A Study on the Formation Reactions and Conversion Mechanisms of HONO and HNO3 in the Atmosphere of Daejeon, Korea

Abstract

Nitrogen oxides (NOX) in the atmosphere cause oxidation reactions with photochemical radicals and volatile organic compounds, leading to the accumulation of ozone (O3). NOX constitutes a significant portion of the NOy composition, with nitrous acid (HONO) and nitric acid (HNO3) following. HONO plays a crucial role in the reaction cycle of NOX and hydrogen oxides. The majority of HNO3 reduction mechanisms result from aerosolization through heterogeneous reactions, having adverse effects on humans and plants by increasing secondary aerosol concentrations in the atmosphere. The investigation of the formation and conversion mechanisms of HONO and HNO3 is important; however, research in this area is currently lacking. In this study, we observed HONO, HNO3, and their precursor gases were observed in the atmosphere using parallel-plate diffusion scrubber-ion chromatography. A 0-D box model simulated the compositional distribution of NOy in the atmosphere. The formation reactions and conversion mechanisms of HONO and HNO3 were quantified using reaction equations and reaction coefficients. Among the various mechanisms, dominant mechanisms were identified, suggesting their importance. According to the calculation results, the produce of HONO was predominantly attributed to heterogeneous reactions, excluding an unknown source. The sink processes were mainly governed by photolysis during daytime and reactions with OH radicals during nighttime. HNO3 showed dominance in its production from N2O5, and in its conversion mechanisms primarily involving aerosolization and deposition.