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Atmospheric Environment (v.41, #35)

Editorial board (pp. i).

Degassing of gaseous (elemental and reactive) and particulate mercury from Mount Etna volcano (Southern Italy) by E. Bagnato; A. Aiuppa; F. Parello; S. Calabrese; W. D’Alessandro; T.A. Mather; A.J.S. McGonigle; D.M. Pyle; Wangberg I. Wängberg (pp. 7377-7388).

There is an urgent need to better constrain the global rates of mercury degassing from natural sources, including active volcanoes. Hitherto, estimates of volcanic fluxes have been limited by the poorly determined speciation of Hg in volcanic emissions. Here, we present a systematic characterisation of mercury partitioning between gaseous (Hg_(g)) and particulate (Hg_(p)) forms in the volcanic plume of Mount Etna, the largest open-vent passively degassing volcano on Earth. We demonstrate that mercury transport is predominantly in the gas phase, with a mean Hg_(p)/Hg_(g) ratio of ∼0.01 by mass. We also present the first simultaneous measurement of divalent gaseous mercury (Hg(g)II) and total gaseous mercury (Hg_(g)) in a volcanic plume, which suggests thatHg(g)0 is the prevalent form of mercury in this context. These data are supported by the results of model simulations, carried out with HSC thermodynamic software. Based on a mean “bulk plume” Hg/SO₂ mass ratio of 8.7×10⁻⁶, and a contemporaneous volcanic SO₂ flux of 0.8Mtyr⁻¹, we estimate an Hg emission rate from Mt. Etna during passive degassing of 5.4tyr⁻¹ (range, 1.1–10tyr⁻¹). This corresponds to ∼0.6% of global volcanic Hg emissions, and about 5% of Hg released from industrial activities in the Mediterranean area.

Keywords: Atmospheric mercury; Volcanic degassing; Gaseous and particulate mercury; Atmospheric budgets

Fire and biofuel contributions to annual mean aerosol mass concentrations in the United States by Rokjin J. Park; Daniel J. Jacob; Jennifer A. Logan (pp. 7389-7400).

We estimate the contributions from biomass burning (summer wildfires, other fires, residential biofuel, and industrial biofuel) to seasonal and annual aerosol concentrations in the United States. Our approach is to use total carbonaceous (TC) and non-soil potassium (ns-K) aerosol mass concentrations for 2001–2004 from the nationwide IMPROVE network of surface sites, together with satellite fire data. We find that summer wildfires largely drive the observed interannual variability of TC aerosol concentrations in the United States. TC/ns-K mass enhancement ratios from fires range from 10 for grassland and shrub fires in the south to 130 for forest fires in the north. The resulting summer wildfire contributions to annual TC aerosol concentrations for 2001–2004 are 0.26μgCm⁻³ in the west and 0.14μgCm⁻³ in the east; Canadian fires are a major contributor in the east. Non-summer wildfires and prescribed burns contribute on an annual mean basis 0.27 and 0.31μgCm⁻³ in the west and the east, highest in the southeast because of prescribed burning. Residential biofuel is a large contributor in the northeast with annual mean concentration of up to 2.2μgCm⁻³ in Maine. Industrial biofuel (mainly paper and pulp mills) contributes up to 0.3μgCm⁻³ in the southeast. Total annual mean fine aerosol concentrations from biomass burning average 1.2 and 1.6μgm⁻³ in the west and east, respectively, contributing about 50% of observed annual mean TC concentrations in both regions and accounting for 30% (west) and 20% (east) of total observed fine aerosol concentrations. Our analysis supports bottom-up source estimates for the contiguous United States of 0.7–0.9TgCyr⁻¹ from open fires (climatological) and 0.4TgCyr⁻¹ from biofuel use. Biomass burning is thus an important contributor to US air quality degradation, which is likely to grow in the future.

Keywords: Aerosols; Wildfires; Biomass burning; Biofuel; Air quality; Visibility

Personal exposure to PM_2.5 and element composition—A comparison between outdoor and indoor workers from two Mexican cities by Horacio Tovalin-Ahumada; Lawrence Whitehead; Salvador Blanco (pp. 7401-7413).

Many individuals work outdoors in the formal and informal economy of the large urban areas in developing countries, where they are potentially exposed for long periods to high concentrations of ambient airborne particulate matter (PM). This study describes the personal exposures to PM of 2.5μm aerodynamic diameter and smaller (PM_2.5) for a sample of outdoor and indoor workers in two cities, Mexico City and Puebla, in central Mexico.Thirty-six workers in Mexico City and 17 in Puebla were studied. Thirty were outdoor workers (i.e., taxi and bus drivers, street vendors, and vehicle inspectors) and 23 were indoor (office) workers. Their personal exposures to PM_2.5 were monitored for a mean 19-h period. In Mexico City, the street vendors and taxi drivers overall exposures were significantly higher than indoor workers were. In Puebla, bus drivers had a higher overall exposure than vehicle inspectors or indoor workers. Most of the exposures were above the 65μgm⁻³24-h Mexican standard.In Mexico City, exposures to Si, Ti, Cr, Mn, Fe, Ni, Cu, Mo and Cd were higher for outdoor than for indoor workers. In Puebla, exposures to Si, S, K, Ca, Ti, V, Mn, and Zn also were higher for outdoor workers. In Mexico City outdoor workers exposures to Cu, Pb, Cr, Se and Mo were 4 or more times higher than for Puebla outdoor workers, while Puebla outdoor workers’ exposures to V, Si, Fe and Ca were 3 or more times higher than Mexico City outdoor workers.These results suggest that for these outdoor workers the elevated local ambient air PM concentrations and an extended period spent outside are more important contributors to total exposures than indoor concentrations. These workers could be at particular risk of increased morbidity and mortality associated with ambient PM.

Keywords: Informal; Workers; PM; _2.5; Outdoor; Indoor; Elemental

Insights into the primary–secondary and regional–local contributions to organic aerosol and PM_2.5 mass in Pittsburgh, Pennsylvania by R. Subramanian; Neil M. Donahue; Anna Bernardo-Bricker; Wolfgang F. Rogge; Allen L. Robinson (pp. 7414-7433).

This paper presents chemical mass balance (CMB) analysis of organic molecular marker data to investigate the sources of organic aerosol and PM_2.5 mass in Pittsburgh, Pennsylvania. The model accounts for emissions from eight primary source classes, including major anthropogenic sources such as motor vehicles, cooking, and biomass combustion as well as some primary biogenic emissions (leaf abrasion products). We consider uncertainty associated with selection of source profiles, selection of fitting species, sampling artifacts, photochemical aging, and unknown sources. In the context of the overall organic carbon (OC) mass balance, the contributions of diesel, wood-smoke, vegetative detritus, road dust, and coke-oven emissions are all small and well constrained; however, estimates for the contributions of gasoline-vehicle and cooking emissions can vary by an order of magnitude. A best-estimate solution is presented that represents the vast majority of our CMB results; it indicates that primary OC only contributes 27±8% and 50±14% (average±standard deviation of daily estimates) of the ambient OC in the summer and winter, respectively. Approximately two-thirds of the primary OC is transported into Pittsburgh as part of the regional air mass. The ambient OC that is not apportioned by the CMB model is well correlated with secondary organic aerosol (SOA) estimates based on the EC-tracer method and ambient concentrations of organic species associated with SOA. Therefore, SOA appears to be the major component of OC, not only in summer, but potentially in all seasons. Primary OC dominates the OC mass balance on a small number of nonsummer days with high OC concentrations; these events are associated with specific meteorological conditions such as local inversions. Primary particulate emissions only contribute a small fraction of the ambient fine-particle mass, especially in the summer.

Keywords: Organic aerosol; Particulate matter; Source apportionment; Molecular markers; CMB; Regional transport; Secondary organic aerosol; Photochemical decay; Pittsburgh Air Quality Study

Rate constant for the reaction of ozone with diethyl sulfide by Lin Du; Yongfu Xu; Maofa Ge; Long Jia (pp. 7434-7439).

The rate constant for the reaction of diethyl sulfide (DES; C₂H₅SC₂H₅) with ozone was determined for the first time, which was (2.77±0.27)×10⁻¹⁹cm³molecule⁻¹s⁻¹ under a room temperature of (289±1)K. Experiments were conducted under supposedly pseudo-first-order decay conditions, keeping [DES]₀>50[O₃]₀, but having different combinations of [DES]₀ and [O₃]₀. Cyclohexane was added into the reactor to eliminate the effect of OH radicals. The wall decay of ozone and the role of cyclohexane were also discussed in the present work.

Keywords: Diethyl sulfide; Ozone; Rate constant

Dilution and aerosol dynamics within a diesel car exhaust plume—CFD simulations of on-road measurement conditions by U. Uhrner; von Lowis S. von Löwis; Vehkamaki H. Vehkamäki; B. Wehner; Brasel S. Bräsel; M. Hermann; F. Stratmann; M. Kulmala; A. Wiedensohler (pp. 7440-7461).

Vehicle particle emissions are studied extensively because of their health effects, contribution to ambient PM levels and possible impact on climate. The aim of this work was to obtain a better understanding of secondary particle formation and growth in a diluting vehicle exhaust plume using 3-d information of simulations together with measurements. Detailed coupled computational fluid dynamics (CFD) and aerosol dynamics simulations have been conducted for H₂SO₄–H₂O and soot particles based on measurements within a vehicle exhaust plume under real conditions on public roads.Turbulent diffusion of soot and nucleation particles is responsible for the measured decrease of number concentrations within the diesel car exhaust plume and decreases coagulation rates. Particle size distribution measurements at 0.45 and 0.9m distance to the tailpipe indicate a consistent soot mode (particle diameter D_p∼50nm) at variable operating conditions. Soot mode number concentrations reached up to 10¹³m⁻³ depending on operating conditions and mixing.For nucleation particles the simulations showed a strong sensitivity to the spatial dilution pattern, related cooling and exhaust H₂SO_4(g). The highest simulated nucleation rates were about 0.05–0.1m from the axis of the plume. The simulated particle number concentration pattern is in approximate accordance with measured concentrations, along the jet centreline and 0.45 and 0.9m from the tailpipe. Although the test car was run with ultralow sulphur fuel, high nucleation particle ( D_p⩽15nm) concentrations (>10¹³m⁻³) were measured under driving conditions of strong acceleration or the combination of high vehicle speed (>140kmh⁻¹) and high engine rotational speed (>3800 revolutions per minute (rpm)).Strong mixing and cooling caused rapid nucleation immediately behind the tailpipe, so that the highest particle number concentrations were recorded at a distance, x=0.45m behind the tailpipe. The simulated growth of H₂SO₄–H₂O nucleation particles was unrealistically low compared with measurements. The possible role of low and semi-volatile organic components on the growth processes is discussed. Simulations for simplified H₂SO₄–H₂O–octane–gasoil aerosol resulted in sufficient growth of nucleation particles.

Keywords: Aerosol dynamics modelling; Particle formation; Particle growth; Soot; Vehicle exhaust plume

Co-combustion performance of coal with rice husks and bamboo by Philip C.W. Kwong; Christopher Y.H. Chao; J.H. Wang; C.W. Cheung; Gail Kendall (pp. 7462-7472).

Biomass has been regarded as an important form of renewable energy due to the reduction of green house gas emission such as carbon dioxide. An experimental study of co-combustion of coal and biomass was performed in a laboratory-scale combustion facility. Rice husks and bamboo were the selected biomass fuels in this study due to their abundance in the Asia-Pacific region. Experimental parameters including the biomass blending ratio in the fuel mixture, relative moisture content and biomass grinding size were investigated. Both energy release data and pollutant emission information were obtained. Due to the decrease in the heating value from adding biomass in the fuel mixture, the combustion temperature and energy output from the co-firing process were reduced compared with coal combustion. On the other hand, gaseous pollutant emissions including carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NO _x) and sulfur dioxide (SO₂) were reduced and minimum energy-based emission factors were found in the range of 10–30% biomass blending ratio. With an increase in the moisture content in the biomass, decreases in combustion temperature, SO₂, NO _x and CO₂ emissions were observed, while an increase in CO emissions was found. It has also been observed that chemical kinetics may play an important role compared to mass diffusion in the co-firing process and the change in biomass grinding size does not have much effect on the fuel burning rate and pollutant emissions under the current experimental conditions.

Keywords: Co-combustion; Coal; Rice husks; Bamboo; Gaseous pollutants

Study of expiratory droplet dispersion and transport using a new Eulerian modeling approach by Alvin C.K. Lai; Y.C. Cheng (pp. 7473-7484).

Understanding of droplet nuclei dispersion and transport characteristics can provide more engineering strategies to control transmission of airborne diseases. Droplet dispersion in a room under the conventional well-mixed and displacement ventilation is simulated. Two droplet nuclei sizes, 0.01 and 10μm, are selected as they represent very fine and coarse droplets. The flow field is modeled using k–ε RNG model. A new Eulerian drift-flux methodology is employed to model droplet phase. Under the conventional ventilation scheme, both fine and coarse droplets are homogeneously dispersed within approximately 50s. Droplet nuclei exhibit distinctive dispersion behavior, particularly for low airflow microenvironment. After 270s of droplet emission, gravitational settling influences the dispersion for 10μm droplets, and concentration gradient can still be observed for displacement ventilation.

Keywords: Dispersion; Drift-flux model; Lagrangian model; Mixing; Ventilation

Characteristics of re-suspended road dust and its impact on the atmospheric environment in Beijing by Lihui Han; Guoshun Zhuang; Shuiyuan Cheng; Ying Wang; Juan Li (pp. 7485-7499).

A sampling campaign of re-suspended road dust samples from 53 sites that could cover basically the entire Beijing, soil samples from the source regions of dust storm in August 2003, and aerosol samples from three representative sites in Beijing from December 2001 to September 2003, was carried out to investigate the characteristics of re-suspended road dust and its impact on the atmospheric environment. Ca, S, Cu, Zn, Ni, Pb, and Cd were far higher than its crustal abundances and Ca²⁺, SO₄²⁻, Cl⁻, K⁺, Na⁺, NO₃⁻ were major ions in re-suspended road dust. Al, Ti, Sc, Co, and Mg in re-suspended road dust were mainly originated from crustal source, while Cu, Zn, Ni, and Pb were mainly derived from traffic emissions and coal burning, and Fe, Mn, and Cd were mainly from industrial emissions, coal combustion and oil burning. Ca²⁺ and SO₄²⁻ mainly came from construction activities, construction materials and secondary gas-particle conversions, Cl⁻ and Na⁺ were derived from industrial wastewater disposal and chemical industrial emissions, and NO₃⁻ and K⁺ were from vehicle emissions, photochemical reactions of NO _X, biomass and vegetable burning. The contribution of mineral aerosol from inside Beijing to the total mineral aerosols was ∼30% in spring of 2002, ∼70% in summer of 2002, ∼80% in autumn of 2003, ∼20% in PM₁₀ and ∼50% in PM_2.5, in winter of 2002. The pollution levels of the major pollution species, Ca, S, Cu, Zn, Ni, Pb, Fe, Mn, and Cd in re-suspended road dust reached ∼76%, ∼87%, ∼75%, ∼80%, ∼82%, ∼90%, ∼45%, ∼51%, and ∼94%, respectively. Re-suspended road dust from the traffic and construction activities was one of the major sources of pollution aerosols in Beijing.

Keywords: Re-suspended road dust; Mineral aerosol; Pollution aerosol; Sources

Modeling the intra-urban variability of outdoor traffic pollution in Oslo, Norway—A GA²LEN project by Christian Madsen; K.C.L. Karin C. Lødrup Carlsen; Gerard Hoek; Bente Oftedal; Per Nafstad; Kees Meliefste; Randi Jacobsen; Wenche Nystad; K.-H. Kai-Håkon Carlsen; Bert Brunekreef (pp. 7500-7511).

Traffic is a major source of air pollutants in urban environments, and exposure to these pollutants may be associated with adverse health effects. However, inconsistencies in observational epidemiological studies may be caused by differential measurement errors in various approaches in assessing exposure.We aimed to evaluate a simple method for assessing outdoor air pollutant concentrations in Oslo, Norway, through a land-use regression method.Samples of nitrogen oxides (NO _x) were collected in two different weeks using Ogawa passive diffusion samplers simultaneously at 80 locations across Oslo. Independent variables used in subsequent regression models as predictors of the pollutants were derived using the Arc 9 geographic information system (GIS) software. Indicators of land use, traffic, population density, and physical geography were tested.The final regression model yielded an adjusted coefficient of determination ( R²) of 0.77 for nitrogen dioxide (NO₂), 0.66 for nitric oxide (NO), and 0.73 for NO _x.The results suggest that a good predictive exposure model can be derived from this approach, which can be used to estimate long-term small-area variation in concentrations for individual exposure assessment in epidemiological studies in a highly cost-effective way. These small-area variations in traffic pollution are important since they may have associations with health effects.

Keywords: Long term; Exposure; Air pollution; Geographic information system; Traffic; Land-use regression modeling; Spatial variability

A comparative analysis of using trip-based versus link-based traffic data for regional mobile source emissions estimation by Song Bai; Y.-C. Yi-Chang (Ethan) Chiu; D.A. Debbie A. Niemeier (pp. 7512-7523).

The current method used for calculating vehicle emissions integrates travel data and associated vehicle emission factors. Travel data from traditional travel demand models are normally link-based (e.g., volumes on roadway segments), while California emission factors are trip-based (i.e., average emission factors over an entire trip), creating a mismatch in the modeling interface. Using dynamic simulation for trip assignment, we present a new modeling framework that consistently provides both trip-based and link-based VMT-speed distributions. Using the Sacramento Metropolitan Area and Kern County in California, we demonstrate the feasibility of this new method and quantify the effects of using trip-based versus link-based travel data on regional peak period emission inventories. The comparison results indicate that for the base scenario in both studied regions, the link-based method generally results in higher emissions than the trip-based method. The sensitivities of the link and trip-based methods to road network variations also appear dissimilar. The link-based emissions are more sensitive to facility-related changes, while the trip-based emissions are more sensitive to demand-related changes. This suggests that greater care may need to be taken to specify the effects of this modeling interface issue within the transportation conformity process and subsequent mobile emissions analysis.

Keywords: Mobile emission; Traffic data; Emission inventory; Air quality; Vehicle trip

Trends in aerosol optical depth for cities in India by William Porch; Petr Chylek; Mavendra Dubey; Steven Massie (pp. 7524-7532).

Recent analysis of trends in global short-wave radiation measured with pyranometers in major cities in India support a decrease in solar radiation in many of those cities since 1990. Since direct and diffuse radiation measurements include cloud effects, spring and summer dust and the variable summer monsoon rains, we concentrate in this paper on wintertime (November–February) aerosol optical depth measurements. The aerosol optical depth is derived from cloud-free turbidity measurements beginning in the 1960s and more recent sun photometer direct aerosol optical depth measurements. We compare the sun photometer derived trends with the pyranometer-derived trends using a radiative transfer model. These results are then compared to total ozone mapping spectrometer (TOMS) satellite-derived regional aerosol optical depths from 1980 to 2000. The results show that inclusion of the earlier turbidity measurements helps to establish an increasing regional turbidity trend. However, most of the increasing trend is confined to the larger cities in the Ganges River Basin of India (mainly Calcutta and New Delhi) with other cities showing a much less increase. Regional satellite data show that there is an increasing trend in aerosol off the coast of India and over the Ganges River Basin. The increase over the Ganges River Basin is consistent with population trends over the region during 1980–2000.

Keywords: Atmospheric aerosols; Climate; Trends; Global dimming; Radiation transfer

The mineral aerosol and its impact on urban pollution aerosols over Beijing, China by Lihui Han; Guoshun Zhuang; Shuiyuan Cheng; Juan Li (pp. 7533-7546).

A campaign of sampling total suspended particles (TSP) and fine particles (PM2.5) in Beijing from 2001 to 2004 were carried out to investigate the mineral aerosol and its impact on urban pollution aerosols, mainly sulfate, nitrate, and ammonium. In urban Beijing, mineral aerosol accounted for 32–67% of TSP, 10–70% ofPM2.5 in normal four seasons, and as high as 74% of TSP and 90% ofPM2.5 in dust storm period. The sources from outside Beijing accounted for 62% of the total mineral aerosols in TSP, and 76% inPM2.5 in spring, 69% and 45% in TSP andPM2.5, respectively, in winter,∼20% of both TSP andPM2.5 in summer and autumn; and it reached as high as 97% of TSP in dust storm days. Mineral aerosol has an important positive influence on formations of sulfate, nitrate, and ammonium, as there was a positive correlation between sulfate/nitrate/ammonium and mineral aerosol under appropriate meteorological conditions. Sulfate, and ammonium mainly existed in fine particles,PM2.5. Sulfate might mostly derive from the formation on the pathways of the long-range transport by the reactions of their precursorsSO2 on the surfaces of dust particles, while nitrate was mostly derived by the homogeneous reaction and the neutralization of their precursorsNO2 on surfaces of mineral aerosol. Nitrate and ammonium mostly derived from the local pollution sources.

Keywords: Mineral aerosol; Urban pollution aerosol; Sulfate; Nitrate; Ammonium

Mercury emissions from automobiles using gasoline, diesel, and LPG by Jong Hyun Won; Jae Young Park; Tai Gyu Lee (pp. 7547-7552).

Mercury (Hg) emissions from gasoline, diesel, and liquefied petroleum gas (LPG) vehicles were measured and speciated (particulate, oxidized, and elemental mercury). First, three different fuel types were analyzed for their original Hg contents; 571.1±4.5ngL⁻¹ for gasoline, 185.7±2.6ngL⁻¹ for diesel, and 1230.3±23.5ngL⁻¹ for LPG. All three vehicles were then tested at idling and driving modes. Hg in the exhaust gas was mostly in elemental form (Hg⁰), and no detectable levels of particulate (Hg^p) or oxidized (Hg²⁺) mercury were measured. At idling modes, Hg concentrations in the exhaust gas of gasoline, diesel, and LPG vehicles were 1.5–9.1, 1.6–3.5, and 10.2–18.6ngm⁻³, respectively. At driving modes, Hg concentrations were 3.8–16.8ngm⁻³ (gasoline), 2.8–8.5ngm⁻³ (diesel), and 20.0–26.9ngm⁻³ (LPG). For all three vehicles, Hg concentrations at driving modes were higher than at idling modes. Furthermore, Hg emissions from LPG vehicle was highest of all three vehicle types tested, both at idling and driving modes, as expected from the fact that it had the highest original fuel Hg content.

Keywords: Automobile mercury emission; Fuel mercury content; Gasoline; Diesel; LPG

Estimating dust emission from a sandbank on the downstream Jhuoshuei River under strong wind conditions by Chi-Wen Lin; Ju-Fang Yeh (pp. 7553-7561).

An empirical emission model based on experimental data was proposed. The total suspended particulates (TSP) emission model obtained by using stepwise multiple-regression analysis was significant ( p<0.001); moreover, the relatively high value of R-squared ( R²=0.85), which indicated that four parameters included in the model (air temperature, soil silt content, soil moisture content, and wind speed) accounted for the particulate emissions from a sandbank. The results of the multiple-regression analysis demonstrated that the TSP emission factors increased with increase in air temperature, soil silt content and wind speed, but were inversely affected by the soil moisture content. The model equation verified the experimental results and proved itself to be an important tool in predicting the dust emissions from a sandbank under strong wind conditions.

Keywords: Emission factors; Fugitive dust; Regression model; Sandbank; TSP

Applications of satellite remote sensing data for estimating dry deposition in eastern Texas by M.S. Feldman; T. Howard; E. McDonald-Buller; G. Mullins; D.T. Allen; A. Webb; Y. Kimura (pp. 7562-7576).

The sensitivity of dry deposition velocities and air quality model predictions to land use/land cover (LULC) is examined. Four LULC data sets are employed; three of the data sets are derived from recent satellite imagery and the fourth data set is the LULC database currently used in air quality models by the State of Texas. Effects of the land cover data on estimates of dry deposition velocities and modeled ozone concentrations are examined using the Comprehensive Air Quality Model with extensions (CAMx) during an 22 August 2000–6 September 2000 episode developed for the Houston/Galveston area. All land cover data sets showed good general agreement with a few significant differences in classification and spatial extent of certain land cover categories. Dry deposition decreased in urban areas with the new land cover data during peak hours on some days, leading to ozone concentrations that were approximately 2ppb higher in the Houston area. Ozone concentrations were lower west of Houston due to increased stomatal uptake by increased agricultural land coverage in the new data sets. These results indicate that the satellite-based LULC data, specifically the data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, can be used to provide periodic updates to land cover information used in CAMx and similar photochemical models.

Keywords: Dry deposition; Texas; Land cover; Air quality modeling; Ozone

Increase in summer European ozone amounts due to climate change by Frederik Meleux; Fabien Solmon; Filippo Giorgi (pp. 7577-7587).

The local and regional distribution of pollutants is significantly influenced by weather patterns and variability along with the spatial patterns of emissions. Therefore, climatic changes which affect local meteorological conditions can alter air quality. We use the regional air quality model CHIMERE driven by meteorological fields from regional climate change simulations to investigate changes in summer ozone mixing ratios over Europe under increased greenhouse gas (GHG) forcing. Using three 30-year simulation periods, we find that daily peak ozone amounts as well as average ozone concentrations substantially increase during summer in future climate conditions. This is mostly due to higher temperatures and reduced cloudiness and precipitation over Europe and it leads to a higher number of ozone events exceeding information and warning thresholds. Our results show a pronounced regional variability, with the largest effects of climate change on ozone concentrations occurring over England, Belgium, Germany and France. The temperature-driven increase in biogenic emissions appears to enhance the ozone production and isoprene was identified as the most important chemical factor in the ozone sensitivity. We also find that summer ozone levels in future climate projections are similar to those found during the exceptionally warm and dry European summer of 2003. Our simulations suggest that in future climate conditions summer ozone might pose a much more serious threat to human health, agriculture and natural ecosystems in Europe, so that the effects of climate trends on pollutant amounts should be considered in future emission control measures.

Keywords: Ozone; Air quality; Climate changes; Modelling; Public information

Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments by Annmarie G. Carlton; Barbara J. Turpin; Katye E. Altieri; Sybil Seitzinger; Adam Reff; H.-J. Ho-Jin Lim; Barbara Ervens (pp. 7588-7602).

Aqueous-phase photooxidation of glyoxal, a ubiquitous water-soluble gas-phase oxidation product of many compounds, is a potentially important global and regional source of oxalic acid and secondary organic aerosol (SOA). Reaction kinetics and product analysis are needed to validate and refine current aqueous-phase mechanisms to facilitate prediction of in-cloud oxalic acid and SOA formation from glyoxal. In this work, aqueous-phase photochemical reactions of glyoxal and hydrogen peroxide were conducted at pH values typical of clouds and fogs (i.e., pH=4–5). Experimental time series concentrations were compared to values obtained using a published kinetic model and reaction rate constants from the literature. Experimental results demonstrate the formation of oxalic acid, as predicted by the published aqueous phase mechanism. However, the published mechanism did not reproduce the glyoxylic and oxalic acid concentration dynamics. Formic acid and larger multifunctional compounds, which were not previously predicted, were also formed. An expanded aqueous-phase oxidation mechanism for glyoxal is proposed that reasonably explains the concentration dynamics of formic and oxalic acids and includes larger multifunctional compounds. The coefficient of determination for oxalic acid prediction was improved from 0.001 to >0.8 using the expanded mechanism. The model predicts that less than 1% of oxalic acid is formed through the glyoxylic acid pathway. This work supports the hypothesis that SOA forms through cloud processing of glyoxal and other water-soluble products of alkenes and aromatics of anthropogenic, biogenic and marine origin and provides reaction kinetics needed for oxalic acid prediction.

Keywords: Secondary organic aerosol; Aqueous-phase atmospheric chemistry; Glyoxal; Oxalic acid; Organic PM; Cloud processing

Effects of particle acidity and UV light on secondary organic aerosol formation from oxidation of aromatics in the absence of NO _x by Gang Cao; Myoseon Jang (pp. 7603-7613).

Recent laboratory observations have shown that particle acidity increases secondary organic aerosol (SOA) yields. However, these studies have mainly focused on biogenic precursors such as isoprene and terpenes. In this paper, the effects of particle acidity on the SOA yields from aromatic precursors under both dark and UV–visible light conditions were characterized through controlled chamber experiments. SOA was produced from oxidation of toluene and 1,3,5-trimethylbenzene (135-TMB) with OH radicals created by ozonolysis of 2-methyl-2-butene (MB). Particle acidity, described with proton concentrations, varied with inorganic seed aerosol composition and humidity (20–52%). Overall, in the presence of acidic seeds, greater increases in SOA yields were observed for the toluene system than the 135-TMB system. UV irradiation reduced SOA yields for both toluene and 135-TMB systems to different extents.

Keywords: SOA formation; Particle acidity; Inorganic seed; Humidity; UV radiation

Formation and emissions of carbonyls during and following gas-phase ozonation of indoor materials by D.G. Poppendieck; H.F. Hubbard; C.J. Weschler; R.L. Corsi (pp. 7614-7626).

Ozone concentrations that are several orders of magnitude greater than typical urban ambient concentrations are necessary for gas-phase ozonation of buildings, either for deodorization or for disinfection of biological agents. However, there is currently no published literature on the interaction of building materials and ozone under such extreme conditions. It would be useful to understand, for example in the case of building re-occupation planning, what types and amounts of reaction products may form and persist in a building after ozonation. In this study, 24 materials were exposed to ozone at concentrations of 1000ppm in the inlet stream of experimental chambers. Fifteen target carbonyls were selected and measured as building ozonation by-products (BOBPs). During the 36h that include the 16h ozonation and 20h persistence phase, the total BOBP mass released from flooring and wall coverings ranged from 1 to 20mgm⁻², with most of the carbonyls being of lower molecular weight (C₁–C₄). In contrast, total BOBP mass released from wood-based products ranged from 20 to 100mgm⁻², with a greater fraction of the BOBPs being heavier carbonyls (C₅–C₉). The total BOBP mass released during an ozonation event is a function of both the total surface area of the material and the BOBP emission rate per unit area of material. Ceiling tile, carpet, office partition, and gypsum wallboard with flat latex paint often have large surface areas in commercial buildings and these same materials exhibited relatively high BOBP releases. The greatest overall BOBP mass releases were observed for three materials that building occupants might have significant contact with: paper, office partition, and medium density fiberboard, e.g., often used in office furniture. These materials also exhibited extended BOBP persistence following ozonation; some BOBPs (e.g., nonanal) persist for months or more at emission rates large enough to result in indoor concentrations that exceed their odor threshold.

Keywords: Ozone; Heterogeneous chemistry; By-products; Carbonyls; Aldehydes

Two-year magnetic monitoring in conjunction with geochemical and electron microscopic data of roadside dust in Seoul, Korea by Wonnyon Kim; S.-J. Seong-Jae Doh; Y.-H. Yong-Hee Park; S.-T. Seong-Taek Yun (pp. 7627-7641).

Mineral magnetic properties of roadside dusts in Seoul, Korea, were measured and compared with the results of geochemical analyses in order to investigate the spatio-temporal patterns of urban pollution. Scanning electron microscope (SEM) observations and energy dispersive X-ray spectroscopy (EDS) analyses were carried out to verify the magnetic materials and their potential sources. A total of 1956 dust samples were collected monthly at eight sites, from June 1998 to June 2000. Thermomagnetic data and SEM observations for magnetic extracts indicated that the major magnetic phase was magnetite-like material. In particular, the highest and the lowest magnetic concentrations were observed in industrial areas and a park area, respectively, whereas, heavy traffic areas showed low to intermediate concentration. A linear correlation between enrichment indexes of magnetic susceptibility and heavy metals suggests that magnetic susceptibility can be used as a proxy for heavy metal pollution. The magnetic concentrations and magnetic particle sizes showed systematic seasonal fluctuations (high and large in winter versus low and small in summer) due to the seasonal influx variations of anthropogenic magnetic materials. On the basis of the morphology and elemental composition, the magnetic materials were grouped into three types: magnetic spherules possibly emitted from factories and domestic heating systems, aggregates derived from vehicle emission or motor vehicle brake system, and angular magnetic particles of natural origin.

Keywords: Heavy metal pollution; Magnetic material; Magnetic monitoring; Roadside dust; Seoul

Source identification of nickel in TSP and PM_2.5 in Tokyo, Japan by Tomoaki Okuda; Shunsuke Nakao; Masayuki Katsuno; Shigeru Tanaka (pp. 7642-7648).

This study investigates the source identification of nickel in the aerosol of the Tokyo metropolitan area. TSP and PM_2.5 samples were collected daily from August to November 2004. The samples were examined by means of the water-extraction method, followed by elemental analysis and SEM/EDX analysis. We distinguished two types of atmospheric nickel sources in the studied area: (1) particles derived from heavy oil combustion, distributed mostly in fine particles such as PM_2.5, relatively water-soluble, and containing vanadium and (2) particles derived from mechanical abrasion/erosion of metallic surfaces, distributed in coarse particles such as TSP, relatively water-insoluble, and containing chromium.

Keywords: Aerosol; Chromium; Heavy metals; LA/ICP-MS; Nickel; PM; _2.5; SEM/EDX; Trace elements; TSP; Vanadium; Water-soluble metals

Exploration of heterogeneous chemistry in model atmospheric particles using extended X-ray absorption fine structure analysis by J. Bramante; Ryan Z. Hinrichs; E.C. Brown; S. Calvin (pp. 7649-7653).

As models of the composition and heterogeneous chemical reactions of the troposphere undergo refinement, novel application of state-of-the-art analytical techniques will be necessary to propound realistic characterizations of mineral dust chemistry. In this study, strontium carbonate particles treated with gaseous nitric acid and nitrogen dioxide were examined with X-ray absorption fine structure analysis (EXAFS). The X-ray spectra of carbonate and nitrate standards were fitted to ab initio calculations, which were used to determine the structure and consistency of strontium nitrate formed on strontium carbonate. By examining differences in mean square radial displacement and lattice spacing values obtained for bulk Sr(NO₃)₂ as compared to Sr(NO₃)₂ formed on SrCO₃, EXAFS proves effective as a tool for investigating the local structure and composition of heterogeneous aerosol particles. The implications of findings on reacted strontium carbonate for atmospheric models of calcium carbonate aerosol are discussed.

Keywords: Atmospheric particles; Strontium carbonate; Strontium nitrate; EXAFS; Mineral dust

Elevated atmospheric CO₂ concentration and temperature across an urban–rural transect by K. George; L.H. Ziska; J.A. Bunce; B. Quebedeaux (pp. 7654-7665).

The heat island effect and the high use of fossil fuels in large city centers are well documented, but by how much fossil fuel consumption is elevating atmospheric CO₂ concentrations and whether elevations in both atmospheric CO₂ and air temperature from rural to urban areas are consistently different from year to year are less well known. Our aim was to record atmospheric CO₂ concentrations, air temperature and other environmental variables in an urban area and compare it to suburban and rural sites to see if urban sites are experiencing climates expected globally in the future with climate change. A transect was established from Baltimore city center (Urban site), to the outer suburbs of Baltimore (suburban site) and out to an organic farm (rural site). At each site a weather station was set-up to monitor environmental variables for 5 years. Atmospheric CO₂ was consistently and significantly increased on average by 66ppm from the rural to the urban site over the 5 years of the study. Air temperature was also consistently and significantly higher at the urban site (14.8°C) compared to the suburban (13.6°C) and rural (12.7°C) sites. Relative humidity was not different between sites whereas the vapor pressure deficit (VPD) was significantly higher at the urban site compared to the suburban and rural sites. An increase in nitrogen deposition at the rural site of 0.6% and 1.0% compared to the suburban and urban sites was small enough not to affect soil nitrogen content. Dense urban areas with large populations and high vehicular traffic have significantly different microclimates compared to outlying suburban and rural areas. The increases in atmospheric CO₂ and air temperature are similar to changes predicted in the short term with global climate change, therefore providing an environment suitable for studying future effects of climate change on terrestrial ecosystems.

Keywords: Microenvironment; Climate change; Urban ecology; Heat island; Long term

A comparison of gas- and liquid-loaded sorbent standards for the calibration of measurements of volatile organic compounds by Nicholas A. Martin; Natalie L.A.S. Barber; John K. Black; Robert P. Lipscombe; Christopher A. Taig (pp. 7666-7671).

The monitoring of volatile organic compounds (VOCs) at environmental levels is commonly carried out in the field using Perkin-Elmer-type sorbent-based passive or active samplers. Measurements of important trace species, such as benzene, toluene and xylenes, are often calibrated using thermal desorption standards that are liquid loaded onto the sorbent. This method is normally adopted over the method of gas loading of standards, on the grounds of ease of application and cost. We report a comparison between sorbent standards prepared by both methods using the sorbent Carbopack X and show that under the conditions used here the two show good agreement with each other. We also present work using liquid-loaded standards on the sorbents Tenax and Chromosorb-106, prepared with the solvents cyclohexane and methanol. The results indicate that, to obtain 100% recovery of the determinands from the desorbed samplers, issues such as type of solvent and sorbent combination together with purge flow should be considered.

Keywords: Carbopack X; Tenax; Chromosorb-106; Time division dilution; Solvent; Purge flow rate

Sampler placement to determine emission factors from ground level area sources by W.B. Faulkner; J.M. Lange; J.J. Powell; B.W. Shaw; C.B. Parnell (pp. 7672-7678).

Emission factors are used by state air pollution regulatory agencies to regulate emissions from sources of atmospheric pollution. Emission factors for ground level area sources (GLASs) can be determined by sampling ambient pollutant levels and using dispersion modeling to back-calculate the emission rate from a source. This manuscript describes a method used to locate samplers downwind of a GLAS to most accurately determine the emission flux from the source. Contributions from other sources, changes in particle size distributions, and measurement uncertainty are considered.

Keywords: Emission factor; Particulate matter; PM; Area source; Gaussian modeling

Comment on “Fumigation of pollutants in and above the entrainment zone into a growing convective boundary layer: A large-eddy simulation” by Si-Wan Kim; Chin-Hoh Moeng; Jeffrey C. Weil; Mary C. Barth (pp. 7679-7682).

Corrigendum to “An integrated MM5-CMAQ modeling approach for assessing trans-boundary PM₁₀ contribution to the host city of 2008 Olympic summer games—Beijing, China” by D.S. Chen; S.Y. Cheng; L. Liu; T. Chen; X.R. Guo (pp. 7683-7683).

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Atmospheric Environment (v.41, #35)