Relationship between Oxidation Level and Optical Properties of Secondary Organic Aerosol

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• 作者：Andrew T. Lambe ; Christopher D. Cappa ; Paola Massoli ; Timothy B. Onasch ; Sara D. Forestieri ; Alexander T. Martin ; Molly J. Cummings ; David R. Croasdale ; William H. Brune ; Douglas R. Worsnop ; Paul Davidovits
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：June 18, 2013
• 年：2013
• 卷：47
• 期：12
• 页码：6349-6357
• 全文大小：547K
• 年卷期：v.47,no.12(June 18, 2013)
• ISSN：1520-5851

文摘

Brown carbon (BrC), which may include secondary organic aerosol (SOA), can be a significant climate-forcing agent via its optical absorption properties. However, the overall contribution of SOA to BrC remains poorly understood. Here, correlations between oxidation level and optical properties of SOA are examined. SOA was generated in a flow reactor in the absence of NOb>xb> by OH oxidation of gas-phase precursors used as surrogates for anthropogenic (naphthalene, tricyclo[5.2.1.0^2,6]decane), biomass burning (guaiacol), and biogenic (伪-pinene) emissions. SOA chemical composition was characterized with a time-of-flight aerosol mass spectrometer. SOA mass-specific absorption cross sections (MAC) and refractive indices were calculated from real-time cavity ring-down photoacoustic spectrometry measurements at 405 and 532 nm and from UV鈥搗is spectrometry measurements of methanol extracts of filter-collected particles (300 to 600 nm). At 405 nm, SOA MAC values and imaginary refractive indices increased with increasing oxidation level and decreased with increasing wavelength, leading to negligible absorption at 532 nm. Real refractive indices of SOA decreased with increasing oxidation level. Comparison with literature studies suggests that under typical polluted conditions the effect of NOb>xb> on SOA absorption is small. SOA may contribute significantly to atmospheric BrC, with the magnitude dependent on both precursor type and oxidation level.