A substantial fraction of fine particulate matter (PM) across the United States is composed of carbon, which may be either emitted in particulate form (i.e., primary) or formed in the atmosphere through gas-to-particle conversion processes (i.e., secondary). Primary carbonaceous aerosol is emitted from numerous sources including motor vehicle exhaust, residential wood combustion, coal combustion, forest fires, agricultural burning, solid waste incineration, food cooking operations, and road dust. Quantifying the primary contributions from each major emission source category is a prerequisite to formulating an effective control strategy for the reduction of carbonaceous aerosol concentrations. A quantitative assessment of secondary carbonaceous aerosol concentrations also is required, but falls outside the scope of the present work.
[1] Fine particle organic carbon in Delhi, Mumbai, Kolkata, and Chandigarh is speciated to quantify sources contributing to fine particle pollution. Gas chromatography/mass spectrometry of 29 particle-phase organic compounds, including n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, and levoglucosan along with quantification of silicon, aluminum, and elemental carbon are used in a molecular-marker based source apportionment model to quantify the primary source contributions to the PM2.5 mass concentrations for four seasons in three sites and for the summer in Chandigarh. Five primary sources are identified and quantified: diesel engine exhaust, gasoline engine exhaust, road dust, coal combustion, and biomass combustion. Important trends in the seasonal and spatial patterns of the impact of these five sources are observed. On average, primary emissions from fossil fuel combustion (coal, diesel, and gasoline) are responsible for about 25–33% of PM2.5 mass in Delhi, 21–36% in Mumbai, 37–57% in Kolkata, and 28% in Chandigarh. These figures can be compared to the biomass combustion contributions to ambient PM2.5 of 7–20% for Delhi, 7–20% for Mumbai, 13–18% for Kolkata, and 8% for Chandigarh. These measurements provide important information about the seasonal and spatial distribution of fine particle phase organic compounds in Indian cities as well as quantifying source contributions leading to the fine particle air pollution in those cities.
The formation of secondary organic aerosol (SOA) in an anthropogenic-influenced region in the southeastern United States is investigated by a comparison with urban plumes in the northeast. The analysis is based on measurements of fine-particle organic compounds soluble in water (WSOC) as a measure of secondary organic aerosol. Aircraft measurements over a large area of northern Georgia, including the Atlanta metropolitan region, and in plumes from New York City and surrounding urban regions in the northeast show that fine-particle WSOC are spatially correlated with vehicle emission tracers (e.g., CO), yet the measurements indicate that vehicles do not directly emit significant particulate WSOC. In addition to being correlated, WSOC concentrations were in similar proportions to anthropogenic tracers in both regions, despite biogenic volatile organic compounds (VOCs) that were on average 10-100 times higher over northern Georgia. In contrast, radiocarbon analysis on WSOC extracted from integrated filters deployed in Atlanta suggests that roughly 70-80% of the carbon in summertime WSOC is modern. If both findings are valid, the combined results indicate that in northern Georgia, fine-particle WSOC was secondary and formed through a process that involves mainly modern biogenic VOCs but which is strongly linked to an anthropogenic component that may largely control the mass of SOA formed. Independent of the radiocarbon results, a strong association between SOA and anthropogenic sources has implications for control strategies in urban regions with large biogenic VOC emissions.
The organic and inorganic species in total suspended particulates (TSP) collected from June to December in 1998 in Hong Kong were identified by gas chromatography-mass spectrometry (GC-MS) and inductively coupled plasma-mass spectrometry (ICP-MS) to investigate the sources of Hong Kong aerosols and the mechanisms that control the chemical compositions and variations in the atmosphere. These samples were classified according to the climate: wet, dry under the influence of southerly winds from the sea (Dry-S) and dry under the influence of northerly winds from the continent (Dry-N). There were significant increases of materials from crustal, biogenic and pollution sources in the Dry-N period by a factor of 5, 4, and 2, respectively. Since the crustal tracers (e.g., Al, Fe) could be from coal flyash, the estimate of crustal material in the Dry-N period may include some materials from pollution source. Therefore, a positive correlation between crustal and pollution elements was observed. From the analysis of solvent-extractable organics (SEOC), microbial and meat cooking sources showed slight increase (1.2-fold). Higher levels of plant wax materials in the Dry-N period were probably due to the higher wind speed during the winter monsoon. The percentage of crustal material in TSP was 47% in the Dry-N period, and only 22% in the wet season and the Dry-S period. Plant wax materials (biogenic source) had a higher percentage in the Dry-N period (39% of SEOC) while microbial and meat cooking sources accounted for 49% of SEOC in the wet season. This study revealed that wind direction and precipitation had a significant influence not only on the concentrations but also on the chemical compositions and sources of Hong Kong aerosols.
The primary emission source contributions to fine organic carbon (OC) and fine particulate matter (PM2.5) mass concentrations on a daily basis in Atlanta, GA, are quantified for a summer (July 3 to August 4, 2001) and a winter (January 2-31, 2002) month. Thirty-one organic compounds in PM2.5 were identified and quantified by gas chromatography/mass spectrometry. These organic tracers, along with elemental carbon, aluminum, and silicon, were used in a chemical mass balance (CMB) receptor model. CMB source apportionment results revealed that major contributors to identified fine OC concentrations include meat cooking (7-68%; average: 36%), gasoline exhaust (7-45%; average: 21%), and diesel exhaust (6-41%; average: 20%) for the summer month, and wood combustion (0-77%; average: 50%); gasoline exhaust (14-69%; average: 33%), meat cooking (1-14%; average: 5%), and diesel exhaust (0-13%; average: 4%) for the winter month. Primary sources, as well as secondary ions, including sulfate, nitrate, and ammonium, accounted for 86 +/- 13% and 112 +/- 15% of the measured PM2.5 mass in summer and winter, respectively.
Sources of carbonaceous aerosols collected from three sites of Chattanooga, TN (CH), Muscle Shoals, AL (MS), and Look Rock, TN (LR) in the Tennessee Valley Region (TVR) were apportioned using both organic tracer-based chemical mass balance (CMB) modeling and radiocarbon (14C) measurement and the results were compared. Eight sources were resolved by CMB, among which wood combustion (averaging 0.92μgm−3) was the largest contributor to primary organic carbon (OC) concentrations, followed by gasoline exhaust (0.35μgm−3), and diesel exhaust (0.18μgm−3). The identified primary sources accounted for 43%, 71%, and 14% of measured OC at CH, MS, and LR, respectively. Contributions from the eight primary sources resolved by CMB could explain 107±10% of ambient elemental carbon (EC) concentrations, with diesel exhaust (66±32%) and wood combustion (37±33%) as the most important contributors. The fossil fractions in total carbon determined by 14C measurements were in reasonably good agreement with that in primary (OC+EC) carbon apportioned by CMB in the MS winter samples. The comparison between the 14C and CMB results revealed that contemporary sources dominated other OC in the TVR, especially in summertime (84% contemporary).
A significant fraction of the fine particulate matter in Hong Kong is made up of organic carbon. In order to quantitatively assess the contributions of various sources to carbonaceous aerosol in Hong Kong, a chemical mass balance (CMB) receptor model in combination with organic tracers was employed. Organic tracers including n-alkanes, polycyclic aromatic hydrocarbons (PAHs), steranes, hopanes, resin acids, cholesterol, levoglucosan, and picene in PM2.5 collected from three air monitoring sites located at roadside, urban, and rural areas in Hong Kong are quantified using gas chromatography-mass spectrometry (GC/MS) in the present study. Analyses of some overlapping species from two separate laboratories will be compared for the first time. Spatial and seasonal source contributions to organic carbon (OC) in PM2.5 from up to nine air pollution sources are assessed, including diesel engine exhaust, gasoline engine exhaust, meat cooking, cigarette smoke, biomass burning, road dust, vegetative detritus, coal combustion, and natural gas combustion. Diesel engine exhaust dominated fine organic carbon in Hong Kong (57 ± 13% at urban sites and 25 ± 2% at the rural site). Other sources that play an important role are meat cooking and biomass burning, which can account for as much as 14% of fine organic carbon. The primary sources identified by this technique explained 49%, 79%, and 94% of the measured fine organic carbon mass concentration at the rural, the urban, and the roadside sites, respectively. The unexplained fine OC is likely due to secondary organic aerosol formation.
Air pollution associated with atmospheric fine particulate matter (PM2.5, i.e., particles with an aerodynamic diameter of 2.5μm or less) is a serious problem in Beijing, China. To provide a better understanding of the sources contributing to PM2.5, 24-h samples were collected at 6-day intervals in January, April, July, and October in 2000 at five locations in the Beijing metropolitan area. Both backward trajectory and elemental analyses identified two dust storm events; the distinctly low value of Ca:Si (<0.2) and high Al:Ca (>1.7) in Beijing PM2.5 appear indicative of contributions from dust storms. Positive matrix factorization (PMF) was used to apportion sources of PM2.5, and eight sources were identified: biomass burning (11%), secondary sulfates (17%), secondary nitrates (14%), coal combustion (19%), industry (6%), motor vehicles (6%), road dust (9%), and yellow dust. The lower organic carbon (OC), elemental carbon (EC), SO42−, and Ca values of yellow dust enable it to be distinguished from road dust. The PMF method resolved 82% of PM2.5 mass concentrations and showed excellent agreement with a previous calculation using organic tracers in a chemical mass balance (CMB) model. The present study is the first reported comparison between a PMF source apportionment model and a molecular marker-based CMB in Beijing.
Source apportionment of fine particulate matter (PM2.5, i.e., particles with an aerodynamic diameter of 2.5 μm or less) in Beijing, China, was determined using two eigenvector models, principal component analysis/absolute principal component scores (PCA/APCS) and UNMIX. The data used in this study were from the chemical analysis of 24-h samples, which were collected at 6-day intervals in January, April, July, and October 2000 in the Beijing metropolitan area. Both models identified five sources of PM2.5: secondary sulfate and secondary nitrate, a mixed source of coal combustion and biomass burning, industrial emission, motor vehicles exhaust, and road dust. On average, the PCA/APCS and UNMIX models resolved 73% and 85% of the PM2.5 mass concentrations, respectively. The results were comparable to previous estimate using the positive matrix factorization (PMF) and chemical mass balance (CMB) receptor models. Secondary products and the emissions from coal combustion and biomass burning dominated PM2.5. Such comparison among various receptor models, which contain different physical constraints, is important for better understanding PM2.5 sources.
Fine particulate matter (PM2.5) was measured for 4 months during 2002–2003 at seven sites located in the rapidly developing Pearl River Delta region of China, an area encompassing the major cities of Hong Kong, Shenzhen and Guangzhou. The 4-month average fine particulate matter concentration ranged from 37 to 71μgm−3 in Guangdong province and from 29 to 34μgm−3 in Hong Kong. Main constituents of fine particulate mass were organic compounds (24–35% by mass) and sulfate (21–32%). With sampling sites strategically located to monitor the regional air shed patterns and urban areas, specific source-related fine particulate species (sulfate, organic mass, elemental carbon, potassium and lead) and daily surface winds were analyzed to estimate influential source locations. The impact of transport was investigated by categorizing 13 (of 20 total) sampling days by prevailing wind direction (southerly, northerly or low wind-speed mixed flow). The vicinity of Guangzhou is determined to be a major source area influencing regional concentrations of PM2.5, with levels observed to increase by 18–34μgm−3 (accounting for 46–56% of resulting particulate levels) at sites immediately downwind of Guangzhou. The area near Guangzhou is also observed to heavily impact downwind concentrations of lead. Potassium levels, related to biomass burning, appear to be controlled by sources in the northern part of the Pearl River Delta, near rural Conghua and urban Guangzhou. Guangzhou appears to contribute 5–6μgm−3 of sulfate to downwind locations. Guangzhou also stands out as a significant regional source of organic mass (OM), adding 8.5–14.5μgm−3 to downwind concentrations. Elemental carbon is observed to be strongly influenced by local sources, with highest levels found in urban regions. In addition, it appears that sources outside of the Pearl River Delta contribute a significant fraction of overall fine particulate matter in Hong Kong and Guangdong province. This is evident in the relatively high PM2.5 concentrations observed at the background sites of 18μgm−3 (Tap Mun, southerly flow conditions) and 27μgm−3 (Conghua, northerly flow conditions).
Spatial variations of source contributions to fine organic carbon (OC) and fine particles in the southeastern United States were investigated using molecular marker-based chemical mass balance modeling (CMB-MM) and carbon isotope analysis. Nine primary emission sources were resolved with wood combustion (average 1.73 μg m−3, 23 ± 14% of measured OC) being the most dominant contributor to OC, followed by gasoline engine exhaust (0.45 μg m−3, 6.1 ± 6.2% of OC), diesel engine exhaust (0.43 μg m−3, 4.8 ± 4.1% of OC), and meat cooking (0.30 μg m−3, 4.1 ± 2.6% of OC). Measurable contributions from vegetative detritus, cigarette smoke, road dust, and natural gas exhaust were found. The impact of coke facilities was estimated for the first time in Birmingham, Alabama, and contributed 0.52 μg m−3 on average to fine OC. The unexplained OC accounted for 54 ± 26% of measured OC, possibly because of contributions from secondary OC, other unidentified primary sources and the possible positive artifact of OC. The urban excess of OC from diesel exhaust, gasoline exhaust and meat cooking can be seen from the results of the urban-rural pair in Alabama. Detailed chemical analysis revealed the wood burning episode at the rural site and an episode of secondary formation in the study region. The 14C analysis, a tool to study the relative contributions of contemporary and fossil carbon contents of fine particles, agreed well with the CMB-MM analysis. Both reflected a higher fossil fraction of carbon at urban sites especially in Birmingham, Alabama.
Inductively coupled plasma-mass spectrometry (ICP-MS) was used to characterize fourteen major and trace elements including Al, Fe, Na, K, Mg, Ti, Ba, Cu, Mn, Pb, Sb, Sr, V, and Zn, in dry and wet deposition samples collected in Hong Kong. Calculated model deposition velocities for various elements showed that marine elements such as Na, Mg, and Sr exhibited the highest deposition velocities (from 1.0 cm s−1 to 1.2 cm s−1), while pollution elements including V, Sb, and Pb had the lowest deposition velocities (0.2 cm s−1). The positive correlation of deposition velocities between crustal and marine elements suggests that the deposition velocities were influenced by the particle size in addition to other factors such as wind speed and humidity. A comparison between modeled dry fluxes (the indirect method) and measured dry fluxes (the direct method) showed that modeled dry fluxes were slightly higher for marine and crustal elements while measured dry fluxes were higher for the pollution elements. Comparisons of measured dry and wet deposition fluxes for various elements in Hong Kong indicated that dry and wet removal processes were of similar significance for crustal and marine elements. However, wet removal was dominant for the pollution elements (93% V, 86% K, 81% Sb, and 75% Pb).
The 24-h PM2.5 samples (particles with an aerodynamic diameter of 2.5μm or less) were taken at 6-day intervals at five urban and rural sites simultaneously in Beijing, China for 1 month in each quarter of calendar year 2000. Samples at each site were combined into a monthly composite for the organic tracer analysis by GC/MS (gas chromatography/mass spectrometry). Compared to the data obtained from other metropolitan cities in the US, the PM2.5 mass and fine organic carbon (OC) concentrations in Beijing were much higher with an annual average of 101 and 20.9μgm−3, respectively. Over one hundred organic compounds including unique tracers for important sources were quantified in PM2.5 in Beijing. Source apportionment of fine OC was conducted using chemical mass balance receptor model (CMB) in combination with particle-phase organic compounds as fitting tracers. Carbonaceous aerosols and major ions (sulfate, nitrate and ammonium) constituted 69% of PM2.5 mass on average. The major sources of PM2.5 mass in Beijing averaged over five sites on an annual basis were determined as dust (20%), secondary sulfate (17%), secondary nitrate (10%), coal combustion (7%), diesel and gasoline exhaust (7%), secondary ammonium (6%), biomass aerosol (6%), cigarette smoke (1%), and vegetative detritus (1%). The lowest PM2.5 mass concentration was found in January (60.9μgm−3), but the contribution of carbonaceous aerosol to PM2.5 mass was maximal during this season, accounting for 57% of the mass. During cold heating season, the contributions from coal combustion and biomass aerosol to PM2.5 mass increased, accounting for 20.9% of fine particle mass in October and 24.5% in January. The contribution of the biomass aerosols peaked in the fall. In April 2000, the impact of dust storms was so significant that dust alone constituted 36% of PM2.5 mass. On average, the model resolved 88% of the sources of the PM2.5 mass concentrations in Beijing.
Seven sets of samples that were taken from sites upwind and downwind of Hong Kong during the summer and winter seasons were analyzed. The solvent extractable organic compounds (SEOC) were separated into four major fractions (n-alkanes, fatty acids, alkanols and (polycyclic aromatic hydrocarbons (PAHs)) and identified using gas chromatography-mass spectrometry (GC-MS). Five different wind directions were detected during the two seasons: southwest, southeast, east, east-northeast and northeast. At one extreme, the southwest wind brought clean aerosols from the South China Sea to Hong Kong, diluting the urban aerosols, and the anthropogenic contribution was found to be fresh and local. At the other extreme, when the northeast wind prevailed, there was a significant increase (10-14 times) in the total SEOC yield and the characteristics of the aerosols indicated a greater impact from outside Hong Kong (i.e., more PAHs, plant wax contribution, and lower C18:1/C18:0 ratios), suggesting the presence of aged aerosols. In the samples taken during prevailing east-northeast winds in November, the loading was low and bore resemblance to the summer samples. In addition, there were changes in the characteristics of the aerosols, such as an increased plant wax contribution in the fatty acid and alkanol fractions, signifying a change in season. The characteristics and loading of the PM2.5 at the downwind site were found to be significantly influenced by the accumulation of locally emitted air pollutants due to no wind conditions and the transport of long-distance (from surrounding regions) and short-distance (within Hong Kong) plumes.
The results from a year-long monthly study of the solvent extractable organic compounds (SEOC) in PM2.5 of the ambient aerosols in Hong Kong are reported. A total of 18 samples were analyzed. The extracted organic compounds were separated into four major fractions (n-alkanes, fatty acids, alkanols and PAHs (polycyclic aromatic hydrocarbons)) and identified with GC-MS (gas chromatography–mass spectrometry). The percentage of each fraction in total yield is as follows: fatty acids at 46–80%, alkanes at 10–34%, alkanols at 4–21%, and PAHs at 1–6%. Compared to the TSP (total suspended particulates) samples from our previous studies, the PAH fraction was higher in PM2.5 than TSP (0.5–2.5%). The bias of PAHs in PM2.5 suggests potential implications in health impact because PM2.5 is respirable. The total yield (defined as the sum of the four fractions) in PM2.5 was in the range of 56.4–233.6ngm−3. The sources of SEOC in PM2.5 could be attributed to vehicular, biogenic and microbial origins. On the average, 79% of the alkanes in PM2.5 came from vehicular emissions. U:R (ratio of unresolved to resolved components), an index to assess the magnitude of petroleum residues in aerosols, exhibited higher values in PM2.5 (average 3.2, range 1.0–5.9) than TSP (average 2.4, range 1.1–3.3). CPI (carbon preference index) of alkanes showed an inverse relationship with U:R, and a positive correlation with the percentage of alkanes from higher plant wax. Although U:R and CPI have been widely used as indices in source apportionment, their effectiveness was demonstrated for the first time from the statistical point of view in this paper. It was discovered that the CPI=1 (a characteristic of petroleum hydrocarbons) envelope and Cmax shifted towards lower carbon numbers in winter, suggesting there was more contribution from vehicular emission. PAHs had the following range 0.7–12.2ngm−3. The positive correlation with benzo(ghi)perylene suggested that they were of vehicular origin. Distinct seasonal variation in PAH concentration was found with higher concentrations in the winter samples. The concentration range of fatty acids in PM2.5 (31.1–168.8ngm−3) indicated that the microbial contribution in the PM2.5 samples was systematically lower in late fall and winter (average 52%) while larger in the hotter weather (over 80%), suggesting higher microbial activities in the summer. A ratio as high as 1.93 in summer for C18:1/C18:0 and only 0.69 in winter suggested that there were more aged aerosols in winter while more fresh emissions were found in summer. The results of SEOC in the PM2.5 aerosols indicated that vehicular emission was the characteristic of Hong Kong's aerosols.
Correlations between 35 different organic and inorganic species or tracers in the aerosols of Hong Kong were derived based on the GC−MS organic results from our 1993−1994 study and Hong Kong Environmental Protection Department inorganic data. Source apportionment is essential in fingerprinting of air pollutants for cross-boundary studies. It is also important in the development of emissions inventory data, control strategies, and legislature. Traditionally, emission sources are identified from either the inorganic or organic tracers in the aerosols, but not both. Each of these techniques yields much source information; however, each by itself provides only a partial picture due to the complicated nature of ambient aerosols. Since many of the organic and inorganic species in aerosols are from the same source, correlations between the two are to be expected. In this study, such correlations were indeed found. For example, benzo[b,k]fluoranthene, the most abundant PAH (polycyclic aromatic hydrocarbon) in all the PAHs detected in Hong Kong, exhibited good correlation with Pb, Zn, As, nss SO42- (nonseasalt sulfate), total PAHs, and benzo[a]pyrene. This paper further demonstrates that a combination of the two techniques could be an improved method for source apportionment than using either method alone.
Polycyclic aromatic hydrocarbons (PAHs) in total suspended particulates (TSP) collected at six rural and urban stations in Hong Kong from 1993–1995 using high volume air samplers were identified using GC-MS (gas chromatography-mass spectrometry). The results showed that the PAHs exhibited distinct spatial and seasonal variability. The total PAH content (PAH) in the samples ranged from 0.41 to 48 ng m-3. The unsubstituted analogs are the characteristic products of high temperature combustion processes. The highest average PAH was measured at the street-level station in Mong Kok indicating that vehicles were high PAHs contributors. The rural station at Hok Tsui exhibited the lowest PAH level, however; influences of city plumes could be seen when northerly or northeasterly winds prevailed in the winter. All stations experienced the highest loading of PAHs in autumn and the lowest in summer; the former was 2.8 times greater than the latter. This seasonal variability is due to the Asian monsoon system, precipitation, micrometeorology, and the rate of photodegradation. In summer, Hong Kong experiences relatively clean oceanic air and high rates of precipitation and photodegradation, while upon the onset of the winter monsoon, local air mass is replaced by polluted air streams from the Asian continent. Benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, indeno(1,2,3-cd)pyrene and benzo(ghi)perylene were the dominant species in the samples. The PAH distribution patterns at different stations were similar within each season. However, seasonal variations existed. For example, phenanthrene contributed up to 14% of the total PAH in summer, while the dominance of benzo(b)fluoranthene, benzo(k)fluoranthene was more significant in autumn and winter.
The results of the inorganic and organic analyses of aerosol samples collected on the east and west sides of Hong Kong during a dust episode (9–10 May 1996) are reported. The origin of the dust was traced to Northern China. The dust reached Hong Kong by way of the East China Sea. The characteristics of the inorganic elements and organic compounds were quite different from the non-episodic samples collected on 1–2 April 1996, EPD (Environmental Protection Department, Special Administrative Region, Hong Kong, China) results for April–May 1994, and our early studies (Zheng et al., 1997. Atmospheric Environment 31(2), 227–237.). Results from X-ray spectrometry showed pronounced increase in the relative abundance of Al, Fe, Ca, S and Cl in the dust samples compared to the non-episodic samples. The high abundance of Cl in the dust samples suggested the aerosols experienced long-range transport by way of the sea. ICP-MS analysis revealed higher concentrations of Fe, Ca, S and Pb in the episodic samples relative to the values measured during April–May 1994 by EPD. The high Ca content in the soil samples is a characteristic of northern Chinese crustal material (Liu et al., 1985). Hong Kong aerosols are characterized by high octadecenoic acid concentration due to heavy urbanization and Chinese-style stir-fry cooking. A much lower C18:1/C18:0 ratio was found in the episodic samples, however, suggesting the aerosols were transported from a long distance. The high ratio of ⩾C20/