Air quality took a turn for the worst Saturday across most of western Montana.

It reached Hazardous levels -- the Montana DEQ's worst air quality designation -- in Missoula, Frenchtown and Hamilton.

At 9:15 p.m., the air was Very Unhealthy in Seeley Lake, the Flathead Valley, and in St. Mary in Glacier National Park.

Ben Schmidt, an Air Quality Specialist in Missoula County, said cumulative exposure was the worst he'd measured in 20 years.

"As time goes on, and we're in the smoke longer and longer, those people who didn't really feel any effect in the beginning, could very easily begin feeling the effects as time goes on," Schmidt said. "It just makes sense. You're accumulating more particulate, and your system's getting tired trying to fight off and deal with the high levels of smoke that's in the air."

Click here for the latest air quality readings and an explanation of the state's air quality levels.