Missoula's air quality is deteriorating because of an inversion that is trapping air down near the valley floor and may be approaching a level at which sensitive groups could be affected.

Air Quality Specialist with the Missoula City County Health Department Ben Schmidt  said on Monday, November 25, that the inversion began to take effect last Thursday.

"We have this high-pressure ridge which creates prime conditions for strong inversions to form," Schmidt said. "It may be nice and sunny outside, but we've got these pockets of cold air on the valley floor that form under these conditions. I've had a few people call me from the top of Snowbowl to say the air looks crystal clear, while down here in the valley it's definitely getting murky. We've had particulate levels of around 20 micrograms per cubic meter, and not the nice low numbers we'd like to see."

Schmidt said that officials saw this inversion coming and took steps to alleviate air quality problems last week.

"One of the things we have done is shut down outdoor burning since Thursday of last week, which we had to do," Schmidt said. "If we'd have had outdoor burning all through the weekend with this kind of weather situation, our particulate levels would be much higher."

Schmidt said conditions are getting close to the point when the health department will start sending out warnings.

"As soon as it gets bad enough for sensitive groups, that's when we'll start sending out our email warnings, and we'll start updating the Air Quality Hotline and website," Schmidt said. "Right now, air quality is sitting at moderate, but we could be working ourselves into an alert as this inversion sits here over us for the next few days."

Air quality is now unhealthy for sensitive groups in Seeley Lake.

Air Quality Specialist with the Missoula City County Health Department Ben Schmidt