key: cord-297372-616042sz authors: Singh, Vikas; Singh, Shweta; Biswal, Akash; Kesarkar, Amit P.; Mor, Suman; Ravindra, Khaiwal title: Diurnal and temporal changes in air pollution during COVID-19 strict lockdown over different regions of India date: 2020-08-13 journal: Environmental Pollution DOI: 10.1016/j.envpol.2020.115368 sha: doc_id: 297372 cord_uid: 616042sz Abstract 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 (PM2.5 and PM10) and gaseous pollutants (NO2, O3, CO, and SO2) during lockdown (25th March – 3rd MHA, 2020) across regions of India using the observations from 134 real-time monitoring sites of Central Pollution Control Board (CPCB). Significant reduction in PM2.5, PM10, NO2, and CO has been found in all the regions during the lockdown. SO2 showed mixed behavior, with a slight increase at some sites but a comparatively significant decrease at other locations. O3 also showed a mixed variation with a mild increase in IGP and a decrease in the South. The absolute decrease in PM2.5, PM10, and NO2 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 O3 has been found over Indo Gangetic plain (IGP) and central India, whereas night-time O3 has increased over IGP due to less O3 loss. The most significant reduction (∼40-60%) was found in PM2.5 and PM10. 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 NO2 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 PM2.5, PM10, NO2, and enhancement in O3 was proportional to the population density. Delhi’s air quality has improved with a significant reduction in primary pollutants, however, an increase in O3 was observed. The changes reported during the lockdown are combined effect of changes in the emissions, meteorology, and atmospheric chemistry that requires detailed investigations. in the meteorology. Although Navinya et al. (2020) have used the data for six weeks and 129 however their study was limited to 17 sites. They reported the changes in diurnal variation Supplementary Table S5 . The changes in pollutants level during the COVID-19 lockdown across India can partially or The overall decrease in the concentration of the six criteria air pollutants is shown in Figure 6 Table 1 . day-time. Night-time enhancement in O 3 of ~20-30% or even higher in the IGP and north-662 west regions due to the reduction in the removal of O 3 at night (Brown et al., 2006) . 663 Moreover, heterogeneous chemistry near the surface involving aerosols can also be 664 responsible for the direct loss of O 3 (Jacob, 2000) . O 3 was found to have mixed variation but 665 a considerable decrease in the South region. The PDF analysis also suggests a reduction in PM 2.5 , PM 10 , NO 2 and CO concentrations, The amount of reduction observed for PM 2.5 , PM 10 , NO 2 was found to reduce with respect to 671 population suggesting a larger decline in populated areas. However, the change in O 3 is found 672 to increase with the population. Air quality in the megacity Delhi improved significantly during the lockdown. The levels of 674 NO 2 , PM 10, and PM 2.5 reduce significantly (~40-60%), whereas a moderate decrease was 675 observed for CO and SO 2 . The O 3 in Delhi follows a site-specific trend but shows a mean 676 increase of ~20% due to increased photolysis production because of the reduction in 677 particulate matter over Delhi. To mitigate air pollution in India, it was planned to implement source and sector-specific Akash Biswal: Visualization, Investigation, writing, reviewing and editing 723 Amit Kesarkar: Discussion, reviewing and editing Ravindra Khaiwal: Investigation, discussion, reviewing Suman Mor: Discussion, reviewing and editing Air quality status during 2020 Malaysia Movement Control Order 730 (MCO) due to Does lockdown reduce air pollution? 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