[Effects of " Air Pollution Prevention and Control Action Plan " on PM and Chemical Compositions in Zhengzhou in Polluted Winters].

The Air Pollution Prevention and Control Action Plan （APPCAP） was promulgated in China in 2013. To explore the effectiveness of APPCAP on PM in winter in Zhengzhou, PM samples were collected in Zhengzhou Monitoring Center during December 2013 and December 2018. The chemical composition of PM was analyzed, including EC, OC, water soluble ions, and metal elements. Pollution episodes under different stages were selected to investigate the changes in PM concentration and composition. The results showed that： ① The average concentration of PM in winter in Zhengzhou decreased from （215.38 ±107.28） μg·m in 2013 to （77.45 ±49.81） μg·m in 2018, with a decrease rate of 64%. ② The concentrations of EC, K, SO, and Cl decreased by 85%, 80%, 78%, and 72%, respectively, and the decrease rate in OC, NH, and NO was 50%, 41%, and 32%, respectively. ③ Compared with those in winter of 2013, the ratios of OC/EC in winter of 2018 increased by 2.6 times, and the proportion of secondary organic carbon in OC increased to 57%； meanwhile, values of sulfur oxidation rate and nitrogen oxidation rate increased by 1.5 and 1.0 times, respectively, indicating heavy secondary pollution in Zhengzhou. ④ The mass ratios of NO/SOincreased from 0.8 ±0.2 in 2013 to 2.5 ±1.0 in 2018, indicating that the contribution of mobile sources increased and surpassed fixed sources as the main source in Zhengzhou. ⑤The comparison results of different stages of the heavy pollution process showed that （PM） decreased significantly in 2018 compared with that in 2013, with the peak concentration decreasing by 61%. The main chemical composition changed from OC, NO, SO, and NH to OC, NO, and NH. The results indicated that the primary emission source control in Zhengzhou had achieved remarkable effects, but the contribution of secondary generation to PM showed an elevated trend； thus, the influence of secondary generation requires further attention in the future.