Fast sulfate formation from oxidation of SO2 by NO2 and HONO observed in Beijing haze

• DOI: 10.1038/s41467-020-16683-x
• Publication Date: 2020-06-05T10:04:22Z
• Authors: Junfeng Wang; Jingyi Li; Jianhuai Ye; Jian Zhao; Yangzhou Wu; Jianlin Hu; Dantong Liu; Dongyang Nie; Fuzhen Shen; Xiangpeng Huang; Dan Dan Huang; Dongsheng Ji; Xu Sun; Weiqi Xu; Jianping Guo; Shaojie Song; Yiming Qin; Pengfei Liu; Jay R. Turner; Hyun Chul Lee; Sungwoo Hwang; Hong Liao; Scot T. Martin; Qi Zhang; Mindong Chen; Yele Sun; Xinlei Ge; Daniel J. Jacob
• Keywords: 660; 550; 13. Climate action; Science; Q; 01 natural sciences; Article; 0105 earth and related environmental sciences

AbstractSevere events of wintertime particulate air pollution in Beijing (winter haze) are associated with high relative humidity (RH) and fast production of particulate sulfate from the oxidation of sulfur dioxide (SO2) emitted by coal combustion. There has been considerable debate regarding the mechanism for SO2 oxidation. Here we show evidence from field observations of a haze event that rapid oxidation of SO2 by nitrogen dioxide (NO2) and nitrous acid (HONO) takes place, the latter producing nitrous oxide (N2O). Sulfate shifts to larger particle sizes during the event, indicative of fog/cloud processing. Fog and cloud readily form under winter haze conditions, leading to high liquid water contents with high pH (>5.5) from elevated ammonia. Such conditions enable fast aqueous-phase oxidation of SO2 by NO2, producing HONO which can in turn oxidize SO2 to yield N2O.This mechanism could provide an explanation for sulfate formation under some winter haze conditions.