Variations of the source-specific health risks from elements in PM2.5 from 2018 to 2021 in a Chinese megacity

To develop health-oriented emission control policies in China, it is necessary to evaluate the effectiveness of emission reduction measures on the concentrations of elements in PM2.5 and their health risks. Concentrations of element species in PM2.5 were continuously recorded in the urban site of Zhengzhou from 2018 to 2021. The source-specific health risks of the elements in PM2.5 were investigated by combining the Positive Matrix Factorization model for source apportionment, a Random Forest model for meteorology normalization, and a health risk assessment model for health impact analysis. The results show that most of the observed element concentrations and their associated health risks decreased from 2018 to 2020, accompanied by the decreasing PM2.5 concentration. However, the element concentrations and their non-carcinogenic risks rebound in 2021. The reduction of emissions from industrial processes and combustion sources dominated the decrease of element health risks from 2018 to 2020. The rebound in non-carcinogenic risks in 2021, particularly from vehicle sources, might be attributed to an increase in emissions even under higher wind speed, which was favorable for pollutant diffusion. In addition, the contribution of vehicle emissions to health risks exhibited an increasing trend from year to year, so further attention should be paid to the health risks associated with vehicles, especially non-exhaust emissions.