Atmospheric Environment (v.42, #4)

Long-term study of NO x behavior at urban roadside and background locations in Seoul, Korea by Sudhir Kumar Pandey; Ki-Hyun Kim; Soo-Yeoun Chung; S.-J. Cho; M.-Y. Kim; Zang-Ho Shon (607-622).
In this study, the fundamental aspects governing the environmental behavior of nitrogen oxides were explored from two air quality-monitoring stations (AQM) in Seoul, Korea, over an 11-year period (1996–2006). The two stations were selected to represent an urban roadside (U-RS) and urban background station (U-BG). The mean concentration levels of NO x at the U-RS area exhibited a gradual decrease through years (from ∼290 ppb (1996) to 100 ppb (2003)), while those measured at the U-BG site maintained fairly stable values (∼70 ppb) throughout the years. The mean concentration levels of NO and NO2 at the U-BG site were almost the same (∼35 ppb), while the U-RS site showed that the mean value of NO (∼127 ppb) is significantly higher than that of NO2 (∼60 ppb). The observation of larger differences in NO level between the two sites reflects the direct impact of vehicular emissions at the U-RS site. Both correlation and factor analyses were conducted between the hourly data sets of NO x species (N=∼90,000) and relevant environmental variables for both the sites. The results of both tests confirm the prominent role of vehicular activities in determining the level of nitrogen oxides at urban roadside environments, although such effects appear to be rather intricate at U-BG. Our comparative analysis of NO x data sets collected over varying temporal scales indicate that their distributions in the urban environment can be distinguished more clearly in spatial factors (i.e., between urban background and urban roadside) than other criteria.
Keywords: NO x behavior; Urban; Vehicular; Spatiotemporal; Long-term; NO2/NO x ratio;

Airborne cadmium in spring season between Asian dust and non-Asian dust periods in Korea by Ki-Hyun Kim; Chang-Hee Kang; Chang-Jin Ma; Jin-Hong Lee; Kum-Chan Choi; Yong-Hoon Youn (623-631).
In an effort to elucidate the environmental significance of the long-range transport of atmospheric pollutants (LRTAP), the particle-bound Cd data for an aerodynamic diameter less than 2.5 (PM2.5) and 10 μm (PM10) fractions were analyzed in the spring periods of four consecutive years between 2001 and 2004. To describe the factors affecting Cd distributions in relation to LRTAP, the Cd measurement data were evaluated after being grouped into several criteria: Asian dust (AD)/non-Asian dust (NAD), particle size, metal specie, source location, etc. According to our analysis, Cd concentrations in the coarse fraction were higher during AD (2.21±1.88 ng m−3) than during NAD (1.58±1.11 ng m−3). In contrast, its fine-fraction counterpart showed a contrary pattern with more enhanced values during NAD (2.60±1.64 ng m−3) than AD (1.60±0.65 ng m−3). Evidence collected from the present study indicates that the occurrence of the AD events generally proceed with the inflow of Cd-deficient particle, as reflected by a persistently low Cd/PM ratio from all particle fractions. Inspection of the Cd data in relation with the back trajectory analysis further suggests that the AD event is not the main route of the Cd transport into Korea, although such mechanism can be efficient depending on such variables as the size of particle as well as the intensity and transport route of AD.
Keywords: Cadmium (Cd); PM2.5; PM10; Asian dust (AD); Non-Asian dust (NAD); Transport pathway;

Weekly cycles in fine particulate nitrate by Dev E. Millstein; Robert A. Harley; Susanne V. Hering (632-641).
Atmospheric responses to changes in emissions are a complex but central issue in control strategy design for pollutants such as ozone and particulate matter. Here, we investigate fine particle nitrate response to weekly cycles in emissions, which includes a large decrease in diesel NO x emissions among other changes. Nitrate concentrations were measured at 10-min time resolution for a year or longer at four US urban sites: Fresno and Claremont in California, St. Louis, and Pittsburgh. Weekly minima in nitrate concentrations were observed at Fresno, Claremont, and St. Louis, with mean reductions of 21–29% below weekly average values on Sundays or Mondays. The day of week with lowest nitrate varied with site and season. No significant day-of-week variations in nitrate were observed at Pittsburgh. Analysis of ammonium and sulfate measurements at Pittsburgh indicates that weekend sulfate reductions observed at this site during spring/summer months do not increase ammonia availability, but rather lead to more complete neutralization of S(VI). Fine particle nitrate measurements at Claremont were resolved into three size ranges (0.07–0.45, 0.45–1.0, and 1.0–2.5 μm); similar weekly reductions were seen for each size range.
Keywords: Weekend effect; Nitrogen oxides; EPA PM supersites;

Ozone consumption and volatile byproduct formation from surface reactions with aircraft cabin materials and clothing fabrics by Beverly K. Coleman; Hugo Destaillats; Alfred T. Hodgson; William W Nazaroff (642-654).
We measured ozone consumption and byproduct formation on materials commonly found in aircraft cabins at flight-relevant conditions. Two series of small-chamber experiments were conducted, with most runs at low relative humidity (10%) and high air-exchange rate (∼20 h−1). New and used cabin materials (seat fabric, carpet, and plastic) and laundered and worn clothing fabrics (cotton, polyester, and wool) were studied. We measured ozone deposition to many material samples, and we measured ozone uptake and primary and secondary emissions of volatile organic compounds (VOCs) from a subset of samples. Deposition velocities ranged from 0.06 to 0.54 cm s−1. Emissions of VOCs were higher with ozone than without ozone in every case. The most commonly detected secondary emissions were C1 through C10 saturated aldehydes and the squalene oxidation products 6-methyl-5-hepten-2-one and acetone. For the compounds measured, summed VOC emission rates in the presence of 55–128 ppb (residual level) ozone ranged from 1.0 to 8.9 μmol h−1  m−2. Total byproduct yield ranged from 0.07 to 0.24 moles of product volatilized per mole of ozone consumed. Results were used to estimate the relative contribution of different materials to ozone deposition and byproduct emissions in a typical aircraft cabin. The dominant contributor to both was clothing fabrics, followed by seat fabric. Results indicate that ozone reactions with surfaces substantially reduce the ozone concentration in the cabin but also generate volatile byproducts of potential concern for the health and comfort of passengers and crew.
Keywords: Cabin air quality; Indoor chemistry; Ozone deposition; Surfaces; Volatile byproducts; Skin oil;

Spectral analysis of weekly variation in PM10 mass concentration and meteorological conditions over China by Yong-Sang Choi; Chang-Hoi Ho; Deliang Chen; Yeon-Hee Noh; Chang-Keun Song (655-666).
This study investigates the region-dependent anthropogenic weekly variation in air pollutants and its relationship with the meteorological conditions over China for the summers of 2001–2005. Spectral analysis was applied to the local daily observations of PM10 (aerosol particulate matter with a diameter <10 μm) mass concentrations and precipitation from 31 ground stations, reanalysis estimates of regional atmospheric variables, and satellite retrievals of clouds. Our analysis shows that the 6–8-day variance of PM10 concentrations from the periodogram is closely correlated with the mean PM10 concentration, which may depend on the size (population) and geographical setting of a city, its prevailing climatic conditions, and the type/degree of human activities. We define normalized variance as the ratio of the 6–8-day to 2–14-day variance of PM10 concentrations, possibly indicating the relative anthropogenic signal to the noise of natural weather variability. The normalized variance of PM10 concentrations has a distinct regional rainfall distribution from that of the mean PM10 concentration in China. As compared to regions with lower normalized variance of PM10 concentrations, the regions with higher normalized variance generally show higher normalized variance of rainfall events, 1000 hPa wind speeds, sea-level pressure, size spectrum and phase of cloud particles, cloud optical depth, and cloud top pressure. Our results confirm the presence of the interaction between PM10 and the meteorological conditions in the boundary layer, and suggest a possible link of cloud formation to PM10 on a weekly scale.
Keywords: PM10; Air pollution index; Weekly variation; Spectral analysis; China;

Inventory and forecasting of maritime emissions in the Belgian sea territory, an activity-based emission model by Liesbeth Schrooten; Ina De Vlieger; Luc Int Panis; Karel Styns; Rudi Torfs (667-676).
Air quality policy has focussed on land-based emissions for decades. In recent years, it has become increasingly clear that emissions from sea-going vessels can no longer be ignored. There is a growing need for detailed emission inventories to evaluate the impact of this transport mode on air quality and health.In this paper we present MOPSEA, an activity-based emission model to determine emissions from sea-going vessels. The model considers shipping activities of sea-going vessels on Belgian territory, combined with individual vessel characteristics. We apply this model to study the effects of recent international efforts to reduce emissions from sea-going vessels in Belgian territorial waters for the current fleet and for two scenarios up to 2010.The emission model for Belgium, based on different vessel operating areas, reveals that most maritime emissions from the main engines will increase. CO2 emissions will increase by 2–9% over the 2004–2010 period due to an increase in shipping activity. NOX emissions are projected to rise between 1% and 8% because the increase in activity offsets the reductions from the international maritime organisation (IMO) and European regulations. In contrast, SO2 emissions will decrease by at least 50% in 6 years time. The switch of auxiliaries from heavy fuel oil to diesel oil at berth results in a large emission reduction (33%) for PM and small reductions for CO2, NOX, CO and HC (4–5%).The choice between a bottom-up versus top-down approach can have important implications for the allocation of maritime emissions. The MOPSEA bottom-up model allocates only 0.7 Mton CO2 to Belgium, compared to 24.2 Mton CO2 based on bunker fuel inventories.
Keywords: Sea-going vessels; Activity-based; Maritime emissions; Air pollution; Forecasting; Legislation;

Air samples were collected at an urban site and a suburban site of Guangzhou city, China, from April 2005 to March 2006, to measure concentrations of organochlorine pesticides (OCPs) in the ambient air and study their seasonal variations and sources. The average concentrations of ∑HCHs, ∑chlordane and ∑DDTs in the air were 93, 287 and 351 pg m−3 at the urban site, and 94, 2258 and 399 pg m−3 at the suburban site, respectively. OCPs in the air were predominantly in gas phase in this study but their concentrations in particle phase were still not neglectable. The air concentrations and seasonal variations of ∑HCHs and ∑DDTs at the urban and suburban sites were similar without obvious difference. The seasonal variations of ∑chlordane concentrations were extremely different at the two sampling sites and the air concentrations were unusually high at suburban site, especially in April and May 2005. The potential sources of HCHs in the air of Guangzhou might come from lindane due to the relative low α-HCH/γ-HCH ratios. Technical chlordane was likely used, especially at or near the suburban site, because the t-chlordane/c-chlordane ratios were >1.2 and the air concentrations of chlordane were extremely high. Present usage of dicofol at or near Pearl River Delta (PRD) region was implied by the much higher ratios of DDT/(DDE+DDD) and o,p′-DDT/p,p′-DDT. The air concentrations of aldrich were low, and dieldrin and endrin were detected in none of the samples.
Keywords: Organochlorine pesticide; HCH; Chlordine; DDT; Air; Guangzhou;

Factors affecting non-tailpipe aerosol particle emissions from paved roads: On-road measurements in Stockholm, Sweden by Tareq Hussein; Christer Johansson; Hans Karlsson; Hans-Christen Hansson (688-702).
A large fraction of urban PM10 concentrations is due to non-exhaust traffic emissions. In this paper, a mobile measurement system has been used to quantify the relative importance of road particle emission and suspension of accumulated dust versus direct pavement wear, tire type (studded, friction, and summer), pavement type, and vehicle speed. Measurements were performed during May–September on selected roads with different pavements and traffic conditions in the Stockholm region. The highest particle mass concentrations were always observed behind the studded tire and the lowest were behind the summer tire; studded-to-summer ratios were 4.4–17.3 and studded-to-friction ratios were 2.0–6.4. This indicates that studded tires lead to higher emissions than friction and summer tires regardless to the asphalt type. By comparing with measurements in a road simulator, it could be estimated that the pavement wear due to the friction tires was 0.018–0.068 of the suspension of accumulated road dust. Likewise for studded tires road-wear was estimated to be 1.2–4.8 the suspension of accumulated dust. This indicates that wear due to friction tires is very small compared to the suspension of accumulated dust and that suspension due to studded tires may sometimes be as large as the wear of the road. But this will vary depending on, e.g. the amount of dust accumulated on the roads. An important dependence on vehicle speed was also observed. During May, the particle mass concentrations behind the studded tire at vehicle speed 100 km h−1 were about 10 times higher than that at 20 km h−1. The speed dependence was not so pronounced in September, which could be due to less accumulated dust on the roads. The particle number size distribution of the emissions due to road wear by studded tire was characterized by a clear increase in number concentrations of the coarse fraction of aerosol particles, with a geometric mean diameter between 3 and 5 μm. The size distribution of the emissions due to the summer tire was very similar with smaller concentrations. An important limitation with the measurements presented is that they were made by using a van, which is bigger than regular cars and has bigger tires. Thus, road wear and dust suspension due to cars are expected to be different.
Keywords: PM10; Road dust; Re-suspension; Tire wear; Road wear; Road traffic; Particle size distribution;

The representation of emissions from megacities in global emission inventories by T.M. Butler; M.G. Lawrence; B.R. Gurjar; J. van Aardenne; M. Schultz; J. Lelieveld (703-719).
We examine the representation of emissions from megacities in three global anthropogenic emission inventories. Despite the many common sources of data between the inventories, and the similarities in their construction methodologies, there are some very large differences (often a factor of two) between the emissions for individual cities, even when the total global emissions are very similar. We find that the geographical distribution of the emissions within countries plays a larger role in explaining the differences between the inventories than differences in the country total emissions. We also find very large differences between the contribution of various sectors to the total emissions from each city, and relate these differences to the respective methodologies used in the inventory construction. By and large, in OECD countries megacity emissions from the global inventories are dominated by road transport, especially for CO and to a lesser degree for NO x . In non-OECD countries, notably in Asia, megacity CO emissions are dominated by residential biofuel use, while industrial emissions predominate for NO x . Non-methane hydrocarbon emissions in OECD megacities are caused by industry and traffic, whereas in non-OECD countries residential biofuel use makes significant contributions. These emission signatures often result from assumptions about the distribution of emissions according to gridded population density maps rather than according to the actual location of the emitting processes. We recommend the use of an ensemble of inventories, that the geographical distribution of emissions receives increased attention, and that local inventories be integrated into global emission inventories.
Keywords: Emissions; Inventories; Megacities; Intercomparison; Global modelling;

Sources of ambient fine particulate matter at two community sites in Detroit, Michigan by Davyda M. Hammond; J. Timothy Dvonch; Gerald J. Keeler; Edith A. Parker; Ali S. Kamal; James A. Barres; Fuyuen Y. Yip; Wilma Brakefield-Caldwell (720-732).
Detroit, Michigan is a non-attainment area of the annual PM2.5 (particles ⩽2.5 μm in diameter) National Ambient Air Quality Standard (NAAQS), and contains a host of local pollution contributors including high diesel traffic from a nearby international border crossing. A source apportionment analysis was conducted using PM2.5 data collected from 1999 to 2002 by the Community Action Against Asthma (CAAA) project in Detroit, Michigan. CAAA used a community-based participatory research approach to identify and address the environmental triggers for asthma among children residing in southwest and east Detroit. The data used for the study included 24-h measurements of PM2.5 mass, elemental and organic carbon, and a suite of trace element species, along with hourly measurements of PM2.5 mass and black carbon. Positive matrix factorization (PMF2) was used to quantitatively apportion the sources of ambient PM2.5 at each of two Detroit community sites. Results showed that southwest Detroit PM2.5 levels can be apportioned to seven source categories: secondary sulfate/coal combustion, gasoline vehicles, diesel vehicles, refinery/oil combustion, iron–steel manufacturing/waste incineration, automotive electroplating, and sewage sludge incineration that includes crustal material from runoff. The PMF2 model apportioned the east Detroit PM2.5 data into five source categories: secondary sulfate/coal combustion, motor vehicles/combustion, refinery/oil combustion, iron–steel manufacturing/waste incineration, and automotive electroplating. For both locations, approximately over 60% of the PM2.5 mass was attributed to secondary sulfate/coal combustion sources, approximately 30% to vehicular sources, and 1–5% to local industrial sources. The unexplained mass accounted for <2% of the measured PM2.5 mass. This study illustrates that regional secondary sulfate/coal combustion and local motor vehicle emissions alone are enough for this mid-western US city to be in non-attainment for the annual PM2.5 NAAQS.
Keywords: Receptor modeling; Positive matrix factorization; PM2.5; Trace elements;

Stable sulphur isotopes and major ionic composition were analysed in precipitation and throughfall samples from a Scots pine (Pinus sylvestris, L.) forest near the Cercs coal-fired power plant (Catalonia, NE Spain). The purpose of the study was to determine the main sources of sulphur deposition on this pine forest. Sulphur isotope measurements from the SO2 power plant stack emissions were used to identify the isotopic signature of this source. Net throughfall fluxes of sulphur (26.1 kg S ha  1  yr−1) and nitrogen (16.3 kg N ha−1  yr−1) were higher—5–25 times higher for S and 5–15 times for N—at this site than in other forests in Catalonia. Sulphur isotope analysis confirmed that the net throughfall fluxes of sulphur were mostly due to the dry deposition of the SO2 power plant emissions onto the pine canopies. Two potential atmospheric end-members were distinguished: regional background rainwater (δ34S=+7.2‰) and power plant emissions (δ34S=−2.8‰). By applying a two-component sulphur isotope mixing model, we found that during periods of low power plant activity (⩽10 emission h day−1), 62% of the throughfall sulphate could be attributed to the power plant emissions. At higher activity periods (⩾14 emission h day−1), this contribution rose to 73%. Although power plant contribution to bulk deposition was lower in both cases (34% and 45%), the possible influence of sulphate coming with long-range transport events from the polluted areas in the Mediterranean basin (δ34S≈0‰) was not discarded.
Keywords: Sulphur isotopes; Sulphate; Throughfall; Power plant emissions;

Passive sampling to capture spatial variability in PM10–2.5 by Darrin K. Ott; Naresh Kumar; Thomas M. Peters (746-756).
This work applied inexpensive passive sampling to measure airborne coarse particles with aerodynamic diameters between 2.5 and 10 μm (PM10–2.5) over three 7-day periods at 33 sites in a medium-sized Midwest City (Iowa City, IA). The number of sites and their locations were selected using an optimal sampling design that captured 95% of the total variance in PM10–2.5 as measured with real-time sampling equipment on a mobile sampling platform. Weekly averages of PM10–2.5 were 15.9 μg m−3 (coefficient of variation between sites, CV=23%), 17.9 μg m−3 (CV=24%), and 6.1 μg m−3 (CV=30%). ANOVA showed that these means were statistically different (p<0.001), and that the spatial variability plus random error accounted for 29% of the total variability. The maximum coefficient of divergence between sites—a relative measure of uniformity—ranged from 0.21 to 0.36. These values indicate that PM10–2.5 was heterogeneous even on the fine spatial resolution studied in this work (average distance between sites was 4.4 km). The spatial patterns of PM10–2.5 measured with the passive samplers closely matched with those of mobile mapping and corresponded with known coarse particle sources in the area. This work demonstrates that passive sampling coupled with effective sampling design may enhance our ability to assess exposure to PM10–2.5 at a local scale. Compared to exposure estimates made with data from centrally located, filter-based samplers, these highly spatially resolved estimates should reduce exposure misclassification errors in epidemiological studies.
Keywords: Exposure assessment; Coarse particles; Spatial variability; PM10–2.5; Particulate matter;

A 2-week intensive measurement campaign of indoor and outdoor air pollution was carried out in September 2006, in a primary school to investigate indoor–outdoor correlations of particle number (PN) concentrations, and the impact of air exchange rate (ACH) on the indoor PN concentration. The ACHs in the classroom for different conditions associated with window opening and the operational status of air conditioners (A/C) and fans were tested. As expected, the lowest ACH (0.12 h−1) was found when the windows were closed and A/C and fans were off. In contrast, the highest ACH (7.92 h−1) was observed when the windows were opened and A/C and fans were all on. The analysis of the PN I/O ratios at different ACHs in the absence of indoor sources indicates that the mean I/O ratio was 0.621±0.007 (mean±95% confidence interval) when the windows were closed, and A/C and fans were off; 0.524±0.023 when windows were closed, fans were off and A/C was on; and 0.502±0.029 when windows were closed, A/C was off and fans were on. To further understand the relationship between indoor and outdoor PN concentrations, the impact of outdoor PN concentration on I/O ratios at different ACHs was investigated. It was found that the relationship between outdoor PN concentration and the I/O ratio at different ACHs followed a power trendline with an equation of I/O ratio=A  PNout −b (A and b are coefficients, PNout is outdoor PN concentration), suggesting that the penetration efficiency decreased with increasing outdoor PN concentration. It is the first time we found that when the outdoor PN concentration increased there was an associated increase in the concentration of nano-particles, which have been demonstrated to have higher deposition rates and lower penetration efficiencies. Based on the above equation, the study also showed a significant effect of ACH on indoor PN concentrations under stable outdoor PN concentrations. In general, the higher the ACH was, the lower the indoor PN concentration was.
Keywords: Indoor to outdoor ratios; Particle number concentration; Air exchange rate; Air-conditioned classroom; Nano-particles;

Carbonyl emissions in diesel and biodiesel exhaust by Sérgio Machado Corrêa; Graciela Arbilla (769-775).
With the use of biodiesel in clear growth, it is important to quantify any potential emission benefits or liabilities of this fuel. Several researches are available concerning the regulated emissions of biodiesel/diesel blends, but there is a lack of information about non-regulated emissions. In a previous paper [Corrêa, S.M., Arbilla, G., 2006. Emissões de formaldeído e acetaldeído de misturas biodiesel/diesel. Periódico Tchê Química, 3, 54–68], the emissions of aromatic hydrocarbons were reported. In this work, seven carbonyl emissions (formaldehyde, acetaldehyde, acrolein, acetone, propionaldehyde, butyraldehyde, and benzaldehyde) were evaluated by a heavy-duty diesel engine fueled with pure diesel (D) and biodiesel blends (v/v) of 2% (B2), 5% (B5), 10% (B10), and 20% (B20). The tests were conducted using a six cylinder heavy-duty engine, typical of the Brazilian fleet of urban buses, in a steady-state condition under 1000, 1500, and 2000 rpm. The exhaust gases were diluted nearly 20 times and the carbonyls were sampled with SiO2–C18 cartridges, impregnated with acid solution of 2,4-dinitrophenylhydrazine. The chemical analyses were performed by high performance liquid chromatography using UV detection. Using average values for the three modes of operation (1000, 1500, and 2000 rpm) benzaldehyde showed a reduction on the emission (−3.4% for B2, −5.3% for B5, −5.7% for B10, and −6.9% for B20) and all other carbonyls showed a significative increase: 2.6, 7.3, 17.6, and 35.5% for formaldehyde; 1.4, 2.5, 5.4, and 15.8% for acetaldehyde; 2.1, 5.4, 11.1, and 22.0% for acrolein+acetone; 0.8, 2.7, 4.6, and 10.0% for propionaldehyde; 3.3, 7.8, 16.0, and 26.0% for butyraldehyde.
Keywords: Carbonyl; Vehicular emissions; Biodiesel; Diesel;

Characteristics and sources of air-borne particulate in Urumqi, China, the upstream area of Asia dust by Juan Li; Guoshun Zhuang; Kan Huang; Yanfen Lin; Chang Xu; Shulong Yu (776-787).
A sampling campaign of aerosols over Urumqi from 2004 to 2007 with detailed and systematic analysis was carried out to investigate the severe air pollution in Urumqi, China, which is located nearby the upstream area of Asia dust. It was found that Urumqi city was the severest polluted city over the world. The average PM2.5 and TSP concentrations in the winter of 2007 were 187 and 385 μg m−3 with maximum of 487 and 1313 μg m−3, respectively, 12 times higher than USA standard for PM2.5 and 3 times the National Ambient Air Quality Standard of China for TSP. The city's industrial emissions of sulfur dioxide were converted to sulfate in the air, and sulfate-rich soil dust was transported to Urumqi's air from agricultural fields south of Jungger Basin and surrounding salt lake areas. The mixing of the local anthropogenic aerosol with the transported soil dust from outside the city was the main sources of the high concentration of sulfate, one of the main factors causing the heavy air pollution over Urumqi. The high concentration of ammonium and sulfate salts in the aerosol from both inside and outside city and the low wind speed might be the main factors to form the heavy haze over the Urumqi.
Keywords: Aerosol; Air pollution; Sulfate; Ammonium; Mixing; Urumqi;

Ultrafine particle concentration (3–100 nm) was continuously measured in summer (6/7/2006–17/8/2006), fall (1/10/2006–31/10/2006), winter (2/2/2007–7/3/2007), and spring (7/4/2007–7/5/2007) in urban Gwangju, Korea. By considering the size range with elevated concentration and hypothesizing the source or formation pathways, we classified ultrafine particle events into: (1) “10–100 nm traffic event,” (2) “50–100 nm residential heating event,” and (3) “10–30 nm photochemical event.” Coincidence of NO x , CO, O3, and solar radiation with ultrafine particle concentration was used as an indicator for the traffic, residential heating, and photochemical contributions. We showed that particles due to traffic and residential heating led to enhanced ultrafine particle concentration in winter, while in summer particles formed by photochemical activity led to increased ultrafine particle concentration. The average ultrafine particle number concentrations were 8.8×103, 7.4×103, and 7.9×103  cm−3 with geometric mean diameters (GMDs) of 25, 48, and 53 nm in the photochemical, traffic, and residential heating events, respectively. Our ultrafine particle concentrations and other gas concentrations (NO x and CO) were found to be lower than observations in Atlanta and in Fresno, probably due to lower source strength such as traffic and residential heating in current site. We occasionally observed particle growth after formation of particles in the photochemical event with growth rates of 2.2–4.7 nm h−1. Morphological and elemental analysis for size-selected ultrafine particles showed that mixtures of sulfate and metals with the presence of semi-transparent part inside the particle were observed in the photochemical event (49 over 200 particles), while in the traffic event agglomerated carbonaceous particles were observed (66 over 130 particles), which were rarely detected in the photochemical event.
Keywords: Ultrafine particle events; Particle concentration; Photochemical event; Growth rate; Particle morphology;

Aerosol particle number size distributions above 0.3 μm in diameter and black carbon mass concentrations in aerosols were observed on Chichi-jima of the Ogasawara Islands in the northwestern Pacific from January 2000 to December 2002. Chichi-jima is suitable to observe polluted air masses from East Asia in winter and clean air masses over the western North Pacific in summer. In winter, aerosols over Chichi-jima were strongly affected by anthropogenic emissions in East Asia. The form of energy consumption in East Asia varies in various regions. Hence, each source region is expected to be characterized by an individual black carbon mass fraction. A three-dimensional Eulerian transport model was used to estimate contribution rates to air pollutants from each source region in East Asia. Because the Miyake-jima eruption began at the end of June 2000, the influence of smokes from Miyake-jima was also considered in the model calculation. The results of model calculations represent what must be noticed about smokes from volcanoes including Miyake-jima to interpret temporal variations of sulfur compounds over the northwestern Pacific. To evaluate black carbon mass fractions in anthropogenic aerosols as a function of source region, the relationships between the volume concentration of aerosol particles and the black carbon mass concentration in the winter were classified under each source region in East Asia. Consequently, the black carbon mass fractions in aerosols from China, Japan and the Korean Peninsula, and other regions were estimated to be 9–13%, 5–7%, and 4–5%, respectively.
Keywords: Aerosol; Black carbon; Number size distribution; Black carbon fraction; Source contribution;

Decrease of lead concentrations in the Western Mediterranean atmosphere during the last 20 years by Christophe Migon; Thomas Robin; Aurélie Dufour; Bernard Gentili (815-821).
Concentrations of lead (Pb) in the atmospheric aerosol were monitored in 1986–87, 1992–93, 1995, 1997–98 and 2003–2005 at a North-Western Mediterranean coastal sampling station. After the implementation of antipollution policies on automotive Pb in the second half of the 1980s, Pb concentrations were markedly lowered and then the decrease slowed down, at the latest in 2003, resulting in average concentrations varying between 6.6 and 5.8 ng m−3 in 2004 and 2005, respectively. This represents a decrease by a factor of 82%, approximately, between 1986–87 and 2005. Reproducible seasonal patterns are observed, with highest Pb loads occurring at the end of winter and at the end of summer/beginning of autumn. The slowing down of aerosol Pb concentration decrease in the troposphere is expected to be rapidly observed in the Western Mediterranean water column.
Keywords: Lead; Antipollution policies; Atmospheric aerosol; North-Western Mediterranean;

Influences of sulfate and nitrate on the hygroscopic behaviour of coarse dust particles by Zongbo Shi; Daizhou Zhang; Masahiko Hayashi; Hiroko Ogata; Hezhe Ji; Wataru Fujiie (822-827).
Asian dust particles of diameter >1 μm collected in southwestern Japan were analyzed with environmental scanning electron microscopy. The hygroscopic behaviour of sea salt-free dust particles were investigated with respect to their contents of sulfate and nitrate. Sulfate- and nitrate-free dust particles (not containing sulfur and nitrogen), as well as sulfate-containing ones, did not change in their crystalline morphology as relative humidity (RH) was increased from 15% to 90%. In contrast, calcium nitrate-containing dust particles appeared in aqueous phase even at 15% RH. These results indicate that nitrate formation on coarse dust particles could substantially enhance the hydrophilicity of the particles and possibly vice versa, whereas sulfate formation could not.
Keywords: Mineral aerosol; Asian dust; Hygroscopicity; Calcium nitrate; Gypsum; Heterogeneous chemistry;

Impingers are common bioaerosol sampling instruments. In the last 20 years, impinger performance for collection of viable and non-viable bioaerosols in the 0.1–10 μm size range has been well documented. An ideal impinger has high collection efficiency for particles >0.1 μm. This research explored how well the 500 ml Greenburg–Smith (G–S) impingers collected particles between 0.1 and 2 μm, simulating virus aerosols, with minimal fluid evaporation during sample collection intervals near 60 min. Various impingers have differing dimensions that come into play when collecting viable samples of bioaerosols. The sampling environment can be modified to create optimum impingement conditions. Moderate differences in flow rate and impingement fluid volume may show distinct differences in the capture rate of viable samples within the bioaerosol impinger.
Keywords: Greenburg–Smith; Bioaerosol; Impinger; Virus-containing aerosol; Impingement; Viability;