Characteristics and sources of PM2.5 in diverse central China cities under various scenarios: Maximum simulated emission reduction based on long-term data.

To control COVID-19, strict restrictions were implemented in China, leading to a decline in pollutant emissions. However, in the post-pandemic era, pollutants rebounded rapidly, particularly in the Central Plains region, without PM2.5 concentrations meeting national standard. This study analyzed Water-soluble inorganic ions (WSIIs) concentration and sources across different pandemic periods using long-term high-resolution PM2.5, WSIIs and meteorological data from Zhengzhou (ZZ), Anyang (AY), and Xinyang (XY). Results indicated that during the lockdown, WSIIs concentration in the three cities were significantly lower compared to other periods, but rebounded shortly after lifting of restrictions due to human activity resumption. Positive Matrix Factorization analysis showed that secondary aerosol sources were dominant in all cities. Simulations revealed a 90 % reduction of secondary aerosol sources in ZZ could lead to an additional decrease of 2.6 μg·m⁻³ of PM2.5 due to pH change. In AY, a 30 % reduction of secondary aerosol sources resulted in an extra reduction of 14.9 μg·m⁻³ in PM2.5. When the contribution of secondary aerosol sources in XY was decreased to 18 %, PM2.5 concentration decreased by 30 %, achieving an additional reduction of 9.5 μg·m⁻³ . This study offers strategies for achieving PM2.5 compliance and mitigating its impact on health and environment in the post-pandemic era.