TIMESCALES IN ATMOSPHERIC CHEMISTRY - CH3BR, THE OCEAN, AND OZONE DEPLETION POTENTIALS

Methyl bromide (CH3Br) supplies about half of the chemically active br omine (Br-y) in the stratosphere, Efforts to control Br-y-catalyzed oz one depletion by phasing out, for example, agricultural use of CH3Br m ay be thwarted by a lack of understanding of how the varied biogeochem ical processes interact as a coupled system: in addition to the chemic al industry, large natural sources come from the ocean; and losses occ ur in the atmosphere, ocean, and soils, A simplified one-dimensional s tratosphere-troposphere-ocean model for {CH3Br, Br-y} that fits curren t understanding of sources and sinks is analyzed in terms of natural m odes, Surface and ocean sources have effectively different steady stat e lifetimes (1.0 and 0.5 years, respectively), but the natural-mode de cay times of the system (1.8 years for CH3Br and 4.5 years for stratos pheric Br-y) do not depend on the location of sources, The cumulative ozone depletion resulting from a single atmospheric release of CH3Br i ntegrates over the consequent slow rise and fall of Br-y in the lower stratosphere, Thus, in spite of the 1-year lifetime of CH3Br, only hal f of the anticipated ozone recovery occurs in the first 7 years.