METHYL-BROMIDE DEPOSITION TO SOILS

Methyl bromide is the single largest contributor of stratospheric Br a nd an important contributor to stratospheric ozone depletion. Soils ha ve recently been identified as a significant sink of methyl bromide (S horter et at., 1995, Nature 377 (6551), 717-719). As is the case for o ther trace gases, methyl bromide deposition rates vary for different e cosystems and depend on soil characteristics. The limited data availab le prevents an accurate global estimate but does allow initial attempt s to establish the importance of this sink. We have investigated the m ethyl bromide sink for four different ecosystems, and found deposition rates that range from about 0.02 +/- 0.005-0.38 +/- 0.170 cm s(-1). T hese rates result in a global sink that is higher, although of the sam e order of magnitude, than that reported by Shorter er ai. (1995). The partial lifetime of methyl bromide with regard to soil sink is estima ted to be between 0.97 and 3.54 yr resulting in a mean total lifetime of 0.61 yr. Estimates of a methyl bromide ozone depletion potential (O DP) range between 0.22 and 0.48. About half of the uncertainty in the ODP estimates is associated with current global methyl bromide soil-si nk estimates. (C) 1998 Elsevier Science Ltd. All rights reserved.