Missoula, MT Air Quality Index (AQI) Today

Missoula’s air problem is its floor plan. The city occupies a valley near 3,200 feet where the Clark Fork comes out of Hellgate Canyon and the Bitterroot joins from the south, with mountains on every side. On a cold, still night the dense air at the bottom has nowhere to go, and whatever is emitted into it stays there until the weather pattern changes.

That has been understood here for a long time. By 1969, with a pulp mill and log yards then working the valley, Life reported residents driving with headlights on in daylight. The mills and most of the yards went; what remained as the cold-season source was residential wood burning, and research across western Montana valley communities has attributed the majority of their wintertime fine particulate to wood smoke. Missoula’s answer was an air stagnation zone covering the valley floor and ground beyond the city limits. No wood stove has been legally installed inside it since 1994 — pellet and gas appliances only — and an uncertified device must come out when a property changes hands, with a certificate of compliance filed at the county before the sale can close.

Summer runs the same trap on a different fuel, regional wildfire smoke settling in and not scouring out overnight. Mount Sentinel and Mount Jumbo rise more than 1,500 feet straight off the valley floor at the east end of town, so on an inversion morning the top of the haze is somewhere on those slopes. The monitor is on the floor, which is where people live.