Lockdown measures to contain COVID-19 pandemic has resulted in a considerable change in air pollution worldwide. We estimate the temporal and diurnal changes of the six criteria air pollutants, including particulate matter (PM 2.5 and PM 10 ) and gaseous pollutants (NO 2 , O 3 , CO, and SO 2 ) during lockdown (25 th March – 3 rd May 2020) across regions of India using the observations from 134 real-time monitoring sites of Central Pollution Control Board (CPCB). Significant reduction in PM 2.5 , PM 10 , NO 2, and CO has been found in all the regions during the lockdown. SO 2 showed mixed behavior, with a slight increase at some sites but a comparatively significant decrease at other locations. O 3 also showed a mixed variation with a mild increase in IGP and a decrease in the South. The absolute decrease in PM 2.5 , PM 10, and NO 2 was observed during peak morning traffic hours (08–10 Hrs) and late evening (20–24 Hrs), but the percentage reduction is almost constant throughout the day. A significant decrease in day-time O 3 has been found over Indo Gangetic plain (IGP) and central India, whereas night-time O 3 has increased over IGP due to less O 3 loss. The most significant reduction (∼40–60%) was found in PM 2.5 and PM 10 . The highest decrease in PM was found for the north-west and IGP followed by South and central regions. A considerable reduction (∼30–70%) in NO 2 was found except for a few sites in the central region. A similar pattern was observed for CO having a ∼20–40% reduction. The reduction observed for PM 2.5 , PM 10 , NO 2, and enhancement in O 3 was proportional to the population density. Delhi’s air quality has improved with a significant reduction in primary pollutants, however, an increase in O 3 was observed. The changes reported during the lockdown are combined effect of changes in the emissions, meteorology, and atmospheric chemistry that requires detailed investigations.

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NCT 01211132.

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