[H-TT18] Environmental Remote Sensing

[HTT18-P07] Changes in the NO2 weekly cycle under COVID-19 pandemic

*Alessandro Damiani¹, Hitoshi Irie¹, Saito Hikaru¹, Ying Cai¹, Dmitry Belikov¹, Raul R. Cordero² (1.CEReS, Chiba University, 2.Santiago de Chile University)

Keywords:Remote sensing, Tropospheric gases, NO2, O3

Urban nitrogen dioxide (NO₂) concentrations arise from anthropogenic activities, mainly from traffic sources. In Chiba and Tsukuba cities, within the Great Tokyo Region (GTR, Japan), partial column MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) NO₂ observations (at 0-1 km) usually show a reduction of about 45-50 %, compared with the business days, during the end of the year holiday season. Corresponding ozonesonde observations carried out in a close location showed enhanced ozone (O₃) concentrations during holiday peaking at the surface (+15 %) and decreasing with the altitude. This suggests that titration processes, under saturated NO₂ conditions, usually occur in the investigated urban region and affect the surface and the lowest atmospheric layers. Keeping this in mind, we examined the so-called weekend effect in MAX-DOAS NO₂. We noted that its extent is getting smaller over the last years, characterized by decreasing NO₂ trends. An evident exception occurred in 2020 when the strongest weekend effect on records has been recorded. This was confirmed by S5P/TROPOMI NO₂ observations showing a weekend effect in 2020 clearly larger than in 2019 over the GTR. In this talk, we will put such findings into context by analyzing the changes in other large urban areas both in Japan and abroad (e.g., US, Europe, South America). We will then examine the results in light of the different responses of the population to COVID-19 as view in mobility data, changes in meteorology, and recent results pointing to enhanced surface ozone during lockdowns.