Non biogenic source is an important but overlooked contributor to aerosol isoprene-derived organosulfates during winter in northern China

Abstract. Previous measurement-model comparisons of atmospheric isoprene levels showed a significant unidentified source of isoprene in some northern Chinese cities during winter. Here, spatial variability in winter aerosol organosulfate (OS) formation in typical southern (Guangzhou and Kunming) and northern (Xi’an and Taiyuan) cities, China, was investigated to reveal the influence of potential non biogenic contributor on aerosol OS pollution levels. Monoterpene-derived OSs were significantly higher in southern cities than in northern cities, which was attributed to temperature dependent emission of monoterpenes (i.e., higher temperatures in southern cities drove more monoterpene emissions). However, isoprene-derived OSs (OS_i) showed the opposite trend, with significantly higher levels in northern cities. Principal component analysis combined with field simulation combustion experiments suggested that biomass burning rather than gasoline, diesel, and coal combustion contributed significantly to the abundance of OS_i in northern cities. The comparison of anthropogenic OS molecular characteristics between particles released from various combustion sources and ambient aerosol particles suggested that stronger biomass and fossil fuel combustion activities in northern cities promoted the formation of more anthropogenic OSs. Overall, this study provides direct molecular evidence for the first time that non biogenic sources can significantly contribute to the formation of OS_i in China during winter.