Sensitivity of Global Ozone and PM2.5 Concentrations to Climate Change

An integrated global model of climate, tropospheric gas-phase chemistry and aerosols has been used to investigate the sensitivity of global O3 and PM2.5 concentrations to climate change. Representative future climate has been imposed on the system using ocean boundary conditions corresponding to the IPCC SRES A2 scenario for the 2050s decade. The simulated future climate corresponds to a 1.7 K increase in the global annual-average surface temperature and a 13% increase in the tropospheric water vapor burden. Tropospheric O3 burden and lifetime in the future climate run decrease due to increased loss rates by O3 photolysis in the presence of water vapor, which more than compensates for the increased O3 chemical production associated with increased temperatures. The predicted changes in surface O3 correlate strongly with the changes in local water vapor concentrations, and to a lesser extent, the changes in local O3 chemical production. The global burdens of PM2.5 species in the future climate run decrease due to increased wet deposition loss rates, associated with increased global annual-average precipitation. Regional-scale changes in the predicted surface PM2.5 concentrations depend upon the changes in the regional precipitation, the processes leading to the formation of the species and transport. The robustness of the predicted regional PM2.5 changes is strongly dependent upon a competition between regional-scale precipitation changes, production rates, and gas-aerosol partitioning.