Measurement of the Deposition and Fate of Sulfur-Dioxide-35 in a Pine Plantation

An experiment was carried out to determine the uptake rate and fate of SO² absorbed by the forest canopy. The radioactive tracer, ³⁵S was used. Branches of loblolly pine were exposed to ³⁵SO₂ in the field with a portable chamber. The exposed branches were excised and a sample of needles was immediately washed with distilled water. The needles and water collected in the field were analyzed for ³⁵S content. The results indicated that a portion of the ³⁵S could be washed from the needles and another portion was not removed with a water rinse. The portion that could not be removed by rinsing was absorbed at a rate and followed patterns of absorption, which suggested that absorption was controlled by stomatal diffusion, and thus was internal. The ³⁵S that could be removed by rinsing appeared to be surface absorption. The average deposition velocity for the entire leaf surface of the pine plantation was 0.0041 m/s. The distribution of ³⁵S was investigated by serial extractions. The fresh whole needles were rinsed in distilled water. Following rinsing, the dried and crushed leaf material was extracted with acetone, and then extracted with hexane. About 50% of the ³⁵S activity was removed by the water rinse. About one-third, 30 to 38%, of the ³⁵S activity remaining after washing was found in each of the two extracts and about one-third in the residual material left after extraction. The information contained in this article was developed during the course of work under a cooperative agreement between the Electric Power Research Institute (RP1813-2) the U.S. Department of Energy (DE-AC0982R11008). By ceptance of this paper, the publisher and/or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper.