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Atmospheric Environment (v.45, #6)

Editorial board (pp. i).

Megacities as hot spots of air pollution in the East Mediterranean by Maria Kanakidou; Nikolaos Mihalopoulos; Tayfun Kindap; Ulas Im; Mihalis Vrekoussis; Evangelos Gerasopoulos; Eirini Dermitzaki; Alper Unal; Mustafa Koçak; Kostas Markakis; Dimitris Melas; Georgios Kouvarakis; Ahmed F. Youssef; Andreas Richter; Nikolaos Hatzianastassiou; Andreas Hilboll; Felix Ebojie; Folkard Wittrock; Christian von Savigny; John P. Burrows; Annette Ladstaetter-Weissenmayer; Hani Moubasher (pp. 1223-1235).

This paper provides a comprehensive overview of the actual knowledge on the atmospheric pollution sources, transport, transformation and levels in the East Mediterranean. It focuses both on the background atmosphere and on the similarities and differences between the urban areas that exhibited important urbanization the past years: the two megacities Istanbul, Cairo and the Athens extended area. Ground-based observations are combined with satellite data and atmospheric modeling. The overall evaluation pointed out that long and regional range transport of natural and anthropogenic pollution sources have about similar importance with local sources for the background air pollution levels in the area.► East Mediterranean is receptor and chemical cooker of transported air pollution. ► Megacities pollution sources are added to high regional background pollutant levels. ► Interactions between anthropogenic and natural emissions enhance air pollution. ► High regional O₃ affected by different VOC/NO_x levels and VOC speciation. ► Coating by pollutants increases dust solubility and deposition of nutrients.

Keywords: Megacities; East Mediterranean; Air pollution; Transport; Anthropogenic impact

Characterization of major offensive odorants released from lake sediment by Janice Susaya; Ki-Hyun Kim; Yoon-Seok Chang (pp. 1236-1241).

The amount of odorants effused from Lake Sihwa during the low tide period was estimated using sediment samples collected from various sites. A wide variety of odorants released from lake sediment were measured such as reduced sulfur compounds (RSCs), aldehydes, nitrogenous compounds, volatile organic compounds (VOCs), and volatile fatty acids (VFAs). A comparison of emission rates (μg m⁻² min⁻¹) showed large mean values from such species as NH₃ (14,550), toluene (370), and DMS (106), while the lowest values were seen from VFAs and some VOCs. If their emission concentrations are converted into odor intensity (OI), the OI values were dominated by such odorants as NH₃ (2.07), H₂S (1.65), DMS (1.80), acetaldehyde (1.52), butyric acid (1.59), butyraldehyde (1.28), isovaleric acid (1.15), and valeric acid (0.78). The dilution to threshold (D/T) ratio derived on the basis of the air dilution sensory (ADS) test yielded a mean of 62 (range: 10–173); 19 out of 21 samples were seen to exceed the guideline D/T value of 15. The sum of odor intensities derived from individual odorants exhibited strong compatibilities with the D/T ratio ( r² = 0.87; α = 0.003). The overall results of this study confirm that the sediment can play an important role in the malodor phenomenon in the area surrounding the Lake Sihwa.► In this study, emission characteristics of odorants released from sediments were evaluated. ► The targets were selected to include VOC, reduced sulfur, aldehyde, acid, and N-compounds. ► The relationship between absolute odorant concentration and their intensities were examined. ► The results will help establish an environmental management scheme for the lake sediments.

Keywords: VOCs; RSCs; Aldehydes; Ammonia; Acids; Malodor

City scale assessment model for air pollution effects on the cultural heritage by D. de la Fuente; J.M. Vega; F. Viejo; I. Díaz; M. Morcillo (pp. 1242-1250).

Damage caused to objects of cultural heritage is one of the most serious detrimental effects of air pollutants. Within the 6th Framework Programme of the EU, the CULT-STRAT project is an inter-agency, multi-disciplinary project that has integrated research and monitoring information to provide answers to policy and management questions, which relate the effects of air pollutants on heritage and the management options available to mitigate them. The overall aim of the project has been to assess and predict the effects of different pollutants on materials and objects of cultural heritage in a multipollutant scenario and to identify indicators and thresholds levels of pollutants. These have been used for development of management strategies for sustainable maintenance and preventive conservation of European Cultural Heritage and air quality policy from continental to local scale.The present paper reports one of the studies carried out in the CULT-STRAT project at city level and focused on the town of Madrid (Spain). Different maps are shown for the present and possible future scenarios (2010 and 2020): inventory of stock of cultural heritage for each selected material, concentration of selected pollutants (SO₂, NO₂, O₃ and PM₁₀), corrosion (cast bronze) and recession (Portland limestone), exceedance of tolerable degradation thresholds for each material and corrosion-cultural heritage overlapped maps.► A methodology for the evaluation of Cultural Heritage at risk has been developed. ► A case-study focused on the city of Madrid, as example, is presented. ► Two materials have been considered: cast bronze and Portland limestone. ► Mainly, the effect of pollution reduction has been studied. ► Mapping: pollutants, corrosivity, exceedance and future scenarios.

Keywords: Cultural heritage; Air pollution; Corrosivity; Mapping

Chemical composition and size distribution of wintertime aerosols in the atmosphere of Mt. Hua in central China by Jianjun Li; Gehui Wang; Bianhong Zhou; Chunlei Cheng; Junji Cao; Zhenxing Shen; Zhisheng An (pp. 1251-1258).

TSP, PM₁₀ and size-segregated aerosols were collected at the summit (2060 m, a.s.l.) of Mt. Hua in central China during the winter of 2009, and determined for organic (OC) and elemental carbon (EC), pH of water-extracts and inorganic ions. OC in TSP and PM₁₀ are 6.9 ± 2.9 and 5.9 ± 2.5 μg m⁻³, while EC in TSP and PM₁₀ are 0.9 ± 0.6 and 0.9 ± 0.5 μg m⁻³, respectively. SO₄²⁻, NO₃⁻, NH₄⁺ and Ca²⁺ are major ions in PM₁₀ with concentrations of 5.8 ± 3.7, 2.7 ± 1.6, 1.6 ± 0.9 and 1.5 ± 0.7 μg m⁻³, respectively. OC/EC ratios (8.2 ± 3.1 in TSP and 6.6 ± 1.8 in PM₁₀) at the mountaintop are 2–4 times higher than those in lowland surface, suggesting an enhanced transformation of organics from gas- to solid- phase because of an increased photochemical oxidation and/or an increased condensation due to lower temperature, as well as an increased organic input from mountain plant emission. Air mass backward trajectories showed that compared with those derived from north/northwest China aerosols transported from the south contained higher concentrations of SO₄²⁻ and NH₄⁺ and lower concentrations of Ca²⁺. Size distributions of NH₄⁺ and K⁺ presented as an accumulation mode with a peak at 0.7–1.1 μm, in contrast to Ca²⁺ and Mg²⁺, which maximized at the size 4.7–5.8 μm as a coarse mode. SO₄²⁻ and NO₃⁻ showed a bimodal pattern with a large peak at the range 0.7–1.1 μm and a small peak at the size of 4.7–5.8 μm, whereas Na⁺ and Cl⁻ displayed a bimodal pattern with two equivalent peaks in the fine (<2.1 μm) and coarse (≥2.1 μm) ranges. pH values of the water-extracts demonstrate that aerosols originate from southern China are more acidic than those from the north/northwest, and the particles with a diameter of 0.7–1.1 μm are most acidic.► An increased photo-oxidation production was observed at the mountaintop. ► Higher concentrations of SO₄^2- and NH₄⁺ suggest aerosol pollution in south China is more serious. ► Sulfate and secondary organic aerosols at Mt. Hua were formed via similar pathway. ► Aerosols derived from north/northwest China are less acidic than those from the south. ► Particles with diameter of 0.7–1.1 μm are most acidic.

Keywords: Mountain aerosols; Organic and elemental carbon; Inorganic ions; Size distribution; Sources

Regional characteristics of dry deposition of sulfur and nitrogen compounds at EANET sites in Japan from 2003 to 2008 by Tomomi Endo; Hiroaki Yagoh; Keiichi Sato; Kazuhide Matsuda; Kentaro Hayashi; Izumi Noguchi; Kiyoshi Sawada (pp. 1259-1267).

The regional characteristics of estimated dry deposition and total atmospheric deposition, including dry and wet deposition, at 10 EANET sites in Japan from April 2003 to March 2008 are discussed. The components examined for dry deposition were sulfur compounds (SO₂ and particulate SO₄²⁻) and nitrogen compounds (HNO₃, NH₃, particulate NO₃⁻, and NH₄⁺). Dry deposition was calculated by the product of the deposition velocity estimated by the inferential method for forest and grass surfaces and the air concentration of each compound. The 5-year mean annual dry deposition amounts for sulfur and nitrogen compounds were in the range of 5–37 and 7–50 mmol m⁻² year⁻¹, respectively. The regional characteristics of dry deposition amounts were similar between sulfur and nitrogen compounds, which showed higher deposition in the Sea of Japan side and in the Western Japan. The 5-year mean annual total deposition amounts for sulfur and nitrogen compounds were in the range of 28–77 and 22–130 mmol m⁻² year⁻¹, respectively. The contribution of dry deposition to the total deposition amounts was 10–55% and 13–56% for sulfur and nitrogen compounds, respectively. The regional characteristic of total deposition was different between sulfur and nitrogen compounds. Total deposition amounts in Japan were larger than those in CASTNET and EMEP because of high wet deposition, which implied that the increasing emissions of air pollutants in East Asia caused high atmospheric depositions.► The regional characteristic of dry and wet depositions for S and N was discussed. ► Dry deposition in Japan was evaluated by the modified inferential method. ► The dry deposition was higher in the Sea of Japan side and the western Japan. ► Higher total deposition for S was possibly caused by transboundary air pollution. ► Dry and wet depositions in Japan were larger than those in CASTNET and EMEP.

Keywords: Dry deposition; Deposition velocity; Sulfur; Nitrogen; EANET

Characteristics of carbonate carbon in PM_2.5 in a typical semi-arid area of Northeastern China by K.F. Ho; R.J. Zhang; S.C. Lee; Steven Sai Hang Ho; S.X. Liu; Kochy Fung; J.J. Cao; Z.X. Shen; H.M. Xu (pp. 1268-1274).

Daily concentrations of carbonate carbon (CC) in PM_2.5 collected in semi-arid area in Northeast China (Tongyu) were quantified by acidification that measures carbon dioxide (CO₂) gas evolved using DRI Model 2001 Thermal Optical reflectance (TOR) Carbon Analyzer. The concentrations of CC during Asian dust storm (DS) and non-dust storm (NDS) periods during 14 April to 21 June, 2006 were determined and the transport pathways and possible sources for the CO₃²⁻ aerosols were identified. Concentrations of CC in PM_2.5 collected from 14 April to 23 June, 2006 in Tongyu are ranged from 0.1 to 7.5μgCm⁻³ with an average of 1.3μgCm⁻³. The average CC concentration during DS events was 2.6±1.7μgm⁻³, which was almost 4 times the daily average concentration of 0.6±0.5μgm⁻³ during non-dust storm (NDS) period. Carbonate carbon accounted for 10% and 4% of total carbon in Tongyu during DS and NDS period, respectively. Carbonate concentrations were also derived by calculating the difference between cations and anions (ionic balance method). And good correlation is observed for the carbonate measured to the values for carbonate calculated from the ionic balance difference ( R²=0.90). Higher correlations were observed between Ca with selected water-soluble ions (sulfate, nitrate or chloride) and elemental carbon in DS than in NDS periods. This is consistent with previous studies that more calcium salts (sulfate, nitrate or chloride) were formed during atmospheric transport during DS period. During the DS in spring 2006, three groups (A to C) of air mass trajectories were identified that passed over Tongyu. In general, when the air mass came from northwest, and south or southwest to Tongyu, high concentrations of carbonate were observed.► A newly modified analytical method was used to analyze the carbonate carbon in PM_2.5 collected in semi-arid area in Northeast China (Tongyu). ► Compare the methods used to estimate the carbonate concentrations with direct measurement. ► Investigate the concentrations of CC and CO₃²⁻ during Asian dust storm (DS) and non-dust storm (NDS) periods at a typical semi-arid area of Northeastern China. ► Identify the transport pathways and possible sources for the CO₃²⁻ aerosols in Tongyu.

Keywords: Semi-arid area; Carbonate carbon; Dust storm; Tongyu

Analysis of optical properties of atmospheric aerosols inferred from spectral AODs and Ångström wavelength exponent by G. Balakrishnaiah; K. Raghavendra kumar; B. Suresh Kumar Reddy; K. Rama Gopal; R.R. Reddy; L.S.S. Reddy; Y. Nazeer Ahammed; K. Narasimhulu; K. Krishna Moorthy; S. Suresh Babu (pp. 1275-1285).

Aerosol measurements over a tropical semi-arid site in Anantapur (14.62°N, 77.65°E, 331 m asl), India, provide the variabilities of aerosol characteristics for the period of January 2007–December 2008. The mean values of aerosol optical depth at 500 nm (AOD_500 nm) over 2-year period are found to be 0.37 ± 0.11, 0.39 ± 0.13 and 0.30 ± 0.10 during winter, summer and monsoon seasons, respectively. A rather systematic variation is seen with AOD peaking in the month of March, falling off gradually to the lowest value in June and increasing slowly superposed with some modulations, which show a weak secondary peak in October. The mean and standard values of the Ångström exponent, α (turbidity coefficient, β), are found to be 1.06 ± 0.33 (0.17 ± 0.05) during winter, 0.97 ± 0.35 (0.22 ± 0.04) during summer and 0.85 ± 0.26 (0.16 ± 0.06) during monsoon. The frequency distribution of α is relatively broad with two modes for dusty (α < 1) and non-dusty (α > 1) situations. This frequency distribution of α reveals a great dispersion of a values in all seasons thus denoting variability in the aerosol-size distribution. In this study, spectral AOD and Ångström exponent data are analyzed to obtain information about the adequacy of the simple use of the Ångström exponent and its variation for characterizing optical properties of aerosols, and exploring possibilities for a more efficient characterization of them. Using the least-squares fit method, the Ångström parameter, α, is calculated in the spectral interval 380–850 nm, along with coefficients a₁ and a₂ of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The correlations between the coefficients a₁ and a₂ with months and α are discussed in the paper.► AOD showed large and small values during summer and monsoon seasons. ► Alpha is low (high) in summer (winter) indicates abundance of coarse (fine) aerosol. ► WVC varies with maximum (minimum) during monsoon (summer). ► The frequency distribution of α denotes variability in the aerosol-size distribution. ► a₂<0 (a₂>0) is characteristic of ASD dominated by fine (coarse) aerosols.

Keywords: Aerosols; Aerosol optical depth; Ångström exponent; Water vapor content; India

Activity size distribution of⁷Be in association with trace metals in the urban area of the city of Thessaloniki, Greece by Alexandra Ioannidou (pp. 1286-1290).

The activity size distributions of the natural radionuclide tracer⁷Be and associated trace metals in different inhalable fractions (<0.39μm, 0.391–0.69μm, 0.69–1.3μm, 1.3–2.1μm, 2.1–4.2μm, 4.2–10.2μm and >10.2μm) were determined in a typical traffic-affected urban site in the center of the city of Thessaloniki, Greece, over a seven month period (June’09–January’10). The activity median aerodynamic diameter (AMAD) ranged from 0.58 to 1.22μm (avg 0.80μm), indicating post-condensation growth either in the upper atmosphere or after mixing in the boundary layer. It was shown that more than 80% of the⁷Be activity was associated with particles smaller than 1.3μm. The AMAD values are anticorrelated with⁷Be activities, while they are correlated with RH% with high confidence ( R=0.92, p<0.00813). The composition of the associated particles is basically Ca, Si and S. Among the heavy metals determined, Fe is the most abundant, followed by Cu. Minor amounts of Pb, Cr, Ni are presented in coarse size ranges. The amount of Fe increased with decreasing particle size, displaying positive correlation with AMAD of⁷Be in case of strong wind from NW direction and indicating the transport of pollutted air from the industrial area of the city of Thessaloniki. The measured distributions are believed to result from a combination of processes including local anthropogenic and natural sources, such as traffic, industrial emissions and resuspension of road dust. However, the local meteorological conditions seem to affect the final activity size distribution of⁷Be and their associated trace element distributions.► The Activity Median Aerodynamic Diameter (AMAD) of radioactive nuclide⁷Be are anticorrelated with⁷Be activities. ► The Activity Median Aerodynamic Diameter (AMAD) of radioactive nuclide⁷Be are correlated with RH% with high confidence ( R=0.92, p<0.00813). ► The activity size distribution of the radioactive nuclide⁷Be seems that can be used as an index of air pollutant conditions. ► Under certain weather conditions⁷Be presents similar behavior with some trace metals like Fe, Cu, in the urban area of a big city.

Keywords: AMAD; ⁷; Be radioactive aerosol; Size distribution; Trace elements; Urban area

NMOC, ozone, and organic aerosol in the southeastern United States, 1999–2007: 3. Origins of organic aerosol in Atlanta, Georgia, and surrounding areas by C.L. Blanchard; G.M. Hidy; S. Tanenbaum; E.S. Edgerton (pp. 1291-1302).

Carbonaceous compounds constitute a major fraction of the fine particle mass at locations throughout North America; much of the condensed-phase organic carbon (OC) is produced in the atmosphere from NMOC reactions as “secondary” OC (SOC). Ten years of particulate carbon and speciated non-methane organic compound (NMOC) data combined with other measurements from Southeastern Aerosol Research and Characterization (SEARCH) and other sites provide insight into the association between elemental carbon (EC), OC and NMOCs. Data are analyzed to characterize the OC and SOC contrasts between urban Atlanta, Georgia, and nearby non-urban conditions in the Southeast. Analysis of the monitoring record indicates that the mean Atlanta urban excess of total carbon (TC) is 2.1–2.8μgm⁻³. The OC/EC ratio of the Atlanta urban excess is in the range 1.3 to 1.8, consistent with OC/EC ratios observed in motor vehicle emissions and a fossil carbon source of urban excess TC. Carbon isotope analysis of a subset of particle samples demonstrates that the urban excess is mainly fossil in origin, even though the majority of the TC is modern at both urban and non-urban sites. Temperature-dependent partitioning of OC between gas and condensed phases cannot explain the observed diurnal and seasonal variations of OC/CO, EC/CO, and OC/EC ratios. Alternatively, a hypothesis involving vertical mixing of OC-enriched air from aloft is supported by the seasonal and diurnal OC, isopentane, aromatic and isoprene observations at the ground. A statistical model is applied to indicate the relative significance of aerometric factors affecting OC and EC concentrations, including meteorological and pollutant associations. The model results demonstrate strong linkages between fine particle carbon and pollutant indicators of source emissions compared with meteorological factors; the model results show weaker dependence of OC on meteorological factors than is the case for ozone (O₃) concentrations.► Southeastern Aerosol Research and Characterization (SEARCH) data are analyzed. ► Mean Atlanta urban excess particulate total carbon (TC) is 2.1–2.8μgm⁻³. ► Carbon isotope analysis demonstrates that the majority of regional TC is modern. ► Atlanta urban excess TC is mainly fossil in origin except in winter. ► OC/EC ratio of Atlanta urban excess is comparable to OC/EC in motor vehicle exhaust.

Keywords: Nonmethane organic compounds; Southeastern United States; SEARCH; Particulate organic carbon; Elemental carbon; Secondary Organic aerosol

The influence of temperature and aerosol acidity on biogenic secondary organic aerosol tracers: Observations at a rural site in the central Pearl River Delta region, South China by Xiang Ding; Xin-Ming Wang; Mei Zheng (pp. 1303-1311).

At a rural site in the central Pearl River Delta (PRD) region in south China, fine particle (PM_2.5) samples were collected during fall-winter 2007 to measure biogenic secondary organic aerosol (SOA) tracers, including isoprene SOA tracers (3-methyl-2,3,4-trihydroxy-1-butene, 2-methylglyceric acid, 2-methylthreitol and 2-methylerythritol), α-pinene SOA tracers ( cis-pinonic acid, pinic acid, 3-methyl-1,2,3-butanetricarboxylic acid, 3-hydroxyglutaric acid and 3-hydroxy-4,4-dimethylglutaric acid) and a sesquiterpene SOA tracer (β-caryophyllinic acid). The isoprene-, α-pinene- and sesquiterpene-SOA tracers averaged 30.8±15.9, 6.61±4.39, and 0.54±0.56ngm⁻³, respectively; and 2-methyltetrols (sum of 2-methylthreitol and 2-methylerythritol, 27.6±15.1ngm⁻³) and cis-pinonic acid (3.60±3.76ngm⁻³) were the dominant isoprene- and α-pinene-SOA tracers, respectively. 2-Methyltetrols exhibited significantly positive correlations ( p<0.05) with ambient temperature, probably resulting from the enhanced isoprene emission strength and tracer formation rate under higher temperature. The significantly positive correlation ( p<0.05) between 2-methyltetrols and the estimated aerosol acidity with a slope of 59.4±13.4ngm⁻³ per μmol [H⁺] m⁻³ reflected the enhancement of isoprene SOA formation by aerosol acidity, and acid-catalyzed heterogeneous reaction was probably the major formation pathway for 2-methyltetrols in the PRD region. 2-Methylglyceric acid showed poor correlations with both temperature and aerosol acidity. The α-pinene SOA tracers showed poor correlations with temperature, probably due to the counteraction between temperature effects on the precursor emission/tracer formation and gas/particle partitioning. Among the α-pinene SOA tracers, only cis-pinonic acid and pinic acid exhibited significant correlations with aerosol acidity with slopes of −11.7±3.7 and −2.2±0.8ngm⁻³ per μmol [H⁺] m⁻³, respectively. The negative correlations observed for α-pinene SOA tracers might result from their transfer from particle to gas phase with the increase of aerosol acidity. The ratio of cis-pinonic acid plus pinic acid to 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) ranged from 0.28 to 28.9 with a mean of 7.19, indicating the relatively fresh α-pinene SOA tracers during our campaign.► Isoprene-SOA tracers exhibited positive correlations with temperature and aerosol acidity. ► Slopes of tracers vs. aerosol acidity showed huge gap between our campaign and chamber simulation.

Keywords: SOA; Tracers; Temperature; Aerosol acidity; Pearl River Delta (PRD)

An oil spill accident and its impact on ozone levels in the surrounding coastal regions by Sang-Keun Song; Zang-Ho Shon; Yoo-Keun Kim; Yoon-Hee Kang; Ki-Hyun Kim (pp. 1312-1322).

An oil spill on the west coast of the Republic of Korea was investigated with regard to its impact on ozone (O₃) concentration levels in the surrounding regions. The accident occurred on December 7, 2007 with the total estimate of 12,500 tons of Iranian Heavy plus Kuwait Export crude oils. The evaporation rates of the volatile hydrocarbon fractions in these crude oils were estimated based on the molar fractions of crude oils and their mass transfer coefficients. Their emission rates parameterized with several key environmental parameters (e.g., wind speed, seawater temperature, and salinity) along with oil type information were then applied in the 3-D chemical transport model. Photochemical production of O₃ in winter just after the accident was relatively insignificant due to very low photochemical activity. For the case/sensitivity study, the photochemical production of O₃ simulated under the hot summer weather conditions was predicted to be significant at the same magnitude of the oil spill. This study confirms that an oil spill, if occurring around coastal regions, can alter O₃ levels to a large extent depending on the meteorological conditions.► We estimate the impact of oil spill at the west coast on O₃. ► Its largest impact on O₃ was predicted to be in the downwind areas by 9 ppb. ► Advection is generally a main contributor to O₃ concentration change. ► O₃ production rate for RO₂+NO was higher than that for HO₂+NO.

Keywords: Oil spill; Ship; Evaporation rate; Photochemical activity; O; ₃

Effect of fireworks display on perchlorate in air aerosols during the Spring Festival by Yali Shi; Ning Zhang; Jianmin Gao; Xin Li; Yaqi Cai (pp. 1323-1327).

Perchlorate is regarded as a new emerging persistent inorganic environmental contaminant. It can result in important neurodevelopmental deficits and goiter in infants and children because of its inhibition of iodine uptake into the thyroid tissue. Furthermore, its presence in the human body can cause improper regulation of metabolism for adults. It is often used as ingredient in the production of fireworks. So fireworks display may influence the perchlorate levels in atmospheric particulate matter (PM). In this paper perchlorate was determined in air aerosol samples (Inhalable particulate matter (PM10) and larger particulate matter (PM10-100)) collected from two locations (Lanzhou City and Yuzhong County) in Gansu province over a month period (February 1rst to March 4th) during the Spring Festival (February 18th) in 2007 in order to study the effect of fireworks display on perchlorate in air aerosol. The results showed that different concentrations of perchlorate were detected in almost all samples, ranging from −3. And the detection frequencies of perchlorate were 91% (100%) and 50% (59%) for PM10-100 (PM10) in Lanzhou City and Yuzhong County, respectively. The highest concentrations were all found in the samples from two sites on New Year’s Eve, which was 39.16ngm⁻³ (PM10-100) and 9.89ngm⁻³ (PM10) for Lanzhou city, 3.43ngm⁻³ (PM10-100) and 4.97ngm⁻³ (PM10) for Yuzhong County, 6.8-26.2 times as the mean concentrations during the period of no or limited fireworks display. This indicated that the fireworks display during the Spring Festival can result in the levels of perchlorate increase.Display Omitted► First report on the changes of perchlorate concentrations in aerosol during the Spring Festival in China. ► Perchlorate was widespread in aerosols collected from two selected locations. ► Fireworks display can result in perchlorate level in aerosols increase.

Keywords: Perchlorate; Fireworks air aerosol; Spring Festival

Quantifying the influence of local meteorology on air quality using generalized additive models by John L. Pearce; Jason Beringer; Neville Nicholls; Rob J. Hyndman; Nigel J. Tapper (pp. 1328-1336).

Recent acknowledgement of the sensitivity of air quality to changes in climate has initiated a closer examination of the relationships between meteorology and air quality. This paper presents the estimated response of daily air pollutant concentrations in Melbourne, Australia to local-scale meteorology. The meteorological-pollutant relationships have been assessed after controlling for long-term trends, seasonality, weekly emissions, spatial variation, and temporal persistence using the framework of generalized additive models (GAMs). Overall, results found that the aggregate impact of meteorological variables in the models explained 26.3% of the variance in O₃, 21.1% in PM₁₀, and 26.7% in NO₂. This indicates that meteorology – at the local-scale, is a relatively strong driver of air quality in Melbourne. Analysis of partial residuals plots found that changes in temperature, particularly when above 35 °C, resulted in the strongest positive response for O₃ (150%), PM₁₀ (150%) and NO₂ (120%). Other variables (boundary layer height, winds, water vapor pressure, radiation, precipitation, and mean sea-level pressure) displayed some importance for one or more of the pollutants, but their impact in the models was less pronounced. In sum, we provide results that form a solid foundation for understanding the importance of local-scale meteorology as a driver of regional air pollution. Additionally, these results can be used to provide a window into how changes in climate may affect air quality.►PM₁₀, and NO₂ all show significant responses to local-scale meteorology. ►Temperature changes are the strongest meteorological driver of air pollution. ►Boundary layer height, winds, and water vapor pressure are also important. ►Results suggest that climate change may worsen air quality.

Keywords: Air pollution; Climate change; Generalized additive models; Meteorology

An intercomparison of the deposition models used in the CASTNET and CAPMoN networks by Donna Schwede; Leiming Zhang; Robert Vet; Gary Lear (pp. 1337-1346).

To assess long-term trends in atmospheric deposition, the U.S. operates the Clean Air Status and Trends Network (CASTNET) and Canada operates the Canadian Air and Precipitation Monitoring Network (CAPMoN). Both networks use modeled dry deposition velocities and measured atmospheric concentrations to compute estimates of dry deposition. While concentration measurements from the two networks are comparable, flux estimates can be significantly different due to differences in the model-estimated dry deposition velocities. This study intercompares the dry deposition velocity models used by the networks to identify those model inputs and model algorithms that are responsible for the differences in the dry deposition velocity predictions of the gaseous trace species ozone (O₃), sulfur dioxide (SO₂), and nitric acid (HNO₃). The Big-Leaf Model (BLM) used for CAPMoN was inserted into the CASTNET modeling framework so that the on-site meteorological data obtained at the CASTNET sites could be used as input to both models. The models were run for four CASTNET sites that spanned different land use types and climatologies. The models were incrementally modified to assess the impacts of algorithmic differences on the predicted deposition velocities. While differences in aerodynamic resistance between the models contributed strongly to differences in predicted dry deposition velocities for HNO₃, it is the non-stomatal (ground and cuticle) resistance parameterizations that cause the largest differences for other chemical species. The study points to the need for further consideration of these resistances. Additionally, comparisons of both models against recent independent flux data are needed to assess the accuracy of the models.► The dry deposition velocity models used by the CASTNET and CAPMoN networks were intercompared. ► To identify inputs and algorithms that drive differences in modeled dry deposition velocities of O₃, SO₂, and HNO₃. The models were run from a consistent framework using common input meteorology. ► Differences in aerodynamic resistance between the models contributed strongly to differences in predicted dry deposition velocities for HNO₃. ► Non-stomatal (ground and cuticle) resistance parameterizations caused the largest differences in O₃ and SO₂ deposition velocities.

Keywords: Atmospheric deposition; Dry deposition; CASTNET; CAPMoN

Mean global and regional distributions of MOPITT carbon monoxide during 2000–2009 and during ENSO by Yongxin Zhang (pp. 1347-1358).

The MOPITT (Measurements Of Pollution In The Troposphere) CO measurements over a 10-year period (2000–2009) reveal consistently positive trends on the order of 0.13–0.19 × 10¹⁶ mol cm⁻² per month in CO total column concentrations over the entire globe and the hemispheres. Two maxima in globally averaged CO concentrations are identified: one in April and one in October, with two minima in July and December. These maxima and minima are attributable to the respective maxima and minima in CO concentrations over the Northern and Southern Hemispheres. Over the Tropics, maximum and minimum CO concentrations are noted in October and June, respectively, due primarily to biomass burning.During El Niño DJF (December–January–February) and JJA (June–July–August), predominantly positive anomalies in CO total column are noted over the entire globe except for the high latitudes of both hemispheres and the central part of the South America where negative anomalies are identified. La Niña DJF and JJA are largely opposite to El Niño DJF and JJA in CO total column anomalies. Negative (positive) anomalies in CO total column tend to be associated with wet (dry) anomalies in precipitation over the major polluted areas during ENSO. It is suggested that changes in the atmospheric circulations during ENSO either enhance or weaken precipitation systems with the associated precipitation modulating CO total column. The correspondence between anomalies in CO total column and anomalies in Terra MODIS fire pixels during ENSO is rather poor over many parts of the world.► The MOPITT CO total column over a ten-year period is examined. ► Anomalies in CO total column during ENSO are constructed and examined. ► Wind, precipitation and fire anomalies during ENSO are employed to explain the anomalies in CO. ► There is a close relationship between precipitation anomalies and CO anomalies. ► Correspondence between fire anomalies and CO anomalies is poor.

Keywords: MOPITT CO; ENSO; Fire

Stable carbon isotopes in aerosols from Chinese cities: Influence of fossil fuels by Jun-ji Cao; Judith C. Chow; Jun Tao; Shun-cheng Lee; John G. Watson; Kin-fai Ho; Ge-hui Wang; Chong-shu Zhu; Yong-ming Han (pp. 1359-1363).

Stable carbon isotope ratios were determined for the OC and EC fractions of PM_2.5 collected from 14 Chinese cities in January and June/July of 2003. The period-averaged isotope values ( δ¹³C) varied from −26.90‰ to −23.08‰ for OC and −26.63‰ to −23.27‰ for EC. A strong correlation ( R²=0.70, p<0.0001) between δ¹³C_OC and δ¹³C_EC was found in winter but not summer. Winter vs. summer differences for δ¹³C_OC and δ¹³C_EC were greater for the seven northern cities (∼1 to 3‰) than the seven southern cities (<1‰). Comparisons with isotopic signatures of putative sources suggest that the carbonaceous PM_2.5 was mainly from fossil fuels, especially coal combustion and motor vehicle emissions; the northern cities in particular were strongly impacted by coal combustion during winter. Studies of stable carbon isotopes in OC and EC are potentially useful for identifying sources for carbonaceous PM_2.5, and this approach may be a useful new tool for the study of air pollution.► Stable carbon isotope ratios were determined for OC and EC in PM_2.5 from Chinese cities. ► The isotopic signatures indicate that coal combustion and motor vehicle exhaust were the major sources for the carbonaceous aerosols. ► Stable carbon isotopes can be useful for distinguishing among major sources for carbonaceous PM_2.5.

Keywords: Carbon isotope; Organic carbon; Elemental carbon; China

Chromium(III/VI) speciation in urban aerosol by Ryszard Świetlik; Artur Molik; Monika Molenda; Marzena Trojanowska; Jan Siwiec (pp. 1364-1368).

Chromium(III/VI) speciation was measured in total suspended particulate (TSP) fraction of urban aerosol collected at five sites with different municipal structures. The results show that the highest airborne chromium(III) concentrations occurred at the industrial zone. In the other parts of city the differences between mean concentrations of total chromium were not statistically significant. The higher concentration of total Cr results, to a small extent, from higher dustiness of air. The industrial dust turned out to be almost fivefold richer in chromium(III). The level of chromium(VI) in air over the whole city was constant, which seems to exclude any presence of local sources of emission of this species of chromium. The mean Cr(VI) concentration of 6.0 ng m⁻³ is close to the Inhalation Reference Concentration of Cr(VI). In the industrial zone airborne chromium(VI) constitutes 11% of total chromium. However, in the city centre with the lowest concentration of airborne Cr(III), the share of Cr(VI) is 50%. The percentage of Cr(VI) remains at 30–40% in aerosol collected close to transit roads.► Valence speciation of chromium in the urban air. ► Monitoring of total Cr and Cr(VI) in TSP fraction of urban aerosol. ► Impact of the local emission sources on the level of Cr(III/VI) species in the air.

Keywords: Speciation; Hexavalent chromium; Trivalent chromium; Urban aerosol; Poland

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Atmospheric Environment (v.45, #6)