Long-term exposure to air pollution has been linked to an increased risk of dying from COVID-19 and, for the first time, a study has estimated the proportion of deaths from the coronavirus that could be attributed to the exacerbating effects of air pollution for every country in the world. The study, published in Cardiovascular Research on Tuesday, estimated that about 15% of deaths worldwide from COVID-19 could be attributed to long-term exposure to air pollution. In Europe the proportion was about 19%, in North America it was 17%, and in East Asia about 27%. In their CVR paper, the researchers write that these proportions are an estimate of "the fraction of COVID-19 deaths that could be avoided if the population were exposed to lower counterfactual air pollution levels without fossil fuel-related and other anthropogenic [caused by humans] emissions". One limitation of the research is that epidemiological data from the US were collected at the level of counties rather than from individuals, which means that it is more difficult to exclude confounding factors. Even though 20 factors that could affect the results were accounted for, additional factors cannot be excluded. A second limitation is that data have been collected in middle- to high-income countries (China, US, and corroborated by data from Europe); the calculations were carried out for the whole world, meaning that the results for low-income countries may be less robust.