coast of the US and assessment of longer-term changes by Samuel J. Oltmans; Allen S. Lefohn; Joyce M. Harris; Douglas S. Shadwick (pp. 6020-6038).

An analysis of surface ozone measurements at a west coast site in northern California (Trinidad Head) demonstrates that this location is well situated to sample air entering the west coast of the US from the Pacific Ocean. During the seasonal maximum in the spring, this location regularly observes hourly average ozone mixing ratios ⩾50ppbv in air that is uninfluenced by the North American continent. Mean daytime values in the spring exceed 40ppbv. A location in southern California (Channel Islands National Park) demonstrates many of the characteristics during the spring as Trinidad Head in terms of air flow patterns and ozone amounts suggesting that background levels of ozone entering southern California from the Pacific Ocean are similar to those in northern California. Two inland locations (Yreka and Lassen Volcanic National Park) in northern California with surface ozone data records of 20 years or more are more difficult to interpret because of possible influences of local or regional changes. They show differing results for the long-term trend during the spring. The 10-year ozone vertical profile measurements obtained with weekly ozonesondes at Trinidad Head show no significant longer-term change in tropospheric ozone.

Keywords: Tropospheric ozone; Surface ozone; Transpacific transport; Ozonesondes; Background ozone

Implementation of a windblown dust parameterization into MODELS-3/CMAQ: Application to episodic PM events in the US/Mexico border by Y.-J. Yu-Jin Choi; H.J.S. Fernando (pp. 6039-6046).

Windblown dust is known to impede visibility, deteriorate air quality and modify the radiation budget. Arid and semiarid areas with unpaved and unvegetated land cover are particularly prone to windblown dust, which is often attributed to high particulate matter (PM) pollution in such areas. Yet, windblown dust is poorly represented in existing regulatory air quality models. In a study by the authors on modeling episodic high PM events along the US/Mexico border using the state-of-the-art CMAQ/MM5/SMOKE air quality modeling system [Choi, Y.-J., Hyde, P., Fernando, H.J.S., 2006. Modeling of episodic particulate matter events using a 3D air quality model with fine grid: applications to a pair of cities in the US/Mexico border. Atmospheric Environment 40, 5181–5201], some of the observed PM₁₀ NAAQS exceedances were inferred as due to windblown dust, but the modeling system was incapable of dealing with time-dependent episodic dust entrainment during high wind periods. In this paper, a time-dependent entrainment parameterization for windblown dust is implemented in the CMAQ/MM5/SMOKE modeling system with the hope of improving PM predictions. An approach for realizing windblown dust emission flux for each grid cell over the study domain on an hourly basis, which accounts for the influence of factors such as soil moisture content, atmospheric stability and wind speed, is presented in detail. Comparison of model predictions with observational data taken at a pair of US/Mexico border towns shows a clear improvement of model performance upon implementation of the dust emission flux parameterization.

Keywords: Windblown dust flux; Semiarid/arid area; PM; ₁₀; CMAQ/MM5/SMOKE

Source characterization of ambient fine particles at multiple sites in the Seattle area by Eugene Kim; Philip K. Hopke (pp. 6047-6056).

To identify major PM_2.5 (particulate matter ≤2.5μm in aerodynamic diameter) sources with a particular emphasis on the ship engine emissions from a major port, integrated 24h PM_2.5 speciation data collected between 2000 and 2005 at five United State Environmental Protection Agency's Speciation Trends Network monitoring sites in Seattle, WA were analyzed. Seven to ten PM_2.5 sources were identified through the application of positive matrix factorization (PMF). Secondary particles (12–26% for secondary nitrate; 17–20% for secondary sulfate) and gasoline vehicle emissions (13–31%) made the largest contributions to the PM_2.5 mass concentrations at all of the monitoring sites except for the residential Lake Forest site, where wood smoke contributed the most PM_2.5 mass (31%). Other identified sources include diesel vehicle emissions, airborne soil, residual oil combustion, sea salt, aged sea salt, metal processing, and cement kiln. Residual oil combustion sources identified at multiple monitoring sites point clearly to the Port of Seattle suggesting ship emissions as the source of oil combustion particles. In addition, the relationship between sulfate concentrations and the oil combustion emissions indicated contributions of ship emissions to the local sulfate concentrations. The analysis of spatial variability of PM_2.5 sources shows that the spatial distributions of several PM_2.5 sources were heterogeneous within a given air shed.

Keywords: Ship emissions; Seattle; Speciation trends network; Source apportionment; PM; _2.5

Evaluation of the community multiscale air quality (CMAQ) model version 4.5: Sensitivities impacting model performance; Part II—particulate matter by K. Wyat Appel; Prakash V. Bhave; Alice B. Gilliland; Golam Sarwar; Shawn J. Roselle (pp. 6057-6066).

This paper is Part II in a pair of papers that examines the results of the Community Multiscale Air Quality (CMAQ) model version 4.5 (v4.5) and discusses the potential explanations for the model performance characteristics seen. The focus of this paper is on fine particulate matter (PM_2.5) and its chemical composition. Improvements made to the dry deposition velocity and cloud treatment in CMAQ v4.5 addressing compensating errors in 36-km simulations improved particulate sulfate (SO₄²⁻) predictions. Large overpredictions of particulate nitrate (NO₃⁻) and ammonium (NH₄⁺) in the fall are likely due to a gross overestimation of seasonal ammonia (NH₃) emissions. Carbonaceous aerosol concentrations are substantially underpredicted during the late spring and summer months, most likely due, in part, to a lack of some secondary organic aerosol (SOA) formation pathways in the model. Comparisons of CMAQ PM_2.5 predictions with observed PM_2.5 mass show mixed seasonal performance. Spring and summer show the best overall performance, while performance in the winter and fall is relatively poor, with significant overpredictions of total PM_2.5 mass in those seasons. The model biases in PM_2.5 mass cannot be explained by summing the model biases for the major inorganic ions plus carbon. Errors in the prediction of other unspeciated PM_2.5 (PM_Other) are largely to blame for the errors in total PM_2.5 mass predictions, and efforts are underway to identify the cause of these errors.

Keywords: Community multiscale air quality (CMAQ) model; Model evaluation; PM; _2.5; Sulfate; Nitrate; Ammonium; Organic and elemental carbon

Bottom-up uncertainty estimates of global ammonia emissions from global agricultural production systems by A.H.W. Beusen; A.F. Bouwman; P.S.C. Heuberger; G. Van Drecht; K.W. Van Der Hoek (pp. 6067-6077).

Here we present an uncertainty analysis of NH₃ emissions from agricultural production systems based on a global NH₃ emission inventory with a 5×5min resolution. Of all results the mean is given with a range (10% and 90% percentile). The uncertainty range for the global NH₃ emission from agricultural systems is 27–38 (with a mean of 32) TgNH₃-Nyr⁻¹, N fertilizer use contributing 10–12 (11) Tgyr⁻¹ and livestock production 16–27 (21) Tgyr⁻¹. Most of the emissions from livestock production come from animal houses and storage systems (31–55%); smaller contributions come from the spreading of animal manure (23–38%) and grazing animals (17–37%). This uncertainty analysis allows for identifying and improving those input parameters with a major influence on the results. The most important determinants of the uncertainty related to the global agricultural NH₃ emission comprise four parameters (N excretion rates, NH₃ emission rates for manure in animal houses and storage, the fraction of the time that ruminants graze and the fraction of non-agricultural use of manure) specific to mixed and landless systems, and total animal stocks. Nitrogen excretion rates and NH₃ emission rates from animal houses and storage systems are shown consistently to be the most important parameters in most parts of the world. Input parameters for pastoral systems are less relevant. However, there are clear differences between world regions and individual countries, reflecting the differences in livestock production systems.

Keywords: Agriculture; Ammonia; Fertilizer; Livestock; Manure; Nitrogen; Uncertainty

Relationship between atmospheric pollution processes and synoptic pressure patterns in northern China by Z.H. Chen; S.Y. Cheng; J.B. Li; X.R. Guo; W.H. Wang; D.S. Chen (pp. 6078-6087).

The air pollution index (API) sequences in 10 cities in northern China and the synoptic pressure patterns during autumn and winter from 2002 to 2006 were analyzed with diagnostic and statistical methods. The results showed that the air qualities in northern China had a prominent correlation with the pressure systems. It revealed that (a) the increasing phase of API was associated with high pressure and the successive low pressure, (b) the preceding part of front (i.e. the retral part of low pressure) was associated with the maximum of API values during a cycle of air pollution process, (c) the pressure systems with high gradient led to the decrease of API, and (d) the synoptic pressure patterns and their evolvements were the main causes of regional air pollution processes. These relations can be used to analyze the variation characteristics and mechanism of regional atmosphere pollution process, and provide important basis for the qualitative prediction, control, and management of regional air pollution problems.

Keywords: Air pollution index (API); Air pollution process; Northern China; Synoptic pressure patterns

Local to regional emission sources affecting mercury fluxes to New York lakes by Revital Bookman; Charles T. Driscoll; Daniel R. Engstrom; Steven W. Effler (pp. 6088-6097).

Lake-sediment records across the Northern Hemisphere show increases in atmospheric deposition of anthropogenic mercury (Hg) over the last 150 years. Most of the previous studies have examined remote lakes affected by the global atmospheric Hg reservoir. In this study, we present Hg flux records from lakes in an urban/suburban setting of central New York affected also by local and regional emissions. Sediment cores were collected from the Otisco and Skaneateles lakes from the Finger Lakes region, Cross Lake, a hypereutrophic lake on the Seneca River, and Glacial Lake, a small seepage lake with a watershed that corresponds with the lake area. Sediment accumulation rates and dates were established by²¹⁰Pb. The pre-anthropogenic regional atmospheric Hg flux was estimated to be 3.0μgm⁻²yr⁻¹ from Glacial Lake, which receives exclusively direct atmospheric deposition. Mercury fluxes peaked during 1971–2001, and were 3 to more than 30 times greater than pre-industrial deposition. Land use change and urbanization in the Otisco and Cross watersheds during the last century likely enhanced sediment loads and Hg fluxes to the lakes. Skaneateles and Glacial lakes have low sediment accumulation rates, and thus are excellent indicators for atmospheric Hg deposition. In these lakes, we found strong correlations with emission records for the Great Lakes region that markedly increased in the early 1900s, and peaked during WWII and in the early 1970s. Declines in modern Hg fluxes are generally evident in the core records. However, the decrease in sediment Hg flux at Glacial Lake was interrupted and has increased since the early 1990s probably due to the operation of new local emission sources. Assuming the global Hg reservoir tripled since the pre-industrial period, the contribution of local and regional emission sources to central New York lakes was estimated to about 80% of the total atmospheric Hg deposition.

Keywords: Mercury; ²¹⁰; Pb dating; Atmospheric deposition; Sediment cores; Northeastern US

Trends in snowpack chemistry and comparison to National Atmospheric Deposition Program results for the Rocky Mountains, US, 1993–2004 by George P. Ingersoll; M. Alisa Mast; Donald H. Campbell; David W. Clow; Leora Nanus; John T. Turk (pp. 6098-6113).

Seasonal snowpack chemistry data from the Rocky Mountain region of the US was examined to identify long-term trends in concentration and chemical deposition in snow and in snow-water equivalent. For the period 1993–2004, comparisons of trends were made between 54 Rocky Mountain Snowpack sites and 16 National Atmospheric Deposition Program wetfall sites located nearby in the region. The region was divided into three subregions: Northern, Central, and Southern. A non-parametric correlation method known as the Regional Kendall Test was used. This technique collectively computed the slope, direction, and probability of trend for several sites at once in each of the Northern, Central, and Southern Rockies subregions. Seasonal Kendall tests were used to evaluate trends at individual sites.Significant trends occurred during the period in wetfall and snowpack concentrations and deposition, and in precipitation. For the comparison, trends in concentrations of ammonium, nitrate, and sulfate for the two networks were in fair agreement. In several cases, increases in ammonium and nitrate concentrations, and decreases in sulfate concentrations for both wetfall and snowpack were consistent in the three subregions. However, deposition patterns between wetfall and snowpack more often were opposite, particularly for ammonium and nitrate. Decreases in ammonium and nitrate deposition in wetfall in the central and southern rockies subregions mostly were moderately significant ( p<0.11) in constrast to highly significant increases in snowpack ( p<0.02). These opposite trends likely are explained by different rates of declining precipitation during the recent drought (1999–2004) and increasing concentration. Furthermore, dry deposition was an important factor in total deposition of nitrogen in the region. Sulfate deposition decreased with moderate to high significance in all three subregions in both wetfall and snowpack. Precipitation trends consistently were downward and significant for wetfall, snowpack, and snow-telemetry data for the central and southern rockies subregions ( p<0.03), while no trends were noted for the Northern Rockies subregion.

Keywords: Chemical trends; Atmospheric deposition; Rocky mountains; Nitrogen; Sulfur

Source characterization of fine and coarse particles at the East Mediterranean coast by Yaacov Mamane; Cinzia Perrino; Osnat Yossef; Maria Catrambone (pp. 6114-6130).

Fine and coarse atmospheric particles were collected in Ashdod—a midsize industrial city on the southeastern Mediterranean coast, and in Gedera—a rural site, to characterize ambient particles and to determine their long-range transport during two major seasons—winter and summer. Manual PM2.5 and PM10 samplers, dichotomous samplers, continuous automated PM10 samplers, and denuders were used to sample particulate and gaseous pollutants.Fine and coarse concentrations in Ashdod were 21.2 and 39.6μgm⁻³, and 23.9 and 30.5μgm⁻³ in the fall–winter and summer campaigns, respectively. Crustal material, as calcites or dolomites mixed with silicates, dominated the coarse fraction and also the fine fraction on dusty days. In the fall–winter, S, P, and Ni were coupled with minerals. Coarse Ni was associated with crustal material during dust storms, while P originated from shipping and deposition of phosphates in the urban area around.Sulfates dominated the fine fractions in the summer season averaging 12μgm⁻³. Multivariate analysis indicated that S was associated with As and Se, V and Ni, both associated with heavy fuel combustion, and Zn and Pb. In winter, those mixed sources were local, but in summer they were part of long-range transport. In the fall–winter, Zn and Pb were strongly associated with Mn, Ga, and Cu—elements emitted from either traffic or metal processing plants.Although the influence of crustal material on both size fractions was significant, most heavy metals were associated with PM2.5. Higher concentrations were linked to a larger number of particles in this fraction, to a larger surface area available for biochemical reaction [Harrison, R., Shi, J., Xi, S., Khan, A., Mark, D., Kinnersley, R., Yin, J., Philos, T., 2000. Measurement of number, mass and size distribution of particles in the atmosphere. Philosophical Transactions of the Royal Society 358, 2567–2579], and finally to a larger concern in regards to health effects.

Keywords: Long-range transport; Fine particles; Coarse particles; Elemental concentrations; Saharan dust

Evolution rates and PCB content of surface films that develop on impervious urban surfaces by Rosa W. Wu; Tom Harner; Miriam L. Diamond (pp. 6131-6143).

Surface films on impervious surfaces mediate the fate of organic contaminants in urban areas. Using sheltered 3-mm diameter glass beads as a surrogate impervious urban surface, studies in downtown Toronto showed that surface films developed at a consistent rate of ∼1.6–2.6nmday⁻¹. Linear film growth was observed up to and including the last day of three studies of 89-, 273-, and 84-day duration. Total PCB content (sum of 15 PCB congeners) also increased linearly, at a similar rate as the surface film. A complementary study using unsheltered beads showed that up to 80% of film mass and PCB content were removed by film wash-off during rain events. The film growth rate on beads exposed at a rural site, 200km northeast of Toronto, was ∼12–20 times lower with PCB burdens that were ∼7–22 times lower compared to Toronto. Based on these findings, it is estimated that approximately 56–226g of PCBs are captured by a 70nm thick film covering just the horizontal surface area of Toronto. This is a substantial quantity of PCB that is available for rapid surface–air exchange and wash-off.

Keywords: Surface films; PCBs; Impervious surfaces; Urban environments

Analysis of polycyclic aromatic hydrocarbons (PAHs) in airborne particles by direct sample introduction thermal desorption GC/MS by Matthew Bates; Paolo Bruno; Mariangela Caputi; Maurizio Caselli; Gianluigi de Gennaro; Maria Tutino (pp. 6144-6151).

The technique of thermal desorption (TD)–GC/MS was evaluated for measuring airborne, 4–6 ring polycyclic aromatic hydrocarbons (PAHs) collected onto quartz filters. TD provides a more readily automated and sensitive alternative to traditional solvent extraction, decreasing the time/cost of analysis and reducing the risk of analyte loss or sample contamination. The developed method was successfully applied to the analysis of PAH standard solutions loaded on sorbent tubes packed with quartz wool and the graphitized carbon black sorbent Carbograph2. The optimized method showed high desorption efficiency over the whole range of target PAHs with good precision, linearity and sensitivity. The proposed method was verified on an urban dust Standard Reference Material (SRM 1649a); the experimentally determined concentrations agreed with the certified ranges (95% confidence limit) for all target compounds except benzo[a]anthracene, which fell just outside the narrow certified range. The desorption efficiency and the reproducibility of the method was evaluated by analysing pieces of real sample filters sampled from urban air for a period of 24h. The results confirmed the homogeneity of the filter and showed high recovery efficiencies for all target PAHs.

Keywords: Thermal desorption; PAHs

Erratum to “Size distribution of trace organic species emitted from biomass combustion and meat charbroiling” [Atoms. Environ. 42 (2008) 3059–3075] by Michael J. Kleeman; Michael A. Robert; Sarah G. Riddle; Philip M. Fine; Michael D. Hays; James J. Schauer; Michael P. Hannigan (pp. 6152-6154).

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Atmospheric Environment (v.42, #24)