Response of warm season secondary pollutants to emissions and meteorology in the North China Plain region during 2018–2022

Air quality in China has continued to improve since 2013, although severe pollution events still occur over the North China Plain (NCP). It is noticeable that contributions from secondary pollutants have increased, but understanding of their formation and variations with changing emissions and meteorological conditions remains limited. In this study, the warm season of May to September from 2018 to 2022 was selected to explore the response of secondary pollutants to meteorology and emissions using the Community Multi-scale Air Quality model (CMAQ). Fine particulate matter (PM2.5) concentrations over the NCP decreased significantly by 31%–37% from 2018 to 2022, while ozone (O3) and nitrogen dioxide (NO2) generally showed decreasing trends by 1% and 0.5% per year, respectively. Secondary inorganic aerosol (including sulfate, nitrate, and ammonium) and secondary organic aerosol (SOA) also decreased significantly, by 9% and 6% per year, respectively. The results showed that emissions contributed 96% to the decreases in PM2.5 concentrations, while O3 fluctuated due to meteorological changes. Although the decreases in sulfate and ammonium were mainly associated with emission reductions, that of nitrate was more sensitive to meteorological changes. Meteorological and emission changes were similarly important for the overall decrease in SOA, with anthropogenic SOA being more sensitive to emissions control, while biogenic SOA was more easily attributed to meteorological changes. This research emphasizes the importance of controlling anthropogenic emissions in relieving summer secondary pollution in the NCP region. 自2013年起, 中国空气质量虽改善, 但华北平原(NCP)重污染仍存且二次污染加剧, 对其成因和变化了解有限.本研究用2018–2022年数据, 借助CMAQ模型探讨此污染响应.结果显示, PM2.5浓度显著下降31%–37%, O3和NO2年降速分别为1%和0.5%.二次污染物同样显著减少.PM2.5主要因排放减少而下降, O3受气象影响.硫酸盐和铵降主因是减排, 而硝酸盐对气象变化敏感.排放和气象变化对SOA减少均有影响, 人为SOA对排放控制敏感, 生物SOA易受气象变化影响.