Analysis of water-soluble ions and their precursor gases over diurnal cycle

- An interactive relationship between ionic components of PM2.5 and gases is assessed.
- Their formation pathways are analyzed over diurnal cycle using the hourly resolution data.
- Their reaction pathways are explained by the competing relationship with ammonium conditions.

A detailed description of an interactive relationship is made between water-soluble ionic components in PM2.5 and their precursor gases using the hourly resolution data measured at an urban monitoring site in Seoul during the year of 2010. Their diurnal variability was found to be correlated with their precursor gases (HNO3 and NH3). In the case of NO3− and NH4+, a close similarity was seen in their diurnal trends, especially during spring. There were no noticeable differences in the formation pathway of NO3−, SO42− , and NH4+ aerosols between day and night. For NO3− formation, heterogeneous hydrolysis of N2O5 might play a significant role in the nighttime enhancement of the oxidation rate. In addition, the concentrations of major anions (e.g. NO3−, SO42− , and Cl−) exhibited highly diverse seasonal patterns with their maximum values occurring in spring, summer, and winter, respectively. The overall results of this study suggest that the formation pathway of NO3− and SO42−  aerosols should be regulated by a competing relationship between the NH3-lean (spring and winter) and NH3-rich conditions (summer and fall).