Possible particulate nitrite formation and its atmospheric implications inferred from the observations in Seoul, Korea

Abstract

Simultaneous measurements of gaseous species and fine-mode, particulate inorganic components were performed at the University of Seoul, Seoul in Korea. In the simultaneous measurements, a certain level of nitrous acid (HONO) was observed in the gas-phase, indicating possible heterogeneous HONO production on the surface of the ambient aerosols. On the other hand, high particulate nitrite (NO 2−) concentrations of 1.41(±2.26) μg/m 3 were also measured, which sometimes reached 18.54 μg/m 3. In contrast, low HONO-to-NO 2 ratios of 0.007(±0.006) were observed in Seoul. This indicates that a significant fraction of HONO is dissolved in atmospheric aerosols. Around the Seoul site, sufficient alkalinity may have been provided to the atmospheric aerosols from the excessive presence of NH 3 in the gas-phase. Due to the alkaline particulate conditions (defined in this study as a particle pH >∼3.29), the HONO molecules produced at the surface of the atmospheric aerosols appeared to have been converted into particulate nitrite, thereby preventing their further participation in the atmospheric O 3/NO y/HO x photochemical cycles. It was estimated that a minimum average of 65% of HONO was captured by alkaline, anthropogenic, urban particles in the Seoul measurements.