Potential Factors Contributing to Ozone Production in AQUAS-Kyoto Campaign in Summer 2020: Natural Source-Related Missing OH Reactivity and Heterogeneous HO2/RO2 Loss

This study presents total OH reactivity, ancillary trace species, HO2 reactivity, and complex isoprene-derived RO2 reactivity due to ambient aerosols measured during the air quality study (AQUAS)-Kyoto campaign in September, 2020. Observations were conducted during the coronavirus disease (COVID-19) pandemic (associated with reduced anthropogenic emissions). The spatial distribution of missing OH reactivity highlights that the origin of volatile organic compounds (VOCs) may be from natural-emission areas. For the first time, the real-time loss rates of HO2 and RO2 onto ambient aerosols were measured continuously and alternately. Ozone production sensitivity was investigated considering unknown trace species and heterogeneous loss effects of XO2 ( HO2 + RO2) radicals. Missing OH reactivity enhanced the ozone production potential by a factor of 2.5 on average. Heterogeneous loss of radicals could markedly suppress ozone production under low NO/NOx conditions with slow gas-phase reactions of radicals and change the ozone regime from VOC- to NOx-sensitive conditions. This study quantifies the relationship of missing OH reactivity and aerosol uptake of radicals with ozone production in Kyoto, a low-emission suburban area. The result has implications for future NOx-reduction policies. Further studies may benefit from the combination of chemical transport models and inverse modeling over a wide spatiotemporal range.

Automated summary

This study presents data on total OH reactivity, ancillary trace species, HO2 reactivity, and complex isoprene-derived RO2 reactivity due to ambient aerosols measured during the AQUAS-Kyoto campaign in September 2020. The study reveals that missing OH reactivity may originate from natural-emission areas and measures the real-time loss rates of HO2 and RO2 onto ambient aerosols continuously and alternately for the first time. The study also finds that missing OH reactivity can enhance ozone production potential and the uptake of radicals by aerosols can significantly suppress ozone production.