January 30, 2023

The same team of Harvard researchers also published the first study last year that found a clear link between long-term exposure to air pollution and Covid-19 death rates.

The new study included reported infections, not just deaths, which makes it particularly interesting, said John Balmes, a professor of medicine at the University of California at San Francisco and an expert on the health effects of pollution who was not involved in the research. “It’s one thing that air pollution increases the severity of coronavirus infection, it’s another that it increases the number of reported cases,” he said.

After decades of tightening air quality regulations, the air in many American cities is cleaner today than it will be in 50 years. But in the west, increasing forest fire smoke threatens to undo these advances, said Loretta Mickley, an atmospheric chemist at Harvard John A. Paulson School of Engineering and Applied Sciences and one of the authors of the paper.

As the planet warms, droughts intensify, and the west becomes drier, forest fires start earlier, get bigger, spread faster, and reach higher altitudes. In California alone, a record 2.5 million acres burned down during the 2020 forest fire season, 20 times what burned the previous year.

“We’re really talking about climate change,” said Francesca Dominici, biostatistician at Harvard TH Chan School of Public Health and senior author on the paper. “I hope this is additional evidence of why it is important to work together to tackle climate change.”

Forest fire smoke can contribute up to half of PM 2.5 in some parts of the western United States. It is still unclear whether forest fire smoke is more or less toxic than smoke from diesel combustion or power plants.

Dr. Dominici noted that the analysis did not include individual patient data or other factors such as mask requirements.

Researchers are currently investigating whether particulate matter can spread the corona virus.

Research does not bode well for this year, said Dr. Dominici, since forest fires started early and the pandemic is still raging in the United States, with a Delta variant that tends to be more contagious. She added, “I think the forest fires will have the same, if not worse, impact on Covid-19 cases and unvaccinated deaths.”