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Wildfire Risk

Air and Air Quality

Large forest fires in the past have produced high density, large scale smoke events that affect air quality. These large fires continue to occur but much less frequently. There is archaeological evidence suggests that Native Americans used burning as a regular means for improving plant growth and of hunting in the Willamette Valley and Cascade foothills. For over 50 years ago field burning has been used to dispose of leftover straw and stubble on fields after grass harvesting to control weeds, insects, plant diseases and helps maintain grass seed purity. It also reduces the use of pesticides and herbicides and crop yield.

Field burning occurs in the Willamette Valley each summer. Since 1991 this practice has been more highly regulated by the Oregon Department of Agriculture Smoke Management Program.

The current limit of 40,000 acres (down from 180,000 acres in the 1980s) was phased in from 1991-1998. In addition there is a limit of 25,000 acres allocated for burning of specified fire-dependent species and grasses grown on steep slopes where high soil erosion is a problem. Prescribed fires are primarily restricted to days when weather conditions vent smoke away from settled areas and as a result, the portion of air pollution attributed to fires has been reduced.

Today, haze affects our ability to see the beauty of this region. It is composed of small particles that absorb and scatter light, affecting our experience of the clarity and color of our surroundings. Sources of haze are both urban and rural. They include emissions from motor vehicles, power plants, industrial and manufacturing plants, as well as the burning of vegetation and debris. But there are natural sources too, such as wildfire and windblown dust.

The State of Oregon provides several tools for monitoring air quality in the Willamette Basin including a daily Air Quality Index (AQI) reading by county for particulate matter, carbon Monoxide, and ozone. Particle pollution is often highest during the coldest times of the day, typically in the evening and early morning.


"Air Quality: Existing conditions." (2005) In Fall Creek Special Interest Area Fire Recovery Project Environmental Assessment (PDF). P. 194. Westfir, OR: USDA Forest Service. Middle Fork Ranger District

Fact Sheet: Open Field Burning in the Willamette Valley (PDF). Salem, OR: Oregon. Department of Environmental Quality. Air Quality Division, Airshed Planning Program, 2007

Fact Sheet: The Regional Haze Rule (PDF). Salem, OR: Oregon. Department of Environmental Quality. Air Quality Division, 2006

Compiled by Bonnie Avery, Natural Resources Librarian (2007)