Examining the status of improved air quality due to COVID-19 lockdown and an associated reduction in anthropogenic emissions
Authors: Sannigrahi Srikanta , Molter Anna , Kumar Prashant , Zhang Qi , Basu Bidroha , Basu Arunima Sarkar , Pilla Francesco 
Published: August 2020

Clean air is a fundamental necessity for human health and well-being. The COVID-19 lockdown worldwide resulted in controls on anthropogenic emission that have a significant synergistic effect on air quality ecosystem services (ESs). This study utilised both satellite and surface monitored measurements to estimate air pollution for 20 cities across the world. Sentinel-5 Precursor TROPOspheric Monitoring Instrument (TROPOMI) data were used for evaluating tropospheric air quality status during the lockdown period. Surface measurement data were retrieved from the Environmental Protection Agency (EPA, USA) for a more explicit assessment of air quality ESs. Google Earth Engine TROPOMI application was utilised for a time series assessment of air pollution during the lockdown (1 Feb to 11 May 2020) compared with the lockdown equivalent periods (1 Feb to 11 May 2019). The economic valuation for air pollution reduction services was measured using two approaches: (1) median externality value coefficient approach; and (2) public health burden approach. Human mobility data from Apple (for city-scale) and Google (for country scale) was used for examining the connection between human interferences on air quality ESs. Using satellite data, the spatial and temporal concentration of four major pollutants such as nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO) and the aerosol index (AI) were measured. For NO2, the highest reduction was found in Paris (46%), followed by Detroit (40%), Milan (37%), Turin (37%), Frankfurt (36%), Philadelphia (34%), London (34%), and Madrid (34%), respectively. At the same time, a comparably lower reduction of NO2is observed in Los Angeles (11%), Sao Paulo (17%), Antwerp (24%), Tehran (25%), and Rotterdam (27%), during the lockdown period. Using the adjusted value coefficients, the economic value of the air quality ESs was calculated for different pollutants. Using the public health burden valuation method, the highest economic benefits due to the reduced anthropogenic emission (for NO2) was estimated in US$ for New York (501M $), followed by London (375M $), Chicago (137M $), Paris (124M $), Madrid (90M $), Philadelphia (89M $), Milan (78M $), Cologne (67M $), Los Angeles (67M $), Frankfurt (52M $), Turin (45M $), Detroit (43M $), Barcelona (41M $), Sao Paulo (40M $), Tehran (37M $), Denver (30M $), Antwerp (16M $), Utrecht (14 million $), Brussels (9 million $), Rotterdam (9 million $), respectively. In this study, the public health burden and median externality valuation approaches were adopted for the economic valuation and subsequent interpretation. This one dimension and linear valuation may not be able to track the overall economic impact of air pollution on human welfare. Therefore, research that broadens the scope of valuation in environmental capitals needs to be initiated for exploring the importance of proper monetary valuation in natural capital accounting.