COVID-19 and Air Pollution in Indian Cities: World's Most Polluted Cities

In the present study, pollutants levels from 24th March-31st May in 2020 were compared with the same time period in 2019 to estimate the impact of lockdown on air pollutants levels in 39 different cities of India (including 10 Indian cities considered among the world's 20 most polluted cities). Data for air pollutants was obtained from the Central Pollution Control Board (CPCB) which was statistically analyzed. Tropospheric NO2 column retrieved from Ozone Monitoring Instrument (OMI) were compared between 2019 and 2020 to compare the NO2 levels. Impact of lockdown measures on Ghaziabad which is the world's most polluted city and Patiala which showed maximum reduction during the lockdown period in the present study was studied in detail. After the implementation of lockdown measures, air pollution decreased but with substantial variation among pollutants. The most significant reduction was observed for nitrogen dioxide (NO2) (3- 79%) and carbon monoxide (CO) (2-61%), pollutants which are mainly related to traffic emissions. Ozone (O-3) showed a mixed trend with increasing levels at some cities which may be attributed to lower titration of O-3 by NO. Maximum reduction observed in PM10 and PM2.5 was 58 and 57%, respectively during the lockdown period in 2020 as compared to the previous year. Air quality of the cities also improved in 2020. During the lockdown period in 2020, AQI of only 15% of cities was in the 'Unhealthy' category (151-200) while in 2019, 56% of cities were in the 'Unhealthy' category. In Ghaziabad and Patiala all the pollutants showed significant reduction after lockdown implementation except O-3. Diurnal patterns of PM10, PM2.5, CO and NO2 showed lower values during lockdown period in 2020 with less distinct bimodal patterns as compared to 2019. The present study provides evidence that widespread implementation of air pollution measures can result in immediate air quality benefits.