SPACCIM: A parcel model with detailed microphysics and complex multiphase chemistry

Multiphase processes, such as the uptake of gases by clouds or the production of gas phase halogens from particulate halides are of increasing importance for the understanding of the tropospheric system. Mass transfer and chemical reactions modify the concentrations of stable compounds and oxidants in either phase. The parcel model SPACCIM is presented which combines a complex multiphase chemical model with a detailed microphysical model. For this purpose, a new coupling scheme is implemented. The description of both components is given for a fine-resolved particle/drop spectrum. The SPACCIM approach allows the coupling of multiphase chemical models with microphysical codes of various types. An efficient numerical solution of such systems is only possible utilizing the special structure. An implicit time-integration scheme with an adapted sparse solver for the linear systems is applied. Its numerical efficiency and robustness is analyzed for two scenarios and versions of different complexity of the multiphase chemistry mechanism CAPRAM. The sensitivity of simulation results against variations in the particle/droplet size resolution, the coupling time step and numerical control parameters is discussed. Guidelines for an “optimal” choice of control parameters are derived from this sensitivity study. The coupling scheme operation is always robust and reliable. Model simulations are compared with several measurements from the FEBUKO field campaign. Simulated and measured results show a reasonable agreement.