Tropospheric sulfur cycle in the Canadian general circulation model

Emission, transport, chemistry, and scavenging of the gaseous sulfur specie s dimethyl sulfide and sulfur dioxide (SO2) and sulfate aerosols are calcul ated on-line with the meteorology in the general circulation model (GCM) of the Canadian Centre for Climate Modelling and Analysis (CCCMA). Additional ly, prognostic equations for cloud water and cloud ice have been introduced . The sensitivity of this sulfur cycle to differences in GCM physics and dy namics has been studied by comparing the results to those obtained with the ECHAM GCM which has a very similar sulfur cycle and cloud scheme, but a di fferent turbulent diffusion and convection scheme, The differences in the g lobal mean burdens of SO2 and sulfate are less than 2%. Simulated surface S O2 concentrations with CCCMA in winter as well as the seasonal cycle are in better agreement with observations at several sites than those simulated w ith ECHAM because of stronger boundary layer mixing in CCCMA. The simulated surface SO42- with CCCMA, however, is often higher than observed and in EC HAM. Additionally, sensitivity experiments showed that the global sulfur bu dgets are most sensitive to changes in the cloud cover parameterization and less sensitive to changes in pH calculation and oxidation of SO2 in convec tive clouds. The results of the sensitivity experiments give evidence for t he importance of all of these effects on the geographical and vertical dist ribution of sulfur and cloud liquid water.