Impact of lockdown during COVID-19 pandemic on the air quality of North Indian cities.

The World Health Organization, which proclaimed the COVID-19 a pandemic in early March 2020, imposed a partial lockdown by the Government of India on 21 March 2020. The aim of this investigation was to measure the change in air pollutants, including particulate matter (PM and PM) and gaseous pollutants (NO, CO and O) during COVID-19 lockdown (25th March to 14th April 2020) across four major polluted cities in North India. In all region, PM, PM, NO and CO were significantly reduced while O has been shown mixed variation with increased in Agra and decreased in all other stations during lockdown. PM was reduced by ~20-50% and highly decreased in Noida. PM was most significantly decreased by 49% in Delhi. NO was reduced by ~10-70%, and high reduction was observed in Noida. Likewise, ~10-60% reduction was found in CO and most significantly decreased in Gurugram. However, an increased in O3 was observed in Agra by 98% while significantly reduced in other sites. Compared to the same timeframe in 2018-2019, PM and PM values for all sites were reduced by more than 40%.