Peculiar COVID-19 effects in the Greater Tokyo Area revealed by spatiotemporal variabilities of tropospheric gases and light-absorbing aerosols

Abstract

Abstract. This study investigated the spatiotemporal variabilities in nitrogen dioxide (NO2), formaldehyde (HCHO), ozone (O3), and light-absorbing aerosols within the Greater Tokyo Area, Japan, which is the most populous metropolitan area in the world. The analysis is based on total tropospheric column, partial tropospheric column (within the boundary layer), and in situ observations retrieved from multiple platforms as well as additional information obtained from reanalysis and box model simulations. This study mainly covers the 2013–2020 period, focusing on 2020 when air quality was influenced by the coronavirus 2019 (COVID-19) pandemic. Although total and partial tropospheric NO2 columns were reduced by an average of about 10 % in 2020, reductions exceeding 40 % occurred in some areas during the pandemic state of emergency. Light-absorbing aerosol levels within the boundary layer were also reduced for most of 2020, while smaller fluctuations in HCHO and O3 were observed. The significantly enhanced degree of weekly cycling of NO2, HCHO, and light-absorbing aerosol found in urban areas during 2020 suggests that, in contrast to other countries, mobility in Japan also dropped on weekends. We conclude that, despite the lack of strict mobility restrictions in Japan, widespread adherence to recommendations designed to limit the COVID-19 spread resulted in unique air quality improvements.

Peculiar weather patterns effects on air pollution and COVID-19 spread in Tokyo metropolis

“…Several epidemiological studies have shown that nitrogen dioxide (NO 2 ) exposure is often associated with adverse health effects such as lung cancer, asthma, and cardiopulmonary mortality ( Wang et al, 2020 ; Berg et al, 2021 ). Based on the average of in-situ observational data at air pollution network stations in Tokyo metropolis, during the lockdown from April–May 2020, NO 2 experienced a decrease of 15.30% compared to the previous year, similar to other studies from satellite data found for Tokyo a value of 19% decrease ( Ghahremanloo et al, 2021 ; Damiani et al, 2022 ).…”

“…In Greater Tokyo Area, the change in people's mobility was smaller and more gradual compared to other worldwide countries because of avoidance of adopted strict legal restrictions, showing the largest mobility drop during the weekends, with decreases about 10% larger than on weekdays. ( Sugawara et al, 2021 ; Damiani et al, 2022 ). However, the implemented COVID-19 pandemic lockdowns during States of Emergency (SOEs) in Tokyo ( Table 1 ) led to a sharp drop in socio-economic activities, including reductions in fossil fuel use, industry productions, and traffic volumes.…”

“…Tokyo is located in a polluted background with various significant PM2.5, PM10, O3, and NO2 sources surrounding it within about a 100 km radius ( Damiani et al, 2022 ). While urbanization has accelerated the conversion of vegetated land covers to built-up areas, the effects of green vegetation as biofilters for particulate matter have been reduced ( Lee et al, 2022 ), urban green and blue spaces being inversely associated with pandemic COVID-19 incidence and mortality ( Peng et al, 2022 ; Ciupa, 2023 ; Falco et al, 2023 ).…”

Changes to Peroxyacyl Nitrates (PANs) Over Megacities in Response to COVID‐19 Tropospheric NO2 Reductions Observed by the Cross‐Track Infrared Sounder (CrIS)

“…PANs did not show marked changes over São Paulo or Tokyo despite major NO x perturbations. O 3 over Tokyo also did not significantly change with COVID‐19 lockdown measures; this has been attributed to a shift in the underlying photochemical regime from VOC‐limited toward the transition zone where O 3 production is expected to be equally sensitive to changes in both NO x and VOCs (Damiani et al., 2022; Ito et al., 2021; Q. Wang & Li, 2021). São Paulo experienced an increase in O 3 in April and May, but largely in areas most seriously impacted by vehicle emissions (Alvim et al., 2023).…”