PCDD/F and aromatic emissions from simulated forest and grassland fires

Abstract

Emissions of polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/F) from simulated grassland and forest fires were quantitatively sampled to derive emission factors in support of PCDD/F inventory development. Grasses from Kentucky and Minnesota; forest shrubs from California and Florida; and pine forest biomass from the Piedmont region of North Carolina, western North Carolina, and coastal Oregon were collected and tested in a burn facility that mimicked a prescribed fire in the natural environment scenario. Ambient sampling methods for PCDD/F were variously accompanied by real-time measurements of major aromatic species, including benzene, toluene, naphthalene, and styrene. Emission factors in mass of toxic equivalent (TEQ) of PCDD/F per kg of carbon burned (kg Cb) for the two grasses averaged 0.32 ng TEQ/kg Cb. Burn tests ( n = 27) on forest biomass from the five sources show PCDD/F emission factors ranging from 0.3 to 26.3 ng TEQ/kg Cb, with a mean and median of 5.8 and 3.3 ng TEQ/kg Cb, respectively. Variation of the forest green/brown needle content, sample size, burn scenario, and facility ventilation rate showed no consistent effects on PCDD/F emissions. For forest burns, 30–35% of the PCDD and 50-55% of the PCDF emissions occurred during the flaming period from 0 to 5 min, while the highest emission factors (per mass of carbon burned) were recorded during the smoldering period from 5 to 60 min. Emissions of PCDD/F exceeded those present in the raw biomass by a factor of four, confirming PCDD/F formation from combustion rather than from simple surface volatilization. The majority of the PCDD/F partitions to the emissions rather than the ash.