Identify sources and multi-generation oxidation products formation of naphthalene during haze events in China

In this work, we have used in-situ PTR-Qi-TOFMS to identify the sources and investigate the photooxidation of naphthalene in atmosphere during a haze event in winter China. Local vehicle emissions and regional scattered coal combustion was identified as the main sources attributed to the pollution. Oxidation products of OH radical initial reactions of naphthalene were measured and their diurnal patterns were discussed first time. We found that 2-formyl-cinnamaldehyde was a key intermediate compound from naphthalene oxidation in atmosphere as reported by previous literatures. Further, subsequent oxidation of 2-formyl-cinnamaldehyde was also investigated, and was compared with the mechanism proposed by previous chamber experiments. It was found that phthalic anhydride exhibited as the most abundant oxidation product in atmosphere, which generated phthalic acid by hydration reaction. Based on the gas particle partitioning theory, phthalic acid in the particle phase was estimated, and compared to the results from filter samples measurement. Improved measurements of both gas and particle phase phthalic anhydride/phthalic acid are needed to better understand the formation process of phthalic acid in ambient aerosol.