Partial picture of methyl bromide demands more pieces


  • Elaine Friebele


Consider the vast area and volume of the Earth's oceans as a large reservoir that produces, removes, and, to some degree, regulates gases—including some ozone-eating chemicals released into the atmosphere by human activities. New modeling studies based on recent monitoring data suggest such a picture, with the oceans taking from the atmosphere more methyl bromide, a source of ozone-destroying bromine, than previously thought. This rapid removal by the ocean shortens the average estimated lifetime of methyl bromide to just 0.7 of a year— much briefer than its former calculated lifetime of 2 years.

“Measurements show that in most of the oceans, methyl bromide is undersaturated, which suggests that sinks outweigh sources in the water,” said James Butler, coauthor of the modeling study, which appeared in the May 15 issue of Geophysical Research Letters. Butler, of NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL) in Boulder, and Shari Yvon-Lewis, of the University of Colorado, used latitude-dependent degradation rate constants based on monitoring data to model methyl bromide flux between the atmosphere and ocean. They found that the undersaturation of methyl bromide in the ocean requires a great deal more degradation than chemical reactions alone could accomplish.