Meteorological influences on PM and O trends and associated health burden since China's clean air actions.

Stringent clean air actions have been implemented to improve air quality in China since 2013. In addition to anthropogenic emission abatements, the changes in air quality may be modulated also by meteorology. In this study, we developed multiple linear regression models to quantify meteorological influences on the trends in fine particulate matter (PM) and ozone (O) concentrations and associated health burden over three polluted regions of China, i.e., North China Plain, Yangtze River Delta, and Fen-wei Plain during 2014-2018, with a novel focus on the contributions of the most influential meteorological factors to PM and O trends as well as the meteorological contributions to PM- and O-related mortality trends. The meteorology-driven PM (O) trends for the three regions were -0.5-2.0 (+0.7+0.8) μg m yr, contributing 10- 26% (12- 18%) of the observed five-year decreasing PM (increasing O) trends. The decreased relative humidity (increased daytime planetary boundary layer height) was identified to be the most influential meteorological factor and explained 55% (42%) of the largest meteorology-driven PM (O) trend among all regions and seasons. The meteorology-driven decreases in PM (increases in O) concentrations led to overall decreases in PM-related (increases in O-related) mortalities with trends of -2.2-7.4 (+0.5+0.9) thousand yr for the three regions, accounting for 10- 26% (15- 31%) of the total decreasing (increasing) trends in PM-related (O-related) mortalities. The results emphasize the important role of meteorology in PM and O air quality and associated health burden over China, and have important implications for China's air quality planning. In particular, more efforts in emission control should be taken to offset the adverse effects on ozone caused by meteorology.