Geographia Technica, Vol 17, Issue 1, 2022, pp. 104-115
NIGHTTIME LIGHT EMISSIONS EXPLAIN THE DECLINE IN NO2 DURING A COVID-19-INDUCED TOTAL LOCKDOWN IN FRANCE
Kamill Dániel KOVÁCS 
ABSTRACT:
Referring to a total lockdown due to COVID-19 in Metropolitan France, this study investigates the geospatial correlation between nighttime light emission and the relative change of NO2 air pollution (dNO2 %). To address the research problem, near-surface NO2 data and nighttime light data were implemented. Stable night lights were obtained for a long period on average (2014-2019) using Day-Night Band (DNB) data from the Visible Infrared Imaging Radiometer Suite (VIIRS). The relative change in tropospheric NO2 was calculated using Sentinel-5P satellite data from the Tropospheric Monitoring Instrument (TROPOMI). The dNO2 calculation was performed considering an equivalent reference period (April 2019) to the major lockdown period in France (April 2020). The correlation between the variables DNB nighttime lights and dNO2 was tested with a statistical T-test. The findings revealed an intense phenomenon of decreasing NO2 air pollution in France (decreases by -25% to -50%). Decreases < -50% were mainly recorded in the greater Paris metropolitan area, in Alsace, and other locations. The results showed a strong and statistically significant inverse geospatial correlation between the two variables under anti-COVID-19 control measures. The higher was the emission of nighttime lights, the higher was the degree of tropospheric NO2 decrease in the regions of France (R2=0.72). It is concluded that employing remote sensing techniques, DNB nighttime light is a reliable indicator to estimate the degree of air decontamination. DNB as an independent variable is recommended for future research on changes in the concentration of other pollutant gases.
Keywords: Satellite data, NO2, Decontamination, Visible to near-infrared, Constraint, France
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