Rate constants for the reactions of OH with CH[sub 3]Cl, CH[sub 2]Cl[sub 2], CHCl[sub 3], and CH[sub 3]Br

Rate constants for the reaction of OH with CH[sub 3]Cl, CH[sub 2]Cl[sub 2], CHCl[sub 3], and CH[sub 3]Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC-152a (CH[sub 3]CHF[sub 2]) and (for CH[sub 2]Cl[sub 2]) HFC-161 (CH[sub 3]CH[sub 2]F). Using absolute rate constants for HFC-152 and HFC-161, which they have determined relative to those for CH[sub 4], CH[sub 3]CCl[sub 3], and C[sub 2]H[sub 6], temperature dependent rate constants of both compounds were derived. The derived rate constant for CH[sub 3]Br is in good agreement with recent absolute measurements. However, for the chloromethanes all the rate constants are lower at atmospheric temperatures than previously reported, especially for CH[sub 2]Cl[sub 2] where the present rate constant is about a factor of 1.6 below the JPL 92-20 value. The new rate constant appears to resolve a discrepancy between the observed atmospheric concentrations and those calculated from the previous rate constant and estimated release rates. 23 refs., 5 figs., 3 tabs.