Formation Mechanism and Source Analysis of Two Heavy Pollution Periods in Winter in a Central Plains City

Abstract

To reveal the process and cause of air pollution in winter in Zhengzhou, Zhengfangji Station was selected as the sampling point to discuss the concentration of air pollutants and the characteristics of meteorological parameters in December 2019, in Zhengzhou. The concentration changes in PM2.5 water-soluble ions, elements, and carbon components in different pollution stages were compared, and air quality model simulation results were used to analyze emissions from pollution sources and regional transmission during sampling of the PM2.5 mass concentration at the sampling point. The results showed that there was a slight difference in the process of formation and dissipation of the first and second heavy pollution occurrences, showing the characteristics of "slow accumulation, slow removal" and "slow accumulation, fast removal", respectively. The mass concentration of NO3-, SO42-, and NH4+ accounted for 41.5% and 46.2% of PM2.5, and the OC/EC ratios were 4.0 and 4.5 in the first and second heavy pollution periods, respectively. The formation of secondary aerosol particles was the main reason for the formation of heavy pollution. During the sampling period, the average contributions of local, eastern, southern, western, and northern regions to the PM2.5 concentration of the sampling point were 58.0%, 2.4%, 6.7%, 6.9%, and 12.7%, respectively. The first heavy pollution period was the result of combined locally sourced pollutant emission and externally sourced regional transmission, during which the contribution from western and southern regions and external industrial sources increased. The second heavy pollution period was mainly affected by the accumulation of local air pollutants, during which the contribution of traffic, dust, and coal-fired sources increased sharply, and the impact of external areas on the PM2.5 concentration of sampling point decreased.