9630694 Crill This proposal was submitted in response to the Environmental Geochemistry & Biogeochemistry solicitation, NSF 96-2. It is being jointly funded by the Division of Earth Sciences, Atmospheric Sciences, and Environmental Biology. The proposed research will address the biogeochemistry of methyl bromide, a trace gas that plays a central role in stratospheric and tropospheric ozone balance. Limited information is available about its sinks, particularly the irreversible uptake and degradation by deposition to soils. The PIs propose to determine the effective CH3Br loss rate and the controlling chemical, physical, and biological parameters on representative soil and vegetative surfaces at near-ambient gas phase mixing ratios. The proposed research has three objectives: (1) to determine the rate and ubiquity of CH3Br consumption by soils at near ambient levels, (2) to determine in a quantitative manner the controls on soils consumption of CH3Br, and (3) to determine the magnitude and seasonality of deposition rates of CH3Br by direct measurements of soil exchange using chambers over a mature forest soil and an agricultural soil in the northeastern U.S..
