What did the lockdowns tell us about air pollution source contributions?

Harish C. Phuleria and Navinya Chimurkar

This commentary is part of a CCAPC series on Communicating air pollution-linked risks in India in light of COVID-19. CCAPC/2020/04 | September 2020 | Edited by Santosh Harish | Posted: September 1, 2020 | Updated: September 3, 2020

Claiming more than 800 thousand lives so far along with more than 25 million people infected across the world, COVID-19 has taken the centerstage of a majority of the research community. This has taken considerable toll in India as well with >65,000 deaths and over 36 lakh people infected (as of 31/08/2020). As there is no known cure of the disease yet, the pandemic has forced most countries to declare lockdown as a preventive measure to avoid the spread of the virus and to develop the necessary healthcare infrastructure. India observed a national lockdown for 11 weeks (25 March - 7 June, 2020) during which all activities other than essential services were completely shut down. Considering the consequence of reduced or stopped activities, the lockdown – a COVID-19 induced natural experiment - was expected to change the air quality over India.

In a recent study [1], we examined 17 cities across the country for the changes in five major air pollutants and three meteorological parameters during (25 Mar- 3 May) and before (1 Feb -24 Mar) the national lockdown. We found that all the pollutants except SO2 showed a significant decline (more than half) across all the cities with little change in meteorological parameters. The major decline was observed in the commuting hours, especially for the PM2.5, PM10 and NO2. Moreover, the largest decline in air pollution levels was observed in metropolitan cities (up to 70%). As these pollutants are primarily emitted by the vehicular road transport in urban areas, the restricted movement of non-essential vehicles during national lockdown may be responsible for such a decline.

Residential cooking and heating, vehicular traffic, industries, and open waste burning are a few of the  major anthropogenic sources of urban air pollution across India. Long-range dust transport in north India, and marine aerosols in the coastal regions can also contribute significantly. According to the power supply report, India, the power supplied to the regions with respect to the requirement remained the same during and before the lockdown as it was part the essential daily needs, however an overall reduction in the power requirement was observed which may be attributed to the shutdown of public transport, commercial and recreational areas such as shopping malls and work places [2]. However, the atmospheric SO2 levels (which power plants contribute the most), did not show consistent decrease across cities during the lockdown, with significant reduction in cities near coal-fired power plants and in industrial hubs while no appreciable decrease in urban centers farther away from power plants. Residential emissions did not decrease during the lockdown, and in fact may have increased (15% increase observed in mobility around residences [3]) due to people spending most time at homes. Field burning events remained constant and slightly increased over central India which shows unchanged emission from agricultural crop residue burning [4]. Additionally, long-range dust transport and marine aerosols also remain unaffected during the lockdown due to their dependency on meteorology and non-anthropogenic sources.

In an additional analysis, these 17 cities were classified into three groups according to the population Class I (>5M), Class II (3M-5M), and Class 3 (<3M). For the three population classes, average decline in NO2 levels during the lockdown was highest for class I (70%) followed by Class II (55%) and the least for class III (12%). The decline in the pollutant levels seems to be directly dependent on the vehicular activity. Google community mobility report for India also shows that the traffic dropped to about half during the lockdown compared to earlier period [3]. Mobility reduction was specifically observed for recreational activities (-56%), visit to public places (-48%), use of public transport (-39%), and workplace commute (-35%) [3]. Out of the three categories, the states with the least mobility showed higher reduction in the atmospheric NO2. Thus, the lockdown induced natural experiment (say minimizing vehicular emissions) enables us to investigate its effect on urban air quality. While the reduction in urban air pollution levels during COVID-19 lockdown can be largely attributed to vehicular emissions reduction, reduction in emissions from local-scale commercial activities, eateries, hotels, open street burning depending on the share of these activities in various cities (as observed in Google mobility report [3]) had also affected the air quality.

As the lockdown eases towards normalcy and the pandemic itself comes under control, the governments, corporations, and industries will scale up their operations to make up for the economic losses leading to a rebound in air pollution levels largely due to sectors like road transportation, industries and open waste burning. The road transportation sector is reviving slowly but over the next period there may be a high pressure on this sector resulting in likely higher exhaust and non-exhaust emissions, e.g. due to overloaded vehicles, more vehicle kilometers traveled etc. Similarly, most non-essential goods industries are operating with a minimal work force and this would drastically change as the demand grows. Revival of this sector is closely related to higher activity in the transportation sector as well. During the lockdown and to a certain extent post-lockdown, eateries using biomass fuels, open street waste burning for campfires etc. were quite eliminated. However, as the situation normalizes and the fear of contraction and transmission of coronavirus reduces, these activities will revive leading to rebound of emissions.

Hence, India needs to accelerate and sustain mitigation efforts: by promoting and investing in public transport infrastructure, more effective vehicle inspection programmes, promotion of electric vehicles, making work hours more flexible and promoting ‘work from home’ few days/ week, and stricter implementation of solid waste management regulations. Lastly, a large number of cities (and almost all rural areas) still do not have any air pollution monitoring. This needs to be established as the benefits of such natural experiments can only be exploited if data is available. Community-scale monitoring with low-cost sensors may be a way towards that.

Harish Phuleria is affiliated with Environmental Science and Engineering Department, IIT Bombay, and the Interdisciplinary Programme in Climate Studies, IIT Bombay. Navinya Chimurkar is affiliated with the Interdisciplinary Programme in Climate Studies, IIT Bombay.

For the rest of this series, click here.

References

1. Navinya, C., Patidar, G. and Phuleria, H. C. (2020). Examining Effects of the COVID-19 National Lockdown on Ambient Air Quality across Urban India. Aerosol Air Qual. Res. https://doi.org/10.4209/aaqr.2020.05.0256

2. Central Electricity Authority (CEA), Ministry of Power, Government of India, Power supply position - energy report, http://cea.nic.in/monthlyarchive.html

3. Google Community mobility report, 2020: https://www.google.com/covid19/mobility/ (last accessed on 22/Jul/2022)

4. Pandey, S. K., & Vinoj, V. (2020, July 6). Surprising increase in aerosol amid widespread decline in pollution over India during the COVID19 Lockdown. https://doi.org/10.31223/osf.io/5kmx2