Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 54, Issue 13, Pages 7836-7847Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.0c01149
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Funding
- National Natural Science Foundation of China (NSFC) [41877408, 41925015, 91644219, 41675120]
- Chinese Academy of Sciences [ZDBS-LY-DQC001]
- National Key Research and Development Program of China [2017YFC0212701]
- Cross Innovative Team fund from the State Key Laboratory of Loess and Quaternary Geology [SKLLQGTD1801]
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The chromophores responsible for light absorption in atmospheric brown carbon (BrC) are not well characterized, which hinders our understanding of BrC chemistry, the links with optical properties, and accurate model representations of BrC to global climate and atmospheric oxidative capacity. In this study, the light absorption properties and chromophore composition of three BrC fractions of different polarities were characterized for urban aerosol collected in Xi'an and Beijing in winter 2013-2014. These three BrC fractions show large differences in light absorption and chromophore composition, but the chromophores responsible for light absorption are similar in Xi'an and Beijing. Water-insoluble BrC (WI-BrC) fraction dominates the total BrC absorption at 365 nm in both Xi'an (51 +/- 5%) and Beijing (62 +/- 13%), followed by a humic-like fraction (HULIS-BrC) and high-polarity water-soluble BrC. The major chromophores identified in HULIS-BrC are nitrophenols and carbonyl oxygenated polycyclic aromatic hydrocarbons (OPAHs) with 2-3 aromatic rings (in total 18 species), accounting for 10% and 14% of the light absorption of HULIS-BrC at 365 nm in Xi'an and Beijing, respectively. In comparison, the major chromophores identified in WI-BrC are PAHs and OPAHs with 4-6 aromatic rings (in total 16 species), contributing 6% and 8% of the light absorption of WI-BrC at 365 nm in Xi'an and Beijing, respectively.
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