AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Fluoride Emissions from Biomass Burning
Thilina Jayarathne, Chelsea Stockwell, Robert J. Yokelson, Shunsuke Nakao, ELIZABETH STONE, University of Iowa
Abstract Number: 289 Working Group: Biomass Burning Aerosol: From Emissions to Impacts
Abstract Fluoride is the 13th most abundant element on earth and widely dispersed throughout the lithosphere, hydrosphere, biosphere and atmosphere. Fluorides enter the atmosphere through soil dust, sea spray, geysers and volcanoes, as well as anthropogenic sources like brick manufacturing, aluminum smelting, fertilizer production and coal burning. Vegetation accumulates fluorides from the surrounding environment, which can be toxic to plants and animals that graze on them. In the study, we test the hypothesis that the burning of biomasses re-emits fluoride into the atmosphere. We analyzed water-soluble inorganic fluoride in 55 fine particulate (PM2.5) samples from biomass burning collected at the USDA Forest Service Fire Sciences Laboratory in Missoula, Montana during FLAME-IV laboratory study, using ion chromatography coupled with conductivity detection. Standard addition experiments and energy dispersive x-ray analysis were used to confirm the presence of fluoride in PM2.5 samples. Water-soluble fluoride was detected in samples from all conifers (n=11) and agricultural residues (n=15), but only 40% of the grasses and other perennial plants (n=13). Fluoride was not detected in remaining samples (n=16) collected from peat, shredded tires and cook-stove burns. A tight correlation (R2 > 0.95) between mass of PM2.5 and fluoride emitted from conifers and agricultural residues reflects a consistent fluoride mass fraction among similar fuels. Fluoride accounted for 0.06 – 0.15 % of PM2.5 emissions from conifers and 0.05 – 0.13 % of fluoride emitted by burning grasses and other perennial plants. Agricultural residues varied considerably, from 0.01 – 0.44 %, with maxima influenced by application of fluoride-containing fertilizers. PM2.5 emissions depended on burning conditions of fuel; hence fluoride emission factors were also influenced by combustion efficiency. These measurements help to explain prior ambient observations in which particulate fluoride in the atmosphere coincided with major biomass burning events and provide new insight to the global cycling of fluoride.