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Researchers at the Harvard School of Public Health and universities across Europe have established a link between air pollution and mortality risk from COVID-19, according to an Oct. 26 study published by the Oxford University Press.

The study utilized satellite imagery and an atmospheric model to calculate pollution levels around the world, then comparing it with epidemiological data on coronavirus deaths from the United States and China through the third week of June 2020.

The researchers focused on PM2.5, or particulate matter with a diameter of less than 2.5 micrometers. They concluded that 15 percent of global COVID-19 deaths could be linked to this type of manmade pollution.

A previous study co-authored by Francesca Dominici, a researcher at the School of Public Health, found that in the United States, for every microgram of PM2.5 per cubic meter of air, the mortality rate of COVID-19 increased by eight percent.

This new study, also co-authored by Dominici, examined these effects on the global level and arrived at similar findings.

“They [PM2.5 molecules] are caused by many types of fossil fuel combustion. Mostly cars and power plants, but there are many other sources, and these particles penetrate very deep into your lungs,” Dominici said.

“They compromise your immune system, they have been associated with an increased risk of asthma and chronic obstructive pulmonary disease, and also they can get in your bloodstream and lead to inflammation and cardiovascular disease.”

According to Dominici, the long-term damage that particulate matter does to the lungs greatly increases the risk of mortality from COVID-19.

“You've been breathing out pollution for a very long time, and then you are contracting the virus,” said Dominici. “Your ability to respond to the virus might be compromised, because evolution has compromised your lungs’ immune system.”

She noted that conditions such as asthma and chronic obstructive pulmonary disease — comorbidities for COVID-19 — are also caused in large part by long-term exposure to PM2.5. These conditions contribute to acute respiratory distress syndrome, one of the primary causes of death due to the coronavirus, where fluid collects in the lungs depriving the body of oxygen.

The global loss in life expectancy caused by exposure to PM2.5 is comparable to a lifetime of smoking tobacco, according to the study.

Andrea Pozzer, the study’s first author and a researcher at the Max Planck Institute for Chemistry, said the atmospheric model used in the study calculated the percentage of pollution observed in satellite imagery that was man-made, rather than connected to “natural pollutants” such as dust and sand.

“We know exactly which fraction of PM2.5 is man-made,” Pozzer said. “So we could estimate what is the mortality or the additional mortality to COVID that could have been avoided if, let's say, human ecological footprint would have been equal to zero.”

He added that studies in 2003 found similar increases in mortality risk for the SARS epidemic, and the body of research that connects air pollution to respiratory illness and death is constantly growing.

“Our take home message is that, actually, no, it's not possible to do anything to protect yourself from poor outdoor air quality as a single person,” Pozzer said. “You can do [that] as a community, of course, as a country, and in general, as a human population. That is clear.”

The paper concludes that the long-term effects of air pollution will outlast the coronavirus.

“The pandemic ends with the vaccination of the population or with herd immunity through extensive infection of the population,” the paper reads. “However, there are no vaccines against poor air quality and climate change.”