Photolysis and chemistry configuration files


You won’t need to edit these configuration files unless you are changing the photolysis and/or chemistry mechanisms used in your GEOS-Chem Classic simulation.

Photolysis configuration files

These are found in the ExtData/CHEM_INPUTS/FAST_JX/ directory structure. Please see Input files for FAST-JX v7.0 for details.

Chemical mechanism configuration files

GEOS-Chem Classic simulations use source code generated by The Kinetic PreProcessor. If you need to update the default chemistry mechanism, you will need to do the following steps:

  1. Modify the relevant KPP configuration files (described below);

  2. Run KPP to generate updated source code for GEOS-Chem Classic;

  3. Compile GEOS-Chem Classic to create a new executable;

  4. Start your GEOS-Chem Classic simulation.

Chemical mechanism configuration files are located in these folders:


Contains configuration files for the default “full-chemistry” mechanism (NOx + Ox + aerosols + Br + Cl + I).

  • fullchem.kpp: Main configuration file for the fullchem mechanism.

  • fullchem.eqn: List of species and reactions for the fullchem mechanism.


Contains configuration files for the mercury chemistry mechanism:

  • Hg.kpp: Main configuration file for the Hg mechanism.

  • Hg.eqn: List of species and reactions for the Hg mechanism.


Contains configuration files that you can edit if you need to create a custom mechanism. We recommend that you create the custom in this folder and leave KPP/fullchem and KPP/Hg untouched.

  • custom.kpp: Copy of fullchem.kpp

  • custom.eqn: Copy of fullchem.eqn.

Please see the following references for more information about KPP:

  1. The KPP user manual (

  2. Supplemental Guide: Update chemical mechanisms with KPP