Sources and oxidative potential of water-soluble humic-like substances (HULIS WS ) in fine particulate matter (PM 2.5 ) in Beijing

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Water-soluble humic-like substances (HULIS WS ) are a major redox-active component of ambient fine particulate matter (PM 2.5 ); however, information on their sources and associated redox activity is limited. In this study, HULIS WS mass concentration, various HULIS WS species, and dithiothreitol (DTT) activity of HULIS WS were quantified in PM 2.5 samples collected during a 1-year period in Beijing. Strong correlation was observed between HULIS WS and DTT activity; both exhibited higher levels during the heating season than during the nonheating season. Positive matrix factorization analysis of both HULIS WS and DTT activity was performed. Four combustion-related sources, namely coal combustion, biomass burning, waste incineration, and vehicle exhausts, and one secondary factor were resolved. In particular, waste incineration was identified as a source of HULIS WS for the first time. Biomass burning and secondary aerosol formation were the major contributors (> 59 %) to both HULIS WS and associated DTT activity throughout the year. During the nonheating season, secondary aerosol formation was the most important source, whereas during the heating season, the predominant contributor was biomass burning. The four combustion-related sources accounted for > 70 % of HULIS WS and DTT activity, implying that future reduction in PM 2.5 emissions from combustion activities can substantially reduce the HULIS WS burden and their potential health impact in Beijing.