Previous studies have found that the pollution known as PM2.5 (particulate matter of no more than 2.5 microns in diameter), which penetrates our lungs and can cause all sorts of issues, does cause thousands of deaths and billions in damage, across various parts of North America. But no one had looked specifically at California before, where some of the country’s most devastating fires have occurred in recent years.

The researchers estimated mortality based on acres burned and a “dose-response” analysis of exposure to PM2.5. At the high end of their estimates, the first over their 11-year study window killed 55,710 people.