Re-evaluation of the reaction rate coefficient of CH3Br + OH with implications for the atmospheric budget of methyl bromide

The reaction rate coefficient k(CH3Br + OH) has been determined in the temperature range 298-373 K, using pulse radiolysis/UV kinetic spectroscopy, and at 298 K using a relative rate method. The Arrhenius expression obtained from a fit to the experimental results is (2.9 ± 0.9) × 10−12 exp(−(1230 ± 125)/T) cm3 molecule−1 s−1, which is greater than the expression currently recommended. The relative rate experiments give k(298 K) = (4.13 ± 0.63) × 10−14 cm3 molecule−1 s−1. The results of the absolute and relative rate experiments indicate that the source budget of atmospheric CH3Br should be reinvestigated, as was recently done for CH3Cl.