[A-AS07] Atmospheric Chemistry

[AAS07-24] Analysis of the COVID-19 influence on an air quality in urban cities in Japan with multiple satellite and ground-based measurements

*Tamaki Fujinawa¹, Satoshi Inomata¹, Takafumi Sugita¹, Kohei Ikeda¹, Hiroshi Tanimoto¹ (1.National Institute for Environmental Studies)

Keywords:COVID-19, Air quality, Remote sensing, Ground-based measurement

Nitrogen dioxide (NO₂) is one of the major air pollutants and is harmful to human health. It is mainly emitted from anthropogenic sources (e.g., power plants and vehicles) and play a key role in the photochemical reaction of tropospheric ozone. Therefore, ambient NO₂ concentrations are monitored by a variety of instruments at ground-based, airborne, and satellite platforms. The coronavirus disease 2019 (COVID-19) has spread worldwide from December 2019 and it derived severe lockdowns in many cities of the world. Due to these lockdowns, human activities including transports, recreations and energy consumption were drastically reduced, resulting in dramatic decline (26~67%) in the tropospheric NO₂ level, especially in megacities. (Liu et al., 2020; Cooper et al., 2022). For Tokyo in Japan, several previous works revealed NO₂ decline up to about 50% using in-situ and satellite observations (Ghahremanloo et al., 2020; Ma and Kang, 2020; Fu et al., 2020; Itahashi, 2022; Damiani et al., 2022), though the lockdown was not strictly implemented as in the other countries (i.e., non-legal movement restriction). However, there is no report to link the decline of NO₂ specifically to that of the human activity in Japan. In this study, we analyzed ground-based in-situ data and satellite observations with the great focus on Japan’s urban cities and found that the decline of NO₂ and related species due to the COVID-19-driven movement restriction in the region including the Tokyo metropolitan area. The comparison of the tropospheric NO₂ vertical column densities (VCD) in March and April between 2019 and 2020 shows a 30-40% decline in the TROPOMI (TROPOspheric Monitoring Instrument) NO₂ tropospheric column amounts. Tropospheric NO₂ VCD observed from OMI (Ozone Monitoring Instrument) shows a similar declining trend of NO₂, though a bias of about 0.4 × 10¹⁶ molec. cm^-2 can be seen against the TROPOMI data. Given the instrumental bias of 0.31 × 10¹⁶ molec. cm^-2 between OMI and TROPOMI (Wang et al., 2020), the bias derived from our analysis is in reasonable agreement with the previous work, and thus, the decline of the NO₂ VCD in March and April in 2020 is independent from the year-to-year factors but by the reduced emissions driven by the movement restriction.