[A-AS11] Atmospheric Chemistry

[AAS11-P10] Determination of tropospheric ozone production rates by using PERCA-CAPS method

*Kouichi Egami¹, Yosuke Sakamoto^1,2,3, Yoshizumi Kajii^1,2,3 (1.Kyoto University Graduate School of Human and Environmental Studies, 2.Kyoto University Graduate School of Global Environmental Studies, 3.National Institute for Environmental Studies)

Keywords:tropospheric ozone, peroxy radicals

Tropospheric ozone, a major photochemical oxidant and a greenhouse gas with radiative forcing next to methane, has been increased in Japan despite reduction of precursors. Accordingly, it is required to clarify the cause of ozone increase for ozone suppression measures. Comparing P(O₃), determined from peroxy radical and NO concentration, with possible contributors: precursors concentration, meteorological conditions, etc., would be a way to investigate the controlling factors of ozone production. PERCA (PEroxy Radical Chemical Amplification)-LIF(laser-induced fluorescence) is one of the established technique to measure total peroxy radical concentration for P(O3) estimation, where NO₂ converted from peroxy radical with ~100-fold amplification by doping NO and CO, is detected by LIF. However, application of PERCA-LIF has limitations in actual operation due to its weight, size, price, skill requirement, electrical power consumption, etc. Recently, commercial LED-based CAPS (Cavity Attenuated Phase Shift spectroscopy) become available for NO₂ detection, which can be installed and operated more easily than the laser system. In this study, we developed a PERCA-CAPS and applied it for ambient measurement. We measured ambient peroxy radicals from Oct 4th to Oct 7th, 2021, at Kyoto University by using PERCA-CAPS, together with measurements of O₃, NOx, humidity and solar irradiation intensity. As the result of field observation, the concentration of peroxy radicals became maximum in the daytime to be 220 ppt, which depended on the square root of solar irradiation corresponding to observed low NOx concentration. In addition, estimated P(O₃) from measured peroxy radicals and NO had a maximum at 3 ppb/min and depended NOx concentration, which is a typical behavior in low NOx condition known as NOx-limited ozone production. Observed P(O₃) was larger than the actual ozone variation which may indicate an importance of ozone loss process. Based on the results, we concluded that P(O₃) can be obtained by using PERCA-CAPS method with simpler operation and better portability than laser system. It is expected that operating PERCA-CAPS system under various conditions will lead to the elucidation of a more detailed ozone production mechanism.