An American Lung Association report on particle pollution gives poor marks to Missoula and Ravalli Counties.
Blame the bad grades partly on those dramatic forest fires we've been having.
In findings gathered over three years, the Association gave Missoula a "D" and Ravalli County an "F" on particulate pollution, while Sanders and Flathead Counties received "A"s.
It blames forest fires as one of the major sources of Montana's particulate pollution.
But the Lung Association reports wood stoves are also major contributors.
It said smokestacks and transportation are also significant.
And in January, said Missoula air quality specialist Ben Schmidt, "because of the wood smoke across all of Western Montana, we had very stagnant air conditions throughout the entire western part of the state."
The American Lung Association said although Missoula is currently meeting the daily and annual pollution standards, the city struggles with summer wildfire smoke as well as inversions and wood stove use.
At #42, the American Lung Association rates Missoula as one of the country's most polluted cities for short-term particle pollution.