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Ambient Aerosol Concentrations of Elements Resolved by Size and by Source: Contributions of Some Cytokine-Active Metals from Coal- and Oil-Fired Power Plants A. E. Suarez and J. M. Ondov* Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742 Received July 17, 2001
Size-segregated aerosol samples were collected with Micro-Orifice Impactors in Baltimore, MD, a typical northeastern port city where air quality is influenced by urban and industrial sources. The size fractions were analyzed for up to 32 elements by Instrumental Neutron Activation Analysis and the results were used in a chemical mass balance model to resolve the contributions to ambient levels by size and by source. Resolution by size improves interpretation of the results as primary accumulation aerosol populations from different sources are frequently resolved in the size spectra of their marker species. With a 15-source model, agreement between measured and predicted concentrations was within 40% for all elements except Co, Cr, Cs, Ti, and W. The results suggest that coal-fired power plants are minor sources of the respirable fractions of several metals, including Cr (19%), V (5%), and Zn (50 to 176 µg/m3) concentrations of sulfuric acid droplets (healthy adults tolerate brief exposures to sulfuric acid droplets at concentrations of 1 mg/m3 8). Concentrated sulfuric acid is a powerful corrosive poison, but neither (NH4)2SO4 nor NH4HSO4 are so classified. More recently, compelling evidence suggests that water-soluble metal components of urban PM are important determinants of the respiratory effects observed (4) Han, M. Coal- and Oil-Fired Power Plant Contributions to the Atmosphere of Maryland. Ph.D. Thesis, University of Maryland, College Park, MD, 1992. (5) Wu, Z. Y.; Han, M.; Lin, Z. C.; Ondov, J. M. Chesapeake Bay Atmospheric Deposition Study, Year 1: Sources and dry deposition of selected elements in aerosol particles. Atmos. Environ. 1994, 28, 14711486. (6) Thurston, G. D.; Ito, K.; Hayes, C. G.; Bates, D. V.; Lippman, M. Respiratory hospital admissions and summertime haze air pollution in Toronto, Ontario: Consideration of the role of acid aerosols. Environ. Res. 1994, 65, 271-290. (7) Hanley, Q. S.; Koenig, J. Q.; Larson, T. V.; Anderson, T. L.; Vanbelle, G.; Rebolledo, V.; Covert, D. S.; Pierson, W. E. Response of Young Asthmatic Patients to Inhaled sulfuric Acid. Am. Rev. Respir. Disease 1992, 145, 326-331.
10.1021/ef010170c CCC: $22.00 © 2002 American Chemical Society Published on Web 03/13/2002
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during air pollution episodes. Metals, particularly reactive transition metals such as V, Zn, Fe, Cu, and possibly Hg, associated with submicrometer aerosol particles may directly initiate or exacerbate irritation of respiratory tissues by stimulating local cells to release reactive oxygen species (ROS, e.g., hydrogen peroxide and superoxide free radicals) and inflammatory mediators, such as cytokines such as TNFR and IL-6.9-15 Cytokines are protein molecules involved in the lung’s immune response to bacteria and, apparently, aerosol particles. They act either by attracting macrophages which subsequently release ROS or by directly manufacturing ROS. Various studies9-15 indicate that the water-soluble inorganic compounds exert the most profound effects on ROS stimulations. Others attribute the response to specific metals. Studies by Carter et al.,10 for example, indicate that exposure to V increases cytokine production in airway epithelial cells and that V compounds, but not those of Fe or Ni, mimic the cytokine response of airway epithelial cells to residual oil fly ash (ROF). Results reported by Becker et al.9 also indicated that the Fe component of aerosol particles was not an important mediator of the cytokine response of alveolar macrophage, again suggesting that the inflammatory response is metal specific. Likewise, a study by Adamson et al.13 suggests that Zn, but not Cu, Fe, Al, Pb, Mg, or Ni, accounted for the inflammatory response induced by an atmospheric dust sample. Moreover, Carter et al.10 suggest that the dose of soluble metals, not particulate mass, relates most closely with associated cardio-pulomonary effects in healthy and compromised hosts. These observations are especially important in view of the fact that the masses of various inorganic constituents, including first-series transition metals capable of producing ROS, are predominately associated with primary aerosol emissions from hightemperature combustion sources (HTCS), such as coaland oil-fired power plants (CFPP and OFPP), municipal and medical incinerators, diesel-powered vehicles, and residential furnaces, and their airborne concentrations are, thus, more highly elevated near local sources, than is usually the case for inter-regionally transported air. (8) Frampton, M. W.; Voter, K. Z.; Morrow, P. E.; Roberts, N. J.; Cu;p, D. J.; Cox, C.; Utell, M. J. Sulfuric Acid Aerosol Exposure in Humans Assessed by Bronchoalveolar Lavage. Am. Rev. Respir. Disease 1992, 146, 626-632. (9) Becker, S.; Soukup, J. M.; Gilmour, M. I.; Devlin, R. B. Stimulation of human and rat alveolar macrophages by urban air particulates: Effects on oxidant radical generation and cytokine production. Toxicol. Appl. Pharmacol. 1996, 141, 637-648. (10) Carter, J. D.; Ghio, A. J.; Samet, J. M.; Devlin, R. B. Cytokine production by human airway epithelial cells after exposure to an air pollution particle is metal-dependent. Toxicol. Appl. Pharmacol. 1997, 146, 180-188. (11) McKenna, I. M.; Waakes, M. P.; Chen, L. C.; Gordon, T. Comparison of inflammatory lung responses in Wistar rats and C57 and DBA mice following acute exposure to cadmium oxide fumes. Toxicol. Appl. Pharmacol. 1997, 146, 196-206. (12) Takano, H.; Ichinose, T.; Miyabara, Y.; Chibuya, T.; Lim, H.B.; Yoshikawa, T.; Sagai, M. Inhalation of Diesel Exhaust Enhances Allergen-Related Eosinophil Recruitment and Airway Hyperresponsiveness in Mice. Toxicol. Appl. Pharmacol. 1998, 150, 328-337. (13) Adamson, I. Y. R.; Prieditis, H.; Vincent, R. Pulmonary Toxicity of an Atmospheric Particulate Sample Is Due to the Soluble Fraction. Toxicol. Appl. Pharmacol. 1999, 157, 43-50. (14) Veronesi, B.; Oortgiesen, M.; Carter, J. D.; Devlin, R. B. Particulate Matter Initiates Inflammatory Cytokine Release by Activation of Capsaicin and Acid Receptors in a Human Bronchial Epithelial Cell Line. Toxicol. Appl. Pharmacol. 1999, 154, 106-115. (15) Adamson, I. Y. R.; Prieditis, H.; Hedgecock, C.; Vincent, R. Zinc is the toxic factor in the lung response to an atmospheric particulate sample. Toxicol. Appl. Pharmacol. 2000, 166, 111-119.
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Moreover, these primary components comprise only a small fraction of the respirable aerosol mass. In HTCSs, both particle composition and size are primarily governed by fuel composition, time-temperature history, and the type and efficiency of emission control devices.16 Most HTCSs are controlled, and virtually all of them emit large fractions of their mass in particles of respirable size, including both coal- and oil-fired power plants. Their unique compositions provide the basis for receptor modeling and, thus, for tracing their movement in the atmosphere. Vanadium, for example, is highly enriched relative to other elements in fuel oil due to the presence of V porphyrins and, for this reason, is extensively used as an inherent tracer of emissions from fuel-oil combustion.17 As coal combustion is the principle atmospheric source of oxidized sulfur, its chemical analogue, selenium, has long been recognized as a useful tracer of primary coal combustion aerosol.18 Likewise, Zn and Cd, Ti, C, and sulfate are inherent tracers (i.e., marker species) of particles from municipal incinerators, paint manufacture and spray painting, diesel motor vehicles, and regionally distributed secondary aerosol, respectively.18 As discussed by Ondov and Wexler (ref 19 and references therein), primary particulate mass emissions from HTCSs are emitted in narrow accumulation aerosol peaks with geometric mean diameters between 0.1 and 0.3 µm, and are observed in this size range in ambient size spectra of their marker elements. Once in the atmosphere, these particles grow by capturing water vapor, sulfur dioxide (which becomes converted to secondary sulfate) and various other materials of secondary origin, including polar organic compounds. Thus, older or more highly processed aerosol particles are substantially larger, i.e., with geometric mean sizes typically between 0.4 and 1 µm19 and carry more secondary aerosol material. Theory and nearly two decades of experimental evidence show that the discrete aerosol particle populations emitted from these sources largely remain discrete over the urban scale.16,17,19 Although masked by the overwhelming presence of the secondary aerosol, these primary aerosol populations are revealed through measurement of key marker species.16,17,19 Contributions of various other components of these aerosol components can be resolved by chemical mass balance methods (CMB,18). Herein, we report concentrations of metals resolved by size and by source using CMB methods applied to size segregated aerosol samples collected in ambient Baltimore, MD, air using micro-orifice impactors and analyzed by instrumental neutron activation analysis (INAA,20). Additionally, these data are interpreted in the context of discrete aerosol populations observed in plumes of nearby HTCSs. The work is part of a larger (16) Dodd, J. A.; Ondov, J. M.; Tuncel, G.; Dzubay, T. G.; Stevens, R. K. Multimodal size spectra of submicrometer particles bearing various elements in rural air. Environ. Sci. Technol. 1991, 25, 890903. (17) Divita, F., Jr.; Ondov, J. M.; Suarez, A. E. Size Spectra and Atmospheric Growth of V-Containing Aerosol in Washington, DC. Aerosol Sci. Technol. 1996, 25, 256-273. (18) Gordon, G. E. Receptor Models. Environ. Sci. Technol. 1988, 22, 1132-1142. (19) Ondov, J. M.; Wexler, A. S. Where Do Particulate Toxins Reside? An Improved Paradigm for the Structure and Dynamics of the Urban Mid-Atlantic Aerosol. Environ. Sci. Technol. 1998, 32, 25472555.
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study21 of the sources of the elemental components of particles depositing onto the Chesapeake Bay by dryparticle deposition. While far from perfect, the results are intended to enhance our understanding of the potential for toxic effects of particulate emissions from coal- and oil-combustion. Methods Size-fractionated aerosol samples were collected with micro-orifice impactors (MOI) operated at a flow rate and pressure drop of 30 L m-1 and 27 kPa, respectively. Along with an integral backup filter, each impactor sample provided 10 discrete particle fractions with midpoint diameters estimated as follows: 21.2, 6.9, 2.4, 1.3, 0.74, 0.40, 0.22, 0.12, 0.070, and 0.033 µm. Gelman 37-mm diameter, 2-µm pore Teflon filters were used as impaction substrates on all stages and in the integral backup filter holder. Substrates used in the first three stages of the impactors were coated with a approximately 2 mg of dimethylpolysiloxane (Dow Corning 200 silicone liquid) to improve large-particle collection efficiency. In addition, numerous laboratory and seven field blanks were collected during the studies by exposing clean, unused impaction substrates in the laboratory during sample preparation and at the field sites during sample changes, respectively, to monitor variability in filter concentrations and potential contamination from sample handling. In each case, the samples were analyzed for up to 32 elements by instrumental neutron activation analysis.20 Lead and S were determined by Energy Dispersive X-ray Fluorescence (XRF) as described by Kellogg.22 Both INAA and XRF measure bulk elemental content. Water-soluble metals content was not determined. Six 12-hour (6:00 AM to 6:00 PM) MOI samples (60 individual stages) collected in August, 1995, on the roof of the Eastern Avenue Fire Station in Downtown Baltimore, were selected for CMB analysis. Meteorological data (wind speed and direction) were collected using a Campbell Scientific (Logan UT) meteorological station equipped with cup anemometer, wind vane, temperature/relative humidity sensor, and CR10 data logger. The site was located in an urban area (see Figure 1) encompassing a mixture of residential and commercial structures. The latter includes the Johns Hopkins Bayshore Medical Center, located directly behind the firehouse, a Bayer plant located across the street, and many small businesses (e.g., gas stations, convenience stores, and restaurants). More than 40 industrial sources, including a steel mill, are located along the Patapsco River in Baltimore’s southeastern quadrant, 3 to 12 km south of the site. On the basis of AIRS23 data, 31% of (20) Ondov, J. M.; Dodd, J. A.; Tuncel, G. Nuclear Analysis of Trace Elements in Size-Classified Submicrometer Aerosol Particles from a Rural Airshed. Aerosol Sci. Technol. 1990, 13, 249-263. (21) Suarez, A. E. Influence of Urban and Industrial Sources in Baltimore to the Dry Deposition Fluxes of Particles Bearing Trace Elements and Soot on the Chesapeake Bay. Ph.D. Thesis, University of Maryland, College Park, MD, 1999. (22) Kellogg, R. B. Standard Operating Procedure for the Source Apportionment Research Branch LBL Energy Dispersive X-ray Fluorescence Spectrometer. 68-DO-0106, U. S. Environmental Protection Agency, Research Triangle Park, NC, 1992. (23) US EPA, Aerometric Information Retrieval System (AIRS)/Airs Facility Subsystem (AFS). www.epa.gov/environ/html/airs/airsover.html.
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PM2.5 emissions in Maryland are attributed to the steel mill, while 29% are attributed to Bay-area electric power plants. Four urban surface dust samples were collected from city streets and parking lots within two blocks of the fire station. Four more were collected at Hart Miller Island, and three were collected at UMBC (including an unpaved parking lot). Surface dust samples from each location were composited and elutriated to isolate particles
