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COVID-19 and air pollution

Studies of the unfolding COVID-19 pandemic have drawn a direct link between air pollution and COVID-19 deaths. Learn more about this relationship.

Research increasingly shows just how much more infectious and dangerous coronaviruses are to those impacted by air pollution.

This type of research goes back many years. 

In 2003, scientists found that people exposed to high air pollution levels were twice as likely to die from SARS, which is 80% similar to the COVID-19 coronavirus, as those with less exposure. People in polluted areas had an 8.9% mortality rate versus 4.08% for those living in less polluted areas.1

The mortality rate of people infected with the SARS coronavirus living in heavily polluted areas was 8.9%, while those infected living in less polluted areas only faced a mortality rate of 4.08%.

COVID-19 and air pollution

Researchers have since dug deeper into why air pollution may increase the risk of death from COVID-19 and other coronavirus infections. A groundbreaking 2020 study looked at three cell receptors in the lungs that the virus uses as entryways into your lungs: the enzyme ACE2 and the proteins DC-SIGN and L-SIGN.2

These receptors keep your basic bodily functions working normally by turning amino acids and sugars into fuel for important processes: ACE2 helps regulate blood pressure, while DC-SIGN and L-SIGN support immune system responses to disease.

Looking at how the lungs of smokers responded to COVID-19 infections, researchers found that ACE2 receptors in smokers’ lungs were more vulnerable to COVID-19 infections than non-smokers.

ACE2 receptors in smokers’ lungs were more vulnerable to COVID-19 infections than non-smokers.

Scientists have also discovered that lung damage in smokers is very similar to lung damage in people who have been exposed to air pollution for long periods of time. 

A 2019 study in the Journal of the American Medical Association found that regular exposure to pollutants like ozone was like smoking a pack of cigarettes a day in terms of how ozone damages the lungs.3

Even areas with relatively low levels of long-term air pollution can be susceptible to higher risks of severe or deadly COVID-19 symptoms from poor air quality. 

A team of researchers from the Harvard T.H. Chan School of Public Health wanted to find out just how deep the relationship between air pollution and the coronavirus goes.4

So they looked at COVID-19 deaths and average PM2.5 pollution in over 3,000 U.S. counties that represented 98% of the U.S. population, finding that every increase of 1 microgram per cubic meter (𝜇g/m3) of PM2.5 increased the risk of severe or deadly COVID-19 symptoms by 8%.

A PM2.5 increase of 1 microgram per cubic meter (𝜇g/m3) increased the risk of severe or deadly COVID-19 symptoms by 8%.

That may not sound like much – but let’s put this number into perspective. 

According to the World Health Organisation (WHO), the highest annual average “safe” concentration that air pollution should reach (including PM2.5) is 10 𝜇g/m3.5

So even if local air pollution levels go from, say, 1 𝜇g/m3 in the morning to 10 𝜇g/m3 after morning and evening rush hour (still below the WHO “acceptable” threshold), your chances of a severe or deadly COVID-19 infection go by up to 70%.

COVID-19 and PM2.5

Let’s look even closer at how the coronavirus interacts with PM2.5 since this particular pollutant is so dangerous.

A group of researchers in China looked at nearly 25,000 COVID-19 cases across 72 cities in China and found a statistically significant link between increases of 10 𝜇g/m3 for PM2.5, even for a single day, and the number of COVID-19 cases reported for the next two weeks.6

Researchers in China found a significant link between single-day PM2.5 increases and the number of COVID-19 cases reported for the next two weeks.

This study suggests that even temporary spikes in air pollution can increase the mortality rate for as long as two weeks after the spike.

Another study released by the World Bank in collaboration with Vrije Universiteit supported the notion that there’s a dangerous link between PM2.5 and COVID-19.7

Examining COVID-19 cases from over 355 cities in the Netherlands, the study noted that for every 20% rise in air pollution, COVID-19 cases could be expected to rise by nearly 100%.

A Dutch study concludes that for every 20% increase in PM2.5, COVID-19 cases can rise by nearly 100%.

According to the study, this huge increase was found even when not considering the previous health or the demographics (i.e., race, income) of those infected with the COVID-19 virus.

This means that the relationship between PM2.5 and COVID-19 could be even more drastic than the study found when taking pre-existing conditions and other risk factors into account.

In another study, Italian and Danish researchers also looked at the disproportionate impact of COVID-19 among various cities in Italy, showing the effect that air pollution had on COVID-19 outcomes.8

To do so, the researchers compared air pollution and COVID-19 cases from cities throughout Italy using public data from Italian Civil Protection, Italy’s national emergency services.

Their analysis suggests that the COVID-19 death rate in Lombardy and Emilia Romagna, in northern Italy, was about 12%, compared to an average of 4% elsewhere in Italy.  

Three times as many people died from COVID-19 in northern Italy, where air pollution levels are some of the highest in Europe, than in the rest of Italy.

This means that three times as many people died from COVID-19 in parts of northern Italy, where air pollution levels are some of the highest in Europe, than in the rest of Italy.9

All these COVID-19 studies build on the clear link that a long list of past research has drawn between particle pollution and respiratory conditions that lead to worse outcomes from viral infections.

A 2013 study from University of Montana found that exposure to PM2.5 from wildfire smoke can make it harder for your body to fight viral infections for up to a week after exposure.10

Exposure to PM2.5 from wildfire smoke can make it harder for your immune system to fight viral infections for up to a week.

This is because PM2.5 can stop immune cells called macrophages from being activated – cells that are on the front lines of infection control in your body. 

A 2014 study in BMC Pulmonary Medicine found that simply having pollutant particles in the lungs could result in:11

  • viruses reproducing and spreading more quickly within the lungs and the body
  • white blood cells losing their ability to attack and destroy the virus 
  • viral material being cleared much more slowly from the lungs 

These studies reveal the unequal impact that COVID-19 can have on communities already suffering from poor air pollution.  

The takeaway

Healthy people even briefly exposed to high concentrations of PM2.5 face a higher risk of severe or deadly COVID-19 infections. 

This means that communities exposed to long-term PM2.5 face risks far beyond those directly related to air pollution. The impact of air pollution further widens the gap between the impact of COVID-19 within different communities. 

Throughout the world, much of the air pollution disproportionately affects poorer communities – further exacerbating the impact of COVID-19 in poorer communities.12,13,14

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Article Resources

[1] Cui Y, et al. (2003).  Air pollution and case fatality of SARS in the People's Republic of China: An ecologic study. DOI: 10.1186/1476-069X-2-15

[2] Cai G, et al. (2020). A hint on the COVID-19 risk: Population disparities in gene expression of three receptors of SARS-CoV. DOI: 10.20944/preprints202002.0408.v1

[3] Wang M, et al. (2019). Association between long-term exposure to ambient air pollution and change in quantitatively assessed emphysema and lung function. DOI: 10.1001/jama.2019.10255

[4] Wu X, et al. (2020). Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study. DOI: 10.1101/2020.04.05.20054502 

[5] Air quality guidelines – global update 2005. (2005). https://www.who.int/phe/health_topics/outdoorair/outdoorair_aqg/en/ 

[6] Wang B, et al. (2020). An effect assessment of airborne particulate matter pollution on COVID-19: A multi-city study in China. DOI: 10.1101/2020.04.09.20060137

[7] Andrée BPJ. (2020). Incidence of COVID-19 and connections with air pollution exposure: Evidence from the Netherlands. http://documents.worldbank.org/curated/en/462481587756439003/Incidence-of-COVID-19-and-Connections-with-Air-Pollution-Exposure-Evidence-from-the-Netherlands 

[8] Conticini E, et al. (2020). Can atmospheric pollution be considered a co-factor in extremely high level of SARS-CoV-2 lethality in Northern Italy? DOI: 

[9] Smog in northern Italy. (2005). https://earthobservatory.nasa.gov/images/15900/smog-in-northern-italy 

[10] Migliaccio CT, et al. (2013). Adverse effects of wood smoke PM2.5 exposure on macrophage functions. DOI: 10.3109/08958378.2012.756086

[11] Esposito S, et al. (2014). Possible molecular mechanisms linking air pollution and asthma in children. DOI: 10.1186/1471-2466-14-31

[12] Hajat A, et al. (2015). Socioeconomic disparities and air pollution exposure: A global review. DOI: 10.1007/s40572-015-0069-5

[13] Air pollution hurts the poorest most. (2019). https://www.unenvironment.org/news-and-stories/story/air-pollution-hurts-poorest-most 

[14] Low-income, black neighborhoods still hit hard by air pollution. (2019). https://www.sciencedaily.com/releases/2019/08/190810094052.htm 

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