Abstract
The spatiotemporal variation characteristics of simultaneous high pollution (SHP) from surface fine particulate matter (PM2.5) and ozone (O3) were explored on the basis of hourly observation data in 1092 sites from 2015 to 2023 across China. Statistics show that the frequency and intensity of SHP days are highest in North China, followed by South China. Seasonally, SHP days occur more frequently in spring and autumn across China, accounting for 43% and 27% over nine years, respectively. The number of SHP days across national sites first decreased (by 48.63% from 2015 to 2021) but then increased (by 49.37% from 2021 to 2023). Gridded PM2.5 component data were analyzed to explore these variations. Despite reductions in anthropogenic emissions, the proportion of secondary inorganic components in PM2.5 increased by 4.51%, 3.6%, and 5.41% in Beijing-Tianjin-Hebei, FenWei Plain, and Yangtze River Delta on SHP days from 2015 to 2021. Concurrently, the detrended PM2.5 and O3 concentrations showed significant positive correlations in most regions. These phenomena may be related to high O3 concentrations and meteorological conditions. The weather analysis reveals that specific weather conditions contribute to the occurrence of SHP, with notable spatial variations: cyclonic low-pressure systems with high temperatures in northern China, anticyclonic high-pressure systems with high temperatures and low humidity in central China, and east winds in southern China. These conditions may promote secondary pollutant formation and hinder pollutant dispersion. In addition, the increase in primary PM2.5 on SHP days after 2021 underscores the importance of controlling anthropogenic emissions. Overall, a comprehensive approach is essential to tackle the SHP challenge.
Published Version
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