Air Stagnation Zone History

In 1983, the Air Board designated the High Impact Zone (HIZ). The HIZ more closely followed the Missoula City limits boundary than the MASZ. Visible emissions from residential solid fuel burning devices were limited or prohibited in the HIZ during high pollution episodes. This prohibition area was later expanded to the entirety of the MASZ in 2010, and the HIZ was phased out.

In 2010, the Air Board designated Impact Zone M – an area that extends well beyond the MASZ boundaries. Impact Zone M is primarily used as a tool to limit outdoor burning emission in heavily populated areas, but there are also rules in place that prohibit emissions from solid fuel burning devices in Impact Zone M during air pollution warnings.

The Air Board adopted the Oxygenated Fuel Control Area (OFCA). following Missoula’s designation as a carbon monoxide nonattainment area. Inside the OFCA, gasoline intended for use in motor vehicles must be oxygenated in the winter months (November through February).

In less than a decade, Missoula’s major source of air pollution shifted from six industrial sources to approximately 20,000 residential woodstoves and fireplaces. The shift occurred because Missoulians wanted to save on rising fuel bills while reducing dependence on fossil fuels. The health department responded to the increase in residential wood burning by identifying its impacts on air quality and by stressing potential threats to public health.

In 1981 and 1982, the health department used several strategies to encourage individuals to assume responsibility for the community’s health. Extensive public education efforts included production of public service announcements, informational pamphlets, and a 20 minute slide show concerning air quality and health effects; creation of air pollution curriculum materials for schools; and establishment of a Speakers’ Bureau which made presentations to 2600 people in one year.

In 1983 and 1985, the Air Pollution Control Board and the County Commissioners adopted regulations on woodstoves.  Only clean burning woodstoves could be installed inside the Air Stagnation Zone and burning during Stage I Air Alerts was limited to Class I stoves, sole source of heat stoves, people with special needs and dealer demonstrations.  A Class I stove is defined as a stove that emits < 4.1 grams/hour by the EPA testing method.  Other rules adopted included limiting the opacity (density of smoke) emitted from a fire and allowing only newspaper and untreated wood to be burned in a woodstove or fireplace. In 1987, a $20 fine for first time residential burning violations during a Stage I Alert was adopted; in 1994 the fine for the first burning violation was increased to $50.

Wood smoke continued to be, and still is, a major source of air pollution in the Missoula valley. As a result, the Air Pollution Control Board adopted even more stringent rules in 1994 to help maintain and improve air quality in the Missoula Valley. In 1994 it became illegal to install woodstoves in the Air Stagnation Zone. Now, only pellet stoves and gas appliances may be installed inside the Air Stagnation Zone. 

In addition, all solid fuel burning devices inside the Air Stagnation Zone that were not permitted as Class I devices between 1987 and 1994 and that emit more than 5.5 grams particulate per hour must be removed upon the sale of a property. The woodstove removal program is credited for the dramatic decrease in winter air pollution since 1994.

In 2010, the air rules were updated to prohibit non-EPA-certified stoves from being installed in Missoula County outside of the Air Stagnation Zone and south of the Swan drainage. Click here to learn more about these regulations.

The 1986/1987 Chemical Mass Balance source apportionment study identified street sanding material as a major contributor to violations of the ambient particulate standard. When the snow and ice melts off the urban streets, vehicles stir the sanding material into the air. In 1987, the Air Pollution Control Board passed regulations mandating that cleaner and more durable material be used for street sanding. To control road dust emissions from streets, street sweeping on major arterials must be done in the winter/spring months as soon as the paved road surface is above 32^°F for longer than 4 hours.

As part of the 1994 Air Pollution Control Program rules update, in 1994, the Board adopted deicer regulations. In a large part of the urban area, except for sloped roads, the use of deicer in place of street sanding material is required when the ambient temperature is above 0⁰F.

The Air Pollution Control Board, County Commissioners and City Council adopted also paving regulations inside the Air Stagnation Zone in 1994. These regulations require all new roads, commercial driveways, parking lots and other commercial vehicle use areas be paved before occupancy. They do make an exception for long term storage of heavy equipment and other vehicles and RV parking sites in RV parks. However, these areas must meet gravel specifications to reduce the amount of dust generated on site and dragged onto paved surfaces. 

These regulations also require that new driveways accessing a paved road be paved at least 20 feet back from the pavement or to the edge of the right-of-way, whichever is longer. If the new driveway is accessing an unpaved road, the owner must sign a waiver of the right to protest an RSID for the paving of the access road in the future. Click here to learn more about dust control.

In Missoula County, all fires require a permit, with the exception of small recreational and cooking fires. Permits are available for purchase online. Permits cost $7 and are good for the entire season. Requiring permits has significantly reduced the number of illegal burns and escaped fires in the County.

Missoula County has specific seasons for different types of burning to reduce the amount and impacts of smoke.

• General outdoor burning: March 1 to Aug. 31
• Essential Agriculture burning: March 1 to Oct. 31
• Wildland burning: March 1 to Nov. 30

These seasons are often suspended in July, August and September due to high fire danger.  In addition, burning can be restricted anytime due to air quality or fire danger concerns. Burners must activate their permits on the day they want to burn to both log the burn and see if any restrictions are in effect.

Within Missoula City limits, there are additional limits on outdoor burning. Only those homeowners with one acre or more can obtain a permit for burning. Recreational fires are not permitted in the city. The only combustion of solid fuel out of doors that is allowed inside city limits is for the use of a barbeque to cook food.