Smoke plume from the burning of wheat residue north of Walla Walla, Washington. The field was burned using a backfire. The light color of the smoke plume indicates low soot content (photo by Emily Lincoln).

September 22, 2016 – Agriculture is a vital part of the Pacific Northwest’s economy and is critical to the region’s rural communities. The production cycle of cereal crops and grasses, which are important agriculture products of the Northwest, includes burning fields of post-harvest residue such as wheat stubble. Like smoke from forest fires, smoke produced by agricultural burning can have harmful effects on public health. To protect public health, smoke management agencies regulate agricultural burning by deciding how much, if any, field burning can occur on a given day.


To determine field burning, they use air quality forecasting models that predict the amount and composition of smoke produced and the dispersion of the smoke and its concentration at population centers. Smoke managers have reported that the models do not work well under certain conditions, resulting in significant smoke impacts on local populations. The developers of the air quality models and smoke managers need an extensive dataset of in situobservations of agricultural smoke production and dispersion in order to improve these critical air pollution forecasting tools.

The RMRS Smoke Emission and Dispersion Research Team, composed of researchers at the Missoula Fire Sciences Laboratory, was asked to participate in a research project organized by the Environmental Protection Agency (EPA). The project was designed to obtain the data necessary to improve the air quality models used by smoke managers and included researchers from the EPA’s Region 10 and Office of Research and Development, the U.S. Forest Service’s Pacific Northwest Research Station, the USDA’s Beltsville Area Agricultural Research Service, Washington State University, Washington State Department of Ecology, and the Nez Perce Tribe. The Smoke Emission and Dispersion Research Team used smoke chemistry measurement instruments on a U.S. Forest Service Cessna aircraft to measure emissions and smoke dispersion from seven agricultural fires in Idaho and Washington during August 2013.

Key Findings

An important initial finding of this study was that the method used to burn a field appeared to impact the amount of soot particles produced. The smoke plumes produced from burning wheat residue using head fires contained more soot than plumes produced using backfires. Soot particles are black aerosol composed primarily of elemental carbon. The World Health Organization reports that soot particles may have significantly greater negative health impacts than other particle types found in smoke and air pollution since these particles can act as a carrier for toxic combustion-derived chemicals.

While results are still preliminary, early indications are that this research may assist smoke managers in protecting public health, while helping to safeguard the economic livelihood of the Northwest’s agricultural communities.