The ‘why’ behind outdoor burning zones in Missoula County
Kerri Mueller
The Missoula City-County Air Pollution Control Program (Air Program) regulates outdoor burning in Missoula County year-round based on weather conditions and current air quality in three airsheds and three burning zones.
In the 1980s, teepee burners, residential wood stove use, and other sources often impaired air quality to the point where streetlights would turn on in the daytime. Through the Clean Air Act of 1967, Missoula established their local air pollution control program in 1969 to address and reduce air pollution prompting the Air Program Rules.
Outdoor burning regulation is part of those rules, which is why the Air Program opens and closes burning periods, issues burn permits and sets daily elevation or time restrictions when necessary. Closures and restrictions can be applied to airshed, burning zones, or applied county-wide.
There are three airsheds in Missoula County. Most neighboring counties only have one to two defined airsheds over their boundaries. An airshed is a geographically defined area that typically experiences similar atmospheric conditions impacted by local topography.
Most of Missoula County falls within Airshed 3a, spanning the entire western side including Huson, Lolo, Missoula, and Clinton up to Potomac. The line between Airshed 3a and 3b falls at the eastern side of Potomac before crossing into Greenough and stretching halfway to Condon from Seeley Lake. North of Airshed 3b lies Airshed 2 which includes Condon and the northern part of Missoula County. There are also three defined burning zones: Missoula (Zone M), Potomac Valley (Zone PV), and Seeley Lake (Zone SL).
The reason behind creating three burning zones in Missoula County was to protect public health. The zones and associated valleys/areas are where most of the county’s population resides and historically experience the greatest impact from inversions and air pollution.
In these zones, smoke from burns pose the greatest risk of exposing a large group of people to the harmful health effects of smoke exposure. Having the ability to open, close, or restrict burning based on airshed or burn zones provides the flexibility to protect public health in highly populated areas when burning conditions are not favorable while still allowing people to burn in areas that are not as populated or have better smoke dispersion conditions.
It’s complicated having three airsheds and three burning zones, but there are real benefits. If dispersion conditions are only poor in Missoula, Frenchtown, and Lolo, burn restrictions are only placed on that zone. Anyone above the elevation restriction or outside of the restricted zone can still burn. Restrictions are usually set by elevation but can also be placed for start and end time of a burn. Some counties don’t have burning zones or more than one airshed so when weather conditions prompt restrictions, burning is restricted for the entire county.
In some cases, outdoor burning is the only reasonable way to remove excess natural vegetation from a property and this is especially the case with large-scale prescribed wildland fires. Outdoor burning is also a necessary tool for some homeowners to create a defensible space around their homes against wildfires.