The very short-lived ozone depleting substance CHBr3 (bromoform): revised UV...

Papanastasiou, D. K., S. A. McKeen, and J. Burkholder (2014), The very short-lived ozone depleting substance CHBr3 (bromoform): revised UV absorption spectrum, atmospheric lifetime and ozone depletion potential, Atmos. Chem. Phys., 14, 3017-3025, doi:10.5194/acp-14-3017-2014.

CHBr3 (bromoform) is a short-lived atmospheric trace compound that is primarily of natural origin and is a source of reactive bromine in both the troposphere and stratosphere. Estimating the overall atmospheric impact of CHBr3 and its transport to the stratosphere requires a thorough understanding of its atmospheric loss processes, which are primarily UV photolysis and reaction with the OH radical. In this study, UV absorption cross sections, σ (λ, T ), for CHBr3 were measured at wavelengths between 300 and 345 nm at temperatures between 260 and 330 K using cavity ring-down spectroscopy. The present results are compared with currently recommended values for use in atmospheric models, and the discrepancies are discussed. A parameterization of the CHBr3 UV spectrum for use in atmospheric models is developed, and illustrative photolysis rate calculations are presented to highlight the impact of the revised σ (λ, T ) values on its calculated local lifetimes. For example, the photolysis rate in the tropical region obtained with the present spectral data is 10–15 % lower (longer lifetime) than obtained using currently recommended cross section values. Seasonally dependent ozone depletion potentials (ODPs) for CHBr3 emitted in the Indian sub-continent were calculated to be 0.10, 0.34, 0.72, and 0.23 (winter, spring, summer, fall) using the semi-empirical relationship of Brioude et al. (2010).

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Upper Atmosphere Research Program (UARP)