Significant geographic gradients in particulate sulfate over Japan determined from multiple-site measurements and a chemical transport model: Impacts of transboundary pollution from the Asian continent

We found a significant geographic gradient (longitudinal and latitudinal) in the sulfate (SO₄^2?) concentrations measured at multiple sites over the East Asian Pacific Rim region. Furthermore, the observed gradient was well reproduced by a regional chemical transport model. The observed and modeled SO₄^2? concentrations were higher at the sites closer to the Asian continent. The concentrations of SO₄^2? from China as calculated by the model also showed the fundamental features of the longitudinal/latitudinal gradient. The proportional contribution of Chinese SO₄^2? to the total in Japan throughout the year was above 50–70% in the control case, using data for Chinese sulfur dioxide (SO₂) emission from the Regional Emission Inventory in Asia (40–60% in the low Chinese emissions case, using Chinese SO₂ emissions data from the State Environmental Protection Administration of China), with a winter maximum of approximately 65–80%, although the actual concentrations of SO₄^2? from China were highest in summer. The multiple-site measurements and the model analysis strongly suggest that the SO₄^2? concentrations in Japan were influenced by the outflow from the Asian continent, and this influence was greatest in the areas closer to the Asian continent. In contrast, we found no longitudinal/latitudinal gradient in SO₂ concentrations; instead SO₂ concentrations were significantly correlated with local SO₂ emissions. Our results show that large amounts of particulate sulfate are transported over long distances from the East Asian Pacific Rim region, and consequently the SO₄^2? concentrations in Japan are controlled by the transboundary outflow from the Asian continent.     

The characterization of water-soluble inorganic ions in PM2.5 during a winter period in Xi'an,China

The characteristics of water-soluble inorganic ions (WSIIs) during a winter period in a suburb of Xi'an, China, were investigated. Our results show that the total mass concentration of the dominant WSIIs (8) was 91.27 µg m^–3, accounting for 50.1% of the total mass concentration of PM_2.5 (particulates with a size of 2.5 µm or less). Secondary inorganic aerosols (SO₄^2?, NO₃^? and NH₄⁺) were the most abundant ions, accounting for up to 95.12% of the total ions. By using the anion and cation equivalence ratio method, PM_2.5 was shown to have weak alkalinity, and the chemical forms of WSIIs were mainly (NH₄)₂SO₄ and NH₄NO₃. The sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) suggested that larger proportions of SO₄^2? and NO₃^? were formed by gas-phase SO₂ and NO₂ in the sampling site. Ratio analysis also indicated that anthropogenic sources significantly contributed to WSII pollution. Among the anthropogenic sources, fixed pollution sources were found to be dominant over mobile sources.     

Characterization of Major Chemical Components of Fine Particulate Matter in North Carolina

Abstract

This paper presents measurements of daily sampling of fine particulate matter (PM_2.5) and its major chemical components at three urban and one rural locations in North Carolina during 2002. At both urban and rural sites, the major insoluble component of PM_2.5 is organic matter, and the major soluble components are sulfate (SO₄ ^2?), ammonium (NH₄ ⁺), and nitrate (NO₃ ^?). NH₄ ⁺ is neutralized mainly by SO₄ ^2? rather than by NO₃ ^?, except in winter when SO₄ ^2? concentration is relatively low, whereas NO₃ ^? concentration is high. The equivalent ratio of NH₄ ⁺ to the sum of SO₄ ^2? and NO₃ ^? is <1, suggesting that SO₄ ^2?and NO₃ ^?are not completely neutralized by NH₄ ⁺. At both rural and urban sites, SO₄ ^2?concentration displays a maximum in summer and a minimum in winter, whereas NO₃ ^?displays an opposite seasonal trend. Mass ratio of NO₃ ^? to SO₄ ^2?is consistently <1 at all sites, suggesting that stationary source emissions may play an important role in PM_2.5 formation in those areas. Organic carbon and elemental carbon are well correlated at three urban sites although they are poorly correlated at the agriculture site. Other than the daily samples, hourly samples were measured at one urban site. PM_2.5 mass concen trations display a peak in early morning, and a second peak in late afternoon. Back trajectory analysis shows that air masses with lower PM_2.5 mass content mainly originate from the marine environment or from a continental environment but with a strong subsidence from the upper troposphere. Air masses with high PM_2.5 mass concentrations are largely from continental sources. Our study of fine particulate matter and its chemical composition in North Carolina provides crucial information that may be used to determine the efficacy of the new National Ambient Air Quality Standard (NAAQS) for PM fine. Moreover, the gas-to-particle conversion processes provide improved prediction of long-range transport of pollutants and air quality.     

NH4+, NO3−, and SO42− in roadside and rural size-resolved particles and transformation of NO2/SO2 to nanoparticle-bound NO3−/SO42−

This study investigates ammonium, nitrate, and sulfate (NH₄⁺, NO₃^?, and SO₄^2?) in size-resolved particles (particularly nano (PM_0.01–0.056)/ultrafine (PM_0.01–0.1)) and NO_x/SO₂ collected near a busy road and at a rural site. The average (mass) cumulative fraction of secondary inorganic aerosols (SO₄^2?+NO₃^?+NH₄⁺) in nano or ultrafine particles at the roadside was found to be three to four times that at the rural site. The above three secondary inorganic aerosol species were present in similar cumulative fractions in particles of size 1–18 μm at both sites; however, dissimilar fractions were observed for Cl^?, Na⁺, and K⁺. The nitrogen ratios (NRs: NR = NO₃^??N/(NO₃^??N + NO₂–N)), sulfur ratios (SRs: SR = SO₄^2??S/(SO₄^2??S + SO₂–S)), dNR/D_P (derivative of NR with respect to D_P (particle diameter)), and dSR/D_P (derivative of SR with respect to D_P) at the roadside were higher than those at the rural site for nano/ultrafine particles. At both sites (particularly the roadside), the nanoparticles had significantly higher dNR/D_P and dSR/D_P values than differently sized particles, implying that NO₃^?/SO₄^2? (from NO₂/SO₂ transformation or NO₃^?/SO₄^2? deposition) were present on these particles.     

Transport and transformation of sulfur compounds over East Asia during the TRACE-P and ACE-Asia campaigns

On the basis of the recently estimated emission inventory for East Asia with a resolution of 1×1°, the transport and chemical transformation of sulfur compounds over East Asia during the period of 22 February through 4 May 2001 was investigated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the regional atmospheric modeling system (RAMS). For evaluating the model performance simulated concentrations of sulfur dioxide (SO₂) and aerosol sulfate (SO₄²⁻) were compared with the observations on the ground level at four remote sites in Japan and on board aircraft and vessel during the transport and chemical evolution over the Pacific and Asian Pacific regional aerosol characterization experiment field campaigns, and it was found that the model reproduces many of the important features in the observations, including horizontal and vertical gradients. The SO₂ and SO₄²⁻ concentrations show pronounced variations in time and space, with SO₂ and SO₄²⁻ behaving differently due to the interplay of chemical conversion, removal and transport processes. Analysis of model results shows that emission was the dominant term in regulating the SO₂ spatial distribution, while conversion of SO₂ to SO₄²⁻ in the gas phase and the aqueous phase and wet removal were the primary factors that controlled SO₄²⁻ amounts. The gas phase and the aqueous phase have the same importance in oxidizing SO₂, and about 42% sulfur compounds (25% in SO₂) emitted in the model domain was transported out, while about 57% (35% by wet removal processes) was deposited in the domain during the study period.     

NCAQ Report to Congress: Review and Response

Airborne measurements of gaseous and particulate sulfur and nitrogen pollutants were made in southwestern Kentucky on the afternoon of October 21, 1979. Back-trajectory analysis indicates that the sampled air parcel moved over northern Florida, Alabama, and western Tennessee during the two days prior to sampling. Before moving over Florida, the air parcel was over the Atlantic Ocean for at least five days. Analytical long-range transport (LRT) model predictions based on anthropogenic emissions account for only about 75% of the airborne measured concentrations of 14.7 μg m^?3 for SO₂ and 4.8 μg m^?3 for SO₄ ^2?. The remaining 25 % is thought to be due to biogenic sulfur emissions from the extensive wetland areas along the Gulf Coast.

Forward-trajectory analysis indicates that the air parcel moved to the Adirondack Mountains of New York State 24 hours after sampling. Model predictions indicate that SO₂ and SO₄ ^2? mean layer concentrations at the Adirondacks were 24 and 16 μg^?3, respectively. Almost half of this sulfur was estimated to come from emissions in the heavily industrialized region along the Ohio River Valley.

Further comparisons used a measurement data base obtained in southeastern Canada and the state of Arkansas during August 1976. An air parcel was tracked for seven days as it entered the north central United States, stagnated over the lower midwest, and then moved to eastern Canada. Model predictions were in substantial agreement with regional SO₄ ^2? concentrations measured at a number of ground-level sites. Average SO₄ ^2? concentrations measured in central Arkansas on August 10, 1976 were 20 μ m^?3 vs. a modeled value of 19 μ m^?3. Average SO₄ ^2? concentrations measured in Nova Scotia four days later were 22 μg^?3 vs. a modeled estimate of 24 μg^?3.     

Deposition of sulphur,nitrogen and acidity in precipitation over Ireland: chemistry,spatial distribution and long-term trends

The chemical composition of pollutant species in precipitation sampled daily or weekly at 10 sites in Ireland for the five-year period, 1994–1998, is presented. Sea salts accounted for 81% of the total ionic concentration. Approximately 50% of the SO₄²⁻ in precipitation was from sea-salt sources. The proportion of sea salts in precipitation decreased sharply eastwards. In contrast, the concentration of NO₃⁻ and the proportion of non-sea-salt SO₄²⁻ increased eastwards reflecting the closer proximity to major emission sources. The mean (mol_c) ratio of SO₄²⁻:NO₃⁻ was 1.6 for all sites, indicating that SO₄²⁻ was the major acid anion.The spatial correlation between SO₄²⁻, NO₃⁻ and NH₄⁺ concentrations in precipitation was statistically significant. The regional trend in NO₃⁻ concentration was best described by linear regression against easting. SO₄²⁻ concentration followed a similar pattern. However, the regression was improved by inclusion of elevation. Inclusion of northing in the regression did not significantly improve any of the relationships except for NH₄⁺, indicating a significant increase in concentrations from northwest to southeast.The spatial distribution of deposition fluxes showed similar gradients increasing from west and southwest to east and northeast. However, the pattern of deposition shows the influence of precipitation volume in determining the overall input. Mean depositions of sulphur and nitrogen in precipitation were ≈30 ktonnes S yr⁻¹ and 48 ktonnes N yr⁻¹ over the five-year period, 1994–1998, for Ireland.Least-squares linear regression analysis indicated a slight decreasing trend in precipitation concentrations for SO₄²⁻ (20%), NO₃⁻ (13%) and H⁺ (24%) and a slight increasing trend for NH₄⁺ (15%), over the period 1991–1998.     

Ionic composition of wet precipitation over the southern slope of central Himalayas,Nepal

Severe atmospheric pollution transported to Himalayas from South Asia may affect fragile ecosystem and can be harmful for human health in the region. In order to understand the atmospheric chemistry in the southern slope of central Himalayas, where the data is limited, precipitation has been sampled at four sites: Kathmandu (1,314 m), Dhunche (2,065 m), Dimsa (3,078 m), and Gosainkunda (4,417 m) in Nepal for over a 1-year period characterized by an urban, rural, and remote sites, respectively. HCO₃ ^? is the dominant anion, while the NH₄ ⁺ is the dominant cation in precipitation at the four sites. Generally, most of ions (e.g., SO₄ ^2?, NO₃ ^?, NH₄ ⁺, HCO₃ ^?, and Ca²⁺) have higher concentrations in urban site compared to the rural sites. Neutralization factor calculation showed that precipitation in the region is highly neutralized by NH₄ ⁺ and Ca²⁺. Empirical orthogonal function and correlation analysis indicated that the precipitation chemistry was mostly influenced by crustal, anthropogenic, and marine sources in Nepal. Among different sites, urban area was mostly influenced by anthropogenic inputs and crustal dusts, whereas remote sites were mostly from marine and crustal sources. Seasonal variations show higher ionic concentrations during non-monsoon seasons mainly due to limited precipitation amount. On the other hand, lower ionic concentrations were observed during monsoon season when higher amount of precipitation washes out aerosols. Thus, precipitation chemistry from this work can provide a useful database to evaluate atmospheric environment and its impacts on ecosystem in the southern slope of central Himalayas, Nepal.     

Rates of Conversion of Sulfur Dioxide to Sulfate in a Scrubbed Power Plant Plume

ABSTRACT

The rate of conversion of SO₂ to SO₄ ^2- was re-estimated from measurements made in the plume of the Cumberland power plant, located on the Cumberland River in north-central Tennessee, after installation of flue gas desulfurization (FGD) scrubbers for SO₂ removal in 1994. The ratio of SO₂ to NO_y emissions into the plume has been reduced to ~0.1, compared with a prescrubber value of ~2. To determine whether the SO₂ emissions reduction has correspondingly reduced plume-generated particulate SO₄ ^2- production, we have compared the rates of conversion before and after scrubber installation. The prescrubber estimates were developed from measurements made during the Tennessee Plume Study conducted in the late 1970s. The post-scrubber estimates are based upon two series of research flights in the summers of 1998 and 1999. During two of these flights, the Cumberland plume did not mix with adjacent power plant plumes, enabling rate constants for conversion to be estimated from samples taken in the plume at three downwind distances. Dry deposition losses and the fact the fact that SO₂ is no longer in large excess compared with SO₄ ^2- have been taken into account, and an upper limit for the conversion rate constant was re-estimated based on plume excess aerosol volume. The estimated upper limit values are 0.069 hr^-1 and 0.034 hr^-1 for the 1998 and 1999 data, respectively. The 1999 rate is comparable with earlier values for nonscrubbed plumes, and although the 1998 upper limit value is higher than expected, these estimates do not provide strong evidence for deviation from a linear relationship between SO₂ emissions and SO₄ ^2- formation.     

Measurements of Rural Sulfur Dioxide and Particle Sulfate: Analysis of CASTNet Data, 1987 through 1996

ABSTRACT

The Clean Air Status and Trends Network (CASTNet) was implemented by the U.S. Environmental Protection Agency (EPA) in 1991 in response to Title IX of the Clean Air Amendments of 1990, which mandated the deployment of a national ambient air monitoring network to track progress of the implementation of emission reduction programs in terms of deposition, air quality, and changes to affected ecosystems. CASTNet evolved from the National Dry Deposition Network (NDDN). CASTNet currently consists of 45 sites in the eastern United States and 28 sites in the West. Each site measures sulfur dioxide (SO₂), nitric acid (HNO₃), particle sulfate (SO₄ ⁼), particle nitrate (NO₃ ^- ), and ozone. Nineteen sites collect precipitation samples. NDDN/CASTNet uses a uniform set of site-selection criteria which provides the data user with consistent measures to compare each site. These criteria also ensure that, to the extent possible, CASTNet sites are located away from local emission sources.

This paper presents an analysis of SO₂ and SO₄ ⁼ concentration data collected from 1987 through 1996 at rural NDDN/CASTNet sites. Annual and seasonal variability is examined. Gradients of SO₂ and SO₄ ⁼ are discussed. The variability of the atmospheric mix of SO₂ and SO₄ ⁼ is explored spatially and seasonally. Data from CASTNet are also compared to SO₂ and SO₄ ⁼ data from concurrent monitoring studies in rural areas.     

Chemical Composition of Fine Particles in the Tennessee Valley Region

ABSTRACT

Fine particles in the atmosphere have elicited new national ambient air quality standards (NAAQS) because of their potential role in health effects and visibility-reducing haze. Since April 1997, Tennessee Valley Authority (TVA) has measured fine particles (PM_2.5) in the Tennessee Valley region using prototype Federal Reference Method (FRM) samplers, and results indicate that the new NAAQS annual standard will be difficult to meet in this region. The composition of many of these fine particle samples has been determined using analytical methods for elements, soluble ions, and organic and elemental carbon. The results indicate that about one-third of the measured mass is SO₄ ^-2, one-third is organic aerosol, and the remainder is other materials. The fraction of SO₄ ^-2 is highest at rural sites and during summer conditions, with greater proportions of organic aerosol in urban areas throughout the year. Additional measurements of fine particle mass and composition have been made to obtain the short-term variability of fine mass as it pertains to human exposure. Measurements to account for semi-volatile constituents of fine mass (nitrates, semi-volatile organics) indicate that the FRM may significantly under-measure organic constituents. The potentially controllable anthropogenic fraction of organic aerosols is still largely unknown.     

Sources,distribution, and acidity of sulfate–ammonium aerosol in the Arctic in winter–spring

We use GEOS-Chem chemical transport model simulations of sulfate–ammonium aerosol data from the NASA ARCTAS and NOAA ARCPAC aircraft campaigns in the North American Arctic in April 2008, together with longer-term data from surface sites, to better understand aerosol sources in the Arctic in winter–spring and the implications for aerosol acidity. Arctic pollution is dominated by transport from mid-latitudes, and we test the relevant ammonia and sulfur dioxide emission inventories in the model by comparison with wet deposition flux data over the source continents. We find that a complicated mix of natural and anthropogenic sources with different vertical signatures is responsible for sulfate concentrations in the Arctic. East Asian pollution influence is weak in winter but becomes important in spring through transport in the free troposphere. European influence is important at all altitudes but never dominant. West Asia (non-Arctic Russia and Kazakhstan) is the largest contributor to Arctic sulfate in surface air in winter, reflecting a southward extension of the Arctic front over that region. Ammonium in Arctic spring mostly originates from anthropogenic sources in East Asia and Europe, with added contribution from boreal fires, resulting in a more neutralized aerosol in the free troposphere than at the surface. The ARCTAS and ARCPAC data indicate a median aerosol neutralization fraction [NH₄⁺]/(2[SO₄^2?] + [NO₃^?]) of 0.5 mol mol^?1 below 2 km and 0.7 mol mol^?1 above. We find that East Asian and European aerosol transported to the Arctic is mostly neutralized, whereas West Asian and North American aerosol is highly acidic. Growth of sulfur emissions in West Asia may be responsible for the observed increase in aerosol acidity at Barrow over the past decade. As global sulfur emissions decline over the next decades, increasing aerosol neutralization in the Arctic is expected, potentially accelerating Arctic warming through indirect radiative forcing and feedbacks.     

Two extreme types of mixing of dust with urban aerosols observed in Kosa particles: ‘After’ mixing and ‘on-the-way’ mixing

Besides well-known episodic Kosa during spring, high concentrations of Ca²⁺ in aerosols were observed early in summer as well as in the semi-continuous data of the aerosols at the summit of Mt. Fuji. We further analysed the data to study the chemical characteristics of the high calcium event during early summer. The back trajectory analyses of the event indicated that Ca was transported from arid and semi-arid regions (e.g. the Taklamakan desert) through the westerly-dominated troposphere higher than the height of the summit of Fuji. The amount of SO₄^2? was always equivalent to that of NH₄⁺ unlike the case of the normal Kosa period where SO₄^2? is in excess with respect to NH₄⁺. This shows the ‘after’ mixing of unreacted CaCO₃ of Kosa origin with (NH₄)₂SO₄, which was only realized by the downward injection of Kosa particles from higher altitudes to the air masses of different origin. In the case of normal Kosa, the air bearing Kosa particles passed through the polluted area to absorb unneutralized acids (‘on-the-way’ mixing), whereas in the case of the Kosa-like phenomena in summer, the acids from the polluted area have been neutralized by NH₄⁺ and become inactive before mixing with CaCO₃ (“after” mixing). We have simplified the chemistry of aerosols using their three major components, Ca²⁺, SO₄^2? and NH₄⁺, and introduced a new triangle diagram with the three assumed end-members of CaCO₃, CaSO₄ and (NH₄)₂SO₄ to quantify the contribution of the ‘after’ mixing to the aerosols (AMI; ‘after’ mixing index). Based on the back trajectories of some high AMI cases, CaCO₃ in Kosa particles was transported through the middle troposphere (5000–7000 m) and descended to meet another air mass where SO₄^2? had been already neutralized by NH₃.     

Evaluation of a CMAQ simulation at high resolution over the UK for the calendar year 2003

A comprehensive ‘operational’ evaluation of the performance of the Community Multiscale Air Quality (CMAQ) modelling system version 4.6 was conducted in support of pollution assessment in the UK for the calendar year 2003. The model was run on multiple grids using one-way nests down to a horizontal resolution as fine as 5 km over the whole of the UK. The model performance was evaluated for pollutants with standards and limit values (e.g. O₃, PM₁₀) and species contributing to acidic and nitrogenous deposition (e.g. NH₃, SO₄^2–, NO₃^–, NH₄⁺) against data from operational national monitoring networks. The key performance characteristics of the modelling system were found to be variable according to acceptance criteria and to depend on the type (e.g. urban, rural) and location of the sites, as well as on the time of the year. As regards the techniques that were used for ‘operational’ evaluation, performance generally complied with expected levels and ranged from good (e.g. O₃, SO₄^2–) to moderate (e.g. PM₁₀, NO₃^–). At a few sites low correlations and large standard deviations for some species (e.g. SO₂) suggest that these sites are subject to local factors (e.g. topography, emission sources) that are not well described in the model. Overall, the model tends to over predict O₃ and under predict aerosol species (except SO₄^2–). Discrepancies between predicted and observed concentrations may be due to a variety of intertwined factors, which include inaccuracies in meteorological predictions, chemical boundary conditions, temporal variability in emissions, and uncertainties in the treatment of gas and aerosol chemistry. Further work is thus required to investigate the respective contributions of such factors on the predicted concentrations.     

Determination of sources of fine particles in different ambient atmospheres in South Korea using a chemical mass balance model

Abstract

To determine the sources of particulate matter less than 2.5?μm (PM_2.5 in different ambient atmospheres (urban, roadside, industrial, and rural sites), the chemical components of PM_2.5 such as ions (Cl^-, NO₃^-, SO₄^2-, NH₄⁺, Na⁺, K⁺, Ca²⁺, and Mg²⁺), carbonaceous species, and elements (Al, As, Ba, Cd, Cu, Fe, Mn, Ni, Pb, Se, V, and Zn) were measured. The average mass concentrations of PM_2.5 at the urban, roadside, industrial, and rural sites were 31.5?±?14.8, 31.6?±?22.3, 31.4?±?16.0, and 25.8?±?12.4?μg/m³, respectively. Except for secondary ammonium sulfate and ammonium nitrate, the model results showed that the traffic source (i.e., the sum of gasoline and diesel vehicle sources) was the most dominant source of PM_2.5 (17.1%) followed by biomass burning (13.8%) at the urban site. The major primary sources of PM_2.5 were consistent with the site characteristics (diesel vehicle source at the roadside site, coal-fired plants at the industrial site, and biomass burning at the rural site). Seasonal data from the urban site suggested that ammonium sulfate and ammonium nitrate were the most dominant sources of PM_2.5 during all seasons. Further, the contribution of road dust source to PM_2.5 increased during spring and fall seasons. We conclude that the determination of the major PM_2.5 sources is useful for establishing efficient control strategies for PM_2.5 in different regions and seasons.     

Evaluation of aerosol sources at European high altitude background sites with trajectory statistical methods

This study has investigated the influence of synoptic weather patterns and long-range transport episodes on the concentrations of several compounds related to different aerosol sources (EC, OC, SO₄^2?, Ca²⁺, Na⁺, K⁺, ²¹⁰Pb, levoglucosan and dicarboxylic acids) registered in PM10 or PM2.5 aerosol samples collected at three remote background sites in central Europe. Air mass back-trajectories arriving at these sites have been analysed by statistical methods. Firstly, air mass back-trajectories have been grouped into clusters. Each cluster corresponds to specific meteorological scenarios, which were extracted and discussed. Finally, redistributed concentration fields have been computed to identify the main potential source regions of the different key aerosol components. A marked seasonal pattern is observed in the occurrence of the different clusters, with fast westerly and northerly Atlantic flows during winter and weak circulation flows in summer. Spring and fall were characterised by advection of moderate flows from northeastern and eastern Europe. Significant inter-cluster differences were observed for concentrations of receptor aerosol components, with the highest concentrations of EC, OC, SO₄^2?, K⁺ and ²¹⁰Pb associated with local and mesoscale aerosol sources located over central Europe related to enhanced photochemical processes. Emissions produced by fossil fuel and biomass burning processes from the Baltic countries, Byelorussia, western regions of Russia and Kazakhstan in spring and fall also contribute to elevated levels of EC, OC, SO₄^2?, K⁺ and ²¹⁰Pb. In the summer period long-range transport episodes of mineral dust from North-African deserts were also frequently detected, which caused elevated concentrations of coarse Ca²⁺ at sites. The baseline aerosol concentrations in central Europe at the high altitude background sites were registered in winter, with the exception of coarse Na⁺. While the relatively high concentrations of Na⁺ can be explained by sea salt advected from the Atlantic, the low levels of other aerosol components are caused by efficient aerosol scavenging associated to advections of Atlantic air masses, as well as lower emissions of these species over the Atlantic compared to those over the European continent and very limited vertical air mass exchange over the continent.     

Linkage between community diversity of sulfate-reducing microorganisms and methylmercury concentration in paddy soil

Sulfate-reducing microorganisms (SRM) have been thought to play a key role in mercury (Hg) methylation in anoxic environments. The current study examined the linkage between SRM abundance and diversity and contents of methylmercury (MeHg) in paddy soils collected from a historical Hg mining area in China. Soil profile samples were collected from four sites over a distance gradient downstream the Hg mining operation. Results showed that MeHg content in the soil of each site significantly decreased with the extending distance away from Hg mine. Soil MeHg content was correlated positively with abundance of SRM and the contents of organic matter (OM), NH₄ ⁺, SO₄ ^2?, and Hg. The abundances of SRM based on dissimilatory (bi) sulfite reductase (dsrAB) gene at 0–40 cm depths were higher than those at 40–80 cm depth at all sites. The SRM community composition varied in the soils of different sampling sites following terminal restriction fragment length polymorphism (T-RFLP) and phylogenetic analyses, which appeared to be correlated with contents of MeHg, OM, NH₄ ⁺, and SO₄ ^2? through canonical correspondence analysis. The dominant groups of SRM in the soils examined belonged to Deltaproteobacteria and some unknown SRM clusters that could have potential for Hg methylation. These results advance our understanding of the relationship between SRM and methylmercury concentration in paddy soil.     

Compositions of Particles from Selected Sources in Philadelphia for Receptor Modeling Applications

As a part of a receptor model study of the Philadelphia, PA atmosphere, particulate samples were collected from seven air pollution sources in the area: two oil-fired power plants, a coal-fired power plant, a fluidized catalytic cracker, a refuse incinerator, a secondary aluminum smelter and an antimony ore roaster. Samples were collected In two size fractions with a dilution source sampler connected to a modified dichotomous sampler. Masses of collected material were determined gravlmetrlcally. Samples were analyzed for elements by x-ray fluorescence followed by Instrumental neutron activation analysis of some samples. Other samples were analyzed by chemical methods for volatile and nonvolatile carbon, SO₄ ^2? and NH₄ ⁺. Data are presented for up to 46 elements and species on fine (<2.5-μm aerodynamic equivalent diameter) and coarse (2.5 μm < diam < 7-10 μm) particles from each source. Although the data were collected for use in Philadelphia, they should be of value for receptor modeling of other areas having similar sources. The most unexpected results were the large amounts of rare earth elements on particles from the catalytic cracker (e.g., 0.31 percent La In fine fraction) and the oil-fired power plants (120 and 420 ppm La in fine fraction). Substantial amounts of primary SO₄ ^2? are released from the oil-fired plants, the SO₄ ^2? concentrations accounting for 40-45 percent of the fine particulate mass.     

Regional Transport and Urban Contributions to Fine Particle Concentrations in Southeastern Canada

Abstract

The impact of various atmospheric transport directions on ambient fine particle (PM_2.5) concentrations at several sites in southeastern Canada was estimated (for May-September) using back-trajectory analysis. Three-day back trajectories (four per day) were paired with 6-hr average PM_2.5 mass concentrations measured using tapered element oscillating microbalances (TEOM). PM_2.5 concentrations at rural locations in the region were affected by nonlocal sources originating in both Canada and the United States. Comparison of sites revealed that, on average, the local contribution to total PM_2.5 in the greater Toronto area (GTA) is approximately 30–35%. At each location, average PM_2.5 concentrations under south/southwesterly flow conditions were 2–4 times higher than under the corresponding northerly flow conditions. The chemical composition of both urban and rural PM_2.5 was determined during two separate 2-week spring/summer measurement campaigns. Components identified included SO₄ ^2?, NO₃ ^?, NH₄+, black carbon and organic carbon (OC), and trace elements. Higher particle mass at the urban Toronto site was composed of a higher proportion of all components. However, black carbon, NO₃ ^?, NaCl, and trace elements were found to be the most enriched over the rural/regional background levels.