Missing OH reactivity contributed by photochemical reactions cause uncertainty to ozone production in AQUAS campaigns in Japan

Tropospheric ozone is harmful to human and the ecosystem, which is by-product of the reaction of OH with VOCs and NO_x. Field campaign is an effective way to assess regional air quality and the detection of OH reactivity provides a top-down approach to understand the general existence of trace species under specific conditions. Concurrent trace species measurement as bottom-up approach gives information on the detailed atmospheric chemistry. We have conducted Air QUAlity Study (AQUAS) campaigns in different sites in Japan over years and explored the missing OH reactivity contributed by unknown trace species that equals to the discrepancy between top-down total OH reactivity and bottom-up calculated OH reactivity. The investigation of missing OH reactivity in field campaigns showed potential contribution from secondary products. Unconsidered missing OH reactivity on ozone production sensitivity will lead underestimation to ozone production potential and overestimation to VOC-limited regime. In addition, field observations at the same site and varied years such as before and after the corona virus (COVID-19) pandemic can also shed light on the reduction of anthropogenic emission, which should be meaningful for a low emission future society. Missing trace species and unconsidered photochemistry in several field campaigns in Japan will be compared in detail and their role should be considered to make effective air quality policies.

Acknowledgement: We acknowledge all collaborators on each of the field campaigns specifically our debts to Dr. Yasuhiro Sadanaga, Dr. Kei Sato, Dr Shungo Kato, and Dr. Yoshihiro Nakashima.