A dynamic aerosol module for global chemical transport models: Model description

We have developed a dynamic aerosol model that is capable of treating the binary nucleation of sulfate gas and its condensation to form aerosol particles. Coagulation among sulfate particles and of sulfate particles with nonsulfate particles is also treated. The model is built in a modular fashion that allows its easy incorporation into a global chemical transport model. The model uses the method of modes and moments to describe the aerosol size distribution, with an arbitrary number of modes possible. The parameterizations in the model are valid for tropospheric as well as stratospheric conditions. No operator splitting or fixed time steps are applied so that all aerosol processes are allowed to fully interact with each other during each time step. Here we examine the predictions of the model in comparison to a sectional model for a suite of test cases chosen to represent the range of possibilities in a global CTM. We show that the predictions for both number and surface area are within a factor of 1.2 of the sectional model for the four mode version of the model and are only slightly degraded if only two modes are specified. The prediction of the number of accumulation mode particles is within a factor of 2.1 of that from the sectional model within the boundary layer.