COVID-19 lockdown-induced changes in NO2levels across India observed by multi-satellite and surface observations

Abstract

We have estimated the spatial changes in NO2levels over different regions of India during the COVID-19 lockdown (25 March-3 May 2020) using the satellite-based tropospheric column NO2observed by the Ozone Monitoring Instrument (OMI) and the Tropospheric Monitoring Instrument (TROPOMI), as well as surface NO2concentrations obtained from the Central Pollution Control Board (CPCB) monitoring network. A substantial reduction in NO2levels was observed across India during the lockdown compared to the same period during previous business-as-usual years, except for some regions that were influenced by anomalous fires in 2020. The reduction (negative change) over the urban agglomerations was substantial (~20 %-40 %) and directly proportional to the urban size and population density. Rural regions across India also experienced lower NO2values by ~15 %-25 %. Localised enhancements in NO2associated with isolated emission increase scattered across India were also detected. Observed percentage changes in satellite and surface observations were consistent across most regions and cities, but the surface observations were subject to larger variability depending on their proximity to the local emission sources. Observations also indicate NO2enhancements of up to~25%during the lockdown associated with fire emissions over the north-east of India and some parts of the central regions. In addition, the cities located near the large fire emission sources show much smaller NO2reduction than other urban areas as the decrease at the surface was masked by enhancement in NO2due to the transport of the fire emissions.