Impacts of missing OH reactivity and aerosol uptake of HO2 radicals on tropospheric O3 production during the AQUAS-Kyoto summer campaign in 2018

Gaining quantitative information about the HOx cycle involved in ozone (O3) production is important for reduction of tropospheric O3. In this study, we evaluated the impacts of both the missing OH reactivity and the heterogeneous loss of HO2 due to ambient aerosol uptake on the photochemical O3 production potential and regime analysis during the Air QUAlity Study (AQUAS)-Kyoto summer campaign in 2018. We examined the missing OH reactivity, which was 50% of the averaged total OH reactivity (9.8 ± 3.8 (1σ) s−1), and the uptake loss rate of HO2 on ambient aerosols of 0.0017 ± 0.0015 s−1. The real-time uptake loss rate of HO2 was measured by employing a versatile aerosol concentration enrichment system (VACES). The O3 production potential increased by a factor of two when the missing OH reactivity was considered and decreased by ∼20% when the HO2 loss due to aerosol uptake was considered. In addition, the missing OH reactivity and the HO2 loss due to aerosol uptake decreased the relative sensitivity of the O3 production rate to volatile organic compounds (VOCs) and increased that to NOx (= NO + NO2). Consequently, the NOx limited regime period, the period in which the relative sensitivity of the O3 production rate to NOx was higher than that to VOCs, was expanded by a few hours. Finally, the effect of aerosol uptake on O3 production was anti-correlated with the NO concentration and peaked around noon when the NO concentration was the minimum. It is concluded that aerosols likely affect tropospheric O3 production in suburban and rural areas, where the concentrations of NOx, particularly NO, are very low ([NO] < 0.3 ppb).