Sources, Composition and Absorption 脜ngstr枚m Exponent of Light-absorbing Organic Components in Aerosol Extracts from the Los Angeles Basin

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• 作者：Xiaolu Zhang ; Ying-Hsuan Lin ; Jason D. Surratt ; Rodney J. Weber
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：April 16, 2013
• 年：2013
• 卷：47
• 期：8
• 页码：3685-3693
• 全文大小：440K
• 年卷期：v.47,no.8(April 16, 2013)
• ISSN：1520-5851

文摘

We investigate the sources, chemical composition, and spectral properties of light-absorbing organic aerosol extracts (i.e., brown carbon, or BrC) in the Los Angeles (LA) Basin during the CalNex-2010 field campaign. Light absorption of PM_2.5 water-soluble components at 365 nm (Abs₃₆₅), used as a proxy for water-soluble BrC, was well correlated with water-soluble organic carbon (WSOC) (r² = 0.55鈥?.65), indicating secondary organic aerosol (SOA) formation from anthropogenic emissions was the major source of water-soluble BrC in this region. Normalizing Abs₃₆₅ to WSOC mass yielded an average solution mass absorption efficiency (MAE₃₆₅) of 0.71 m²g^鈥?C. Detailed chemical speciation of filter extracts identified eight nitro-aromatic compounds that were correlated with Abs₃₆₅. These compounds accounted for 4% of the overall water-soluble BrC absorption. Methanol-extracted BrC in LA was approximately 3 and 21 times higher than water-soluble BrC at 365 and 532 nm, respectively, and had a MAE₃₆₅ of 1.58 m²g^鈥?C (Abs₃₆₅ normalized to organic carbon mass). The water-insoluble BrC was strongly correlated with ambient elemental carbon concentration, suggesting similar sources. Absorption 脜ngstr枚m exponent (脜_a) (fitted between 300 and 600 nm wavelengths) was 3.2 (卤1.2) for the PILS water-soluble BrC measurement, compared to 4.8 (卤0.5) and 7.6 (卤0.5) for methanol- and water-soluble BrC from filter extracts, respectively. These results show that fine particle BrC was prevalent in the LA basin during CalNex, yet many of its properties and potential impacts remain unknown.