Smoke from Wildland Fires

Although wildland fires occur throughout the nation, the largest fires and greatest number of fires occur in Alaska, the Southeastern States, and the West. During the 2000 fire season, 90,674 fires burned 7,259,159 acres (2,938,931 ha) at a fire suppression cost of $1.6 billion. The 10-year average acreage burned between 1990 and 1999 was 3.78 million acres (1.53 million ha), testifying to the severity of the 2000 wildfire season. The National Interagency Fire Center (NIFC) reports other statistics for recent fire seasons in the U.S.

Wildfires occur throughout the year. The 2000 wildfire season began with a Florida fire on January 1, continued with two 40,000-acre fires in New Mexico, an early May, 47,000-acre fire near Los Alamos and peaked on August 29, 2000, when fires that eventually burned 1,642,579 acres were burning in 16 States (NIFC 2001a). Generally, the occurrence of wildfires moves northward from the Southeastern and South- western States as summer approaches, fuels dry and fire danger increases.

Wildfires, both in number and total acreage burned, vary widely from year to year and from region to region, with no consistent relation between the number of fires and acres burned. It is known, however, that smoke from these fires impacts air quality on both an episodic and long-term average basis over wide regions.

Wildfires occur as episodic events. For example, in 1999, smoke from fires reduced visibility to less than 100 feet (30 m) in Florida, prompting officials to advise people with respiratory problems to stay indoors (New York Daily News 1999). In the West, fires in six States (California, Nevada, Oregon, Montana, Washington, and Idaho) put thick smoke in many communities. In Reno and cities in Californias Central Valley, smoke from nearby wildfires prompted authorities to warn residents with asthma to avoid unnecessary activity (USA Today 1999). Wildfire smoke is also transported across international boundaries. Fires in Canada were found to cause high concentrations of carbon monoxide and ozone over a period of 2 weeks in the Southeastern United States and across the Eastern seaboard during the summer of 1995 (Wotawa and Trainer 2000).

Smoke impacts during these episodic events can threaten public health, cause smoke damage to buildings and materials, and disrupt community activities. Although particulate concentrations in ambient air rarely reach health-threatening levels within major cities, several communities in the United States have experienced particulate matter concentrations from wildfire smoke that exceeded the Environmental Protection Agency (EPA) significant harm emergency action level of 600 µg/m3 defined as an "imminent and substantial endangerment of public health" (EPA 1992b).

For example, the Yellowstone National Park wildfires of 1988 impacted communities in three States. Concentrations of suspended particulate matter -- both total suspended particulate (TSP) and PM10 -- measured in communities near the fires exceeded NAAQS, triggering public health alerts and advisories (Core 1996). An estimated 200,000 people were exposed to high concentrations of smoke. In 1987, the Klamath fires of northern California burned for more than 60 days, resulting in widespread smoke intrusions into numerous communities in northern California and southern Oregon. More recently, wildfire impacts during the 2000 season were also severe in several communities. Twenty-four average PM10 concentration measured in Salmon, ID, reached 225 µg/m3 on August 15, 2002, and 281 µg/m3 on August18, 2000, during wildfire smoke intrusions (Idaho Department of Environmental Quality n.d.).

Wildfire smoke can also be the dominant cause of visibility reduction during episodic events in the Rocky Mountain States, on the Pacific Coast, and in the Southeast (National Research Council [NRC] 1993).  Dense plumes of smoke that can be transported over hundreds of kilometers across State and international boundaries, degrading air quality, scenic values, and highway safety. Between 1979 and 1988, 28 fatalities and more than 60 serious injuries were attributed to smoke that drifted across roadways in the Southern United States (Mobley 1989).