3506B24 Final Report
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- Major Findings
- Outlook and Recommendations
- 2 INTRODUCTION
1 EXECUTIVE SUMMARY Guided by the Endangered Species Act (ESA), the Department of the Interior (DOI) through the Fish and Wildlife Service encourages land managers at Army and Air Force bases in the southeastern US to use prescribed fire to maintain the health of its native long leaf pine forest and thus protect the habitat of threatened and endangered species such as the red-cockaded woodpecker and the gopher tortoise. Other installations across the Nation utilize prescribed fire to control invasive plants, which would otherwise disrupt the ecological balance. Recognizing the benefits, many land managers of privately owned lands are also using prescribed fire. Annually, more than 1 million acres of government and private lands in Georgia are subject to prescribed burning. Releasing primary and contributing to the formation of secondary gas- and particle-phase pollutants, biomass burning however, can contribute significantly to already burdened local and regional air pollutant loads, and challenge the air quality standards mandated by the EPA and the Clean Air Act (CAA). Recognizing the conflicting requirements between the ESA and CAA statutes, the “Study of Air Quality Impacts Resulting from Prescribed Burning on Military Facilities” was initiated and sponsored by the Department of the Army, Construction Engineering Research Laboratories (DOA/CERL) in support of the Department of Defense (DOD) Pollution Prevention Partnership. The motivation for this Study stemmed from observations made at a research monitoring station, established near Fort Benning, Georgia at the Oxbow Meadows Environmental Learning Center (OLC) as part of the Georgia Environmental Protection Division (GA-EPD) sponsored Fall-line Air Quality Study (FAQS, see http://cure.eas.gatech.edu/faqs/index.html for more details). The OLC itself is supported by the Columbus Water Works and is operated by personnel from the Columbus State University. Among all FAQS monitoring network sites, the OLC was the only one where the 24-h average National Ambient Air Quality Standard (NAAQS) for PM2.5, which is 65 µg m-3, was exceeded on five different days during a three-week period in the fall of 2001. Both sites operated by GA-EPD as part of the State’s regulatory monitoring network for PM2.5, which are located closer to the city of Columbus and further away from the OLC site (and Fort Benning), did not register these exceedances, due to their 1-per-3-day sampling schedule. Analysis of the conditions leading to these locally confined exceedances in 2001 showed that fine PM concentration is most sensitive to wind speed and atmospheric stability, leading to PM accumulation under calm conditions especially associated with nocturnal inversions. The relatively high uncertainties in wind direction measurements and plume trajectory calculations under such calm conditions, complicate the prediction of boundary layer mixing heights that effectively promote dilution of fine PM emitted near the ground at day, or on the other hand trap PM that are being emitted at night. The analysis also demonstrated that under stagnant atmospheric conditions smoldering fires represent a significant source for additional local air pollution extending continued emissions into the lower atmosphere over the next day or more, until the weather pattern changes significantly. A sampling strategy has been developed to include the measurement of gas- and particle-phase tracers, indicative of biomass burning emissions, both at the source and the OLC site. The sampling occurred between mid January and end of May 2003, and was conducted in close collaboration with personnel from Fort Benning’s Environmental Management Division (EMD) and Land Management Branch (LMB), who also provided valuable information on the type and amount of fuel burned. For the purposes of comparison, limited sampling was also conducted at Fort Gordon, near Augusta, Georgia in conjunction with prescribed burning activities there. Major Findings VOC emission profiles for both flaming and smoldering phases were similar for burns at Forts Benning and Gordon, with the only significant differences in α-, and ß-pinene and i-pentane. Ranking the VOC emissions according to their reactivity with OH, emphasized the importance, with respect to ozone formation, of isoprene, and α-, and ß-pinene in the biogenic VOC measured. VOC that are potentially involved in the formation of Secondary Organic Aerosol (SOA, e.g. the main aromatic species benzene, toluene, and xylenes), were emitted by prescribed burns in quantities similar to those of county-wide emissions from mobile sources (on road cars and trucks). Among ten aromatic species investigated, toluene was estimated to be the major SOA precursor species for the flaming phase, whereas the xylenes became the dominant precursor for potential SOA formation from smoldering emissions. VOC source apportionment using a chemical mass balance (CMB) method, showed diesel exhaust, gasoline exhaust, evaporative gasoline, refinery fugitive, primers and enamel, biogenic, and prescribed burns all contributing to VOC concentrations at the OLC receptor site. Prescribed burning reached a peak of 15% of the total VOC late at night. Biogenic sources contributed more towards the end of the measurement period (early May), when the vegetation entered a more photosynthetically active period. Regional CO background concentrations determined from intercepts of monthly CO-NOy regressions at OLC, correspond with the prescribed burn activities in the counties surrounding Fort Benning and remaining Georgia, indicating a more regional character of this air pollution source, and greater importance of its smoldering emissions. With increasing time and acres burned, the PM2.5 mass concentration increased, and with it the organics fraction. As the burns were conducted in the warmer season, the increased abundance of ozone and other photo-oxidants led to more oxygenated particulate organics and more rapid SOA formation, indicated by increasing ratios of organic mass to organic carbon (OM/OC) and organic to elemental carbon (OC/EC). At OLC, the strongest direct impact in PM2.5 pollution from prescribed burning emissions were encountered at night under clear skies, nocturnal temperature inversion, and slow moving easterly component flow (along the Upatoi Creek), contributing up to ~52 % to the total OC. Outlook and Recommendations The results from the investigation of the Oct/Nov 2001 period suggest that the clear skies with moderate to calm wind conditions typically encountered during “good” burning opportunities bear the potential to accumulate smoldering emissions in the shallow nocturnal inversion layers. Therefore, it may be advantageous to wait one day between burnings, in order to dilute and vent the emissions by a convectively well-mixed (daytime) boundary layer. This should be reflected in the recommendations published by the Georgia Forestry Commission (GFC), which the private land owners, who conduct the majority of prescribed burns state-wide, can follow and reduce the impact on regional air quality. The five exceedances of the 24-h NAAQS PM2.5 level observed locally confined to the OLC site during the Oct/Nov 2001 period contributed to an annual arithmetic mean of 16.9 μg m-3, which is 1.9 μg m-3 above the annual PM2.5 NAAQS. Excluding these five exceedances yields an annual mean of 14.4 μg m-3, clearly below the NAAQS. Correspondingly, the three-year annual averages including 2001 would have not violated the NAAQS. Since the most severe exceedances in 2001 were caused by Fort Benning wildfires, and considering such far-reaching consequences, it is advisable to consider more aggressive attempts to extinguish large unintentional fires. One practice that might be reconsidered is allowing wildfires to continue to burn on land parcels on which fire management is desirable. Given the implications on air quality, it may be more reasonable to extinguish the wildfire and conduct a controlled burn at a later, more appropriate time. Both the fine PM mass and the organics mass fraction increased as prescribed burns were conducted later in spring and early summer likely due to increased abundance of and contribution from SOA. Compared to other years, the SOA formations derived for March and May 2003 must have been below normal, because of the above normal precipitation across Georgia that year. The SOA contributions to total fine PM mass observed during the much drier April, however, were the highest overall, with maximum O3 levels indicating an already high oxidative capacity of the lower atmosphere. Since burns were not exclusively conducted on Georgia’s military installations only but region-wide, the creation of incentives to minimize burns in the warmer, photochemically more active months seems beneficial for lowering regional fine PM levels. In order to further develop potential benefits for the public health and welfare of the State of Georgia in meeting air quality standards, and in response to the need for guidance in the development of a Smoke Management Plan (SMP) for Georgia, the development of detailed source profiles for the specific prescribed burning activities on and around Georgia’s military installations is necessary. In a Phase I continuation of this project here, first smoke samples were collected in a brief field intensive in April 2004, and analyzed for various aerosol constituents in order to develop more realistic emissions profiles of organic compounds and tracers than what is currently available from laboratory-based combustion experiments. Currently, the conventional GC/MS analysis is being improved and other methods being developed by different research groups in the scientific community, that will include the detection of more polar (acidic and alkaline) organic compounds in the particle phase, which constitute a large fraction of the primary PM2.5 emitted by open biomass burning. With the sampling and advanced analysis of more plumes, more precise source profiles will be established. Thus, with the information gained from improved source apportionment analyses of samples collocated at routine network sites, the development of an effective SMP can begin, providing the ecological benefits afforded by prescribed burning without compromising an area’s ability to meet clean air goals. 2 INTRODUCTION Uncontrolled wild fires are a potential threat to life and property across the Nation and especially in the western United States. Prescribed fires are currently considered to become an integral part of public land management practices. For example, the National Interagency Fire Center (NIFC) is the nation’s support center for wild land firefighting. The NIFC collaborates with several federal and state agencies to coordinate and support wild land fire and disaster operations. It collects and publishes wild land fire data reported by the various agencies. While wild fires have been reported since 1960, prescribed burn data have been gathered since 1995 from five major US land management agencies, the USDA Forest Service (USFS), the Bureau of Indian Affairs (BIA), the Bureau of Land Management (BLM), the National Park Service (NPS), and the US Fish and Wildlife Service (FWS). Figure 1 depicts the history of wild land fires in terms of sizes (in acres burned) and frequencies (locations and occurrences) relative to the - more limited – record of acres burned per prescription. While the graph seems to indicate a trend towards less fire occurrences over time, the variability of total acres burned seems to increase, with particularly large total areas burned in 1996, 2000, and 2002, pointing to the occurrence of fewer but larger fires. Also, the 5-year averaged trend indicates an increase of long-term average total areas burned nation wide over the last 10 years. The hoped for benefits of prescribed burns causing an overall reduction of the frequency and size of wild fires is not readily discernible, and requires more data for any conclusive statistical evaluation, although the increase in prescribed burning activity beginning in 1996 coincides with a reduction in overall wild land fire areas nation wide. 
Figure 1: Nation wide annual total wild land fires burned and occurrence frequency in comparison with annual total prescribed burning areas from five major US land management agencies [NIFC, 2004]. The yellow trace is the 5-year smoothed trend line of the average annual wild land area burned. Large wildfires now blazing in California, Arizona and New Mexico are the latest evidence that the plan to “fireproof” the West’s forests has backfired. Fire suppression, logging and grazing on fire-prone public land were intended to reduce the risk of fires, but many Western forests are now more flammable [Norm Christensen, Duke University fire ecologist in an ISDN broadcast interview, May 24, 2004]. Current wildfire management practices in the Western US apparently fail to take into account local conditions like weather and topography, and do not give top priority to the most hazardous fuel source, i.e. ground fuel such as dry grasses, pine needles and low shrubs. The attempt to suppress wildfires by indiscriminate logging is considered to aggravate the problem by thinning a fire-prone forest’s canopy and littering its floor with sawdust and other combustible debris, which can accumulate to dangerous levels. The loss of canopy increases wind speed and air temperature, and decreases humidity inside the forest. As a result, ground fuel fires that break out can spread faster and farther than they would normally. The U.S. Army manages over 12 million acres of federal and state training lands and testing areas on more than 300 installations throughout the 50 States. These installations vary in size from tens of acres to millions of contiguous acres, with the largest installations found in the southwestern and western regions of the nation, as well as in Alaska. The three largest military installations in Georgia are Forts Stewart, Benning, and Gordon, occupying total land areas of 275,000, 180,000 and 55,000 acres, respectively. Like many other Army lands, the training areas of these Georgia installations are relatively undeveloped, providing important ecological settings and habitat for a variety of flora and fauna, including many threatened and endangered species. Prescribed burning is the preferred method of choice to manage forested land in the South-Eastern US, and mandated by the Endangered Species Act (ESA) for areas that represent the natural habitat of endangered species, as is the case for most of the long leaf pine forests in the South-East. Hence, private land owners and land managers on military installations a like use prescribed burning. Of the 24.4 million acres forested land in Georgia, which is ~66 % of the State’s total land area, 72 % are privately owned, 21 % used in the forest industry, 4 % are otherwise public, and 3 % are national forests [Thompson, 1998]. The open burning of biomass and bio-fuel is essential in creating and maintaining functional ecosystems and achieving other land use objectives [Hardy and Leenhouts, 2001]. For example, Georgia’s economy is heavily supported by agriculture and forestry. Both of these vocations utilize prescribed burning practices to cultivate agriculture, maintain natural forests, protect endangered species, and ultimately protect human lives and property. The State of Georgia regulates open burning to assure air quality, minimize fire danger and protect wildlife species such as Bob White Quail, Red-cockaded Woodpecker, Eastern Wild Turkey, and White Tail Deer that are designated by state initiatives for wildlife management. Native songbirds and flora are also dependent on fire in many of these ecosystems. Benefits similar to the ones illustrated above for the entire nation, have been observed for the prescribed burns conducted on Fort Benning’s military installation: The occurrence of wild fires has decreased with increasing total area treated by prescribed burning as shown in Figure 2. 
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