During the summer of 2023, Canada experienced its most intense wildfire season on record. More than 40 million acres burned, an area the size of Georgia, injecting an enormous amount of smoke into the atmosphere, where photochemical reactions generated ozone pollution. In late spring, which is early for the wildfire season, wave after wave of smoke billowing from burning forests in western Canada poured across the sky and into the upper U.S. Midwest.

A new analysis led NOAA’s Chemical Sciences Laboratory (CSL) and co-authored by CIRES scientists found that ozone pollution readings in the Upper Midwest caused by these massive fires were the worst in decades.

“We were watching the Environmental Protection Agency’s air quality indices, and all across the Upper Midwest they were showing ozone exceedances,” said Owen Cooper, a research physical scientist at CSL. “On June 3, 2023, every ozone monitor in Iowa, about a dozen of them, exceeded the ozone standard of 70 parts-per-billion. It was unbelievable. Then it happened again on June 20th.”

The findings were published in the journal Geophysical Research Letters. 

Read the full story from NOAA Research.