The Impact of Changes in Anthropogenic Activity Caused by COVID-19 Lockdown on Reducing Nitrogen Dioxide Levels in Thailand Using Nighttime Light Intensity

Coronavirus disease 2019 (COVID-19) was first identified in Wuhan, China and has since become a pandemic. Thailand’s first lockdown started in the middle of March 2020, restricting anthropogenic activities and inter-provincial traffic. There are few studies on the association between nitrogen dioxide (NO₂) levels and human activity, primarily because of the difficulty in identifying the changes in anthropogenic activities at a high geographical resolution. Here, we have highlighted satellite-based nighttime light (NTL) as an indicator of anthropogenic activities and investigated the relationship between NTL and reductions in NO₂ levels during Thailand’s first lockdown in 2020. We applied geographically weighted regression (GWR) to analyze the regional relationship between NTL and changes in NO₂ levels during the first lockdown. Sentinel-5 Precursor satellite observation indicated that the NO₂ levels decreased by 10.36% compared with those of the same period in 2019. The level of NTL decreased in most urban and built-up (31.66%) categories. According to GWR results, NTL and NO₂ levels represent a positive local correlation around the country’s central, western, and northern parts and negative correlations in the peripheral regions. These findings imply that NTL observations can be used to monitor changes in NO₂ levels caused by urban anthropogenic activities.