Oxidative Potential of Water-Soluble Matter Associated with Chromophoric Substances in PM2.5 over Xi’an, China

Organic compounds are important contributors to the oxidative potential (OP) of atmospheric aerosols. This study is the first to report the OP of water-soluble organic matter (WSOM) related to the chromophoric substances in PM2.5 over Xi'an, China. The dithiothreitol (DTT) activity levels in PM2.5 extracted by water were quantified as well as the relationships between DTT activity and light absorption and fluorescence properties. The results show that the DTT activity has significantly correlated with colored WSOM, in which we identified three light absorbing substances (BrC1-3) and eight fluorescent substances (C1-8). It is further found that BrC3 and C7 accounted for almost all of the DTT activity by colored WSOM, although these two factors contributed only a small fraction of light absorption and fluorescence. BrC3 and C7 are clearly distinguished from other chromophoric substances because of their long absorption wavelength (λmax = 475 nm) and fluorescence emission wavelength (λmax = 462 nm), respectively. This discovery will help to better interpret and understand the mechanism of oxidation activity generation by light absorbing organic aerosols and provide guidance for predicting the OPs of light absorbing organic aerosols based on their optical properties.