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The smell. It's all anyone could talk about during mid-January. Inescapable, unremitting and offensive, it drove locals indoors and onto social media feeds where they puzzled over the odor's origins. Only those lucky enough to be suffering from stuffy noses were spared the discomfort of going about life in a fog of raw sewage.

The culprit turned out to be a combination of poor timing and Missoula's quirky meteorology. One of those familiar pockets of stagnant cold air we've all come to know as an "inversion" had settled over the valley, and EKO Compost unwittingly chose Jan. 12 to break into one of its older piles. With nowhere else to go, the subsequent release of foul odor gradually built up and spread out horizontally in all directions. County air quality specialist Sarah Coefield says the olfactory fallout prompted conversations with EKO about avoiding similar timing issues in the future.

"This was the worst it's been since I've been here," she says, "so it's the first time we've had to have that talk."

The smell may have caught the town's attention, but Missoula's inversion activity has been exceptional all winter. While inversions are common this time of year, Coefield's colleague Ben Schmidt says the past few months have seen longer lasting periods of stagnant air than usual, starting as far back as Thanksgiving. It takes a considerable amount of action to break up those inversions, Schmidt continues. Either sunlight can heat up the ground and cause that pocket of cold air to rise, or a weather system can move in and "mix up" the air.

"There's a pretty significant mass of air [in the valley]," Schmidt says. "It takes energy to start breaking down that layer and working its way through and getting down to the floor of the valley."

According to Schmidt, longer lasting inversions can be typical of El Nino years like this one. However, because they occur in non-El Nino years too, he's reluctant to lean solely on that explanation. One thing is for sure, though. Inversions become less common after January as higher temps and longer days begin adding energy to the air again. Schmidt says we should be out from under our worst inversions come February.

"But you never know," he adds.

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