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Smoke chokes air: 'It's bad, but it's not going to be bad forever'

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A biker pedals down the Kim Williams trail near Caras Park on Sept. 8 as smoke-filled skies continue to drown the Missoula valley.

Air quality in Missoula ranked among the worst in the U.S. on Monday, with wildfire smoke locally and from around the region inundating the Missoula and Bitterroot valleys. 

The smoke-choked skies also represented the worst air quality in the area so far this year, but conditions could improve somewhat after Tuesday. 

Video courtesy of National Weather Service.

Around noon Monday, air in Hamilton registered 243 on the 500-point Air Quality Index, down from a high of 308 at 9 a.m. The noon measurement placed Bitterroot Valley air in the "very unhealthy" category, according to the U.S. Air Quality Index, meaning that it was a health risk to everyone. The morning's measurement of 308 crossed into the "hazardous" category indicating "health warning of emergency conditions: everyone is more likely to be affected." Hamilton's AQI values had been hovering around 170 on Sunday afternoon. 

Air quality in Missoula was only slightly better. At noon Monday, air in town measured 169 — solidly within the "unhealthy" category and relatively unchanged since about 6 p.m. Sunday. Air quality earlier Sunday was down into the less severe "unhealthy for sensitive groups" category. 

"It's definitely the worst we've seen so far in our area, in Missoula and Ravalli counties," Sarah Coefield, an air quality specialist with Missoula City-County Health Department, said on Monday. "This is as bad as it's gotten all year." 

Coefield said that people should stay indoors as much as possible when air is this unhealthy, and that people who go outside should wear a well-fitting N95 mask, which offers significantly more protection from smoke than a cloth or surgical mask. Indoors, it's "important for folks to be able to clean their air," whether it's through a HEPA filter in a closed room, or via a well-maintained ventilation system in larger public and commercial buildings. 

The air quality caused Missoula County Public Schools to cancel outdoor competitions scheduled for Monday afternoon and many athletic practices were moved indoors as space was available. Additionally, recesses throughout the district were moved inside while the air quality is in the "unhealthy" category. 

"We will continue monitoring air quality updates from the health department, and will expect to make decisions about practices and competitions as early in the day as possible going forward," said Tyler Christensen, the district's communications specialist. 

Smoke from everywhere

The smoke clogging the region right now is from "everywhere," Coefield said.

Unlike other hazy periods in Missoula's relatively smoke-free summer before September, smoky air now is less a result of being situated immediately downwind of a large fire and more because atmospheric conditions are trapping local and regional smoke in valleys.  

"Right now we're being impacted by really kind of a mixture," she said, "a mixture of smoke from throughout the region. People who are right next to an active burning fire can be really confident where their smoke is coming from." 

That's the case in the Bitterroot, where the Trail Ridge fire east of Sula and a slew of fires pockmarking the Bitterroot Range and central Idaho have sent smoke spilling down into the valley. But there and around Missoula, some of the smoke is also from other fires burning across Washington, Oregon, northern California, Idaho and far-western Montana. 

"Everything looks like a blur on the satellite, there's no real plume we can point to," Coefield said, describing a "blob of smoke" parked over the area. 

A high-pressure ridge over the region is trapping that smoke in valleys, and a seasonal shift to cooler nights and shorter days is making smoke-trapping inversions more pronounced, according to Coefield and Travis Booth, a meteorologist for the National Weather Service in Missoula. 

"With high pressure, you have a general subsiding of air," Booth said on Monday. "It tends to put a lid on things so there's not much mixing between the surface and the free atmosphere." 

That means that smoke in the area "can't really go anywhere," Coefield said. 

The sunlight-blocking smoke exacerbates a normal seasonal phenomenon of cool nights, short days and low sun angle, creating a positive-feedback cycle in which smoky conditions create longer, more robust inversions, which then trap more smoke and perpetuate a cycle of increasingly smoky conditions. Smoke allows long-wave radiation to leave the ground at night and travel up into the atmosphere, making for cool autumn nights, Booth said. But it blocks short-wave radiation from sunlight that helps heat surface air during the day and could break an inversion. 

Webcamera images from Glacier National Park and the Montana Department of Transportation show much of Montana is smoked over. (images from Sept. 12, 2022)

Some relief in sight

Western Montana had a brief respite from smoke on Friday and early Saturday, when an uncharacteristic "backdoor front" of cold air moved in from the east, over the Continental Divide, and pushed smoke back over Idaho to the west. But "it wasn't a strong enough push," Booth said, and cool, clear-skied Saturday morning soon gave way to thick smoke. 

A different phenomenon could bring relief as soon as Tuesday evening. Coefield and Booth cited a flow of air from the west and southwest that could bump the high-pressure ridge eastward and facilitate some atmospheric mixing. 

"It's not something that'll clean the valley out very well," Booth said, but midweek thunderstorms could create additional smoke-clearing air movement. 

If the inversion-trapped smoke clears out Wednesday, Coefield said, "then our main issue will go back to being which fire are we downwind from and how active is that fire." 

"The overhead winds are still going to be from the direction of all the active fires in Idaho and Oregon over the next couple days," she said, "so it really depends on what those fires do." 

The good news long term, Coefield said, is that winter is on its way: "Winter is coming. The fall precipitation will get here eventually, the nights will get cold enough that the fires will slow down. It's bad, but it's not going to be bad forever." 

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Outdoors Reporter

Joshua Murdock covers the outdoors and natural resources for the Missoulian.

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