[A-AS08] Atmospheric Chemistry

[AAS08-P14] Formation Mechanisms of Secondary Inorganic Aerosols in PM_2.5 at Yongin, Korea, Downwind of Seoul, during winter 2026

*Huijae Seong¹, Seora Woo¹, Jiyi Lee², Yongjoo Choi¹ (1.Department of Environmental Sciences, Hankuk University of Foreign Studies, Yongin, South Korea, 2.Department of Environmental Sciences and Engineering, Ewha Women University, Seoul, South Korea)

Secondary inorganic aerosols (SIAs) are major constituents of PM_2.5, accounting for more than 50% of the total mass. High PM_2.5 events frequently occur during winter in East Asia due to the important role of SIAs under meteorological conditions favorable for secondary formation and atmospheric stagnation. The formation pathways of SIAs vary regionally depending on precursor concentrations, oxidation pathways, the neutralizing role of ammonia, and meteorological conditions. Therefore, elucidating region-specific secondary formation mechanisms is essential for establishing effective PM_2.5 mitigation policies. To investigate the secondary formation of SIAs, we analyzed hourly water-soluble ions in PM2.5 (SO₄^2-, NO₃^-, NH₄⁺, Na⁺, K⁺, Mg²⁺, and Ca²⁺) and major gaseous precursors (HCl, HNO₂, HNO₃, SO₂, and NH₃) using a Monitor for AeRosols and Gases in ambient Air (MARGA) from December 2025 to March 2026. The site is on the rooftop of a building at Hankuk University of Foreign Studies in Yongin, Korea (37.34°N, 127.27°E). The relative contributions of nitrate and sulfate were quantified using the neutralization ratio (NR), which represents the neutralizing role of ammonia. In addition, sulfur and nitrogen oxidation ratios (SOR and NOR) were investigated to assess the influence of oxidative processes on SIA formation and their relationships with meteorological parameters. This study aims to identify the key factors governing wintertime SIA formation in suburban environments and to provide scientific evidence for evaluating seasonal PM_2.5 management policies in Korea.