Wetlands: a potentially significant source of atmospheric methyl bromide and methyl chloride

Tropospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl) are significant sources of ozone (O-3) destroying halogens to the stratosphere. Their O-3 depletion potential (ODP) can be determined from atmospheric lifetimes and therefore their atmospheric budgets, both of which are out of balance with known sink terms larger than identified sources. We have discovered a new source of CH3Br and CH3Cl emissions to the atmosphere at two wetland sites in the Northeastern United States. We have reason to believe that these compounds are biologically produced in situ. Our measurements indicate that the global annual flux of CH3Br and CH3Cl from wetlands could be as high as 4.6 Gg yr(-1) of CH3Br and 48 Gg yr(-1) of CH3Cl. These are preliminary estimates based on measurements made during the end of the 1998 growing season, a time period of decreased emissions of other trace gases such as methane (CH4).