Prescribed burning is an accepted practice to manage biomass both in the United States and throughout the world. It is a particularly important management practice in pine (Pinus spp.) forests, many of which have evolved in the presence of fire and are a prominent vegetation type on Department of Defense (DoD) lands. Millions of hectares of pine forest land in the southeastern United States (U.S.), in particular, are treated with prescribed burning for silvicultural purposes, such as hazardous fuel reduction, wildlife habitat improvement, and forest regeneration. Indeed, in a typical year, more than twice as much land (ca. 8 x 10⁶ ha) in the contiguous U.S. is burned under prescribed conditions for forestry and agricultural purposes as compared to the amount of land burned by naturally occurring wildfires (<4 × 10⁶ ha). DoD annually conducts more prescribed burning (about 2.4 × 10⁵ ha total) than any Federal agency other than the US Forest Service (USFS), despite managing a fraction of the USFS’s acreage.

Fire emissions are regulated in many areas and, as a result, the smoke that is produced must be managed based on its composition, production rate, and potential for transport away from the fires. Smoke resulting from biomass burning can have potential health effects and also can contribute to climate warming, if the use of fire is not managed properly, via both its emitted gases and particulate matter. Although many advantages can be attributed to prescribed burning, a key aspect is better control of its emissions because the fires are planned. Still, research into the relative contributions of both prescribed fire and wildland fires to health and climate effects is needed. In particular, two areas of knowledge that SERDP-funded research has attempted to resolve are (1) characterization of fuel types, condition and loading, fuel consumption, and resultant emission factors and (2) understanding the relationships between these factors.

In a series of three linked SERDP projects, Principal Investigators Dr. Wayne Miller (University of California, Riverside), Dr. Talat Odman (Georgia Institute of Technology), and Dr. Tim Johnson (Pacific Northwest National Laboratory), along with chief scientists Dr. Bob Yokelson (University of Montana), Dr. Jim Reardon (USFS, Rocky Mountain Research Station), and Dr. David Weise (USFS, Pacific Southwest Research Station), recently completed a five-year study addressing the above research needs for vegetation types managed at DoD installations. Project RC-1648 focused on southwestern (chaparral) fuels, whereas RC-1649 focused on southeastern (coastal plain and sand hills) fuels. Project RC-1647 was primarily a modeling effort using results from the aforementioned two projects to better understand the transport and dispersion of the smoke plumes at local and regional scales.&nbsp;The overall effort was designed as a program to characterize the fuels, smoke chemistry, and transport associated with prescribed burning on DoD installations in the U.S. with technical oversight provided by a Technical Advisory Committee. The research included detailed measurements of gaseous and particulate emissions in both the laboratory and field experiments. Field campaigns included regularly and infrequently burned pine, mixed pine-hardwood stands, chaparral shrublands, and Emory oak (Quercus emoryi) woodland.

The experimental parts of the RC-1648 and RC-1649 projects consisted of three components: (1) a laboratory effort to derive the infrared spectral absorption coefficients of those gases contained in smoke from wildland fires and thus expand and improve the detection capability of infrared-based gas sampling instruments, (2) detailed measurements of both gaseous and particulate emissions from burning fuel beds in a large combustion laboratory, and (3) detailed ground and aerial measurement of gaseous and particulate emissions from operational prescribed burns both in the Southeast at Marine Corps Base Camp Lejeune in North Carolina and Fort Jackson in South Carolina, as well as in the Southwest at Fort Hunter Liggett and Vandenberg AFB in California, and Fort Huachuca in Arizona.

The experimental parts of the RC-1648 and RC-1649 projects consisted of three components: (1) a laboratory effort to derive the infrared spectral absorption coefficients of those gases contained in smoke from wildland fires and thus expand and improve the detection capability of infrared-based gas sampling instruments, (2) detailed measurements of both gaseous and particulate emissions from burning fuel beds in a large combustion laboratory, and (3) detailed ground and aerial measurement of gaseous and particulate emissions from operational prescribed burns both in the Southeast at Marine Corps Base Camp Lejeune in North Carolina and Fort Jackson in South Carolina, as well as in the Southwest at Fort Hunter-Liggett and Vandenberg AFB in California and Fort Huachuca in Arizona.

The laboratory and field studies both used a technique called Fourier transform infrared (FTIR) spectroscopy to generate the reference spectra of over 50 wildland fire gas-phase smoke components. These data were added to a publicly-available database to support identification via infrared spectroscopy and were used throughout the program to determine emissions information in the form of emission factors (gram of effluent produced per kilogram of fuel burned) for a host of different gaseous species. Detailed information on particulate matter was developed from the laboratory experiment, with less detailed information available for the field burns in the southern U.S. Fuel loading for the field experiments was similar to previously measured fuels, except for Fort Jackson fuels that had received less frequent burning. The five-year study produced new emissions information for more than 100 trace gases and particulate matter in smoke for the fuel types studied using state-of-the-art instrumentation in both laboratory and field experiments. Emission factors (EFs) for flaming, smoldering, and residual smoldering phases were developed for all of the field studies. The derived EFs for the laboratory- and field-based emission factors were subsequently compared, and the agreement was good in most cases.&nbsp;Much progress was made in understanding the composition of biomass smoke, but further research is clearly warranted. Other products of the research program include an emissions factor database that compiled much of the wildland fire emissions information published in the 1970s through 2011.

For more information on these projects, visit SERDP and ESTCP’s Air Quality web page.