Air quality index and criteria pollutants in ambient atmosphere over selected sites:Impact and lessons to learn from COVID-19

World Health Organization (WHO) declared the disease COVID-19, caused by novel virus SARS-CoV-2, as pandemic in March 2020 following which different countries adopted immediate stringent measures to save human lives. In order to restrict the spread of disease, intra- and interstate movements of public by road/rail and air were completely halted except for those involved in essential services. India followed the option of complete lockdown (LD) in phase 1 (25th March to 14th April 2020) followed by phase 2 (15th April to 3rd May), phase 3 (4th May to 17th May), and phase 4 (18th May to 31st May 2020). Restrictions on agriculture and industrial sector were eased out in each successive phase after LD 1 and eventually country started unlock phase from 1st June to 30th June and so on. In this chapter, a discussion is made based on the data on criteria pollutants and air quality index (AQI) for selected sites in New Delhi and for selected cities across the country, respectively to spell out impacts of COVID-19 (which are initially positive) and the lessons for long-term planning for improvement of air quality. During LD 1, emissions from vehicles, industries, and construction activities were substantially down and therefore, levels of criteria pollutants CO, NOx, SO(2), Pb, O(3), PM(2.5) in ambient atmosphere came down and AQI showed improvement which was considered as silver line of the COVID-19 pandemic. Interestingly, not all criteria pollutants showed decrease to same extent and rather some still stayed above the National Ambient Air Quality Standard (NAAQS) values over New Delhi, the national capital of India. As the restrictions eased out in LD 3 and LD 4, pollution levels started increasing but again not uniformly for all pollutants and for all locations in New Delhi. During Unlock 1.0, emissions did not increase suddenly rather in a systematic linear fashion. In addition, air quality and AQI did not deteriorate much during Unlock 1.0 due to onset of monsoon rains in the country. It is suggested that all emission sources and people’s movement cannot be restricted during normal days in any country, as it has hit the socioeconomic health of nation very hard. A close examination of pollution levels and emission sources during lockdown to unlock could help us in devising a long-term strategy to bring down air pollution particularly in worst hit regions such as New Delhi. Systematic restrictions on major pollution sources with intermittent relaxations could be a possible approach to constrain air pollution.