Table 1.
Summary of the recent studies conducted in India.
| Authors | Pollutants | Study period | Study areas | Major findings |
|---|---|---|---|---|
| Sharma et al. (2020) | PM10, PM2.5, CO, NO2, O3 and SO2 | 16 March-14 April (2017–2020) | 22 Indian cities | During the lockdown period, concentrations were reduced up to 43% in PM2.5, 31% in PM10, 10% in CO, and 18% NO2 when compared with the previous years' concentrations (2017–2019). |
| Kumar et al. (2020) | PM2.5 | January 2015–May 2020 | Delhi, Kolkata, Chennai, Mumbai, Hyderabad | Reduction in PM2.5 concentrations during the lockdown period ranged from 41% to 53% in Delhi, 24%–36% in Kolkata, 19%–43% in Chennai, 10%–39% in Mumbai and 26%–54% in Hyderabad. |
| Singh et al. (2020) | PM2.5, NO2 and AQI | March 2019 and March 2020 | Delhi, Mumbai, Hyderabad, Kolkata, and Chennai | During March 2020, the highest percentage reductions in PM2.5 were observed in Kolkata (34.52%) followed by Delhi (27.57%) and the lowest in Hyderabad (3.99%). |
| Jain and Sharma (2020) | PM10, PM2.5, NO2, O3 and CO | March–April (2019 and 2020); 10–20 March 2020 (before lockdown); and 25 March-6 April 2020 (during lockdown) | Delhi, Mumbai, Chennai, Kolkata and Bangalore | The highest reduction was reported in PM10 (52%), followed by NO2 (51%), PM2.5 (41%) and CO (28%) during the lockdown in Delhi. |
| Mahato et al. (2020) | PM10, PM2.5, SO2, NO2, CO, O3 and NH3 | 2–21 March 2020 (before lockdown); and 25 March-14April 2020 (during the lockdown | Delhi | The highest decline in concentrations were observed in PM10 (60%),NO2 (53%), PM2.5 (39%), and CO levels (30%) compared to the previous year. |
| Srivastava et al. (2020) | PM2.5, NO2, SO2 and CO | 25th March to April 14, 2020 (21-day lockdown period) | Lucknow and Delhi | NO2 and CO concentrations were reduced in Lucknow; and PM2.5, NO2 and CO concentrations were reduced in Delhi during the 21 days lockdown. |
| Mitra et al. (2020) | CO2 | April 2019 and April 2020 | Kolkata | CO2 level decreased up to 30–40% with temporal variation with p < 0.01 during April 2020. |
| Ranjan et al. (2020) | Aerosol optical depth | 25 March – 15 May (2000–2019); and 25 March – 15 May (2020) | Delhi, Kolkata, Bengaluru, and Mumbai | AOD level reduced up to 37% in these cities during the lockdown period compared to mean AOD level during 2000–2019. |