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C. The Many Sources of an Ozone-depleting Substance

Narrator: This is Science Today. Methyl bromide is a substance that's produced naturally by the oceans and plants on land. But it's also a widely manufactured pesticide and by-product of fuel combustion. Robert Rhew, a researcher at the University of California's Scripps Institution of Oceanography, says because methyl bromide is an ozone-depleting substance, there are national efforts to control its production.

Rhew: And the big question is - how much is being produced by humans and how much is being produced by nature? And what I'm working on is trying to figure out how the natural system works independent of the human system. In order to try to understand what's happening currently in the atmosphere, that's a prerequisite to trying to predict what's going to happen in the future - especially when we want to implement certain regulations.

Narrator: Rhew and his colleagues recently discovered salt marshes are one of the largest land sources of methyl bromide - but there's still about 30% that's unaccounted for.

Rhew: By identifying this new terrestrial source for these compounds, we're adding a piece to the puzzle.

Narrator: For Science Today, I'm Larissa Branin.