Mechanisms of O3 and PM2.5 evolution along the cold wave passage in Eastern China

Cold wave (CW) systems in China, driven by strong northerly winds, typically clean the atmosphere but can also transport pollutants. However, elevated PM2.5 and O3 levels often precede CW events, with key processes remaining unclear. This study analyzes over 2000 in-situ observations (2014–2022), atmospheric reanalysis, and WRF-CAMx simulations to examine CW impacts on air pollution over eastern China. A three-day compressional heating period before CW events alters planetary boundary layer (PBL) dynamics, influencing pollutant levels. PM2.5 is driven by wind speed, PBL height (PBLH), and mean sea level pressure (MSLP), while O3 is influenced by temperature, humidity, solar radiation, PBLH, and MSLP. Though CWs generally clean the air on the day of its arrival, ~18% of cases show increased PM2.5 due to enhanced secondary formation and suppressed PBLH. Numerical simulations reveal CW-induced long-range pollutant transport and highlight critical meteorological-pollution interactions before CW events.