The Use and Effectiveness of Emission Reduction and Redistribution Techniques

The overall potential for emission reductions from prescribed fire depends on the frequency of use of emission reduction techniques and the amount of emission reduction that each method offers. This section provides information on the overall potential for emission reduction and redistribution from prescribed fire based on

• the frequency of use of each emission reduction and emission redistribution technique by region of the country,
• the relative effectiveness of each smoke management technique, and
• constraints on application of the technique (administrative, legal, physical, etc.).

Much of the information provided on emission reduction and redistribution techniques was provided by participants in regional workshops. The information provided can, and should, be improved upon by local managers who will have better information about specific, local burning situations.

The use of each smoke management technique is organized by U.S. region as shown in figure 8.9. They are the Pacific Northwest including Alaska (PNW), Interior West (INT), Southwest (SW), Northeast (NE), Midwest (MW), and Southeast including Hawaii (SE) regions. Each region has its own vegetation cover types, climatology, and terrain characteristics, all of which influence the land manager’s decision to burn and the appropriateness of various emission reduction techniques.

Manager use of emission reduction techniques is influenced by numerous factors including land management objectives, the type and amount of vegetation being burned, safety considerations, costs, laws and regulations, geography, etc. The effect of some of these many influencing factors can be assessed through general knowledge of the frequency of use of a particular technique in a specific region. Table 8.1 provides general information about frequency of use of each smoke management technique by region of the country, grouped as shown in figure 8.9.

Information in table 8.1 summarizes regional applicability of each of the twenty-nine smoke management methods. Interviews with fire practitioners demonstrate that, on a national scale, several smoke management techniques are rarely used. These include biomass for electrical generation, biomass utilization, site conversion, land use change, burning before litter fall, burning under dry conditions, air curtain incineration, and burning smaller units. In most of the regions, firewood sales and chemical treatments are also seldom used. The methods most commonly applied include aerial ignition/mass ignition, burning when dispersion is good, sharing the airshed, and avoiding sensitive areas.

The general effectiveness of the emission reduction and redistribution techniques is described in table 8.2 based on input from managers at the workshops. Local managers will have better information about specific situations and can improve upon the information in the tables. Each technique was assigned a general rank of “High” for those techniques most effective at reducing emissions or “Low” for those techniques that are less effective. Some emission reduction techniques also have secondary benefits of delaying or eliminating the need to use prescribed fire. Some smoke management techniques, are also effective for reducing local smoke impacts if they promote plume rise or decrease the amount of residual smoldering combustion where smoke is more likely to get caught in drainage winds and carried into populated areas. These factors are also addressed in table 8.2.

Table 8.3 summarizes significant constraints identified by fire managers that limit the wider application of techniques to reduce and redistribute emissions. This table excludes consideration of the objective of the burn, which is generally the overriding constraint. Some of the techniques would probably be used more frequently if specific constraints could be overcome.

Smoke management techniques that, in the opinion of workshop participants, show particular promise for wider use in the future are listed below:

1. Mosaic Burning: Since this method reduces the area burned and replicates the natural role of fire, it is being increasingly used for forest health restoration burning on a landscape scale.
2. Mechanical Removal: In areas where slope and access are not a problem and fuels have economic value, the wider use of whole tree yarding, YUM yarding, cut-to- length logging practices and other methods that remove fuel from the unit prior to burning (if the unit is burned at all) may have potential for wider application if economic markets for the removed fuels can be found.
3. High Moisture in Large Woody Fuels, and/or Moist Litter and Duff: In situations where the objective is not to maximize the consumption of large woody debris, litter, and/or duff, this option is favored by fire practitioners as an effective means of reducing emissions, smoldering combustion, and smoke impacts.
4. Pile and Windrow Burning: Pile burning, although already widely used in all regions, is gaining popularity among land managers because of the flexibility offered in scheduling burning and the resultant lower impacts on smoke sensitive locations. Lower impacts may not result if piles or windrows are wet or mixed with dirt.
5. Aerial/Mass Ignition: Little clear information currently exists as to the extent to which aerial ignition achieves true mass ignition and associated emission reduction benefits. More effort to achieve true mass ignition using aerial techniques may yield significant emission reduction benefits.
6. Burn More Frequently: Fire managers generally favor more frequent burning practices to reduce fuel loading on second and subsequent entry, thereby reducing emissions over long time periods. This will increase daily or seasonal emissions.

Estimated Emission Reductions

While the qualitative assessment of emission reduction technique effectiveness shown in table 8.2 is a useful way to gauge how relatively successful a particular technique may be in reducing emissions, it is also useful to model potential quantitative emission reduction. Table 8.4 summarizes potential emission reductions that may be achieved by employing various techniques as estimated by the fuel consumption and emissions model Consume 2.1 (Ottmar and others [in preparation]). For example, use of mosaic burning techniques in natural, mixed conifer fuels in which one-half of a 200-acre project is burned is projected to reduce PM_2.5 emissions from 14.8 to 7.4 tons for a 50% reduction in emissions. A 33% reduction in PM_2.5 emissions can be achieved by pile burning mixed conifer fuels under the conditions noted in the table. Specific simplifying assumptions were made in each case to produce the estimates of emission reduction potential seen in table 8.4. Other models using the same field assumptions would yield similar trends.

Wildfire Emission Reduction

Little thought has been given to reducing emissions from wildfire, but many fire management actions do affect emission production from wildfires because they intentionally reduce wildfire occurrence, extent, or severity. For example, fire prevention efforts, aggressive suppression actions, and fuel treatments (mechanical or prescribed fire) all reduce emissions from wildfires. Although fire suppression efforts may only delay the emissions rather then eliminate them altogether. Allowing fires to burn without suppression early in the fire season to prevent more severe fires in drier periods would reduce fuel consumption and reduce emissions. All fire management plans that allow limited suppression consider air quality impacts from potential wildfires as a decision criterion. So, although only specific emission reduction techniques for prescribed fires are discussed in this chapter, we should remember that there is an inextricable link between fuels management, prescribed fire, wildfire severity, and emission production.