| Summary: | Tropospheric methyl bromide (CH3Br) is the largest source of bromine to the stratosphere and plays an important role in ozone depletion. Here, the first stable bromine isotope composition (%26dgr%3B81Br) of atmospheric CH3Br is presented. The %26dgr%3B81Br of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of %26minus%3B0.04%26plusmn%3B0.28%26permil%3B ranging up to +1.75%26plusmn%3B0.12%26permil%3B. The Stockholm %26dgr%3B81Br versus concentration relationship corresponds to an apparent isotope enrichment factor of %26minus%3B4.7%26plusmn%3B3.7%26permil%3B, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric %26dgr%3B81Br measurements, which in the future may be combined with other isotope systems in a top-down inverse approach to further understand key source and sink processes of methyl bromide.
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