Figure 4.30 Schematic of the partitioning between BrO and Br (the sum of which is BrJ. Each arrow is marked with the reaciants that facilitate the conversion indicated by the arrow.

To complete the cycle, Br is converted back to BrO in the reaction

Using reactions (4.74)-(4,77) and assuming photochemical steady state, the ratio [Brl/fBrO] can be written as

Figure 4.31 plots the related quantity [BrO|/[BrJ, the fraction of Br, that is in the form of BrO (]BrO]/[Br,] = 1 /(1 + [Br]/[BrO])). BrO makes up the vast majority of Br, in the lower stratosphere, and about 50% in the upper stratosphere. This can be contrasted to the CI, family, in which CIO makes up the vast majority of CI, throughout the stratosphere.

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