Magnitude of Fire Contributions to Air Quality Impact

Characterization of the true extent of effects of smoke from prescribed fires and wildland fires on ambient air quality is incomplete due to the deficiency of air quality monitoring sites in rural areas. Also, particulate standards are based on 24-hour and annual averages, whereas smoke plumes may significantly degrade air quality in a community for just a few hours before moving or dispersing. These short-term, acute impacts likely cause discomfort at the least, and possibly even affect health, but may not result in a violation of the National Ambient Air Quality Standards (NAAQS).

Air quality impacts associated with wildland fires are distinguished from those resulting from prescribed burning because emissions from these two sources have in the past been treated differently under the Clean Air Act and by State and local air quality regulations. Numerous exceedances of 24-hour PM10 and PM2.5 standards have been attributed to wildfires but, as the Natural Event Policy explains, violations of NAAQS caused by wildfire do not result in nonattainment if a State can document that the cause of the violation was truly wildfire and then prepares a natural events action plan for future events.

At present, prescribed fires are not considered to be a significant cause of nonattainment, but with increased burning to reduce fuels, this situation may change as land managers move forward with implementing a several-fold increase in the use of fire to sustain ecosystems (USDI and USDA 1995; USDA 1997). In general, little information is available on a national level to identify the contribution of prescribed burning to PM10 or PM2.5 within nonattainment areas (EPA 1992a). It appears, however, that there is no clear relation between total acres burned (or particulate emissions) and the nonattainment status of nearby airsheds, possibly because of successful smoke management programs.

In areas where air quality standards are being or may be violated, however, land managers are being directed to reduce air quality impacts through smoke management programs. This is because any source that contributes even a few micrograms per cubic meter of particulate matter toward violation of the NAAQS may be required to reduce emissions to assure that air quality standards are attained.

In addition, it is important to have a historical perspective of these issues given the increased use of fire in the recent past. A comparison by Leenhouts (1998) of estimated levels of biomass burning suggests that 10 times more area burned annually in the pre industrial era than in the contemporary era. After accounting for land use changes such as urbanization and agriculture, Leenhouts concluded that about 50 percent of historical levels would burn today if historical fire regimes were restored to all wildlands to maintain ecosystem health. This suggests a four- to six- fold increase from the current magnitude of wildland fire emissions.

See Estimating Air Quality Impacts of Fire for additional information.