In GEOS-Chem v11-01, we replaced the legacy SMVGEAR chemistry solver with FlexChem, a new, clean implementation of the KPP chemical solver. We did this in order obtain the best performance when running GEOS-Chem in high-performance computing environments.
The new GEOS-Chem species database (also introduced in v11-01) provides a central location for storing the physical properties of GEOS-Chem species, including names, indices, molecular weights, and Henry's law constants. It also stores logical flags that denote whether each species is advected, is dry deposited, or is wet scavenged.
These new structural modifications also allowed us to remove some redundant infrastructure. Prior to v11-01, we had used two separate arrray fields to store species concentrations. Transported species (aka 'tracers") were kept in the State_Chm%Tracers array in units of either ppbv or kg. The species used in the SMVGEAR chemical mechanism were kept in the State_Chm%Species and CSPEC arrays in units of molec/cm3. Once we removed SMVGEAR from GEOS-Chem, we were also able to remove the duplicate array storage. In v11-01 and later versions, all species are now just stored in the State_Chm%Species array.
Please see the following resources for detailed information about the species used in GEOS-Chem simulations as well as the data structures in which they are stored: