Characteristics of PM2.5 Composition and Precursor Gases in Urban Seoul during 2021∼2022

In this study, the secondary inorganic ions including NO3-, SO42-, and NH4+, and the precursor gases including NH3 were measured every hour using the Monitor for AeRosols and Gases in ambient Air (MARGA) in urban Seoul from May 2021 to November 2022, and examined their monthly distributions and characteristic relationship between PM2.5 composition and precursor gases. PM2.5 and particulate nitrate concentrations were highest in the late fall and lowest in the summer. While NO2 and SO2 were higher in the cold months than in the warm months, NH3 showed the opposite tendency, except for November 2022. Nitrate oxidation ratio (NOR) was lower than 0.1, which is even lower than those of Chinese cities, which is indicative of the nonlinear nature of the nitrate formation processes. The monthly analysis of neutralization factor (fN), reveals that NH4+ was sufficient to neutralize SO42- and NO3-.