- GIM was formed as a merger project from the International Global Aerosol Program (IGAP) project MEARC in 1997 and was implemented under the IGAC Global Focus. GIM aimed to address the development and application of advanced 3-D global chemical transport and coupled climate and chemistry models, emphasizing tropospheric applications. It conducted a series of model intercomparison exercises focusing on key problems in tropospheric chemistry as well as collaborated with other modeling development efforts.