Description

Although forest burning is prescribed widely across the United States, it is most commonly practiced in the Northwestern and the Southern United States. In 1978, approximately 37 million metric tons of forest fuels on all forest ownerships were burned by prescription; approximately 12.5 million metric tons were burned in the South. This burning produces an estimated 0.6 million metric tons of total suspended particulate matter (TSP) annually in the United States. Of that total, about 0.2 million metric tons of TSP originate in the South. Considerable uncertainty exists over the estimation of benzo(a)pyrene (BaP) produced by prescribed burning. Forest and agricultural burning were estimated by the National Academy of Sciences to emit 127 metric tons per year in 1968, but that figure was reduced to 9.5 metric tons per year in 1972. In a 1977 report, EPA estimated BaP emissions from prescribed burning to be 4.5 metric tons nationally, which was 0.5 percent of the BaP from all sources. A serious limitation in these results was that they represented only one fuel type burned by prescription in the South. Perhaps more important, they represented a fire environment in which pine needles were isolated from all natural variations in conditions of duff, soil, moisture, and wind. Questions were raised. Are the order of magnitude differences between BaP/TSP ratios from backing and heading fires seen in laboratory fires also characteristic of fires in natural forest settings? What is the range of BaP/TSP ratios for some other fuels commonly prescribed burned in the South? The study described here was directed toward these questions.