Elucidating the formation and conversion mechanisms of HONO and HNO3 in the atmosphere of Daejeon, Korea

Nitrogen oxide (NO_X) in the atmosphere causes oxidation reactions with photochemical radicals and volatile organic compounds, causing ozone (O₃) accumulation. In the composition of NO_y, NO_X accounts for the highest portion, and followed by nitrous acid (HONO) and nitric acid (HNO₃). HONO significantly contributes to the reaction cycle of NO_X and hydrogen oxide (OH). The generation of OH radicals and nitric oxide by photolysis is the main HONO removal mechanism in the morning. The OH radicals generated at this time trigger O₃ accumulation in the atmosphere, affecting photochemical smog in urban areas. HNO₃ in the atmosphere is produced by the reaction between NO₂ and OH during the day while N₂O₅ and H₂O during night time. Aerosolization by heterogeneous reactions of HNO₃ is the major mechanism of HNO₃ reduction. Aerosolization (heterogeneous) reactions adversely affect humans and plants by increasing the secondary aerosol concentration in the atmosphere and lowering visibility; therefore understanding the conversion mechanism of HNO₃ to aerosols is important. In this study, HONO, HNO₃, and their precursor gases in the atmosphere were observed using parallel-plate diffusion scrubber-ion chromatography. And a 0-D box model simulated the compositional distribution of NO_y in the atmosphere, and the formation reactions and conversion mechanisms of HONO and HNO₃ were analyzed.

Acknowledgments:

This research was supported by Particulate Matter Management Specialized Graduate Program through the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Environment (MOE)