Assessment of Air Quality Changes in the Four Metropolitan Cities of India during COVID-19 Pandemic Lockdown

ABSTRACT

In view of emerging threat of COVID-19 pandemic, stringent lockdown measures have been implemented in India since 25^th March, 2020. The present study aims to assess the changes in air quality before and during lockdown in the four major metropolitan cities of India viz., Delhi, Mumbai, Kolkata and Chennai. The data on major air quality parameters and meteorological parameters was collected for 15 days before lockdown (i.e., March 10^th to March 24^th, 2020) and 15 days after implementation of lockdown (25^th March to April 8^th, 2020). The lockdown measures reflected a significant reduction in air pollutants, most significant fall was estimated for NO₂ (29.3- 74.4%) while the least reduction was noticed for SO₂. On the contrary, levels of ground level ozone were found to be increased (except in Mumbai), could be related to the lower utilization of O₃ owing to decrease of NO_x in the environment. Since, the lockdown period has been extended, therefore further reduction of most pollutants is expected. Among the various metrological parameters, significant increase in diurnal temperature was observed at Delhi, Kolkata and Mumbai, however relative humidity has changed significantly only in Mumbai. In the absence of any major violent meteorological phenomena in India during recent months the significant difference in air quality parameters could be majorly attributed to the effect of lockdown measures. However, the regional differences may be because of the local emission of pollutants and the prevailing effects of secondary pollutants. These observations highlight the contribution of anthropogenic sources in air pollution, therefore, sustainable polices for mitigation of air pollution are essential in India.