Air Pollution and COVID-19 Mortality
Author: Mikayla Briare
A glimpse at the emerging research from across the globe linking certain criteria air pollutant exposures to COVID-19 mortality
Air Pollution: The Basics
Air pollution is detrimental to both human and environmental health. Ambient (outdoor) air pollution was estimated to cause 4.2 million premature deaths worldwide in 2016 according to the World Health Organization.¹² Most air pollution is a direct result of human activity and industry, with primary sources of air pollution being: factories, power plants, vehicle emissions, incinerators, construction activity, and the agricultural industry.⁷
The Environmental Protection agency has set National Ambient Air Quality Standards for six air pollutants (called the “criteria air pollutants”), which have considerable health effects [See Figure 1]. These pollutants include: ground-level Ozone, particulate matter (PM), Carbon monoxide (CO), Lead, Sulfur Dioxide (SO₂), and Nitrogen Dioxide (NO₂).
Air pollutants affect both the cardiovascular and respiratory systems, causing symptoms such as: lung inflammation, bronchoconstriction, and reduced lung function.⁴ ⁷ ¹³ Pollutants can also increase susceptibility to infection and enhance the risk of developing lung diseases (such as asthma and COPD).⁷ ¹³ According to the WHO, 58% of premature deaths related to air pollutant exposure in 2016 were due to ischaemic heart disease and stroke, 18% to COPD (Chronic Obstructive Pulmonary Disease), and 6% to lung cancer.¹³
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The burden of air pollution mortality is not distributed equally across the globe, with populations in low and middle-income countries experiencing a disproportionate amount of premature air pollutant related deaths (about 91%).¹³
Figure 1. Criteria Air Pollutants
Figure 1. Criteria Air Pollutants: Sources and Health Effects.
Source: Botin & Keller (2007). Air Pollution. Weebly. http://noair-rors.weebly.com/air-pollution.html
Air pollutants are distributed disproportionately across the globe
Air pollutant concentrations are dependent on weather patterns and emissions (from industry, transportation, energy production, etc.). You can explore the burden of air pollution across different areas of the globe at earth.nullschool.net. Click the image below to open the page.
To navigate earth.nullschool.net: -Click Earth in bottom left corner of page.-In MODE section select either: Chem or Particulates. -Have ANIMATE in Wind (depicts wind patterns). -In Chem mode, explore concentrations of pollutants like: SO2, CO2, CO, NO2. In Particulates mode, explore concentration of different sizes of particulate matter. -Click on a location on the globe to obtain calculated concentration of the selected pollutant in that area.
The Link Between Air Pollution and COVID-19 Mortality
COVID-19
COVID-19 is a viral infection that can cause inflammation in the lungs, leading to pneumonia or acute respiratory distress syndrome (ARDS) in severe cases.⁶ Underlying health conditions, such as: COPD, Type II diabetes, heart failure, and coronary artery disease, put one at an increased risk for experiencing severe illness from COVID-19 infection.¹ Emerging data also demonstrates that conditions like asthma or hypertension may increase one’s risk of severe illness if infected with COVID-19.¹
Air pollution as a risk-factor for severe COVID-19 infection?
Research across the globe has emerged linking certain criteria air pollutant exposures (PM₂.₅ and NO₂) to COVID-19 mortality. As noted in “Air Pollution: The Basics” exposure to air pollutants can cause lung inflammation and reduced lung function, which enhance the risk of developing chronic cardiovascular and respiratory diseases.⁷ ¹³ Thus, both acute, and historic, exposure to air pollutants may exacerbate COVID-19 symptoms and increase mortality risk.² ⁹ ¹⁰ ¹¹
The United States
In the United States, Wu et al. (2020) performed a national cross-sectional study comparing average PM₂.₅ exposure between the years 2000-2016 to COVID-19 mortality rates across 3,087 counties (accounting for 98% of the population).¹¹ After adjusting for numerous factors (SES, demographics, weather patterns, quarantine isolation measures, etc.), Wu et. al found that an increase of just 1 ug/m³ in long-term PM₂.₅ exposure was associated with a statistically significant 8% increase in COVID-19 death rate.¹¹ The graphic from Wu et. al’s study [Figure 2] captures the association between average PM₂.₅ concentrations across the United States and COVID-19 deaths per 1 million.
Another study conducted by Liang et al. (2020) found a significant positive association between NO₂ pollutant levels and county-level COVID-19 mortality rates across the United States. This study identified that a one IQR (about 4.6ppb) increase in NO₂ concentration was associated with an 11.3% increase in COVID-19 case-fatality when controlling for numerous covariates.⁹ These results imply that a one IQR reduction in long-term exposure to NO₂ would have avoided 14,672 deaths among those who tested positive for COVID-19.⁹
Studies conducted across the globe have garnered similar findings linking air pollutant exposures to COVID-19 morality.
The Netherlands
COVID-19 cases per 100,000 people and annual concentrations of PM 2.5, NO2 and SO2 averaged over the period 2015-2019.
In the Netherlands, a study that examined the relationship between COVID-19 mortality and PM₂.₅, NO₂, and SO₂ concentrations across 355 Dutch municipalities found that municipalities with 1 ug/m³ more PM₂.₅ concentrations had between 9.4-15.1 times more COVID-19 cases, 2.9-4.4 more COVID-19 related hospital admissions, and between 2.2-2.8 more COVID-19 related deaths.² A one unit increase in NO₂ exposure resulted in a smaller, though still statistically significant, increase in COVID-19 cases (2.2 times more) and COVID-19 related deaths (0.35 times more).² Interestingly, this study found no significant impact of SO₂ on COVID-19 outcomes.²
Italy
At the impetus of the COVID-19 pandemic, Italy experienced a severe COVID-19 outbreak. However, the outbreak disproportionately affected certain regions of Italy. In Northern Italy (Lombardy and Romagna regions), COVID-19 lethality was 12% compared to 4.5% lethality for Italy as a whole.³ In their study, Can atmospheric pollution be considered a co-factor in extremely high level of SARS-CoV-2 lethality in Northern Italy?, Conticini et al. (2020) hypothesize that both the higher prevalence, and more considerable lethality, of COVID-19 in Northern Italy may be mediated by chronic exposure to air pollution-- as Northern Italy is one of the most polluted regions in Italy.³ As can be seen in the maps below, during the years 2005 and 2010 hourly mean concentrations of PM₂.₅, NO₂, and SO₂ were substantially higher in Northern Italy compared to other Italian regions.
Distribution of COVID-19 confirmed cases by province (rates by 100,000 resident population, data up to May 4th).
Source: Michelozzi, P., de'Donato, F., Scortichini, M., Pezzotti, P., Stafoggia, M., Costa, G., Fiammetta, N., Riccardo, F., Bella, A., Demaria, M., Rossi, P., Brusaferro, S., Rezza, G., & Davoli, M. (2020). Temporal dynamics in total excess mortality and COVID-19 related deaths in Italian cities. BMC Public Health, 20. https://doi.org/10.1186/s12889-020-09335-8
SO2, NO2, O3, and PM2.5 annual mean of hourly concentrations in 2005 and 2010 in Italy
Source: De Marco, A., Proietti, C., Anav, A., Ciancarella, L., Fares, S., Fornasier, M., Fusaro, L., Gualtieri, M., Manes, F., Marchetto, A., Mircea, M., Paoletti, E., Piersanti, A., Rogora, M., Salvati, L., Salvatori, E., Screpanti, A., & Leonardi, C. (2019). Impacts of air pollution on human and ecosystem health, and implications for the National Emission Ceilings Directive: Insights from Italy. Environmental International, 125, 320-333. https://doi.org/10.1016/j.envint.2019.01.064
Global Cases
Expanding to a global air pollution scope, it has been estimated that, worldwide, anthropogenic (human caused) air pollution contributes 15% to COVID-19 mortality.¹⁰ The estimated COVID-19 mortality burden differs regionally, however, with East Asia experiencing about 35% of COVID-19 mortality attributed to anthropogenic emissions, Central Europe about 25%, and the Eastern USA about 25% [Figure 3].¹⁰ Comparatively, in regions with relatively low levels of air pollution, like Oceania (including Australia), it’s estimated that air pollution contributes only 3% to COVID-19 mortality.¹⁰
Figure 3. Estimated percentages of COVID-19 mortality attributed to air pollution from all anthropogenic sources (top), and from fossil fuel use only (bottom). The regions with high attributable fractions coincide with high levels of air pollution
How Do We Move Forward?
Though conclusions cannot be made about individual COVID-19 infection risk with population-level (ecological regression) analyses, clearly, as the studies reviewed demonstrate, certain air pollutant (PM₂.₅ and NO₂) exposures likely enhance the risk for severe COVID-19 infection and thus increase COVID-19 mortality.² ³ ⁹ ¹⁰ ¹¹ This research also illuminates that the burden of COVID-19 may be experienced disproportionately across certain geographic regions due to higher air pollutant concentrations in these areas.² ³ ⁹ ¹⁰ ¹¹ Though the US's Environmental Protection Agency (EPA) and other environmental regulatory bodies across the globe have set air-quality standards for criteria air pollutants, movement towards green energy sources and more stringent emission regulations are needed to further reduce air pollution and mitigate the associated COVID-19 mortality risk.
“A lesson from our environmental perspective of the COVID-19 pandemic is that the quest for effective policies to reduce anthropogenic emissions, which cause both air pollution and climate change, needs to be accelerated”.¹⁰
As Pozzer et. al (2020) found in their global study linking air pollution to COVID-19 mortality, regions/countries with more stringent air quality regulations, like Australia, experienced less attributable COVID-19 mortality risk from air pollutants.¹⁰ For instance, Australia reduced the maximum allowed concentration for criteria air pollutants in 2016.⁸ In Australia, only 8 ug/m³ yearly PM₂.₅ exposure is allowed, comparatively 12.0 ug/m³ of exposure is allowed in the United States.⁵ ⁸ And as research demonstrates, just a 1 ug/m³ increase in PM₂.₅ exposure can significantly enhance COVID-19 mortality risk. ² ¹¹ Clearly systemic policy change is needed to regulate harmful emissions and reduce air pollution. As Wu et al. illuminate, “Research on how modifiable factors may exacerbate COVID-19 symptoms and increase mortality risk is essential to guide policies and behaviors to minimize fatality related to the pandemic. Such research could also provide a strong scientific argument for revision of the U.S. Ambient Air Quality Standards for PM₂.₅ and other environmental policies in the midst of a pandemic”.¹¹
A Silver Lining?
Though the COVID-19 pandemic has caused substantial loss of human life and disrupted day-to-day functioning/how we interact with one another, policies enacted to help mitigate COVID-19 spread appear to be contributing to improvements in air quality. In countries like China, stringent lockdown and self-quarantine measures reduced the mobility of people and led to a decrease in transportation.¹² The resulting reduction in emissions associated with transportation (one study found PM₂.₅ decreased by 18.9 ug/m³, and NO₂ decreased by 12.9 ug/m³, across China during quarantine)¹² is a testament to the impact that anthropogenic sources have on air quality. It’s estimated that the improvement in air quality during the quarantine/lock-down period avoided a total of 8,911 NO₂ related deaths and 3,124 PM₂.₅ related deaths in China.¹²
Visit Air Policy and Global Air pages for further exploration of the short-term, and potential long-term, impacts of COVID-19 policies on air quality.
It took a global pandemic to alter the way humans travel, work, and socialize-- which has made a notable impact on the environment. As we look forward to returning to “normal life" after the pandemic, we must question if going back to business as usual is best for human and environmental health. Clearly air quality has improved due to policies implemented to reduce COVID-19 spread.¹² Though adjustment to life during a pandemic has been challenging, a continued alteration of our work/travel/socialization habits, coupled with policies to decrease emissions and improve air quality standards, are steps toward improving both environmental and human health and slowing the detrimental impacts of climate change.
A Summary Video
Summary Video Transcript
References
CDC. (2020, Nov. 2) People with Certain Medical Conditions. Coronavirus Disease 2019.https://www.cdc.gov/coronavirus/2019-ncov/need-extra-precautions/people-with-medical-conditions.html
Cole, M., Ozgen, C., & Strobl, E. (2020). Air Pollution Exposure and COVID-19 in Dutch Municipalities. Environmental and Resource Economics, 76, 581-610. https://doi.org/10.1007/s10640-020-00491-4
Conticini, E., Frediani, B., & Caro, D. (2020). Can atmospheric pollution be considered a co-factor in extremely high level of SARS-CoV-2 lethality in Northern Italy? Environ Pollut, 261. 10.1016/j.envpol.2020.114465
EPA. (n.d.) Health and Environmental Effects of Particulate Matter (PM). Particulate Matter Pollution. https://www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm
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Liang, D., Shi, L., Zhao, J., Liu, P., Sarnat, J., Gao, S., Schwartz, J., Liu, Y., Ebelt, S., Scovronick, N., & Chang, H. (2020). Urban Air Pollution May Enhance COVID-19 Case-Fatality and Mortality Rates in the United States. The Innovation, 1(3). https://doi.org/10.1016/j.xinn.2020.100047
Pozzer, A., Dominici, F., Haines, A., Witt, C., Munzel, T., & Lelieveld, J. (2020). Regional and global contributions of air pollution to risk of death from COVID-19. Cardiovascular Research, 288. https://doi.org/10.1093/cvr/cvaa288
Wu, X., Nethery, R., Sabath, M., Braun, D., & Dominci, F. (2020). Air pollution and COVID-19 mortality in the United States: Strengths and limitations of an ecological regression analysis. Science Advances, 6(45). doi: 10.1126/sciadv.abd4049
Wang, M., Chen, K., Huang, C., Kinney, P., & Anastas, P. (2020). Air pollution reduction and mortality benefit during the COVID-19 outbreak in China. The Lancet, 4. https://doi.org/10.1016/ S2542-5196(20)30107-8
WHO. (2018, May 2). Ambient (outdoor) air pollution. https://www.who.int/en/news-room/fact-sheets/detail/ambient-(outdoor)-air-q