KINETICS OF THE REACTIONS OF CL ATOMS WITH CH3BR AND CH2BR2

The rate coefficients for the reactions of Cl atoms with CH3Br, (k1) and CH2Br2, (k2) were measured as functions of temperature by generating Cl atoms via 308 nm laser photolysis Of Cl2 and measuring their temporal profiles via resonance fluorescence detection. The measured rate coefficients were: k1 = (1.55 +/-0.18) X 10(-11) exp{(-1070 +/- 50)/T} and k2 = (6.37 +/- 0.55) X 10(-12) exp{(-810 +/- 50)/T} cm3 molecule-1 s-1. The possible interference of the reaction of CH2Br product with Cl2 in the measurement of kl was assessed from the temporal profiles of Cl at high concentrations of Cl2 at 298 K. The rate coefficient at 298 K for the CH2Br + Cl2 reaction was derived to be (5.36 +/- 0.56) X 10(-13) cm3 molecule-1 s-1. Based on the values of k1 and k2, it is deduced that global atmospheric lifetimes for CH3Br and CH2Br2 are unlikely to be affected by loss via reaction with Cl atoms. In the marine boundary layer, the loss via reaction (1) may be significant if the Cl concentrations are high. If found to be true, the contribution from oceans to the overall CH3Br budget may be less than what is currently assumed. (C) 1994 John Wiley & Sons, Inc.