PAST AND FUTURE CHANGES IN GLOBAL TROPOSPHERIC OZONE - IMPACT ON RADIATIVE FORCING

Calculations by a global three-dimensional chemical transport model of the atmosphere suggest that increased surface emissions of chemical c ompounds caused by industrial activities at mid-latitudes in the north ern hemisphere and by biomass burning in the tropics since the middle of the 19th century have produced an increase in the abundance of trop ospheric ozone along with a reduction in the oxidizing capacity of the atmosphere (globally averaged OH concentration reduced by 17% and met hane lifetime enhanced by 1.5 years). These perturbations in troposphe ric ozone result in a change in annually averaged radiative forcing of 0.37 W m(-2) (0.62 W m(-2) in the northern hemisphere during the summ er months). Future changes (1990-2050) in tropospheric ozone associate d with population increase and economic development (primarily in deve loping countries) are expected to be largest in the tropics, specifica lly in South and Southeast Asia. Further changes in the oxidizing capa city of the atmosphere could be small if the abundance of tropospheric water vapor increases as a result of anticipated climate change.