AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Missing Source of Atmospheric Sulfate Formation in Wintertime Beijing Haze: Linking SO2 Oxidation and HONO Chemistry
JUNFENG WANG, Jingyi Li, Jian Zhao, Jianhuai Ye, Xinlei Ge, Yiming Qin, Pengfei Liu, Shaojie Song, Hong Liao, Mindong Chen, Yele Sun, Qi Zhang, Scot T. Martin, Daniel Jacob, Harvard University
Abstract Number: 357 Working Group: Aerosol Chemistry
Abstract Sulfate comprises a large fraction of atmospheric fine particulate matter and exerts nontrivial impacts on regional air quality and global climate. Current atmospheric models with known mechanisms often fail to explain the high sulfate levels observed under complex environmental conditions. An intensive field campaign was conducted during the winter time of 2016 (December 16 to December 23) in Beijing, and formation of secondary sulfate was investigated.
Compared to the less-polluted days, secondary sulfate concentration increased by nearly two times during a severe fog-haze event. We found that sulfate concentrations correlated tightly with HONO as well as N2O concentrations in fog-haze days, suggesting a sulfate formation pathway: 2HONO+2H2SO3 → 2H2SO4+N2O+H2O. The reaction takes place in aqueous particles with HONO acting as an oxidant to transform S(IV) to S(VI) and N2O formed as a tracer product.
This novel sulfate formation pathway in the presence of HONO was further examined by using a chemical box model and a regional-scale model (i.e., Community Multiscale Air Quality Modeling). Results demonstrate that the enhancement of sulfate formation in the droplets (liquid water contents of 0.1-0.5 g m-3) under foggy conditions was closely associated with HONO, and matched well with the observed sulfate concentrations. The work presented herein highlights a long-ignored secondary source of atmospheric sulfate and a potential sink of nighttime atmospheric HONO.