THE GLOBAL IMPACT OF HUMAN ACTIVITY ON TROPOSPHERIC OZONE

Within a conceptual framework of stratospheric injection, CO-CH4 backg round tropospheric chemistry, parameterized pollution production in th e continental boundary layer and surface deposition, we use an 11 leve l GCTM to simulate global distributions of present and pre-industrial tropospheric O-3. The chemistry is driven by previously simulated pres ent and preindustrial NOx fields, while prescribed fields of CO, CH4 a nd H2O are held constant. An evaluation with measurements from 12 surf ace sites, 21 ozonesonde sites and 1 aircraft campaign finds agreement within +/-25% for 73% of the observations while identifying systemati c; errors in the wintertime high-latitude Northern Hemisphere (NH), th e Southern Hemisphere (SH) tropics during biomass burning, and the rem ote SH. We predict that human activity has increased the annual integr al of tropospheric ozone by 39% with 3/4's of that increase in the fre e troposphere, though the boundary layer [BL] annual integral has incr eased by 66%. The 2 largest components of the global O-3 budget are st ratospheric injection at 696 TgO(3)/yr, and loss through dry depositio n, which increases from 459 TgO(3)/yr to a present level of 825 TgO(3) /yr. While tropospheric chemistry's net contribution is relatively sma ll, changing from a preindustrial destruction of -236 TgO(3)/yr to a p resent production of +128 TgO(3)/yr, it is a balance between two much larger terms, -558 TgO(3)/yr of destruction in the background troposph ere and +686 TgO(3)/yr of production in the polluted boundary layer. H uman impact on O-3 predominates in the summertime extratropical NH and in the tropics during their biomass burning seasons [increases of 50% -100% or more]. Conversely, there has been little increase in most of the upper troposphere [<20%], where ozone's influence on tropospheric climate is strongest.