Problem Smoke: What is being done to Minimize the Problem?

As population growth in the South continues, there is an increasing likelihood that more people will be adversely impacted by smoke. Unless methods are found to mitigate the impacts of smoke, increasingly restrictive regulations may curtail the use of prescribed fire, or fire as a management tool may be prohibited. Several approaches are underway to reduce the uncertainty in predicting smoke movement.

• Several states have devised smoke management guidelines to regulate the amount of smoke put into the atmosphere from prescribed burning. The South Carolina Forestry Commission (1998) has established guidelines to define smoke sensitive areas, amounts of vegetative debris that may be burned, and atmospheric conditions suitable for burning this debris.
• The Forestry Weather Interpretation System (FWIS) was developed by the U.S. Forest Service in the late 1970’s and early 1980’s in cooperation with the southern forestry community (Paul 1981; Paul and Clayton 1978). The system has been enhanced and automated by the Georgia Forestry Commission (Paul et al. 2000) to serve forestry sources in Georgia and clients in other southern states. The GFC provides weather information and forecasts specified for forest districts, and indices used for interpretations for smoke management, prescribed fire, fire danger, and fire behavior. Indices include the Keetch-Byram Drought Index, National Fire Danger Rating System, Ignition component, Burning Index, and Manning Class Day.
• High resolution weather prediction models promise to provide increased accuracy in predictions of wind speeds and directions and mixing heights at time and spatial scales useful for land managers. The Florida Division of Forestry (FDOF) is a leader in the use of high resolution modeling for forestry applications in the South (Brackett et al. 1997). Accurate predictions of sea/land breezes and associated changes in temperature, wind direction, atmospheric stability and mixing height are critical to the success of the FDOF system as much of Florida is located within 20 miles of a coastline. High resolution modeling consortia are also being established by the U.S. Forest Service to serve clients with interests as diverse as fire weather, air quality, oceanography, ecology, and meteorology.
• Several smoke models are in operation or are being developed to predict smoke movement over Southern landscapes. VSMOKE (Lavdas 1996), a Gaussian plume model that assumes level terrain and unchanging winds, predicts smoke movement and concentration during the day. VSMOKE is now part of the FDOF fire and smoke prediction system. It is a screening model that aids land managers in assessing where smoke might impact sensitive targets as part of planning for prescribed burns. PB-Piedmont (Achtemeier 2001) is a wind and smoke model designed to simulate smoke movement near the ground under entrapment conditions at night. The smoke plume is simulated as an ensemble of particles that are transported by local winds over complex terrain characteristic of the shallow (30-50 m) interlocking ridge/valley systems typical of the Piedmont of the South. PB-Piedmont does not predict smoke concentrations as emissions from smoldering combustion are usually not known. Two sister models are planned, one that will simulate near ground smoke movement near coastal areas influenced by sea/ land circulations and the other for the Appalachian mountains.

In summary, the enormous wildland/urban interface and dense road network located in a region where up to six million acres of wildlands per year are subject to prescribed fire combine to make problem smoke the foremost land management-related air quality problem in the South. During the daytime, smoke becomes a problem when it drifts into areas of human habitation. At night, smoke can become entrapped near the ground and, in combination with fog, create visibility reductions that cause roadway accidents. Public outcry regarding problem smoke usually occurs before smoke exposures increase to levels that violate air quality standards. With careful planning and knowledge of local conditions, the fire manager can usually avoid problematic smoke intrusions on the public.