HONO Measurement in Seoul during Summer 2018 and its Impact on Photochemistry

Abstract HONO photolysis is an early morning source of OH radicals in urban environment, which expedites the photooxidation of volatile organic compounds (VOC), leading to O₃ production. From July 14^th to August 22^nd 2018, HONO was measured at Korea University using a parallel plate diffusion scrubber coupled with Ion Chromatography (PPDS-IC), in conjunction with major reactive gases(O₃, NO, and NO₂). The collection effciency of PPDS was estimated as 91.8~99.9% from the side-by-side measurement. HONO mixing ratio ranged between 0.01 to 0.79 ppbv with a mean of 0.28 ppbv, which was higher in high-O₃ episode than non-episode. Likewise, the OH production from HONO photolysis was higher by 0.04 pptv sec^-1 in high-O₃ episodes, when the daily maximum O₃ exceeded 100 ppbv, than non-episode. The hourly maximum O₃ reached 170 ppbv under severe heat waves. When the diurnal variations of O₃ was simulated with the measured HONO using the Framework for 0-D Atmospheric Modelling (F0AM), the daily maximum O₃ changed by 8~17 ppbv according to the HONO and VOC levels. In particular, the daily maximum O₃ was increased under non-episode conditions with an increased HONO, albeit low level.