Inter-comparison of HONO field measurements and its summertime variation in Seoul, Korea

HONO is a key source of OH radical responsible for atmospheric oxidative capacity and plays an important role in heterogeneous oxidation of some species. To understand the oxidative mechanisms that lead to urban ozone and aerosol formation we need to know the sources and behavior of this trace gas. Despite its importance, HONO budgets, especially in the urban conditions in Korea are not well understood. In this study, HONO measurement was conducted in Olympic Park located in Seoul, Korea from May 19 to June 15 of 2016 using Quantum Cascade-Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS), High Efficiency Diffusion Scrubber-Ion Chromatography (HEDS-IC) and Monitor for AeRosols & Gases in ambient Air (MARGA). Overall, the measurements obtained with the three instruments agreed within analysis uncertainty. The resulting detection limits of all instruments were close to 0.10 ppbv for HONO. HONO concentrations over the measurement period varied from the detection limit to 3.46 ppbv (QC-TILDAS), 3.03 ppbv (HEDS-IC) and 4.81 ppbv (MARGA), respectively. Using a chemical box model including varying PBL heights and emissions, major paths of HONO production and its contributions to ozone was identified. The model showed significant underestimation compared to observations, which suggests additional unknown HONO production or direct HONO emission.