Methyl bromide deposition to soils

Methyl bromide is the single largest contributor of stratospheric Br and an important contributor to stratospheric ozone depletion. Soils have recently been identified as a significant sink of methyl bromide (Shorter et al., 1995, Nature 377 (6551), 717–719). As is the case for other trace gases, methyl bromide deposition rates vary for different ecosystems and depend on soil characteristics. The limited data available prevents an accurate global estimate but does allow initial attempts to establish the importance of this sink. We have investigated the methyl 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. These rates result in a global sink that is higher, although of the same order of magnitude, than that reported by Shorter et al. (1995). The partial lifetime of methyl bromide with regard to soil sink is estimated 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 (ODP) range between 0.22 and 0.48. About half of the uncertainty in the ODP estimates is associated with current global methyl bromide soil-sink estimates.