Article pubs.acs.org/est
Microscopic Observation of Metal-Containing Particles from Chinese Continental Outflow Observed from a Non-Industrial Site Weijun Li,*,†,§ Tao Wang,‡ Shengzhen Zhou,†,‡ ShunCheng Lee,‡ Yu Huang,‡ Yuan Gao,‡ and Wenxing Wang† †
Environment Research Institute, Shandong University, Jinan, Shandong 250100, P. R. China Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong, P. R. China § State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 250100, P. R. China ‡
S Supporting Information *
ABSTRACT: Atmospheric metal-containing particles adversely affect human health because of their physiological toxicity. Mixing state, size, phase, aspect ratio, and sphericity of individual metal-containing particles collected in Hong Kong air in winter are examined through transmission electron microscopy (TEM). Eighteen percent of the sulfate particles have one or more tiny metal inclusions. Size distributions of metal and fly ash particles (or inclusions) with diameters from 15 nm to 2.7 μm show the same peak at 210 nm. The major metal particles were classified as Fe-rich (e.g., hematite), Zn-rich (e.g., zinc sulfate and zinc oxide), Pb-rich (e.g., anglesite), Mn-rich, and As-rich, which were likely emitted from industries and coal-fired power plants at high temperatures in mainland China. Compared to fly ash and S-rich particles, metal particles display a lower sphericity of 0.51 and a higher aspect ratio of 1.47, which means their shapes are poorly defined. The elemental mapping of individual particles reveal that sulfate areas without metal inclusions also contain minor Fe, Mn, or Zn. Therefore, the internal mixing of metals and acidic constituents likely solubilize metals and modify metal inclusion shapes. Solubilization of metals in airborne particles can extend their toxicity into nontoxicity parts in the particles. The structure of the metal-containing particles may provide important information for assessing health effects of fine sulfate and nitrate particles with metal inclusions in urban areas. and fate in the atmosphere.9,16,17 Therefore, it is important to characterize individual metal-containing particles among the complex mixture of airborne particulate matter. Transmission electron microscopy (TEM) can provide detailed information of individual particles at high spatial resolution.14−17 The World Health Organization estimated that exposure to fine particulate air pollution causes most of the deaths and diseases in the developing countries of Southeast Asia.18 Rapidly industrializing China is a significant source of fine particles (PM2.5) on the global scale, and annual mean PM2.5 concentrations exceed 80 μg m−3 over eastern China,19 which are the highest ground-level PM2.5 concentrations measured at a regional scale anywhere.19,20 The Pearl River Delta (PRD), one of the most polluted areas in eastern Asia, recently had its fine-particle metal concentrations (e.g., Pb, Zn, Fe, and Cr) evaluated,21,22 and these particles were transported across downwind coastal cities with high population23,24 into the Pacific Ocean10 during the winter monsoon. In this manner, it is necessary to fully understand the characteristics of long-range transported metal-containing particles in the coastal cities.
1. INTRODUCTION Ambient air pollution is one of the major public health concerns on regional and global scales. Many epidemiological studies have indicated that elevated concentrations of fine particles are associated with increased mortality and morbidity (e.g., respiratory symptoms, asthma exacerbations, pulmonary function) from respiratory and cardiovascular disease.1−3 Metals in fine ambient particles play a role in the health effects epidemiologically associated with particulate exposure.4−6 Dry and wet deposition of heavy and trace metals in the atmosphere can also affect the ecosystem because of their ecological toxicity and through biogeochemical accumulation.7−9 Recent evidence demonstrates that anthropogenic metal particles may reach the open ocean from polluted continents and affect the ocean ecosystem.10−12 In urban areas, anthropogenic sources of fine and ultrafine metal-containing particles are abundant by particle number.13−15 These fine particles emitted by anthropogenic sources can be transported for long distances, and their chemical composition, physical properties, size, and shape can be altered due to particle−particle coagulation and gas−particle condensation processes. The metal oxidation state and total particulate mass are most often considered in evaluating their toxicity, but particle size, shape, surface area, structure, and chemical composition also influence their reactivity, toxicity, © 2013 American Chemical Society
Received: Revised: Accepted: Published: 9124
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used to collect particles and evaluate the size-segregated mass concentration. 2.2. Aerosol Sampling and Analysis of MetalContaining Particles. Individual particle samples were analyzed with a JEOL JEM-2100 TEM operated at 200 kV for composition, mixing state, phase, and morphology of individual aerosol particles and with a JEOL JEM2100F TEM with scanning TEM (STEM) operation mode for elemental mapping of some typical aerosol particles. Elemental composition was determined semi-quantitatively by an energy-dispersive X-ray spectrometer (EDS) that can detect elements heavier than C. EDS spectra were collected for 5−10 s in order to quickly check the composition of individual aerosol particles. Once metal peaks occurred in the EDS spectra, the average composition of metallic components in the individual particle were further measured for 30 s using an electron beam spot size about 10−25 nm in diameter. Because this electron beam process is labor intensive, the EDS spectra of 608 particles were manually saved in the computer for elemental composition analysis. Copper (Cu) was excluded from the analyses because the TEM grids are made of Cu. For some metal-containing particles, EDS data and elemental mapping was combined with selected-area electron diffraction (SAED) to verify their identities. Elemental mapping of individual aerosol particles were obtained from the EDX scanning operation mode of TEM. Particles examined by TEM were dry at the time of observation in the vacuum of the electron microscope. In our study, the effects of water, other semivolatile organics, and ammonium nitrate were not considered. To quantitatively characterize the structure of ambient particles, we obtained physical parameters such as aspect ratio (AR), area, equivalent circle diameter (ECD), perimeter, and sphericity (Tables S1 and S2, Supporting Information). Aspect Ratio. The maximum ratio of width and height of a bounding rectangle for the measured object is the aspect ratio. An aspect ratio of 1 (the lowest value) indicates a particle is not elongated in any direction. Sphericity. Sphericity describes the sphericity or “roundness” of the measured object by using central moments. A sphericity of 1 (the highest value) indicates a particle is perfectly spherical. These two physical parameters of individual particles adequately describe particle shapes.31 In this study, these parameters were determined by using the iTEM software (Olympus soft imaging solutions GmbH, Germany) for statistical analysis. The iTEM is the image analysis platform for electron microscopy. Altogether, 4483 particles were measured for statistic analyses.
When wind directions are mainly from the west, north, and northeast, the polluted air masses from the PRD can significantly elevate PM2.5 and primary gaseous concentrations.22,25−28 Among the four seasons, the pollutant levels are 2−10 folder higher in winter than in summer. For this purpose, coastal Hong Kong (HK) was chosen for this study because the residents of densely populated HK without industrial activities are faced with air pollution problems in the winter, at least some of which are from upwind China mainland transport. Previous studies mainly focused on the chemical characterization of bulk metal particles and further on identifying their sources.21−24 The heavy metals (e.g., Fe, Mn, V, Pb, Zn, Cr, Cu) in fine particles in HK are mainly transported from north and northeast areas near Guangzhou city and have been traced to sources such as the combustion of fossil fuels and industrial processes. The size, shape, surface area, and chemical composition of individual metal-containing particles in the area, however, have not been determined. To evaluate the properties of individual metal-containing particles, aerosol samples were collected in HK during the winter monsoon. Our goal is to characterize size, shape factor (i.e., aspect ratio and sphericity), mixing state, composition, and relative abundance of metal-containing particles from multiple anthropogenic sources. Temporal, physical, and chemical information regarding these particles suggest that they were mainly emitted from industrial processes and coal-fired power plants in the PRD.
2. EXPERIMENT SECTION 2.1. Atmospheric Research Project in HK. HK is situated in the southeast part of the PRD. The sampling site was on the rooftop of a seven-story building (22°18′ N, 114°11 ′E and 15 m above sea level) on the campus of Hong Kong Polytechnic University, which is situated in the urban center of Kowloon. In addition to the influence of local vehicular and ship emissions, the sampling site is affected by polluted continental air masses from the highly industrialized PRD region of mainland China.29 Thirty samples were collected using an individual particle sampler at the university site and one sample inside one 1800 m cross-harbor tunnel that connects Kowloon to Hong Kong Island. Aerosol particles were collected onto copper TEM grids coated with carbon film (carbon type B, 300 mesh copper, Tianld Co., China) by a single-stage cascade impactor with a 0.5 mm diameter jet nozzle and an air flow rate of 1.0 l min−1. Theory calculation of collection efficiency for the impactor can be expressed as Marple et al.30 This sampler has a collection efficiency of 100% and a 0.5 μm aerodynamic diameter if the density of the particles is 2 g cm−3. Sampling times varied from one to five minutes, depending on the particle loading as estimated from visibility. Three or four samples were collected around 0900, 1200, and 1800 h each day, with a total of 30 samples between December 1−17 , 2010. After collection, each sample was placed in a sealed dry plastic tube and stored in a desiccator at 25 °C and 20 ± 3% RH to minimize exposure to ambient air and preserve it for analysis. Before we analyzed the samples using TEM, one optical microscopy was employed to check aerosol dispersion on the substrates. On the basis of the sampling time and sample quality, we finally used 14 aerosol samples for TEM analysis. In addition, an eight-stage microorifice uniform deposit impactor (MOUDI) sampler (30 L min−1, Model 100, MSP, U.S.A.) with 50% cut off diameters of 18.0 (inlet), 10.0, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, and 0.18 μm was
3. RESULTS AND DISCUSSION 3.1. Air Mass Back Trajectory. Mass concentrations of PM3.2 and PM1.8 were 52 μg m−3 (range: 43−70 μg m−3) and 42 μg m−3 (range: 33−52 μg m−3) in HK in the winter, respectively. In addition, Ho et al.28 measured the mass concentration of PM2.5 at 51 μg m−3 and PM10 at 84 μg m−3 in the same sampling site. In general, meteorological conditions strongly influence air quality, and HK is no exception. Figure 1 shows that polluted air masses from the PRD in mainland China frequently influenced the HK area from November to January. Eighty percent of the 60 air mass back trajectories transported across the PRD area (Figure 1). Lee et al.21 showed that such air masses significantly elevated concentrations of various metals (major metals: Al, Fe, Mg, Mn and trace metals: Cd, Cr, Cu, Pb, V, and Zn) in HK. 9125
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Figure 1. Forty-eight hour air mass back trajectories arriving at 24:00 (local time) to Hong Kong at 500 m from November 20 to January 10 (http://ready.arl.noaa.gov/HYSPLIT.php). 48 back trajectories are indicated by red lines transported across the PRD area (light yellow box).
Figure 2. TEM images at low magnifications of metal and fly ash particles internally mixed in sulfates.
3.2. Occurrences of Metal Particles and Their Mixing States. TEM observations show that the major particles with diameters from 20 nm to 2 μm were fly ash, metal, organic matter (OM), ammoniated sulfate (AS), and soot. In this study, of the 4483 particles examined using TEM and iTEM, 18% of them included one or more tiny metal particles. All of the OM, 56% of the 908 soot, and 92% of the 1142 metal and fly ash particles were internally mixed with AS particles (Figure 2 and Figure S1, Supporting Information), which indicates that these particles had complicated aging processes during transport. These particles containing metals are called “metal-contaminated particles” (MCP). TEM detected not only abundant metal particles but also fly ash particles containing minor metals such as Fe and Mn in the the HK atmosphere. This type of particle should have been emitted mainly from coal-fired power plants in South China.32 TEM images show that metal and fly ash particles were mostly embedded within AS particles (Figure 2). 3.3. Composition of Metal Particles. Fourteen metals including Fe, Zn, Mn, Pb, Cr, As, Ti, Co, Sn, Ba, Ni, Sb, V, and Sc were detected by TEM/EDS in 608 particles. Fe is the most frequent metal in the samples, occurring in 37% of the analyzed particles (Figure 3). Figure 3 demonstrates that Zn, Mn, Pb, Cr, As, and Ti are major metals in aerosol particles in the HK atmosphere. On the basis of composition and morphology of metal particles, we classified them into three major metal types (Fe-rich, Zn-rich, and Pb-rich) and two minor metal types (Mn-rich and As-rich) (Figure S2, Supporting Information). Fe-rich particles were the most common in the HK atmosphere. EDS spectra of Fe-rich particles exhibit Fe and O (Figure 4a), suggesting that they could be iron oxides. The
Figure 3. Frequency of elemental metals in 608 particles.
SAED pattern confirm that Fe-rich particles are hematite (Fe2O3) (Figure 5c and Figure S3, Supporting Information). This kind of particle usually contains minor metal (e.g., Mn, Ti, Cr, and Zn) oxides. High-resolution TEM images show that some Fe-rich particles are aggregations of several Fe spheres (Figure 4a and Figure S3, Supporting Information). They were probably emitted by the steel plants from the molten process of iron materials at high temperature.15 Furthermore, many Ferich particles with similar composition occurred in the tunnel sample. The morphology of Fe-rich particles resembles mineral particles with irregular shapes; most of these Fe-rich particles were internally mixed with soot particles (Figure S4, Supporting Information). This admixture suggests that these Fe-rich particles likely come from vehicular abrasion on the roadways in the HK area. In addition, fly ash particles with major Si and Al frequently contain minor Fe (Figure 4b). Chen 9126
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Figure 4. TEM images and EDS of the typical metal-contaminated particles. (a) Mixture of Fe-rich and S-rich particles. (b) Mixture of fly ash and Srich particles. (c) Mixture of Fe-rich and Zn-rich particels. (d) Mixture of Pb-rich and S-rich particles. (e) Mn-rich particles. (f) Mixture of As-rich and S-rich particles. Compositions in the red circle on individual particles were examined by EDS, and the corresponding EDS spectrum is shown. Elements in square brackets represent the major particulate compositions. The Cu* peaks in the spectra are considered from the TEM grids.
et al.11,33 stated that hematite and magnetite probably condense on the surface of the fly ash particles. Zn-rich particles are the second most common particles and contain Zn, S, and C. The morphology of Zn-rich particles does not display any well-defined shape; in fact, they look like viscous liquids. This kind of particle containing Zn, S, and C has no any reflection in SAED, suggesting their amorphous phase. Some Zn-rich particles are also associated with Fe-rich, Pb-rich, Mn-rich, or As-rich particles (Figures 4 and 5 and Figure S3, Supporting Information). For example, Figure 5c shows that one Zn-rich inclusion in a sulfate particle contains Fe and Mn, and the SAED pattern indicates iron zinc oxide. In this study, some spectra of the S-rich particles contain minor Zn, but TEM images do not show any Zn-rich particles (Figures 4d and 5a). The elemental mapping shows that Zn associated with S disperses into the whole particle. Therefore, these viscous Zn-rich particles are expected to be soluble zinc sulfate (ZnSO4) in the atmosphere. Furukawa and Takahashi34 reported that the Zn-rich particles in urban atmospheres are hygroscopic zinc oxalate complexes and zinc sulfate. Similar particles widely detected in urban Beijing and Mexico City are emitted in industrial incineration.13,15 Pb-rich particles commonly occur in the PRD and mainly contain Pb and S with minor amounts of Mn, Fe, Zn, and Sn.
The morphology of Pb-rich particles is irregular (Figure 4d and Figure S3, Supporting Information). The SAED pattern and EDS data confirmed that the Pb-rich particles are anglesite (PbSO4). Sources of Pb-rich particles in the area have been well documented through Pb isotopic composition analysis after leaded gasoline was phased-out in 2000.21−23,35 The smelting and industrial uses of Pb ores and coal-fired power plants in the vicinity of Guangzhou and north of the city significantly contributed Pb-rich particles into the atmosphere. Although most Mn and As are associated with Fe-rich, Znrich, and Pb-rich particles, a few unique Mn-rich and As-rich particles were also found (Figure 4e,f). These particles are nearly spherical and are likely emitted or formed at high temperatures, probably from combustion processes. 3.4. Size and Shape of Aerosol Particles. ECDs of aerosol particles measured by iTEM software range from 15 nm to 2.7 μm for 832 metal particles, 25 nm to 1.5 μm for 310 fly ash particles, and 40 nm to 6.5 μm for 3562 S-rich particles (Figure 6). The size distributions of metal and fly ash both have their peaks at 210 nm, much smaller than the peak of S-rich particles at 750 nm. High-resolution TEM images and elemental mapping show that these tiny metal and fly ash particles were generally mixed with S-rich particles (Figures 4 and 5). We noticed that some S-rich particles include one or 9127
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Figure 5. Elemental mapping and SAED pattern of metal-associated particles. (a) Dark-field image of individual sulfate particles with Zn-rich and Pbrich inclusions. Elemental mapping images show S, Zn, and Pb distribution in the individual particle. (b) Bright-field image, dark-field image, and S and Pb mapping of individual sulfate with anglesite (PbSO4) confirmed by SAED. (c) Bright-field image, dark-field image, and S, Fe, Mn, and Zn mapping of individual sulfate with iron zinc oxide (ZnFe2O4) and hematite (Fe2O3) (Figure S3,Supporting Information) confirmed by SAED.
more separated metal and/or fly ash particles (Figures 4 and 5 and Figure S3, Supporting Information). On the basis of TEM observations, about 18% of S-rich particles were the MCP in the HK atmosphere. Metal and fly ash particles averagely comprise 17% of the area of the related individual MCP. Therefore, the secondary sulfates likely govern the hygroscopicity and lifetime of these particles. The shape of a particle is an important clue to understanding its emission source, aging processes,31 and toxicity.16 Figure 7 shows the AR and sphericity of metal, fly ash, and S-rich particles. As expected, most fly ash particles exhibited the highest average sphericity at 0.73 (number fraction above 10% at a range of 0.82−1.0) and the lowest average AR at 1.25 (number fraction above 10% at a range of 1−1.15) (Tables S1 and S2, Supporting Information). These spherical fly ash particles form through high-temperature combustion followed by a fast cooling process.11,17 Li and Shao15 proposed that most
Figure 6. Size distributions of metal, fly ash, and S-rich particles collected in the Hong Kong atmosphere. Ninety-two percent of the metal and fly ash particles are inclusions of S-rich particles.
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4. IMPLICATIONS FOR HUMAN HEALTH AND MARINE ECOSYSTEM The emission sources and concentrations of metal-containing particles in the HK atmosphere have been investigated in previous work.21,23,24,35 Their studies suggest that metals for the most part are transported from the PRD area and come from the combustion of fossil fuels and industrial processes during the winter monsoon. The low sphericity and high AR of metal particles suggest that the internal mixings of metals and acidic aerosols likely solubilize metals and modify metal particles from spherical shapes to irregular shapes. These water-soluble metal materials can be homogeneously mixed with sulfate particles, enhancing the toxicity of the latter. Most submicrometer MCP are deposited into deeper parts of the human respiratory tract.39 When inhaled, the water-soluble metals in the MCPs may induce airway epithelial injury and cytokine gene expression.4 Once the finer soluble metals dissolve in lung tissues, they can then migrate to different physiological areas and cause different adverse health effects.14,40 In particular, Zn-rich particles in the urban atmosphere tend to become soluble through atmospheric chemical reactions. One recent study suggests that Zn has robust positive associations with different blood pressures (e.g., diastolic and systolic blood pressure) in the urban atmosphere of China.5 TEM reveals that these toxic metal particles (i.e., i.e., Fe-rich, Zn-rich, Pb-rich, Mn-rich, and As-rich) usually exhibited nanometer sizes and large numbers in the atmosphere. During the winter monsoon, particulate metals from the polluted PRD area reach HK and the South China Sea. Finally, many metal-containing particles are transported and deposited in the further reaches of the Pacific Ocean, affecting the oceanic ecosystem. Recently, two studies investigated how Asian industrial aerosols significantly contribute Pb and Fe to surface waters in the Pacific Ocean.10,36 In particular, increasing amounts of soluble Fe in nanometal and fly ash particles would be an important micronutrient for marine organisms.37 In summary, the present study further extends our understanding of the size, shape, phase, composition, and mixing state of metal particles in the coastal urban atmosphere. Such information ought to be useful to better evaluate their effects on health and alongshore marine ecosystems and to identify sources for possible regulatory action.
Figure 7. Sphericity and aspect ratio of metal, fly ash, and S-rich particles.
spherical fly ash particles containing Si and Al came from coalfired power plants in China. Figure 7 displays the sphericity at 0.64 (above 10% at a range of 0.45−1) and AR (above 10% at a range of 1−1.38) at 1.31 of S-rich particles and the sphericity at 0.51 (above 10% at a range of 0.2−0.75) and AR (above 10% at a range of 1.05−1.5) at 1.47 of metal particles. These results show that S-rich particles are more spherical than metal particles. On the basis of TEM observations, S-rich particles smaller than 1 μm are virtually spherical; the circular ring surrounding individual S-rich particles can be clearly observed (Figure 2 and Figure S1, Supporting Information). Li et al.32 suggested that the surfaces of these S-rich particles were coated with liquid film. The lowest circularity and highest AR of the metal particles indicate that most of them generally show poorly defined shape. However, metal particles like fly ash particles from metal smelting and industrial emissions21−23,35 are expected to have spherical shapes and smaller sizes (most ∼200 nm), and only a small number of metal particles emitted from vehicular abrasion on the road have irregular shapes and larger sizes (most ∼900 nm) (Figure S5, Supporting Information). These metal particles from vehicular abrasion emission commonly show larger diameters (900 nm) than those from anthropogenic sources at high temperature (210 nm). Interestingly, minor metal peaks were frequently detected in the sulfate portion of individual MCPs, demonstrating that dissolved metal ions were contained within the sulfates. Elemental mapping in individual particles obtained by STEM shows that Zn distributing into individual S-rich particles is associated with the zinc oxide inclusion (Figure 5). The only explanation is that zinc oxide has undergone heterogeneous reactions with acids to form viscous liquid materials (e.g., zinc oxalate and zinc sulfate) of undefined shape (Figures 4 and 5). Such metal particles undergoing heterogeneous reactions change their shape, leading to a decrease in their sphericity. It has been suggested that Fe-rich particles from combustion were internally mixed with sulfuric acid, organic acids, or sulfates and further may solubilize iron oxidation.9,11,36−38 Also, other metal particles such as Zn and Mn embedded in acidic sulfate or OM became soluble materials in the atmosphere.34 Figures 4 and 5 and Figure S3 of the Supporting Information show aged particles that have undergone heterogeneous reactions leading to a decrease in sphericity. It should be noted that the sphericity of some hydrated aerosol particles determined by iTEM could not be representative of what is in the atmosphere.
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ASSOCIATED CONTENT
S Supporting Information *
Low magnification TEM images show metal and fly ash particles embedded in sulfate particles in different samples. Figure S1: Frequency of different metal types in metalcontaining particles examined by EDS. Figure S2: Highresolution TEM images show fly ash; Fe-rich, Zn-rich, and Pb-rich particles; and other metals in individual aerosol particles in different samples. Figure S3: High-resolution TEM images show that most of the Fe-rich particles are internally mixed with soot particles in one tunnel sample. Figure S4: Size distributions of metal particles in one tunnel sample. Figure S5: Sphericity of metal, fly ash, and S-rich particles. Table S1: Sphericity of metal, fly ash, and S-rich particles. Table S2: Aspect ratio of metal, fly ash, and S-rich particles. This material is available free of charge via the Internet at http://pubs.acs.org. 9129
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(14) Adachi, K.; Buseck, P. R. Hosted and free-floating metal-bearing atmospheric nanoparticles in Mexico City. Environ. Sci. Technol. 2010, 44 (7), 2299−2304. (15) Li, W. J.; Shao, L. Y. Transmission electron microscopy study of aerosol particles from the brown hazes in northern China. J. Geophys. Res. 2009, 114, (D09), DOI:10.1029/2008JD011285. (16) Utsunomiya, S.; Jensen, K. A.; Keeler, G. J.; Ewing, R. C. Direct identification of trace metals in fine and ultrafine particles in the Detroit urban atmosphere. Environ. Sci. Technol. 2004, 38 (8), 2289− 2297. (17) Giere, R.; Blackford, M.; Smith, K. TEM study of PM2.5 emitted from coal and tire combustion in a thermal power station. Environ. Sci. Technol. 2006, 40 (20), 6235−6240. (18) Cohen, A. J.; Anderson, H. R.; Ostro, B.; Pandey, K. D.; Krzyzanowski, M.; Kuenzli, N.; Gutschmidt, K.; Pope, C. I.; Romieu, I.; Samet, J. M.; Smith, K. Urban Air Pollution. In Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors, 1st ed.; Ezzati, M., Rodgers, A. D., Lopez, A. D., Murray, C. J. L., Eds.; World Health Organization: Geneva, 2004; Vol. 2, pp 1353−1453. (19) van Donkelaar, A.; Martin, R. V.; Brauer, M.; Kahn, R.; Levy, R.; Verduzco, C.; Villeneuve, P. J. Global estimates of ambient fine particulate matter concentrations from satellite-based aerosol optical depth: Development and application. Environ. Health Perspect. 2010, 118, (6). (20) Brauer, M.; Amann, M.; Burnett, R. T.; Cohen, A.; Dentener, F.; Ezzati, M.; Henderson, S. B.; Krzyzanowski, M.; Martin, R. V.; Van Dingenen, R.; van Donkelaar, A.; Thurston, G. D. Exposure assessment for estimation of the global burden of disease attributable to outdoor air pollution. Environ. Sci. Technol. 2011, 46 (2), 652−660. (21) Lee, C. S. L.; Li, X. D.; Zhang, G.; Li, J.; Ding, A. J.; Wang, T. Heavy metals and Pb isotopic composition of aerosols in urban and suburban areas of Hong Kong and Guangzhou, South China: Evidence of the long-range transport of air contaminants. Atmos. Environ. 2007, 41 (2), 432−447. (22) Hagler, G. S. W.; Bergin, M. H.; Salmon, L. G.; Yu, J. Z.; Wan, E. C. H.; Zheng, M.; Zeng, L. M.; Kiang, C. S.; Zhang, Y. H.; Lau, A. K. H.; Schauer, J. J. Source areas and chemical composition of fine particulate matter in the Pearl River Delta region of China. Atmos. Environ. 2006, 40 (20), 3802−3815. (23) Wong, C. S. C.; Li, X. D.; Zhang, G.; Qi, S. H.; Peng, X. Z. Atmospheric deposition of heavy metals in the Pearl River Delta, China. Atmos. Environ. 2003, 37 (6), 767−776. (24) Tanner, P. A.; Ma, H.-L.; Yu, P. K. N. Fingerprinting metals in urban street dust of Beijing, Shanghai, and Hong Kong. Environ. Sci. Technol. 2008, 42 (19), 7111−7117. (25) Wang, T.; Poon, C. N.; Kwok, Y. H.; Li, Y. S. Characterizing the temporal variability and emission patterns of pollution plumes in the Pearl River Delta of China. Atmos. Environ. 2003, 37 (25), 3539−3550. (26) Yao, X.; Fang, M.; Chan, C. K.; Ho, K. F.; Lee, S. C. Characterization of dicarboxylic acids in PM2.5 in Hong Kong. Atmos. Environ. 2004, 38 (7), 963−970. (27) Pathak, R. K.; Yao, X.; Lau, A. K. H.; Chan, C. K. Acidity and concentrations of ionic species of PM2.5 in Hong Kong. Atmos. Environ. 2003, 37 (8), 1113−1124. (28) Ho, K. F.; Lee, S. C.; Chan, C. K.; Yu, J. C.; Chow, J. C.; Yao, X. H. Characterization of chemical species in PM2.5 and PM10 aerosols in Hong Kong. Atmos. Environ. 2003, 37 (1), 31−39. (29) Guo, H.; Jiang, F.; Cheng, H. R.; Simpson, I. J.; Wang, X. M.; Ding, A. J.; Wang, T. J.; Saunders, S. M.; Wang, T.; Lam, S. H. M.; Blake, D. R.; Zhang, Y. L.; Xie, M. Concurrent observations of air pollutants at two sites in the Pearl River Delta and the implication of regional transport. Atmos. Chem. Phys. 2009, 9 (19), 7343−7360. (30) Marple, V. A.; Rubow, K. L.; Olson, B. A. Inertial, Gravitational, Centrifugal, and Thermal Collection Techniques. In Aerosol Measurement; Willike, K., Baron, P. A., Eds.; Van Nostrand Reinhold: New York, 1993; pp 206−233.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We appreciate Peter Hyde’s comments and proofreading. Financial supports were provided by the National Natural Science Foundation of China (41105088), Niche Area Development Program of the Hong Kong Polytechnic University (1-BB94), National Basic Research Program of China (2011CB403401), and State Key Laboratory for Coal Resources and Safe Mining (SKLCRSM11KFB03).
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REFERENCES
(1) Dockery, D. W.; Pope, C. A. Acute respiratory effects of particulate air-pollution. Annu. Rev. Public Health 1994, 15, 107−132. (2) Kan, H.; London, S. J.; Chen, G.; Zhang, Y.; Song, G.; Zhao, N.; Jiang, L.; Chen, B. Differentiating the effects of fine and coarse particles on daily mortality in Shanghai, China. Environ. Int. 2007, 33 (3), 376−384. (3) Peters, A.; Liu, E.; Verrier, R. L.; Schwartz, J.; Gold, D. R.; Mittleman, M.; Baliff, J.; Oh, J. A.; Allen, G.; Monahan, K.; Dockery, D. W. Air pollution and incidence of cardiac arrhythmia. Epidemiology 2000, 11 (1), 11−17. (4) Dye, J. A.; Adler, K. B.; Richards, J. H.; Dreher, K. L. Role of soluble metals in oil fly ash-induced airway epithelial injury and cytokine gene expression. Am. J. Physiol.: Lung Cell. Mol. Physiol. 1999, 277 (3), L498−L510. (5) Wu, S.; Deng, F.; Huang, J.; Wang, H.; Shima, M.; Wang, X.; Qin, Y.; Zheng, C.; Wei, H.; Hao, Y.; Lv, H.; Lu, X.; Guo, X. Blood pressure changes and chemical constituents of particulate air pollution: Results from the Healthy Volunteer Natural Relocation (HVNR) Study. Environ. Health Perspect. 2013, 121, 66−72. (6) Shao, L. Y.; Li, J. J.; Zhao, H. Y.; Yang, S. S.; Li, H.; Li, W. J.; Jones, T.; Sexton, K.; BeruBe, K. Associations between particle physicochemical characteristics and oxidative capacity: An indoor PM10 study in Beijing, China. Atmos. Environ. 2007, 41 (26), 5316− 5326. (7) Denkhaus, E.; Salnikow, K. Nickel essentiality, toxicity, and carcinogenicity. Crit. Rev. Oncol. Hemat. 2002, 42 (1), 35−56. (8) Chang-Graham, A. L.; Profeta, L. T. M.; Johnson, T. J.; Yokelson, R. J.; Laskin, A.; Laskin, J. Case study of water-soluble metal containing organic constituents of biomass burning aerosol. Environ. Sci. Technol. 2011, 45 (4), 1257−1263. (9) Li, W.; Wang, Y.; Collett, J. L.; Chen, J.; Zhang, X.; Wang, Z.; Wang, W. Microscopic evaluation of trace metals in cloud droplets in an acid precipitation region. Environ. Sci. Technol. 2013, 47 (9), 4172− 4180. (10) Gallon, C.; Ranville, M. A.; Conaway, C. H.; Landing, W. M.; Buck, C. S.; Morton, P. L.; Flegal, A. R. Asian industrial lead inputs to the North Pacific evidenced by lead concentrations and isotopic compositions in surface waters and aerosols. Environ. Sci. Technol. 2011, 45 (23), 9874−9882. (11) Chen, H.; Laskin, A.; Baltrusaitis, J.; Gorski, C. A.; Scherer, M. M.; Grassian, V. H. Coal fly ash as a source of iron in atmospheric dust. Environ. Sci. Technol. 2012, 46 (4), 2112−2120. (12) Van Malderen, H.; Hoornaert, S.; Van Grieken, R. Identification of individual aerosol particles containing Cr, Pb, and Zn above the North Sea. Environ. Sci. Technol. 1996, 30 (2), 489−498. (13) Moffet, R. C.; Desyaterik, Y.; Hopkins, R. J.; Tivanski, A. V.; Gilles, M. K.; Wang, Y.; Shutthanandan, V.; Molina, L. T.; Abraham, R. G.; Johnson, K. S.; Mugica, V.; Molina, M. J.; Laskin, A.; Prather, K. A. Characterization of aerosols containing Zn, Pb, and Cl from an industrial region of Mexico City. Environ. Sci. Technol. 2008, 42 (19), 7091−7097. 9130
dx.doi.org/10.1021/es400109q | Environ. Sci. Technol. 2013, 47, 9124−9131
Environmental Science & Technology
Article
(31) Coz, E.; Leck, C. Morphology and state of mixture of atmospheric soot aggregates during the winter season over Southern Asia−A quantitative approach. Tellus, Ser. B 2011, 63 (1), 107−116. (32) Li, W. J.; Zhou, S. Z.; Wang, X. F.; Xu, Z.; Yuan, C.; Yu, Y. C.; Zhang, Q. Z.; Wang, W. X. Integrated evaluation of aerosols from regional brown hazes over northern China in winter: Concentrations, sources, transformation, and mixing states. J. Geophys. Res. 2011, 116, (D9), DOI:10.1029/2010JD015099. (33) Chen, H.; Grassian, V. H.; Saraf, L. V.; Laskin, A. Chemical imaging analysis of environmental particles using the focused ion beam/scanning electron microscopy technique: Microanalysis insights into atmospheric chemistry of fly ash. Analyst 2013, 138 (2), 451−460. (34) Furukawa, T.; Takahashi, Y. Oxalate metal complexes in aerosol particles: Implications for the hygroscopicity of oxalate-containing particles. Atmos. Chem. Phys. 2011, 11 (9), 4289−4301. (35) Cheng, H.; Hu, Y. Lead (Pb) isotopic fingerprinting and its applications in lead pollution studies in China: A review. Environ. Pollut. 2010, 158 (5), 1134−1146. (36) Moffet, R. C.; Furutani, H.; Rödel, T. C.; Henn, T. R.; Sprau, P. O.; Laskin, A.; Uematsu, M.; Gilles, M. K. Iron speciation and mixing in single aerosol particles from the Asian continental outflow. J. Geophys. Res. 2012, 117 (D7), D07204. (37) Shi, Z.; Krom, M. D.; Bonneville, S.; Baker, A. R.; Jickells, T. D.; Benning, L. G. Formation of iron nanoparticles and increase in iron reactivity in mineral dust during simulated cloud processing. Environ. Sci. Technol. 2009, 43 (17), 6592−6596. (38) Oakes, M.; Rastogi, N.; Majestic, B. J.; Shafer, M.; Schauer, J. J.; Edgerton, E. S.; Weber, R. J. Characterization of soluble iron in urban aerosols using near-real time data. J. Geophys. Res. 2010, 115 (D15), D15302. (39) Oberdorster, G.; Oberdorster, E.; Oberdorster, J. Nanotoxicology: An emerging discipline evolving from studies of ultrafine particles. Environ. Health Perspect. 2005, 113 (7), 823−839. (40) Shao, L.; Shi, Z.; Jones, T. P.; Li, J.; Whittaker, A. G.; BéruBé, K. A. Bioreactivity of particulate matter in Beijing air: Results from plasmid DNA assay. Sci. Total Environ. 2006, 367 (1), 261−272.
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