1Earth System Research Laboratory, Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80305, USA
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
*currently at: Institute of Chemical Engineering and High Temperature Chemical Processes (ICE-HT), Foundation for Research and Technology Hellas (FORTH), Patras, 26504, Greece
Received: 20 Nov 2013 – Published in Atmos. Chem. Phys. Discuss.: 16 Dec 2013
Abstract. 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).
Revised: 14 Feb 2014 – Accepted: 14 Feb 2014 – Published: 26 Mar 2014
Papanastasiou, D. K., McKeen, S. A., and Burkholder, J. B.: 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, 2014.