Role of climate change in global predictions of future tropospheric ozone and aerosols

[ 1] A unified tropospheric chemistry-aerosol model within the Goddard Institute for Space Studies general circulation model II' is applied to simulate an equilibrium CO2-forced climate in the year 2100 to examine the effects of climate change on global distributions of tropospheric ozone and sulfate, nitrate, ammonium, black carbon, primary organic carbon, secondary organic carbon, sea salt, and mineral dust aerosols. The year 2100 CO2 concentration as well as the anthropogenic emissions of ozone precursors and aerosols/aerosol precursors are based on the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (SRES) A2. Year 2100 global O-3 and aerosol burdens predicted with changes in both climate and emissions are generally 5-20% lower than those simulated with changes in emissions alone; as exceptions, the nitrate burden is 38% lower, and the secondary organic aerosol burden is 17% higher. Although the CO2-driven climate change alone is predicted to reduce the global O-3 burden as a result of faster removal of O-3 in a warmer climate, it is predicted to increase surface layer O-3 concentrations over or near populated and biomass burning areas because of slower transport, enhanced biogenic hydrocarbon emissions, decomposition of peroxyacetyl nitrate at higher temperatures, and the increase of O-3 production by increased water vapor at high NOx levels. The warmer climate influences aerosol burdens by increasing aerosol wet deposition, altering climate-sensitive emissions, and shifting aerosol thermodynamic equilibrium. Climate change affects the estimates of the year 2100 direct radiative forcing as a result of the climate-induced changes in burdens and different climatological conditions; with full gas-aerosol coupling and accounting for ozone and aerosols from both natural and anthropogenic sources, year 2100 global mean top of the atmosphere direct radiative forcings by O-3, sulfate, nitrate, black carbon, and organic carbon are predicted to be + 0.93, - 0.72, - 1.0, + 1.26, and - 0.56 W m(-2), respectively, using present-day climate and year 2100 emissions, while they are predicted to be + 0.76, - 0.72, - 0.74, + 0.97, and - 0.58 W m(-2), respectively, with year 2100 climate and emissions.