Examining Effects of the COVID-19 National Lockdown on Ambient Air Quality across Urban India

Abstract

Lockdown seems the most effective way to prevent the spread of Coronavirus disease (COVID-19) as no vaccine is currently available in the market to cure it. Thus, India has enforced nation-wide lockdown from 25 th March to lower the spread of this contagious virus and associated illness. This study aims to quantify the changes in pollution levels as well as meteorology during the 6-weeks COVID-19 lockdown over 17 cities of India for 5 major criteria pollutants using publicly available air quality data. Hourly averaged data is accessed from the air quality monitoring stations during the lockdown and immediate pre-lockdown periods and also corresponding data from the previous year (2019). During the lockdown, PM 2.5 , PM 10 , NO 2, and CO reduced significantly with relatively small changes in meteorological conditions compared to the prelockdown period. The highest decline is observed over Ahmedabad (68%), Delhi (71%), Bangalore (87%), and Nagpur (63%) for PM 2.5 , PM 10 , NO 2 , and CO, respectively. The Northern region shows the highest decline for all the pollutants with most days below NAAQS during lockdown-86%, 68%, and 100% compared to 18%, 0%, and 38% in 2019 for PM 2.5 , PM 10 , and NO 2 , respectively. The smaller cities Dewas and Jorapokhar show lesser improvement with only 3% and 16% improvement in days under NAAQS for PM 2.5 . SO 2 is the least affected pollutant with little improvement. The major decline is observed during 7-10 am and 7-10 pm hours of the day for PM 2.5 , PM 10 , NO 2 , and CO with more than 40% reduction. The meteorological changes are very small and heterogeneous over India showing a similar extent of changes compared to the previous year but the pollution levels have reduced significantly. Thus, the sharp decline in pollutant concentration during the ~6 weeks period national lockdown can be attributed to the reduced economic and transport activities.

COVID-19 lockdown induced changes in NO<sub>2</sub> levels across India observed by multi-satellite and surface observations

“…In the case of the present study, recent work (e.g. Singh et al, 2020;Navinya et al, 2020;Sharma et al, 2020) has shown that meteorological conditions remained relatively consistent over recent years during the dates of the lockdown period. Therefore, we assume that the changes observed during the lockdown were due to the change in the emissions.…”

“…Satellite observations of VCDtrop NO2 were obtained from OMI (2016-2020) and TROPOMI (2019)(2020). Surface NO2 observations (2016-2020) at 139 sites across India were from the Central Pollution Control Board (CPCB).…”

“…The satellite-based studies by Biswal et al (2020) and Pathakoti et al (2020) estimated the change in NO2 levels using OMI observations whereas Siddiqui et al (2020) utilised TROPOMI to compute the change over eight major urban centres of India. Biswal et al (2020) reported that average OMI NO2 over India decreased by 12.7 %, 13.7 %, 15.9 %, and 6.1 % during the subsequent weeks of the lockdown.…”

Effect of Lockdown due to COVID-19 on the Aerosol and Trace Gases Spatial Distribution over India and Adjoining Regions

“…The Air Quality Index (AQI) over several parts of the globe improved significantly since enforcing lockdowns. The decline in the levels of pollutants like PM2.5, PM10, SO2, CO, NO2, NO, and CO have been reported in many recent studies including Brazil (Nakada and Urban, 2020), Mainland China (Chen et al, 2020;Bauwens et al, 2020), Ecuador (Zalakeviciute et al, 2020), South Korea and western Europe (Bauwens et al, 2020), Iran (Broomandi et al, 2020), India (Navinya et al, 2020;Jain and Sharma 2020), Tehran (Faridi et al, 2020), Spain (Tobias et al, 2020, USA (Berman and Ebisu, 2020;Bauwens et al, 2020). Global CO2 also reduced by 17% when compared to 2019 levels (Le Quéré et al, 2020), though Safarian et al (2020) reported a 7% reduction only.…”

“…They also reported a reduction in NO2 concentrations by 52% during DLD. In another study byNavinya et al (2020) over 17 cities in India, reported a reduction in NO2 varying between 35 and 86%…”