Chemical Composition, Sources, and Health Risk Assessment of PM2.5 and PM10 in Urban Sites of Bangkok, Thailand

Of late, air pollution in Asia has increased, particularly in built-up areas due to rapid industrialization and urbanization. The present study sets out to examine the impact that pollution can have on the health of people living in the inner city of Bangkok, Thailand. Consequently, in 2021, fine particulate matter (PM_2.5) and coarse particulate matter (PM₁₀) chemical composition and sources are evaluated at three locations in Bangkok. To identify the possible sources of such particulates, therefore, the principal component analysis (PCA) technique is duly carried out. As determined via PCA, the major sources of air pollution in Bangkok are local emission sources and sea salt. The most significant local sources of PM_2.5 and PM₁₀ in Bangkok include primary combustion, such as vehicle emissions, coal combustion, biomass burning, secondary aerosol formation, industrial emissions, and dust sources. Except for the hazard quotient (HQ) of Ni and Mn of PM_2.5 for adults, the HQ values of As, Cd, Cr, Mn, and Ni of both PM_2.5 and PM₁₀ were below the safe level (HQ = 1) for adults and children. This indicates that exposure to these metals would have non-carcinogenic health effects. Except for the carcinogenic risk (HI) value of Cr of PM_2.5 and PM₁₀, which can cause cancer in adults, at Bangna and Din Daeng, the HI values of Cd, Ni, As, and Pb of PM_2.5 and PM₁₀ are below the limit set by the U.S. Environmental Protection Agency (U.S. EPA). Ni and Mn pose non-carcinogenic risks, whereas Cr poses carcinogenic risks to adults via inhalation, a serious threat to the residents of Bangkok.

The Impact of Long-Range Transport of Biomass Burning Emissions in Southeast Asia on Southern China

The long-range transport of biomass burning pollutants from Southeast Asia has a significant impact on air quality in China. In this study, the Moderate Resolution Imaging Spectroradiometer (MODIS) fire data and aerosol optical depth (AOD) products and the Tropospheric Monitoring Instrument (TROPOMI) carbon monoxide (CO) data were used to analyze the impact of air pollution caused by biomass burning in Southeast Asia on southern China. Results showed that Yunnan, Guangdong and Guangxi were deeply affected by biomass burning emissions from March to April during 2016–2020. Comparing the data for fires on the Indochinese Peninsula and southern provinces of China, it is obvious that the contribution of pollutants emitted by local biomass burning in China to air pollution is only a small possibility. The distribution of CO showed that the overall emissions increased greatly from March to April, and there was an obvious transmission process. In addition, the MODIS AOD in areas close to the national boundary of China is at a high level (>0.6), and the AOD in the southwest of Guangxi province and the southeast of Yunnan Province is above 0.8. Combined with a typical air pollution event in southern China, the UVAI combined with wind direction and other meteorological data showed that the pollutants were transferred from the Indochinese Peninsula to southern China under the southwest monsoon. The PM2.5 data from ground-based measurements and backward tracking were used to verify the pollutant source of the pollution event, and it was concluded that the degree of pollution in Yunnan, Guangxi and Guangdong provinces was related to the distance from the Indochinese Peninsula. Results indicate that it is necessary to carry out in-depth research on the impact of cross-border air pollution transport on domestic air quality as soon as possible and to actively cooperate with foreign countries to carry out pollution source research and control.

Persistent Influence of Wildfire Emissions in the Western United States and Characteristics of Aged Biomass Burning Organic Aerosols under Clean Air Conditions

Wildfire-influenced air masses under regional background conditions were characterized at the Mt. Bachelor Observatory (∼2800 m a.s.l.) in summer 2019 to provide a better understanding of the aging of biomass burning organic aerosols (BBOAs) and their impacts on the remote troposphere in the western United States. Submicron aerosol (PM₁) concentrations were low (average ± 1σ = 2.2 ± 1.9 μg sm^-3), but oxidized BBOAs (average O/C = 0.84) were constantly detected throughout the study. The BBOA correlated well with black carbon, furfural, and acetonitrile and comprised above 50% of PM₁ during plume events when the peak PM₁ concentration reached 18.0 μg sm^-3. Wildfire plumes with estimated transport times varying from ∼10 h to >10 days were identified. The plumes showed ΔOA/ΔCO values ranging from 0.038 to 0.122 ppb ppb^-1 with a significant negative relation to plume age, indicating BBOA loss relative to CO during long-range transport. Additionally, increases of average O/C and aerosol sizes were seen in more aged plumes. The mass-based size mode was approximately 700 nm (D_va) in the most oxidized plume that likely originated in Siberia, suggesting aqueous-phase processing during transport. This work highlights the widespread impacts that wildfire emissions have on aerosol concentration and properties, and thus climate, in the western United States.

Chemical Characteristics of Atmospheric PM10 and PM2.5 at a Rural Site of Lijiang City, China

Emissions from biomass burning are very serious in Southeast Asia and South Asia in April. In order to explore the effect of long-range transport of biomass emissions from the Indochina Peninsula in Southwest China during the period of the southeast monsoon season and to find out the main pollution sources in local atmospheric PM_2.5, a field campaign was conducted from 6–26 April 2011 in Lijiang, China. Twenty-four-hour PM₁₀ and PM_2.5 filter samples were collected, and inorganic ions, elements, and carbonaceous components (including organic carbon (OC) and elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs (NPAHs)) were measured. The monthly mean mass concentrations of particulate matter (PM) were 40.4 and 14.4 μg/m³ for PM₁₀ and PM_2.5, respectively. The monthly mean concentrations of OC and EC in PM₁₀ were 6.2 and 1.6 μg/m³, respectively. The weekly mean concentrations of ∑PAHs and ∑NPAHs were 11.9 ng/m³ and 289 pg/m³, respectively, in atmospheric PM₁₀ of Lijiang. The diagnostic ratios of PAH and NPAH isomers were used to analyze the sources of PAHs and NPAHs in PM₁₀. The ratios of Benz(a)anthracene/(Chrysene+Benz(a)anthracen), Fluoranthene/(Fluoranthene+Pyrene) and Indeno(1,2,3-cd)pyrene/(Benzo(g,h,i)perylene+Indeno(1,2,3-cd)pyrene) were 0.45 ± 0.04, 0.61 ± 0.01, and 0.53 ± 0.03, respectively, indicating the contribution from coal combustion and biomass burning. The 1-nitropyrene/Pyrene (1-NP/Pyr) ratio was 0.004 ± 0.001, suggesting that the contribution to NPAHs mainly came from coal combustion. Sulfate was the most prominent inorganic ionic species, with monthly mean levels of 2.28 and 1.39 μg/m³ in PM₁₀ and PM_2.5, respectively. The monthly mean mass ratios of NO₃⁻/SO₄²⁻ were 0.40 and 0.23 in PM₁₀ and PM_2.5, respectively, indicating that the contribution of atmospheric anions from coal combustion sources was much more important than that from other sources. Based on the relatively high SO₄²⁻ concentrations and low NO₃⁻/SO₄²⁻ ratios, combined with the data analysis of isomer ratios of PAHs and NPAHs, we can conclude that coal combustion, traffic, and dust were the major contributors to local atmospheric PM in Lijiang city, while biomass burning may also have contributed to local atmospheric PM in Lijiang city to some degree.

Change in characteristics of water-soluble and water-insoluble brown carbon aerosols during a large-scale biomass burning

Light-absorbing organic aerosol (brown carbon (BrC)) can significantly affect Earth's radiation budget and hydrological cycle. Biomass burning (BB) is among the major sources of atmospheric BrC. In this study, day/night pair (10-h integrated) of ambient PM_2.5 were sampled every day before (defined as T1, n = 21), during (T2, n = 36), and after (T3, n = 8) a large-scale paddy-residue burning during October-November over Patiala (30.2° N, 76.3° E, 250 m amsl), a site located in the northwestern Indo-Gangetic Plain (IGP). PM_2.5 concentration varied from ~ 90 to 500 μg m^-3 (average ± 1σ standard deviation 230 ± 114) with the average values of 154 ± 57, 271 ± 122, and 156 ± 18 μg m^-3 during T1, T2, and T3 periods, respectively, indicating the influence of BB emissions on ambient air quality. The absorption coefficient of BrC (b_abs) is calculated from the high-resolution absorption spectra of water-soluble and methanol-soluble organic carbon measured at 300 to 700 nm, and that at 365 nm (b_{abs_365}) is used as a general measure of BrC. The b_{abs_365_Water} and b_{abs_365_Methanol} ranged ~ 2 to 112 Mm^-1 (avg 37 ± 27) and ~ 3 to 457 Mm^-1 (avg 121 ± 108), respectively, suggesting a considerable presence of water-insoluble BrC. Contrasting differences were also observed in the daytime and nighttime values of b_{abs_365_Water} and b_{abs_365_Methanol}. Further, the levoglucosan showed a strong correlation with K⁺ (slope = 0.89 ± 0.06, R = 0.92) during the T2 period. We propose that this slope (~ 0.9) can be used as a typical characteristics of the emissions from paddy-residue burning over the IGP. Absorption Ångström exponent (AAE) showed a clear day/night variability during the T2 period, and lower AAE_Methanol compared to AAE_Water throughout the sampling period. Further at 365 nm, average relative atmospheric radiative forcing (RRF) for BrC_Water is estimated to be ~ 17%, whereas that of BrC_Methanol ~ 62% with respect to elemental carbon, suggesting that BrC radiative forcing could be largely underestimated by studies those use BrC_Water only as a surrogate of total BrC.

Influence of biomass burning on local air pollution in mainland Southeast Asia from 2001 to 2016

In this study, various remote sensing data, modeling data and emission inventories were integrated to analyze the tempo-spatial distribution of biomass burning in mainland Southeast Asia and its effects on the local ambient air quality from 2001 to 2016. Land cover changes have been considered in dividing the biomass burning into four types: forest fires, shrubland fires, crop residue burning and other fires. The results show that the monthly average number of fire spots peaked at 34,512 in March and that the monthly variation followed a seasonal pattern, which was closely related to precipitation and farming activities. The four types of biomass burning fires presented different tempo-spatial distributions. Moreover, the monthly Aerosol Optical Depth (AOD), concentration of particulate matter with a diameter less than 2.5 μm (PM_2.5) and carbon monoxide (CO) total column also peaked in March with values of 0.62, 45 μg/m³ and 3.25 × 10¹⁸ molecules/cm², respectively. There are significant correlations between the monthly means of AOD (r = 0.74, P < 0.001), PM_2.5 concentration (r = 0.88, P < 0.001), and CO total column (r = 0.82, P < 0.001) and the number of fire spots in the fire season. We used Positive Matrix Factorization (PMF) model to resolve the sources of PM_2.5 into 3 factors. The result indicated that the largest contribution (48%) to annual average concentration of PM_2.5 was from Factor 1 (dominated by biomass burning), followed by 27% from Factor 3 (dominated by anthropogenic emission), and 25% from Factor 2 (long-range transport/local nature source). The annually anthropogenic emission of CO and PM_2.5 from 2001 to 2012 and the monthly emission from the Emission Database for Global Atmosphere Research (EDGAR) were consistent with PMF analysis and further prove that biomass burning is the dominant cause of the variation in the local air quality in mainland Southeast Asia.

Spatial Distributions and Sources of Inorganic Chlorine in PM2.5 across China in Winter

Chlorine is an important atmospheric photochemical oxidant, but few studies have focused on atmospheric chlorine. In this study, PM2.5 samples were collected from urban and rural sites across China in January 2018, and concentrations of Cl− and other water-soluble ions in PM2.5 were analyzed. The size-segregated aerosol Cl− data measured across Chinese cities by other studies were compiled for comparison. The observed data demonstrated that the Cl− concentrations of PM2.5 in northern cities (5.0 ± 3.7 µg/m3) were higher than those in central (1.9 ± 1.2 µg/m3) and southern cities (0.84 ± 0.54 µg/m3), suggesting substantial chlorine emissions in northern cities during winter. The concentrations of Cl− in aerosol were significantly higher in urban regions (0.11–26.7 µg/m3) compared to than in rural regions (0.03–0.61 µg/m3) across China during winter, implying strong anthropogenic chlorine emission in cities. Based on the mole ratios of Cl−/Na+, Cl−/K+ and Cl−/ SO 4 2 − and the PMF model, Cl− in northern and central cities was mainly sourced from the coal combustion and biomass burning, but in southern cities, Cl− in PM2.5 was mainly affected by the equilibrium between gas-phase HCl and particulate Cl−. The size-segregated statistical data demonstrated that particulate Cl− had a bimodal pattern, and more Cl− was distributed in the fine model than that in the coarse mode in winter, with the opposite pattern was observed in summer. This may be attributed to both sources of atmospheric Cl− and Cl− involved in chemical processes. This study reports the concentrations of aerosol Cl− on a national scale, and provides important information for modeling the global atmospheric reactive chlorine distribution and the effects of chlorine on atmospheric photochemistry.

High time-resolved measurements of water-soluble sulfate, nitrate and ammonium in PM2.5 and their precursor gases over the Eastern Mediterranean

High time-resolved measurements of aerosol SO₄^2-, NO₃^-, NH₄⁺ and their precursor gases HNO₃, SO₂, NH₃ between 27 and 02 January/February and 19-01 August/September 2015 were carried out by applying AIM-IC at a rural site located on the coast of the Eastern Mediterranean, Erdemli, Turkey. The comparison between online and offline techniques revealed better correlation coefficients for SO₄^2- and NH₄⁺ (r > 0.90) than that of NO₃^- (0.63). Mean concentrations of water-soluble species were found in decreasing order SO₄^2- (2814 ng m^-3) > NH₄⁺ (1371 ng m^-3) > NO₃^- (495 ng m^-3). NH₃ (3390 ng m^-3) concentration was more than enough to neutralize SO₂ (879 ng m^-3) and HNO₃ (346 ng m^-3). The gas-to-particle conversion ratios (>0.3) implied that SO₄^2-, NO₃^- and NH₄⁺ were mainly influenced by non-local sources. SO₄^2-, NO₃^-, NH₄⁺, HNO₃, SO₂ exhibited remarkable decrease (leastways 40%) in the atmosphere over the Eastern Mediterranean throughout fifteen years. In winter, day time NH₃ concentrations illustrated significant relationship with temperature (positive) and humidity (negative), implying evaporation of dew or emission from plant stoma. Whereas, diurnal cycle of SO₄^2- and SO₂ was considerably influenced by populated City of Mersin in winter. During summer, HNO₃ and SO₂ (r = 0.74) demonstrated similar diurnal cycle, suggesting a common source for these precursor gases whilst NH₃ was considerably affected by biomass burning emissions. Variability of all species was governed by local or nearly mesoscale transport in winter possibly due to frequent rain events. In summer, air flow from Eastern Mediterranean denoted aged air masses (GPC > 0.65) containing rather uniform concentrations of SO₄^2- (~65 nmol m^-3) and NH₄⁺ (~140 nmol m^-3). The highest NH₃ along with the greatest % K_BB contribution to PM_2.5 mass was observed under the influence of Northerly airflow, exhibiting significance of biomass burning emissions as a source of NH₃ in summer.

Pollution characteristics in a dusty season based on highly time-resolved online measurements in northwest China

To investigate the pollution characteristics and potential sources in a dusty season, an online analyzer was used to measure trace gases and major water-soluble ions in PM₁₀ from April 1st to May 29th, 2011 in Lanzhou. The average concentrations of HONO, HNO₃, HCl, SO₂ and NH₃ were 0.93, 1.16, 0.48, 9.29 and 5.54 μg/m³, respectively, and 2.8, 2.76, 8.28 and 2.48 μg/m³ for Cl^-, NO₃^-, SO₄^2- and NH₄⁺. In the non-dust period, diurnal variations of SO₄^2-, NO₃^- and their gaseous precursors showed similar change trend. NH₄⁺ showed unimodal pattern whereas NH₃ illustrated a bimodal pattern. HCl and Cl^- showed an opposite diurnal pattern. In the dust event, temporal profiles of HCl and Cl^-, SO₂ and SO₄^2- all presented similar change trend, and SO₄^2- and Cl^- preceded dust ions (Ca²⁺ and Mg²⁺) 13 h. The ratios of NO₃^- to SO₄^2- were 0.65 in the non-dust period and 0.31 in the dust event. In the dust event, the sulfur oxidation ratio (SOR) was a factor of 1.33 greater than that in the non-dust period, and [SO₄^2-]/[SO₂] was 2.31 times of that in the non-dust period. The source apportionment using Probabilistic Matrix Factorization (PMF) suggested that fugitive dust (58.09%), secondary aerosols (33.98%), and biomass burning (7.93%) were the major sources in the non-dust period whereas dust (67.01%), salt lake (29.68%), biomass burning (0.8%), and motor vehicle (2.51%) were the primary sources in the dust event. Concentration weighted trajectory (CWT) model indicated that NO₃^-, Cl^- and K⁺ could be regarded as local source species, the potential sources of Na⁺, Mg²⁺ and Ca²⁺ concentrated in the two large areas with the one covered in the junction areas of Xinjiang, Qinghai and Gansu and another one covered the places around in Lanzhou, the potential sources of SO₄^2- were mainly localized in the areas adjacent to Lanzhou.

Abundance and origin of fine particulate chloride in continental China

Particulate chloride can be converted to nitryl chloride (ClNO₂) through heterogeneous reactions with dinitrogen pentoxide (N₂O₅), and photolysis of ClNO₂ affects atmospheric oxidative capacity. However, the characteristics and sources of chloride, especially those with an anthropogenic origin, are poorly characterized, which makes it difficult to evaluate the effects of ClNO₂ on radical chemistry and air quality in polluted regions. Aerosol composition data from the literature were compiled to derive the spatial distributions of particulate chloride across China, and hourly aerosol composition data collected at a highly polluted inland urban site in eastern China and at a coastal site in southern China were analysed to gain further insights into non-oceanic sources of chloride. The results show that particulate chloride is concentrated mainly in fine particles and that high chloride loadings are observed in the inland urban areas of northern and western China with higher Cl^-/Na⁺ mass ratios (2.46 to 5.00) than sea water (1.81), indicative of significant contributions from anthropogenic sources. At the inland urban site, the fine chloride displays distinct seasonality, with higher levels in winter and summer. Correlation analysis and positive matrix factorization (PMF) results indicate that coal combustion and residential biomass burning are the main sources (84.8%) of fine chloride in winter, and open biomass burning is the major sources (52.7%) in summer. The transport of plumes from inland polluted areas leads to elevated fine chloride in coastal areas. A simulation with WRF-Chem model confirmed a minor contribution of sea-salt aerosol to fine chloride at the inland site during summer with winds from the East Sea. The widespread sources of chloride, together with abundant NOx and ozone, suggest significant ClNO₂ production and subsequent enhanced photochemical processes over China.

Biomass burning in Indo-China peninsula and its impacts on regional air quality and global climate change-a review

Although, many biomass burning (BB) emissions products (particulate matter and trace gases) are believed to be trans-boundary pollutants that originates from India and China (the two most populous countries in Asia), the information about BB emission and related contents is limited for Indo-China Peninsula (ICP) region. This motivated us to review this region pertaining to BB emission. The main objective of the review is to document the current status of BB emission in ICP region. In order to highlight the impact of BB on regional air quality and global climate change, the role of BB emission in ICP region is also discussed. Based on the available literature and modeling simulations studies, it is evidenced that ICP is one of the hotspot regional source for aerosols in terms of BB emissions. In addition, regional emissions through BB have significant implications for regional air quality especially in the neighboring countries such as China, Taiwan and India. Our assessment highlight that there is still a general lack of reliable data and research studies addressing BB related issues in context of environmental and human health. There is therefore a critical need to improve the current knowledge base, which should build upon the research experience and further research into these issues is considered vital to help inform future policies/control strategies.

Size distribution characteristics of carbonaceous aerosol in Xishuangbanna, southwest China: a sign for biomass burning in Asia

In 2012, size-segregated aerosol samples were collected in Xishuangbanna, a forest station in southwest China. The concentrations of organic and elemental carbon (OC and EC for short) were quantified with thermal/optical carbon analyzer in the filter samples. OC and EC exhibited similar seasonal patterns, with the highest concentrations in spring, possibly due to the influence of biomass burning in south and southeast Asia. The mass size distributions of OC and EC were bimodal in all the sampling seasons, each with a dominant peak in the fine mode of 0.4-0.7 μm and a coarse peak in the size range of 2.1-4.7 μm. In fine mode, OC and EC showed smaller geometric mean diameters (GMDs) during winter. OC and EC were prone to be more concentrated in fine particles in spring and winter than in summer and autumn. Furthermore, EC was more abundant in fine particles than OC. Good correlations (R(2) = 0.75-0.82) between OC and EC indicated that they had common dominant sources of combustion such as biomass burning and fossil fuel combustion emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, more elevated OC/EC ratios being found in the winter.

PM₂.₅., EC and OC in atmospheric outflow from the Indo-Gangetic Plain: temporal variability and aerosol organic carbon-to-organic mass conversion factor

Temporal variability (November'09-March'10) in the mass concentrations of PM2.5, mineral dust, organic carbon and elemental carbon (OC and EC), water-soluble organic carbon (WSOC) and inorganic species (WSIS) has been studied in the atmospheric outflow to the Bay of Bengal from a sampling site [Kharagpur: 22.02°N, 87.11°E] in the Indo-Gangetic Plain (IGP). Based on diagnostic ratios of carbonaceous species [OC/EC ≈ 7.0 ± 2.2, WSOC/OC ≈ 0.52 ± 0.16, and K(+)/EC≈0.48±0.17], we document dominant impact from biomass burning emissions (wood-fuel and post-harvest agricultural-waste burning) in the IGP-outflow. Relatively high concentration of sulphate (SO4(2-) ≈ 6.9-25.3 μg m(-3); SO4(2-)/ΣWSIS=45-77%) and characteristic ratios of nss-SO4(2-)/EC (3.9 ± 2.1) and nss-SO4(2-)/OC (0.61 ± 0.46) provide information on absorption/scattering properties of aerosols. Based on quantitative assessment of individual components of PM2.5, we document aerosol organic carbon-to-organic mass (OC to OM) conversion factor centring at 1.5 ± 0.2 (range: 1.3-2.7) in the atmospheric outflow from IGP. The aerosol composition over the Bay of Bengal shows striking similarity with the diagnostic ratios documented for the IGP-outflow. Relatively high conversion factor for assessing the mass of organic aerosols over the Bay of Bengal (1.1-3.7) provides evidence for their oxidation during long-range atmospheric transport.

An aerosol climatology for a rapidly growing arid region (southern Arizona): Major aerosol species and remotely sensed aerosol properties

This study reports a comprehensive characterization of atmospheric aerosol particle properties in relation to meteorological and back trajectory data in the southern Arizona region, which includes two of the fastest growing metropolitan areas in the United States (Phoenix and Tucson). Multiple data sets (MODIS, AERONET, OMI/TOMS, MISR, GOCART, ground-based aerosol measurements) are used to examine monthly trends in aerosol composition, aerosol optical depth (AOD), and aerosol size. Fine soil, sulfate, and organics dominate PM_2.5 mass in the region. Dust strongly influences the region between March and July owing to the dry and hot meteorological conditions and back trajectory patterns. Because monsoon precipitation begins typically in July, dust levels decrease, while AOD, sulfate, and organic aerosol reach their maximum levels because of summertime photochemistry and monsoon moisture. Evidence points to biogenic volatile organic compounds being a significant source of secondary organic aerosol in this region. Biomass burning also is shown to be a major contributor to the carbonaceous aerosol budget in the region, leading to enhanced organic and elemental carbon levels aloft at a sky-island site north of Tucson (Mt. Lemmon). Phoenix exhibits different monthly trends for aerosol components in comparison with the other sites owing to the strong influence of fossil carbon and anthropogenic dust. Trend analyses between 1988 and 2009 indicate that the strongest statistically significant trends are reductions in sulfate, elemental carbon, and organic carbon, and increases in fine soil during the spring (March-May) at select sites. These results can be explained by population growth, land-use changes, and improved source controls.

Spatial and seasonal distribution of aerosol chemical components in New York City: (1) Incineration, coal combustion, and biomass burning

We describe spatial and temporal patterns of fine particulate matter (PM(2.5)) and of 12 of its constituent chemical elements commonly observed in measurements at residential locations in New York City (NYC). These elements, that is, Ni, V, As, Se, S, Cl, Na, K, Pb, Cu, Zn, and Mn, had significant spatial and temporal variability at 10 PM(2.5) sampling locations during our winter and summer sampling campaigns. By grouping the elements into traditional source apportionment categories, we show that specific chemical components of PM(2.5) considered to have a common source category, such as As and Se for coal combustion, do not always follow the same temporal or spatial pattern. PM(2.5) mass had only limited spatial variability and a slight summertime concentration enhancement. Measurements at residential locations were, on average, consistent with EPA sampling network measurements, although we found that during times of low regional concentration, EPA measurements underestimated the PM(2.5) concentration at residential locations. These results have implications for improved understanding of exposures to specific sources of PM(2.5), and raise some concerns about source profiles used in source-receptor modeling tracer input selection.

Surface-level fine particle mass concentrations: from hemispheric distributions to megacity sources

Since 1990, basic knowledge of the "chemical climate" of fine particles, has greatly improved from Junge's compilation from the 1960s. A worldwide baseline distribution of fine particle concentrations on a synoptic scale of approximately 1000 km can be estimated at least qualitatively from measurements. A geographical distribution of fine particle characteristics is deduced from a synthesis of a variety of disparate data collected at ground level on all continents, especially in the northern hemisphere. On the average, the regional mass concentrations range from 1 to 80 microg/m3, with the highest concentrations in regions of high population density and industrialization. Fine particles by mass on a continental and hemispheric spatial scale are generally dominated by non-sea salt sulfate (0.2 to approximately 20 microg/m3, or approximately 25%) and organic carbon (0.2-> 10 microg/m3, or approximately 25%), with lesser contributions of ammonium, nitrate, elemental carbon, and elements found in sea salt or soil dust. The crustal and trace metal elements contribute a varied amount to fine particle mass depending on location, with a larger contribution in marine conditions or during certain events such as dust storms or volcanic disturbances. The average distribution of mass concentration and major components depends on the proximity to areal aggregations of sources, most of which are continental in origin, with contributions from sea salt emissions in the marine environment. The highest concentrations generally are within or near very large population and industrial centers, especially in Asia, including parts of China and India, as well as North America and Europe. Natural sources of blowing dust, sea salt, and wildfires contribute to large, intermittent spatial-scale particle loadings beyond these ranges. A sampling of 10 megacities illustrates a range of characteristic particle composition, dependent on local and regional sources. Long-range transport of pollution from spatially aggregated sources over hundreds of kilometers creates persistent regional- and continental-scale gradients of mass concentration, sulfate, and carbon species especially in the northern hemisphere. Data are sparse in the southern hemisphere, especially beyond 45 degrees S, but are generally very low in mass concentrations.

Diagnosis of aged prescribed burning plumes impacting an urban area

An unanticipated wind shift led to the advection of plumes from two prescribed burning sites that impacted Atlanta, GA, producing a heavy smoke event late in the afternoon on February 28, 2007. Observed PM2.5 concentrations increased to over 140 microg/m3 and O3 concentrations up to 30 ppb in a couple of hours, despite the late hour in February when photochemistry is less vigorous. A detailed investigation of PM2.5 chemical composition and source apportionment analysis showed that the increase in PM2.5 mass was driven mainly by organic carbon (OC). However, both results from source apportionment and an observed nonlinear relationship between OC and PM2.5 potassium (K) indicate that the increased OC was not due solely to primary emissions. Most of the OC was water-soluble organic carbon (WSOC) and was dominated by hydrophobic compounds. The data are consistent with large enhancements in isoprenoid (isoprene and monoterpenes) and other volatile organic compounds emitted from prescribed burning that led to both significant O3 and secondary organic aerosol (SOA) production. Formation of oligomers from oxidation products of isoprenoid compounds or condensation of volatile organic compounds (VOCs) with multiple functional groups emitted during prescribed burning appears to be a major component of the secondary organic contributor of the SOA. The results from this study imply that enhanced emissions due to the fire itself and elevated temperature in the burning region should be considered in air quality models (e.g., receptor and emission-based models) to assess impacts of prescribed burning emissions on ambient air quality.