3.2.5 Air Quality (Issue #5) 



3.2.5.1 Products of Combustion 



When forest fuels bum, complex organic molecules composed primarily of 

 carbon, hydrogen and oxygen break down and then recombine with oxygen. 

 If combustion were 100% complete the only products produced would be 

 water vapor and carbon dioxide. However complete combustion is only 

 achieved under very controlled conditions and combustion of forest fuels is 

 very incomplete. Some of the products of incomplete combustion are carbon 

 monoxide, particulate matter and a wide variety of volatile organic 

 compounds (VOCs). A fire that bums at a high temperature bums more 

 completely and produces less particulate and other partial combustion 

 products than a fire that bums at a lower temperature. Dry fuel that bums 

 with flaming combustion bums hotter and therefore cleaner than fuel that is 

 wet and burning at a lower temperature. Fuel that bums with an adequate 

 supply of oxygen bums hotter and cleaner than fuel that is buried by dirt and 

 therefore getting an inadequate supply of oxygen. Fire that is in the 

 smoldering stage of combustion is cooler than the flaming stage and therefore 

 produces more partial combustion products. 



3.2.5.2 Characteristics of Smoke in the Missoula Valley 



The project area is located approximately 6 miles southwest of downtown 

 Missoula. The mountain valleys of Westem Montana are prone to cold air 

 inversions in the fall and winter when stationary high-pressure systems create 

 a stable air mass that traps pollutants in the valley bottom. During the spring 

 season the atmosphere is much more unstable and stable cold air does not 

 settle into the valleys to the extent it does in the fall or winter. Due to this 

 atmospheric instability, smoke is transported out of the valley much better in 

 the spring than in the fall. 



3.2.5.3 Effects of Smoke on Human Health 



The most problematic pollutant in the Missoula area is particulate matter. 

 Particulate is produced by a number of sources such as road dust from 

 vehicles, forest and agricultural buming, industrial sources, windblown dust 

 from plowed fields, smoke from wildfires and other sources. Particulate is 

 classified by its size. PM-10 is less than 10 microns in diameter. PM-2.5 is 

 less then 2.5 microns. The smaller a particle is, the greater impact it can have 

 on human health. Smaller particles are able to penetrate farther into the human 

 respiratory system. Smaller particles are also more difficult for the human 

 body's natural processes to remove. 



3.2.5.4 Regulation of Open Burning 



Missoula County is a PM-10 Non-Attainment area as designated by the 

 Environmental Protection Agency and the Montana Department of 

 Environmental Quality. Open buming is allowed in Missoula County from 

 March 1 to August 30 of each year. From September 1 to November 30 



Deadman Gulch Timber Sale Environmental Assessment 3-7 



