Delhi, India’s capital, is a massive metropolitan state in the northern area of the country and is among one of the most polluted capitals in the globe. Due to overpopulation and other responsible factors for urbanization, the pessimistic anthropogenic impact on the environment is at maximum. But, COVID-19 pandemic confinement facilitates the environment to retain its health which can be observed as a significant reduction in the air pollutant level in Delhi. At site 1—ITO, Delhi, during confinement period, the mean concentrations of PM2.5, PM10, NO2, NH3, and SO2 significantly plummeted by 49%, 33%, 29%, 63%, and 24% respectively due to reduction in anthropogenic activities including traffic and manufacturing industries. Besides, due to high temperature and insolation during the confinement period, mean ozone concentration was highly elevated by 109% as shown in Table 1.
Table 1 Air quality assessment—variations and change (%) of average concentrations for different air pollutants during the pre and COVID-19 pandemic confinement, 2020 among populous sites of four major metropolitan cities in India
Pollutants Pre-lockdown values Lockdown Variation and % change (pre-lockdown and lockdown)
Site 1 Site 2 Site 3 Site 4 Site 1 Site 2 Site 3 Site 4 Site 1 Site 2 Site 3 Site 4
AQI 238 151 144 68 134 62 59 64 − 104 (44%) − 89 (59%) − 86 (59%) − 4 (6%)
PM2.5 238 132 135 56 122 36 36 26 − 116 (49%) − 96 (73%) − 99 (73%) − 30 (54%)
PM10 150 116 122 60 100 61 45 49 − 50 (33%) − 54 (47%) − 77 (63%) − 10 (17%)
NO2 44 48 55 9 31 7 11 10 − 13 (29%) − 41 (86%) − 43 (79%) 1 (7%)
NH3 10 2 8 14 4 1 2 9 − 6 (63%) − 1 (58%) − 6 (74%) − 4 (30%)
SO2 19 12 11 14 14 5 9 9 − 4 (24%) − 7 (58%) − 2 (15%) − 6 (39%)
CO 53 28 33 25 84 13 22 35 31 (59%) − 15 (55%) − 11 (32%) 9 (37%)
O3 35 85 29 36 73 34 51 65 38 (109%) − 51 (60%) 22 (77%) 29 (80%)
PM2.5 in μg/m3, PM10 in μg/m3, CO in μg/m3, NH3 in μg/m3, NO2 in μg/m3, SO2 in μg/m3, and O3 in μg/m3
AOI air quality index