Relative roles of climate and emissions changes on future tropospheric oxidant concentrations

A Lagrangian chemistry-transport model (STOCHEM) was driven with meteorolog y derived from a slab ocean general circulation model for conditions approp riate to the present-day and at double CO2, and with emission scenarios app ropriate for present day conditions and for the year 2075. The results show conclusively that the effect of including the predicted chang eu to future climate is to reduce the simulated tropospheric ozone concentrations. The response of global tropospheric ozone in the period 1990-2075 was an increa se of 6.4 ppb when both climate and emissions changes were included, compar ed to an increase of 10.3 ppb when only emissions changes were considered. This difference is mainly due to water vapor and temperature increases, tog ether with some dynamical effects. There are considerable changes to other tropospheric oxidants, with OH, HO2, and H2O2 all increasing considerably i n response to climate changes. In contrast, OH decreases when only the emis sions are allowed to change. A replicate run of the control scenario with S TOCHEM using; a different year of meteorology showed considerable interannu al variability in local monthly mean ozone concentrations.