Characteristics and source apportionment of water-soluble inorganic ions in PM2.5 in central China background region.

To investigate the characteristics, formation mechanisms, and sources of water-soluble inorganic ions (WSIIs) in PM2.5 in the central China background area, the study conducted a one-year sampling observation at the Jinsha atmospheric background station. The results showed that the average annual mass concentration of PM2.5 was (31.40±2.05) µg/m3, showing remarkable seasonal variations of the highest level in winter and lowest in summer. Secondary inorganic aerosol (SNA, i.e., SO42-, NO3-, and NH4+) was an important component of PM2.5. The proportions of SNA in WSIIs in spring, summer, autumn, and winter were 84.0%, 77.6%, 79.8%, and 84.5%, respectively, indicating secondary formation was pronounced. The average molar equivalent ratio of anions and cations (AE/CE) during the study period was 0.91, and PM2.5 showed weak alkalinity. (NH4)2SO4, NH4NO3, and NH4Cl were the main forms of ion species in summer, while (NH4)2SO4 may be the main form in spring, autumn, and winter. The sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) were 0.48 and 0.14, respectively, showing a significant positive correlation with PM2.5, indicating that secondary conversion was an important reason for the increase in PM2.5 concentration. The potential sources and transmission paths of WSIIs had obvious seasonal characteristics. The secondary transformation of pollutants during the migration process from the source area to the background area was obvious, and the concentration of pollutants carried by long-distance air masses from the northwest or due north was relatively high. © 2024 Chinese Society for Environmental Sciences. All rights reserved.