Evaluation of Ozone Depletion Potentials for chlorobromomethane (CH₂ClBr)and 1-bromo-propane (CH₂BrCH₂CH₃)

Chlorobromomethane (CH₂ClBr) and 1-bromo-propane (CH₂BrCH₂CH₃ or simplified as 1-C₃H₇Br) are being considered for use as solvents and potentially in other applications. As with other chemicals that contain chlorine and/or bromine, it is important to determine the potential environmental effect from use and emissions of such compounds, including effects on stratospheric ozone. In this paper, the Ozone Depletion Potentials (ODPs), an important measure of the potential effects on ozone, are evaluated for these two compounds using our two-dimensional chemical-transport model of the troposphere and stratosphere. This is the first time these compounds have, to our knowledge, been evaluated with atmospheric models. Our model results show that the main removal process (ca. 99%) in the atmosphere for these compounds is the reaction with OH radicals. Photolysis has only a minor ( ≤ 1%) effect on the atmospheric lifetimes of either compound. The atmospheric lifetimes of CH₂ClBr and 1-C₃H₇Br due to atmospheric reactions are evaluated to be 0.40 yr (146 d) and 0.03 y (11 d), respectively. However, oceanic losses are likely to be important for CH₂ClBr. Because of limited data on solubility and degradation in sea water, the lifetime for ocean loss currently has a range of 0.43-0.65 yr. This results in a total lifetime for CH₂ClBr of 0.21-0.25 yr. An ocean sink for 1-C₃H₇Br is likely to have an insignificant effect on its atmospheric lifetime or ODP. The ODP for 1-C₃H₇Br is evaluated to be 0.006, while the ODP for CH₂ClBr including the effects of the ocean sink is 0.11-0.13. There are additional uncertainties in these values due to ambiguities in measured reaction rates and in the model treatment of atmospheric processes.