RATE CONSTANTS FOR THE REACTIONS OF OH WITH CH3CL, CH2CL2, CHCL3, ANDCH3BR

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br have been measured by a relative rate technique m which the reac tion rate of each compound was compared to that of HFC-152a (CH3CHF2) and (for CH2Cl2) HFC-161 (CH3CH2F). Using absolute rate constants for HFC-152a and HFC-161, which we have determined relative to those for C H4, CH3CCl3, and C2H6, temperature dependent rate constants of both co mpounds were derived. The derived rate constant for CH3Br is in good a greement with recent absolute measurements . However, for the chlorome thanes all the rate constants are lower at atmospheric temperatures th an previously reported, especially for CH2Cl2 where the present rate c onstant is about a factor of 1.6 below the JPL 92-20 value. The new ra te constant appears to resolve a discrepancy between the observed atmo spheric concentrations and those calculated from the previous rate con stant and estimated release rates.