Kinetics of the OH Reaction with Methyl Chloroform and Its Atmospheric Implications

The rate coefficients for the reaction of hydroxyl (OH) radicals with methyl chloroform (CH(3)CCI(3)) were measured between 243 and 379 kelvin with the pulsed photolysis-laserinduced fluorescence method. The measured rate coefficients at 298 and 277 kelvin were approximately 20 and approximately 15%, respectively, lower than earlier values. These results will increase the tropospheric OH concentrations derived from the CH(3)CCI(3) budget analysis by approximately 15%. The predicted atmospheric lifetimes of species whose main loss process is the reaction with OH in the troposphere will be lowered by 15% with consequent changes in their budgets, global warming potentials, and ozone depletion potentials.

The oxidizing capacity of the earth's atmosphere: probable past and future changes

The principal oxidants in the lower atmosphere are ozone (O3) and two by-products of O3 photodissociation, the hydroxyl radical (OH) and hydrogen peroxide (H2O2). A number of critical atmospheric chemical problems depend on the earth's "oxidizing capacity," which is essentially the global burden of these oxidants. There is limited direct evidence for changes in the earth's oxidizing capacity since recent preindustrial times when, because of industrial and population growth, increasing amounts of O3 precursor trace gases (carbon monoxide, nitrogen oxides, and hydrocarbons) have been released into the atmosphere. The concentrations of O3 and possibly H2O2 have increased over large regions. Models predict that tropospheric O3 will increase approximately 0.3 to 1% per year over the next 50 years with both positive and negative trends possible for OH and H2O2. Models and the observational network for oxidants are improving, but validation of global models is still at an early stage.