Determination of the human impact on the drop in NO air pollution due to total COVID-19 lockdown using Human-Influenced Air Pollution Decrease Index (HIAPDI).

This study investigates the relationship between territorial human influence and decreases in NO air pollution during a total COVID-19 lockdown in Metropolitan France. NO data from the confinement period and the Human Influence Index (HII) were implemented to address the problem. The relative change in tropospheric NO was calculated using Sentinel-5P (TROPOMI) satellite data. Hotspot-Coldspot analysis was performed to examine the change in NO. Moreover, the novel Human-Influenced Air Pollution Decrease Index (HIAPDI) was developed. Weather bias was investigated by implementing homogeneity analysis with χ test. The correlations between variables were tested with the statistical T-test. Likewise, remote observations were validated with data from in-situ monitoring stations. The study showed a strong correlation between the NO decrease during April 2020 under confinement measures and HII. The greater the anthropogenic influence, the greater the reduction of NO in the regions (R = 0.62). The new HIAPDI evidenced the degree of anthropogenic impact on NO change. HIAPDI was found to be a reliable measure to determine the correlation between human influence and change in air pollution (R = 0.93). It is concluded that the anthropogenic influence is a determining factor in the phenomenon of near-surface NO reduction. The implementation of HIAPDI is recommended in the analysis of other polluting gases.