Major Factors Affecting the Ambient Levels of Particulate Nitro(so) Compounds

초록

Nitro(so) compounds in the atmosphere can be directly emitted through vehicle exhaust, landfill emissions, and combustion of plastics and rubber, and/or secondarily formed through reactions of amines in the atmosphere. Previous studies have investigated their formation mechanisms through chamber experiments for gas-phase reactions, laboratory studies for aqueous aerosol phase reactions, field measurements, and box modeling analyses. These studies indicated that gas-phase formation may be limited due to rapid photolysis, aqueous-phase reactions showed low yields, gas-liquid partitioning was identified as an important pathway, and reduced photolysis rates in aqueous phase could allow nitro(so) compounds to persist in aqueous phase including aerosols with water. This study comprehensively reviewed the major emission sources and the roles of major factors influencing the formation of particulate nitro(so) compounds. We further analyzed the major reaction pathways based on the measurement results in Seoul and Seosan during 2018 similar to 2019 reported in previous studies, by incorporating findings on atmospheric chemical reaction characteristics from other earlier studies. Additionally, we summarize cancer risks associated with atmospheric nitro(so) compounds from existing literature. The concentration of particulate nitrosamines generally increased with aerosol liquid water content, while nitramines showed no significant correlation. Nitrogen oxides exhibited distinct patterns of influence on nitrosamines and nitramines. Nitrosamines showed strong correlations with both NO and NO2, with NO correlations being particularly pronounced in winter, indicating the importance of the N2O3 formation pathway. Nitramines demonstrated stronger correlations with NO2, suggesting different formation mechanisms. Both compounds showed significantly reduced correlations with nitrogen oxides during summer, highlighting the seasonal variability in atmospheric chemical conditions affecting their formation. Ozonation reactions contributed to nitro(so) compound formation to varying degrees across seasons, with the highest contribution observed during summer when O-3/NOx ratios were elevated. Further study directions are suggested.

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