Uneven Improvements in Secondary Inorganic Aerosol Components across Eastern China Driven by Differential Precursor Emission Reductions and Divergent Formation Mechanisms
摘要
In recent years, PM2.5 pollution in China has improved substantially, yet the reduction rates of different PM2.5 components have varied significantly. This study investigated the interannual changes in PM2.5 and its major secondary inorganic components (sulfate, nitrate and ammonium) in eastern China during 2013–2020 using the CHAP dataset and an atmospheric NH3 reanalysis dataset, with the aim of exploring the region-specific improvement characteristics and the driving factors. The results showed that PM2.5 (3.50 µg·m− 3·yr− 1) and all major secondary inorganic species (0.34 ~ 0.64 µg·m− 3·yr− 1) declined substantially over the study period. Among secondary inorganic components, sulfate exhibited the largest decrease nationwide (0.64 µg·m− 3·yr− 1 and 5.74% yr− 1), whereas nitrate declined more slowly (0.50 µg·m− 3 yr− 1 and 5.69% yr− 1) in relative terms, indicating a gradual shift in PM2.5 chemical composition from sulfate-dominated to nitrate-enhanced characteristics. However, the decreasing trends of sulfate and nitrate also showed significant regional differences. In southern China, nitrate exhibited a larger decline, with a reduction ratio 17% larger than that of sulfate. These south-north differences are collectively driven by regional variations in precursor emission reductions, ammonia-poor versus ammonia-rich conditions, and heterogeneous formation pathways of nitrate. This study highlights the importance of secondary inorganic aerosols for the continued improvement of PM2.5 in the future and provides insights for region-specific pollution control strategies.