The Global Modeling Initiative (GMI) Chemical Transport Model (CTM) is part of the NASA Modeling Analysis and Prediction (MAP) program. The GMI CTM is used to assess the impacts of atmospheric circulation and composition change due to anthropogenic emissions, such as those from aircraft, biomass burning, fossil fuel combustion, and use of ozone depleting substances (ODS). GMI studies investigate changes in stratospheric ozone and the roles of long-range transport and changing emissions on air quality.

GMI CTM simulations use a combined stratospheric-tropospheric chemical mechanism that has been adopted by the GEOS models. This mechanism was first used in 2004 and has been extensively vetted through comparisons with satellite and ground-based measurements of a wide range of trace gases. Updates to the GMI mechanism are first evaluated in the GMI CTM prior to adoption by GEOS. The GMI stratospheric reactions are considered the gold standard for stratospheric chemistry and have been added to the Harvard GEOS-Chem model’s tropospheric chemical mechanism, now called the UCX mechanism.

The GMI CTM integrates multi-decadal simulations with the MERRA2 analysis for composition and transport studies. The simulations are maintained in near real-time and each year parallel simulations are integrated with heterogeneous halogen reactions turned off, allowing the quantification of Antarctic and Arctic ozone depletion.