An improved estimate of the oceanic lifetime of atmospheric CH₃Br

Abstract

Previous estimates of the partial atmospheric lifetime of CH3Br with respect to degradation in the ocean have not fully accounted for co-variation of sea-surface and boundary layer properties. Here we substantially reduce uncertainty in this calculation by using a coupled, ocean-atmosphere box model and a tightly gridded data set of oceanic and atmospheric properties. The best estimate of the partial atmospheric lifetime of CH3Br with respect to the ocean is 2.7 y with a possible range, due mainly to the choice of computational procedures for critical terms, of 2.4 to 6.5 y. This range is about one-third of that estimated previously. The total atmospheric lifetime, based upon oceanic, atmospheric, and proposed soil losses with all of their uncertainties, is 0.8 (0.6 to 1.4) y. Only 28% of this total uncertainty is attributable to the uncertainty in oceanic loss. Oceanic consumption of CH3CC13: Implications for tropospheric OH,,/. Geophys. Res., 96, 22347-22355, 1991. J.H. Butler and S. A. Yvon, Climate Monitoring and Diagnostics Cardone, V.J., J.G. Greenwood, and M.A. Cane, On trends in historical Laboratory, National Oceanic and Atmospheric Administration. 325 marine wind data, ,/. of Climate, 3,113-127, 1990. Broadway, Boulder, CO 80303. (e-mail: syvon•cmdl.noaa. gov) De Bruyn, W.J. and E.S. Saltzman, Measurement of the diffusivity of methyl bromide in pure water and the solubility of methyl bromide in seawater, (

Changing concentrations of CO, CH 4 , C 5 H 8 , CH 3 Br, CH 3 I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments

“…However, the production term dominated, driving the saturation anomaly from negative to nearly neutral, meaning that the fertilized patch was no longer a sink for atmospheric CH 3 Br. Although some regions of the oceans are a major source of CH 3 Br, overall the oceans may be a net sink (42). Previous measurements in the Southern Ocean (43) show that it is an important sink for atmospheric CH 3 Br, a result of bacterial degradation (40), consuming Ϸ12 Gg⅐year Ϫ1 and representing 6% of the total estimated global sink (S. Yvon-Lewis, personal communication; refs.…”

The potential effect of oceanic biological degradation on the lifetime of atmospheric CH3Br

“…The scenarios more likely to represent the real ocean are Cases 5 and 6, which yield a partial atmospheric lifetime of 1.8-1.9 y (Figure 1 c and d). The full possible range, calculated with all uncertainties as done in Yvon and Butler [1996], is now 1.1 -3.9 y. This yields a total atmospheric lifetime of 0.7 y (0.6 -0.9 y).…”

Atmospheric methyl halides and dimethyl sulfide from cattle

“…The most reliable quantity in (1) is the atmospheric burden: 145 Gg of CH3Br (1 Gg = 10 9 g) and 5000 Gg of CH3C1 (these data are from Butler [1994], Khalil et al [1993], and Singh et al [1983] and are probably accurate to within Gg yr -x [Yvon-Lewis and Butler, 1997]. Alternatively, current sink estimates may be too large; for relevant data and discussion of individual sources and sinks, see Yvon and Butler [1996] and Butler and Rodriguez [1996]. Briefly, major sources are thought to be biomass burning and emissions from fumigated agricultural soils.…”