Investigation of the Influence of Water Vapor on Heavy Pollution and Its Relationship With AOD Using MAX‐DOAS on the Coast of the Yellow Sea

• Published in: Journal of geophysical research. Atmospheres 2021-10, Vol.126 (20), p.n/a
• Main Authors: Ren, Hongmei, Li, Ang, Xie, Pinhua, Hu, Zhaokun, Xu, Jin, Huang, Yeyuan, Li, Xiaomei, Zhong, Hongyan, Tian, Xin, Ren, Bo, Wang, Shuai, Chai, Wenxuan
• Format: Article
• Language: English
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2020JD034143

Multi‐AXis Differential Optical Absorption Spectroscopy (MAX‐DOAS) observations were carried out from March 1, 2019 to February 29, 2020 in Qingdao, China, on the coast of the Yellow Sea (120.67°E, 36.35°N). Atmospheric parameters retrieved from the MAX‐DOAS instrument included vertical profiles of aerosol extinction, gaseous aerosol precursors (NO2, SO2), and H2O. First, the seasonal relationship between aerosol optical depth (AOD) and the H2O vertical column density (VCD) was analyzed. The correlation coefficients (r) between AOD and H2O VCD were largest in the winter, followed by spring, autumn, and summer. In addition, the correlation during heavily polluted weather was much higher than that during clean weather or slightly polluted weather. Then, an analysis of the wind speed and direction, and trace gas VCDs during the months with frequent pollution (December 2019 and January 2020) found that heavy pollution episodes easily occurred in Qingdao due to a combination of high H2O concentrations and low wind speeds. Out of four pollution events (P1, P2, P3, P4), both the H2O concentration and pollution were highest during the first event (P1). The H2O VCD, AOD, sulfate AOD, and total column HNO3 simultaneously increased during P1, while the NO2 and SO2 VCDs decreased. These trends are consistent with liquid phase reactions. Finally, the 1,000 m backward trajectory for the wind and the gas profiles during P1 revealed that the pollutants increased in Qingdao due to the influence of a polluted air mass from the western inland regions. Plain Language Summary Water vapor and aerosols are important components of the atmosphere. An increase in H2O concentration will accelerate the liquid phase reactions of trace gas and aggravate haze pollution. In recent years, heavy haze pollution has frequently occurred in China, especially during the winter in the northern China. The relationship between H2O and the aerosol optical depth (AOD), and how this relationship impacts haze formation, are of great significance for understanding the mechanisms driving heavy air pollution. Multi‐AXis Differential Optical Absorption Spectroscopy (MAX‐DOAS) is a remote sensing method that can simultaneously measure H2O, aerosols, and gaseous precursors (NO2, SO2). MAX‐DOAS instruments are low‐cost, simple to operate, and provide high time resolution, making them well‐suited for atmospheric observations across large geographic regions. The ability of MAX‐DOAS observations to simultaneous