Dual carbon isotopes (C-14 and C-13) and optical properties of WSOC and HULIS-C during winter in Guangzhou, China

Water-soluble brown carbon (ws-BrC) exerts an important influence on climate change, but its emission sources and optical properties remain poorly understood. In this study, we isolated two ws-BrC proxies, water-soluble organic carbon (WSOC) and humic-like substance carbon (HULIS-C), from particulate matter collected in Guangzhou, China, during December 2012 for the measurement of dual carbon isotopes (C-14 and C-13) and light absorption. The mass absorption efficiencies of WSOC and HULIS-C at 365 nm were 0.81 +/- 0.16 and 1.33 +/- 0.21 m(2) g(-1) C, respectively. The C-14 results showed that two-thirds of WSOC and HULIS-C were derived from non-fossil sources (e.g., biomass burning and biogenic emission), and the remaining third was derived from fossil sources. The delta C-13 values of WSOC and HULIS-C were -23.7 +/- 1.2 parts per thousand and -24.2 +/- 0.9 parts per thousand, respectively, underlining the limited influences of C4 plants and natural gas on ws-BrC. Fitting the data to a multiple linear regression, we further concluded that approximately 80% and 10% of the light absorption at 365 nm was due to non-fossil and fossil carbon, respectively. Non-fossil sources of ws-BrC, such as the burning of agricultural residue, were responsible for the light absorption recorded in Guangzhou. (c) 2018 Elsevier B.V. All rights reserved.