Coronavirus patients in areas that had high levels of air pollution before the pandemic are more likely to die from the infection than patients in cleaner parts of the country, according to a new nationwide study that offers the first clear link between long-term exposure to pollution and Covid-19 death rates. In an analysis of 3,080 counties in the United States, researchers at the Harvard University T.H. Chan School of Public Health found that higher levels of the tiny, dangerous particles in air known as PM 2.5 were associated with higher death rates from the disease. For weeks, public health officials have surmised a link between dirty air and death or serious illness from Covid-19. The Harvard analysis is the first nationwide study to show a statistical link, revealing a "large overlap" between Covid-19 deaths and other diseases associated with long-term exposure to fine particulate matter. The paper found that if Manhattan had lowered its average particulate matter level by just a single unit, or one microgram per cubic meter, over the past 20 years, the borough would most likely have seen 248 fewer Covid-19 deaths by this point in the outbreak. The paper ... found that just a slight increase in long-term pollution exposure could have serious coronavirus-related consequences, even accounting for other factors like smoking rates and population density. The study also could have far-reaching implications for clean-air regulations, which the Trump administration has worked to roll back over the past three years.