Stable bromine isotopic composition of atmospheric CH3Br.

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 (δ⁸¹Br) of atmospheric CH₃Br is presented. The δ⁸¹Br of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of −0.04±0.28‰ ranging up to +1.75±0.12‰. The Stockholm δ⁸¹Br versus concentration relationship corresponds to an apparent isotope enrichment factor of −4.7±3.7‰, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric δ⁸¹Br 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. [ABSTRACT FROM AUTHOR]