Air pollution in the time of Covid-19
Valerio Ferracci
Cranfield University
v.ferracci@cranfield.ac.uk
ECG Bulletin July 2020
Cranfield University
v.ferracci@cranfield.ac.uk
ECG Bulletin July 2020
With strict lockdown policies enforced in many countries across the globe, the emissions of many atmospheric pollutants have decreased dramatically. What are the implications for urban and regional air quality, human health and the future of air pollution?
The ongoing Covid-19 pandemic, has had enormous and far-reaching repercussions across the globe in the first half of 2020. Nationwide lockdowns and social distancing have been enforced to prevent the spread of the virus and reduce the death rate. These measures have caused a rapid decline in economic activities, as well as road and air traffic, leading to dramatic changes in the emissions of atmospheric pollutants.
The ongoing Covid-19 pandemic, has had enormous and far-reaching repercussions across the globe in the first half of 2020. Nationwide lockdowns and social distancing have been enforced to prevent the spread of the virus and reduce the death rate. These measures have caused a rapid decline in economic activities, as well as road and air traffic, leading to dramatic changes in the emissions of atmospheric pollutants.
Analyses have focused on metrics commonly used for urban air quality monitoring, such as abundances of nitrogen oxides (NOx, consisting of two rapidly interconverting species: nitrogen monoxide, NO, and nitrogen dioxide, NO2) and particulate matter (typically with dynamic diameter < 2.5 μm, referred to as PM2.5), both emitted primarily by vehicle exhaust.
The first signs of changes in air quality came from China, the first country to be hit by the virus. Satellite measurements revealed significant decreases (~40-60%) in NO2 columns over urban and industrial regions in February and March 2020, relative to the same period in 2019 (1). This was confirmed by ground-level observations from the Chinese air quality monitoring network. In Wuhan, the first city where cases of Covid-19 were reported and to undergo strict lockdown, NO2 and PM2.5 concentrations were 54 and 31% lower respectively during lockdown than in the same time period in 2019 (2). However, ground level ozone, a secondary pollutant formed from the interaction of sunlight with NOx and volatile organic compounds, rose by a factor of 2. This is due to the titration of ozone by NO, and a drop in NOx will result in reduced ozone removal under the conditions found in most urban areas.
The first signs of changes in air quality came from China, the first country to be hit by the virus. Satellite measurements revealed significant decreases (~40-60%) in NO2 columns over urban and industrial regions in February and March 2020, relative to the same period in 2019 (1). This was confirmed by ground-level observations from the Chinese air quality monitoring network. In Wuhan, the first city where cases of Covid-19 were reported and to undergo strict lockdown, NO2 and PM2.5 concentrations were 54 and 31% lower respectively during lockdown than in the same time period in 2019 (2). However, ground level ozone, a secondary pollutant formed from the interaction of sunlight with NOx and volatile organic compounds, rose by a factor of 2. This is due to the titration of ozone by NO, and a drop in NOx will result in reduced ozone removal under the conditions found in most urban areas.
Similar trends were observed in other countries that enforced lockdowns, with reports of plummeting NO2 levels in the Po Valley (Italy) and Madrid (Spain) among many others (Figure 1). In the UK, data from the national monitoring network, analysed by the National Centre for Atmospheric Science, showed decreasing NO2 and PM2.5 levels in many cities relative to the 2015-19 average (3). In London, a recent report by King’s College London paints a more complex picture: while NO2 concentrations were falling across the whole city, PM2.5 and ozone concentrations appear to have increased (4). As in Wuhan, the change in ozone is primarily driven by the reduction in NOx (and also by the warm spring weather), while the rise in PM2.5 is attributed to the prevailing easterly winds during the lockdown, transporting air from continental Europe and affecting particulate levels in the capital.
The “new normal” enforced by lockdown measures also resulted in people spending more time in their homes. This produces a knock-on effect on personal exposure as pollutants such as PM2.5 are often more abundant indoors as a result of activities such as cooking, smoking and wood-burning (5). A number of recent studies (6-8) also highlighted the potential link between the Covid-19 fatality rate and poor air quality, as some of the worse-hit regions (e.g. Lombardy in Italy) are also chronically affected by air pollution. |
It is argued that the health conditions caused by exposure to poor air quality, such as cardiovascular disease, asthma and general chronic respiratory stress may contribute to an increase in the lethality of Covid-19. However compelling, there are also a plethora of other factors at play in densely populated areas severely affected by Covid-19 (e.g. income levels, access to services) that contribute to the incidence of the very same health conditions, and it might simply be too early to determine a clear effect of air pollution on the Covid-19 death rate (9).
With most economic activities brought to a near standstill during lockdown, the emissions of carbon dioxide (CO2) have also decreased. As increasing atmospheric concentrations of CO2 and other greenhouse gases due to anthropogenic emissions are driving the ongoing warming of the planet, trends in their emission rates are closely scrutinised (10). Flux measurements by the Centre for Ecology and Hydrology (CEH) in central London have shown that CO2 emissions in the capital during lockdown decreased ~60% relative to the 2015-19 average, matching the observed reduction in road traffic (11). These were accompanied by similar trends in other European cities such as Berlin, Basel and Florence (12). However the overall global CO2 emissions for the year 2020 are projected to be only 4-7% lower than those in 2019 (13). While this would be one of the largest drops in emissions on records, it also points out the difficult road ahead on the path to decarbonisation, and how systemic changes are needed to reach the milestones set by the Paris Agreement.
At the time of writing of this article, a number of countries are reporting a decline in infection and death rates. As a result, lockdown measures are being gradually relaxed and road traffic and industrial activities begin to bounce back. A number of different scenarios lie ahead, with a “business as usual” approach leading to a return of emissions to their pre-lockdown levels, or with more long-lasting changes in behaviour dictated by social distancing (e.g. more people working from home, less travel) leading to a lasting reduction in emissions from the transport sector. Whatever the outcome, the effects of the pandemic on anthropogenic emissions have offered an unprecedented glimpse into the air we might be breathing in the (near?) future as regulations become more stringent, and may also help draft more informed abatement policies in years to come.
References
1. Bauwens, M. et al., Impact of coronavirus outbreak on NO2 pollution assessed using TROPOMI and OMI observations. Geophysical Research Letters, (2020), https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2020GL087978
2. Shi, X. and Brasseur, G.P., The Response in Air Quality to the Reduction of Chinese Economic Activities during the Covid-19 Outbreak. Geophysical Research Letters, (2020) https://news.agu.org/files/2020/05/2020GL088070RR-Brasseur.pdf.
3. https://www.ncas.ac.uk/en/18-news/3057-air-pollution-falling-across-uk-cities-latest-data-shows (March 2020)
4. https://www.kcl.ac.uk/news/mixed-pollution-results-london-during-lockdown (May 2020)
5. Bramwell, L. and Ferracci, V., Meeting Report: Indoor air quality. ECG Bulletin January 2020. https://www.envchemgroup.com/indoor-air-quality-2019.html
6. Ogen, Y., Science of the Total Environment, 726, 138605, (2020).
7. Conticini, E. et al., Environmental Pollution, 261, 114465 (2020).
8. Travaglio, M. et al. (2020). Links between air pollution and Covid-19 in England, MedRXiv, (2020), https://doi.org/10.1101/2020.04.16.20067405
9. Lewis, A. (2020). What we do and don’t know about the links between air pollution and coronavirus, https://theconversation.com/what-we-do-and-dont-know-about-the-links-between-air-pollution-and-coronavirus-137746
10. Ferracci, V. (2018). Update on WMO Greenhouse Gas Bulletin No 13, ECG Bulletin July 2018.
11. https://www.envchemgroup.com/wmo-greenhouse-gas-bulletin-13.html
12. https://www.ceh.ac.uk/news-and-media/blogs/london-co2-emissions-fallen-60-percent-lockdown (May 2020)
13. Papale., D. et al. (2020), Clear evidence of reduction in urban CO2 emissions as a result of Covid-19 lockdown across Europe, https://data.icos-cp.eu/objects/w6pTmRGYKqAm3c-siQrg5kgd
14. Le Quéré, C. et al., Temporary reduction in daily global CO2 emissions during the Covid-19 forced confinement, Nature Climate Change (2020), https://doi.org/10.1038/s41558-020-0797-x
1. Bauwens, M. et al., Impact of coronavirus outbreak on NO2 pollution assessed using TROPOMI and OMI observations. Geophysical Research Letters, (2020), https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2020GL087978
2. Shi, X. and Brasseur, G.P., The Response in Air Quality to the Reduction of Chinese Economic Activities during the Covid-19 Outbreak. Geophysical Research Letters, (2020) https://news.agu.org/files/2020/05/2020GL088070RR-Brasseur.pdf.
3. https://www.ncas.ac.uk/en/18-news/3057-air-pollution-falling-across-uk-cities-latest-data-shows (March 2020)
4. https://www.kcl.ac.uk/news/mixed-pollution-results-london-during-lockdown (May 2020)
5. Bramwell, L. and Ferracci, V., Meeting Report: Indoor air quality. ECG Bulletin January 2020. https://www.envchemgroup.com/indoor-air-quality-2019.html
6. Ogen, Y., Science of the Total Environment, 726, 138605, (2020).
7. Conticini, E. et al., Environmental Pollution, 261, 114465 (2020).
8. Travaglio, M. et al. (2020). Links between air pollution and Covid-19 in England, MedRXiv, (2020), https://doi.org/10.1101/2020.04.16.20067405
9. Lewis, A. (2020). What we do and don’t know about the links between air pollution and coronavirus, https://theconversation.com/what-we-do-and-dont-know-about-the-links-between-air-pollution-and-coronavirus-137746
10. Ferracci, V. (2018). Update on WMO Greenhouse Gas Bulletin No 13, ECG Bulletin July 2018.
11. https://www.envchemgroup.com/wmo-greenhouse-gas-bulletin-13.html
12. https://www.ceh.ac.uk/news-and-media/blogs/london-co2-emissions-fallen-60-percent-lockdown (May 2020)
13. Papale., D. et al. (2020), Clear evidence of reduction in urban CO2 emissions as a result of Covid-19 lockdown across Europe, https://data.icos-cp.eu/objects/w6pTmRGYKqAm3c-siQrg5kgd
14. Le Quéré, C. et al., Temporary reduction in daily global CO2 emissions during the Covid-19 forced confinement, Nature Climate Change (2020), https://doi.org/10.1038/s41558-020-0797-x