Smoke 101

Prescribed burn team standing on road near smoky forest

Differences between wildfire and prescribed fire smoke in Western States in the U.S.

What Is Smoke?

Smoke is a byproduct of living and dead vegetation and organic soil, collectively referred to as fuels, consumed by fire. It is comprised of hundreds of gases and particles that are diverse in size, composition, and optical properties.

Smoke composition is the combination of gases and particles and is described by emissions factors.

Smoke emission factors quantify the yields of pollutants from the combustion of wildland fuels. For every ton of fuel consumed by
fire, emission factors describe pounds of fine particulate matter (PM) and other air pollutants produced. Both short-term and long-term exposure to PM2.5, particles with a diameter less than 2.5 microns, can have harmful health effects (U.S. EPA 2023).

Smoke emissions,
in contrast to composition, refers to the where, when, and how much of various pollutants are produced by wildland fire such as how much PM is produced by a given fire over a time period. Emissions of a specific pollutant are calculated by emissions factors and fuel consumption. Importantly, different amounts of fuel layers (i.e.,litter, understory, canopy) burn depending on fire conditions, which translates to different mixes of emissions factors.

Smoke impacts
are the concentration of PM2.5 (or other pollutants) experienced on the fireline, in a community, or at a location far from the wildfire.

Smoke dispersion is the process by which the atmosphere mixes and transports particulates and other pollutants. Sometimes smoke will rise and disperse higher in the atmosphere during the heat of the day. In mountainous terrain, smoke will often settle into lower elevation areas with a nighttime inversion (a portion of the atmosphere in which temperature increases with altitude, inhibiting vertical mixing of air near the surface). Smoke is not static; it ages over time and creates different chemicals and impacts downwind.

What Do We Know About the Differences Between Wildfire and Prescribed Fire Smoke?

It is difficult to make generalizations about differences between wildfire and prescribed fire smoke. Both occur across a spectrum of fire intensities and conditions. Smoke varies with season of burning, intensity of burning, fuel conditions, and weather conditions, to name a few. Not all prescribed fires are low intensity fires and not all wildfires are high intensity fires. Some ecosystems require stand replacing fire to be ecologically significant and, in such a case, there may be little difference between a prescribed fire and wildfire. In ecosystems frequently burned at low intensities, a wildfire or prescribed fire in that system would likely also be of lower intensity.

The key difference between wildfire and prescribed fires is that prescribed fires are planned in advance. Managers have decision space to initiate a prescribed fire or wait for more favorable conditions to minimize smoke impacts. On a regional basis, numerous groups engaging in prescribed burning are able to interact and adjust cumulative smoke emissions and impacts. During a wildfire, however, there is little to be done about ambient smoke condition as a wildfire simply exists in the shared airspace.

Read the whole article!

Sign Up For Our Newsletter

Join our newsletter list to receive updates on forest restoration activity in the Deschutes National Forest, including temporary trail closures, prescribed fire announcements, and related community events.

* indicates required
(c) 2023 Deschutes Collaborative Forest Project