Comprehensive study on impact assessment of lockdown on overall ambient air quality amid COVID-19 in Delhi and its NCR, India.

Indian government announced the complete lockdown from 25 March, 2020 for all outdoor activities across the country due to containment of COVID-19. This study is an attempt to assess the impacts of lockdown on ambient air quality in five cities of Indian National Capital Region including Delhi, Gurugram, Noida, Ghaziabad and Faridabad. In this context, the data of air pollutants (PM, PM, NOx, NO, NO, SO, NH, SO, CO, and CH) from 36 locations of the study area were analyzed from 1 March to 1 May, 2020. The results showed that PM and PM level decreased upto 55-65 %. NOx and NO have shown maximum reduction (∼ 50-78 %). Similarly, consistent and significant reduction in other air pollutants such as SO (∼33 %), CO (∼45 %), NH (∼27 %) and CH (∼53 %) has been observed. During lockdown Air Quality Index (AQI) shows improvement as its value significantly decreased (∼ 45 %-68 %). An interesting feature observed that during first week of lockdown O decreased but later it increased by ∼19-27%. The study suggests that this pandemic gives lessons for interventions for urban air pollution mitigation in controlling the health impact due to urban air pollution.