New research indicates that exposure to pollutants in wildfire smoke may have led to thousands more COVID-19 cases and deaths. The new study, published in the journal Science Advances, links fine particle pollution known as PM2.5, which measures 2.5 micrometers across and is produced by wildfires, among other sources, to a significant increase in COVID-19 cases and deaths in California, Oregon, and Washington state. “The wildfires exacerbated the pandemic substantially,” said Francesca Dominici, a Harvard biostatistician and author of the study, in remarks to National Geographic. The study sought to gauge the impact of last year’s wildfires in the three states on excess COVID-19 cases and deaths by evaluating their correlation with data on short-term PM2.5 exposure, while seeking to account for a number of confounding factors, including weather, seasonality, long-term trends, mobility, and population size. Evaluating data from 92 counties affected by fires, the study’s authors “found strong evidence …