As the COVID-19 pandemic spread around the globe early in the spring of 2020, researchers began investigating how air pollution, which has been known for decades to have deleterious effects on human health, could be affecting this respiratory disease. Inspired by the work of a group of researchers in the US who reported in April that high levels of air pollution correlated to a higher risk of dying from COVID-19, Jos Lelieveld, an atmospheric chemist at the Max Planck Institute for Chemistry, and others widened their scope, looking at more areas of the world.
The danger of pollution to respiratory health comes from tiny emissions particles that are inhaled. Fine particulate matter is defined as anything smaller than 2.5 micrometers (PM2.5). The smaller the particles, the further down the respiratory system they can get, causing big problems by way of oxidative stress and an exuberant inflammatory response. Some particles can even trigger apoptosis. Short-term exposure to particle-laden air can cause acute irritation, leading to a cough, while long-term exposure is linked to chronic conditions such as chronic obstructive pulmonary disorder (COPD), heart disease, and cancer.
A study published in Cardiovascular Research on October 26 claims that fine particulate matter has increased the risk of deaths from COVID-19 by 15 percent globally, with certain areas such as East Asia reaching a 27 percent increase. The Scientist talked to Lelieveld to learn more about the relationship between pollution and COVID-19.
TS: Why do these particles leave people more vulnerable to dying from COVID-19?
JL: You have long-term effects [when people are] exposed for basically a lifetime to air pollution and then they develop chronic diseases. . . . These diseases are also preconditions for severe development of COVID-19. . . . Many of the lung diseases like pneumonia, COPD, lung cancer, heart disease, strokes, [are] the sort of thing that are aggravated by air pollution. And these are the sorts of things that also make people die from COVID. A healthy, young subject who has not been developing chronic diseases typically does not die from COVID.
TS: What can someone who lives in a place with more air pollution do to reduce their exposure to these particles?
JL: We write in our paper that there is no remedy like vaccinations for air pollution, so the only remedy here is that you have to clean the air. You have to go to cleaner sources of fuels and cleaner fuels and cleaner energy use. And of course, this also helps the climate. There are many arguments to do this. . . . I’m convinced that climate change is a big problem for this planet. And what I’m hoping is that some of the people who think it’s not an issue [that] carbon dioxide makes the world a bit warmer, maybe I can help convince them by showing that the same sources that create greenhouse gases are also creating pollutants that make you ill.
TS: Can you tell me how you collected your data and designed the study?
JL: We used the data from the paper attached to calculate PM2.5 exposure-response functions, plus data from China collected for the SARS epidemic in 2003. We tested different types of these functions, leading to the same result. To characterize exposure, we used a combination of satellite data and an atmospheric model, the latter to compute the anthropogenic fraction of PM2.5 and the contribution of fossil fuel use.
TS: Are there benchmarks of PM2.5 levels that correspond to low or high risk?
JL: There is a threshold of 2.4 µg/m3 below which the air is considered “clean”, precluding health impacts.
TS: Are there certain fine particles that are worse than others?
JL: There are indications that combustion-related black and organic carbon particles are more toxic than most other particles. But this is not quantitatively known, hence it is common practice to assume that all fine particulates are equally toxic.
TS: How long do fine particles stay with a person after they leave a highly polluted area?
JL: The atmospheric lifetime of aerosol particles is about one week. Once inhaled and deposited in the lungs, the damage is done (much like smoking). The cumulative damage during many years of exposure causes or aggravates chronic cardiopulmonary diseases (much like smoking), which are preconditions that influence the severity of COVID-19 outcomes.
This interview was completed over the phone and via email. It has been edited for clarity and brevity.