Air Quality during the COVID–19 Lockdown and Unlock Periods in India Analyzed Using Satellite and Ground-based Measurements

ABSTRACT: A nationwide lockdown was imposed in India from 24 March 2020 to 31 May 2020 to contain the spread of COVID-19. The lockdown has changed the atmospheric pollution across the continents. Here, we analyze the changes in two most important air quality related trace gases, nitrogen dioxide (NO(2)) and tropospheric ozone (O(3)) from satellite and surface observations, during the lockdown (April–May 2020) and unlock periods (June–September 2020) in India, to examine the baseline emissions when anthropogenic sources were significantly reduced. We use the Bayesian statistics to find the changes in these trace gas concentrations in different time periods. There is a strong reduction in NO(2) during the lockdown as public transport and industries were shut during that period. The largest changes are found in IGP (Indo-Gangetic Plain), and industrial and mining areas in Eastern India. The changes are small in the hilly regions, where the concentrations of these trace gases are also very small (0–1 × 10(15) molec./cm(2)). In addition, a corresponding increase in the concentrations of tropospheric O(3) is observed during the period. The analyses over cities show that there is a large decrease in NO(2) in Delhi (36%), Bangalore (21%) and Ahmedabad (21%). As the lockdown restrictions were eased during the unlock period, the concentrations of NO(2) gradually increased and ozone deceased in most regions. Therefore, this study suggests that pollution control measures should be prioritized, ensuring strict regulations to control the source of anthropogenic pollutants, particularly from the transport and industrial sectors. HIGHLIGHTS: • Most cities show a reduction up to 15% of NO(2) during the lockdown • The unlock periods show again an increase of about 40–50% in NO(2) • An increase in tropospheric O(3) is observed together with the decrease in NO(2) SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40710-022-00585-9.