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Western Pacific subtropical high movement can cause local air pollution episode and influence the formation processes and mechanisms

A team led by Professor CHEN Jinsheng in the Institute of Urban Environment, Chinese Academy of Sciences (IUE-CAS), found that Western Pacific subtropical high movement can cause local air pollution episode and influence the formation processes and influencing mechanisms.

Western Pacific subtropical high (WPSH), which affected China directly, is one of the warm high cells locating on Pacific. Shor-term movement of WPSH leads to a series of variations of surface meteorology and atmospheric environment. One small-step move of WPSH might result in weather variations in one city, further cause air quality change. Hence, continuous shifts eastward and westward can possibly result in fluctuation of air quality. Atmospheric photo-oxidizing capability with high concentration of Ox depended on gaseous precursors and pre-existing aerosol, as well as high temperature and relative humidity, which were common meteorological conditions accompanying with WPSH.

The observation of air pollution episode was based on the equipment of air monitoring supersite locating on IUE-CAS. The meteorological parameters, concentrations of pollutants, chemical components and optical properties were detected to investigate the formation processes and influencing mechanisms of the episode. The results showed that the episode in Xiamen was possibly driven by Western Pacific subtropical high with high Ox, temperature and relative humidity. Shifted WPSH at 500hpa, accompanied with slightly variation of wind directions at surface layer, formed a complete situation to derive this episode. WPSH movement caused the ambient air pollution fluctuation, including the atmospheric oxidation, which affected the formation processes and influencing mechanisms. The high level of atmospheric oxidation accelerated the formation of secondary aerosols, which contributed to air pollution with stable meteorology. Secondary aerosol formed through atmospheric photo-chemical reactions, including gas-phase and liquid-phase reactions, in which gaseous precursors were oxidized under the circumstance of high Ox. Chemical components directly/indirectly contributed to aerosol light extinction promotion and the reduction of atmospheric visibility.

The results mentioned above has been published at Science of the Total Environment (2019, 692, 1135-1145), and titled as ‘The air pollution governed by subtropical high in a coastal city in Southeast China: Formation processes and influencing mechanisms’. PhD student Xin Wu is the first author, Professor CHEN Jinsheng and Associated Professor LI Mengren are the corresponding authors. This study was funded by the National Natural Science Foundation of China (41575146), the National Key Research and Development Program (2016YFC02005 & 2016YFE0112200), the Chinese Academy of Sciences Interdisciplinary Innovation Team Project, and Young Talents Projects of Institute of Urban Environment, Chinese Academy of Sciences (Y8L0221B20).

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