| 14 Sep 2026
The 2022 AQUAS–Tsukuba campaign: Part I. OH reactivity analysis and NO-corrected reactivity ratios for improved ozone regime evaluation
Abstract. Revisiting an intensive field campaign is important for assessing the influences of human activity and natural event on on-site air quality. We conducted observations in Tsukuba, Japan, during the summer of 2022 at the same site as the 2017 AQUAS–Tsukuba summer campaign, enabling a comparison of OH reactivity and related trace species after a lustrum. The combined WRF-CMAQ model simulations provided supplementary speciation of the OH reactivity, enabling extrapolation to unmeasured trace gases. Substantial reductions in anthropogenic emissions over the five years reduced the average total OH reactivity from 12.9 s-1 to 6.0 s-1. However, total OH reactivity was not fully explained by the concurrently measured trace species or model simulations, and at least 35 % remained unidentified in both campaigns. High total OH reactivity and observation-based missing OH reactivity were associated with high wind speeds that brought air pollutants from the Tokyo metropolitan area. The model showed bias in the spatiotemporal variations of meteorological conditions and trace species, with large underestimation at noon when the air influx was from a pristine site, and from afternoon to midnight when the air influx was from a polluted site. A constrained model simulation that combined 2017 emission inventories (except biogenic emissions) with 2022 meteorological conditions quantified the significance of primary emissions’ contributions to the 2022 campaign. Additionally, we propose evaluating the ozone regime via using kVOCkNOx= 28.9·[NO] (NO in ppbv), which reduces the overestimation of the VOC-limited regime under low NO conditions and supports for ozone mitigation strategies.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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