Distribution and Formation Causes of PM2.5 and O3 Double High Pollution Events in China during 2013–20

Fine particulate matter (PM2.5) and ozone (O3) double high pollution (DHP) events have occurred frequently over China in recent years, but their causes are not completely clear. In this study, the spatiotemporal distribution of DHP events in China during 2013–20 is analyzed. The synoptic types affecting DHP events are identified with the Lamb–Jenkinson circulation classification method. The meteorological and chemical causes of DHP events controlled by the main synoptic types are further investigated. Results show that DHP events (1655 in total for China during 2013–20) mainly occur over the North China Plain, Yangtze River Delta, Pearl River Delta, Sichuan Basin, and Central China. The occurrence frequency increases by 5.1