期刊
ATMOSPHERIC ENVIRONMENT
卷 63, 期 -, 页码 22-31出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.atmosenv.2012.09.012
关键词
Brown carbon; Secondary organic aerosol; Ammonia; Mass absorption coefficient
资金
- NSF [AGS-1227579, CHE-0909227]
- Direct For Mathematical & Physical Scien [909227] Funding Source: National Science Foundation
- Division Of Chemistry [909227] Funding Source: National Science Foundation
Filter samples of secondary organic aerosols (SOA) generated from the ozone (O-3)- and hydroxyl radical (OH)-initiated oxidation of various biogenic (isoprene, alpha-pinene, limonene, alpha-cedrene, alpha-humulene. farnesene, pine leaf essential oils, cedar leaf essential oils) and anthropogenic (tetradecane, 1,3,5-trimethylbenzene, naphthalene) precursors were exposed to humid air containing approximately 100 ppb of gaseous ammonia (NH3). Reactions of SOA compounds with NH3 resulted in production of light-absorbing brown carbon compounds, with the extent of browning ranging from no observable change (isoprene SOA) to visible change in color (limonene SOA). The aqueous phase reactions with dissolved ammonium (NH4+) salts, such as ammonium sulfate, were equally efficient in producing brown carbon. Wavelength-dependent mass absorption coefficients (MAC) of the aged SOA were quantified by extracting known amounts of SOA material in methanol and recording its UV/Vis absorption spectra. For a given precursor, the OH-generated SOA had systematically lower MAC compared to the O-3-generated SOA. The highest MAC values, for brown carbon from SOA resulting from O-3 oxidation of limonene and sesquiterpenes, were comparable to MAC values for biomass burning particles but considerably smaller than MAC values for black carbon aerosols. The NH3/NH4+ + SOA brown carbon aerosol may contribute to aerosol optical density in regions with elevated concentrations of NH3 or ammonium sulfate and high photochemical activity. (C) 2012 Elsevier Ltd. All rights reserved.
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