Customize simulations with research options

Most of the time you will want to use the “out-of-the-box” settings in your GEOS-Chem simulations, as these are the recommended settings that have been evaluated with benchmark simulations. But depending on your research needs, you may wish to use alternate simulation options. In this Guide we will show you how you can select these research options by editing the various GEOS-Chem and HEMCO configuration files.

Aerosols

Aerosol microphysics

GEOS-Chem incorporates two different aerosol microphysics schemes: APM (Yu and Luo [2009]) and TOMAS (Trivitayanurak et al. [2008]) as compile-time options for the full-chemistry simulation. Both APM and TOMAS are deactivated by default due to the extra computational overhead that these microphysics schemes require.

Follow the steps below to activate either APM or TOMAS microphysics in your full-chemistry simulation.

APM

Create a run directory for the Full Chemistry simulation with APM as the extra simulation option.
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DAPM=y
$ make -j
$ make install

TOMAS

Create a run directory for the Full Chemistry simulation with TOMAS as the extra simulation option.
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DTOMAS=y -DTOMAS_BINS=15
$ make -j
$ make install

This will create a GEOS-Chem executable for the TOMAS15 (15 size bins) simulation. To generate an executable for the TOMAS40 (40 size-bins) simulation, replace -DTOMAS_BINS=15 with -DTOMAS_BINS=40 in the cmake step above.

Chemistry

Adaptive Rosenbrock solver with mechanism auto-reduction

In Lin et al. [2023], the authors introduce an adaptive Rosenbrock solver with on-the-fly mechanism reduction in The Kinetic PreProcessor (KPP) version 3.0.0 and later. While this adaptive solver is available for all GEOS-Chem simulations that use the fullchem simulation, it is disabled by default.

To activate the adaptive Rosenbrock solver with mechanism auto-reduction, edit the line of geoschem_config.yml indicated below:

chemistry:
  activate: true
  # ... Previous sub-sections omitted
  autoreduce_solver:
    activate: false   # <== true activates the adaptive Rosenbrock solver
    use_target_threshold:
      activate: true
      oh_tuning_factor: 0.00005
      no2_tuning_factor: 0.0001
    use_absolute_threshold:
      scale_by_pressure: true
      absolute_threshold: 100.0
    keep_halogens_active: false
    append_in_internal_timestep: false

Please see the Lin et al. [2023] reference for a detailed explanation of the other adaptive Rosenbrock solver options.

Alternate chemistry mechanisms

GEOS-Chem is compiled “out-of-the-box” with KPP-generated solver code for the fullchem mechanism. But you must manually specify the mechanism name at configuration time for the following instances:

Carbon mechanism

Follow these steps to build an executable with the carbon mechanism:

Create a run directory for the Carbon simulation
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DMECH=carbon
$ make -j
$ make install

Custom full-chemistry mechanism

We recommend that you use the custom mechanism instead of directly modifying the fullchem mechanism. The custom mechanism is a copy of fullchem, but the KPP solver code will be generated in the KPP/custom folder instead of in KPP/fullchem. This lets you keep the fullchem folder untouched.

Follow these steps:

Create a run directory for the full-chemistry simulation (whichever configuration you need).
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DMECH=custom
$ make -j
$ make install

Hg mechanism

Follow these steps to build an executable with the Hg (mercury) mechanism:

Create a run directory for the Hg simulation.
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DMECH=Hg
$ make -j
$ make install

HO2 heterogeneous chemistry reaction probability

You may update the value of \(\gamma_{HO2}\) (reaction probability for uptake of HO2 in heterogeneous chemistry) used in your simulations. Edit the line of geoschem_config.yml indicated below:

chemistry:
  activate: true
  # ... Preceding sections omitted ...
  gamma_HO2: 0.2   # <=== add new value here

TransportTracers

In GEOS-Chem 14.2.0 and later versions, species belonging to the TransportTracers simulation (radionuclides and passive species) now have their properties defined in the species_database.yml file. For example:

CH3I:
  Background_VV: 1.0e-20
  Formula: CH3I
  FullName: Methyl iodide
  Henry_CR: 3.6e+3
  Henry_K0: 0.20265
  Is_Advected: true
  Is_Gas: true
  Is_Photolysis: true
  Is_Tracer: true
  Snk_Horiz: all
  Snk_Mode: efolding
  Snk_Period: 5
  Snk_Vert: all
  Src_Add: true
  Src_Mode: HEMCO
  MW_g: 141.94

where:

Is_Tracer: true indicates a TransportTracer species
Snk_* define species sink properties
Src_* define species source properties
Units: specifies the default units for species (added mainly for age of air species at this time which are in days)

For TransportTracers species that have a source term in HEMCO, there will be corresponding entries in HEMCO_Config.rc:

--> OCEAN_CH3I             :       true

# ... etc ...

#==============================================================================
# CH3I emitted over the oceans at rate of 1 molec/cm2/s
#==============================================================================
(((OCEAN_CH3I
0 SRC_2D_CH3I 1.0 - - - xy molec/cm2/s CH3I 1000 1 1
)))OCEAN_CH3I

Sources and sinks for TransportTracers are now applied in the new source code module GeosCore/tracer_mod.F90.

Note

Sources and sinks for radionuclide species (Rn, Pb, Be isotopes) are currently not applied in GeosCore/tracer_mod.F90 (but may be in the future). Emissions for radionuclide species are computed by the HEMCO GC-Rn-Pb-Be extension and chemistry is done in GeosCore/RnPbBe_mod.F90.

TransportTracer properties for radionuclide species have been added to species_database.yml but are currently commented out.

Diagnostics

GEOS-Chem and HEMCO diagnostics

Please see our Diagnostics reference chapter for an overview of how to archive diagnostics from GEOS-Chem and HEMCO.

RRTMG radiative transfer diagnostics

You can use the RRTMG radiative transfer model to archive radiative forcing fluxes to the GeosRad History diagnostic collection. RRTMG is implemented as a compile-time option due to the extra computational overhead that it incurs.

To activate RRTMG, follow these steps:

Create a run directory for the Full Chemistry simulation, with extra option RRTMG.
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DRRTMG=y
$ make -j
$ make install

Then also make sure to request the radiative forcing flux diagnostics that you wish to archive in the HISTORY.rc file.

Emissions

Offline vs. online emissions

Emission inventories sometimes include dynamic source types and nonlinear scale factors that have functional dependencies on local environmental variables such as wind speed or temperature, which are best calculated online during execution of the model. HEMCO includes a suite of additional modules (aka HEMCO extensions) that perform online emissions ccalculations for a variety of sources.

Some types of emissions are highly sensitive to meteorological variables such as wind speed and temperature. Because the meteorological inputs are regridded from their native resolution to the GEOS-Chem or HEMCO simulation grid, emissions computed with fine-resolution meteorology can significantly differ from emissions computed with coarse-resolution meteorology. This can make it difficult to compare the output of GEOS-Chem and HEMCO simulations that use different horizontal resolutions.

In order to provide more consistency in the computed emissions, we now make available for download offline emissions. These offline emissions are pre-computed with HEMCO standalone simulations using meteorological inputs at native horizontal resolutions possible. When these emissions are regridded within GEOS-Chem and HEMCO, the total mass emitted will be conserved regardless of the horizontal resolution of the simulation grid.

You should use offline emissions:

For all GCHP simulations
For full-chemistry simulations (except benchmark)

You should use online emissions:

For benchmark simulations
If you wish to assess the impact of changing/updating the meteorlogical inputs on emissions.

You may toggle offline emissions on (true) or off (false) in this section of HEMCO_Config.rc:

# ----- OFFLINE EMISSIONS -----------------------------------------------------
# To use online emissions instead set the offline emissions to 'false' and the
# corresponding HEMCO extension to 'on':
#   OFFLINE_DUST        - DustDead or DustGinoux
#   OFFLINE_BIOGENICVOC - MEGAN
#   OFFLINE_SEASALT     - SeaSalt
#   OFFLINE_SOILNOX     - SoilNOx
#
# NOTE: When switching between offline and online emissions, make sure to also
# update ExtNr and Cat in HEMCO_Diagn.rc to properly save out emissions for
# any affected species.
#------------------------------------------------------------------------------
    --> OFFLINE_DUST           :       true     # 1980-2019
    --> OFFLINE_BIOGENICVOC    :       true     # 1980-2020
    --> OFFLINE_SEASALT        :       true     # 1980-2019
    -->  CalcBrSeasalt         :       true
    --> OFFLINE_SOILNOX        :       true     # 1980-2020

As stated in the comments, if you switch between offline and online emissions, you will need to activate the corresponding HEMCO extension:

Offline emissions and corresponding HEMCO extensions
Offline base emission	Corresponding HEMCO extension	Extension #
OFFLINE_DUST	DustDead	105
OFFLINE_BIOGENICVOC	MEGAN	108
OFFLINE_SEASALT	SeaSalt	107
OFFLINE_SOILNOX	SoilNOx	104

Example: Disabling offline dust emissions

Change the OFFLINE_DUST setting from true to false in HEMCO_Config.rc:

--> OFFLINE_DUST           :       false    # 1980-2019

Change the DustDead extension setting from off to on in HEMCO_Config.rc:

105     DustDead               : on    DST1/DST2/DST3/DST4

Change the extension number for all dust emission diagnostics from 0 (the extension number for base emissions) to 105 (the extension number for DustDead) in HEMCO_Diagn.rc.

###############################################################################
#####  Dust emissions                                                     #####
###############################################################################
EmisDST1_Total     DST1   -1    -1   -1   2   kg/m2/s  DST1_emission_flux_from_all_sectors
EmisDST1_Anthro    DST1  105     1   -1   2   kg/m2/s  DST1_emission_flux_from_anthropogenic
EmisDST1_Natural   DST1  105     3   -1   2   kg/m2/s  DST1_emission_flux_from_natural_sources
EmisDST2_Natural   DST2  105     3   -1   2   kg/m2/s  DST2_emission_flux_from_natural_sources
EmisDST3_Natural   DST3  105     3   -1   2   kg/m2/s  DST3_emission_flux_from_natural_sources
EmisDST4_Natural   DST4  105     3   -1   2   kg/m2/s  DST4_emission_flux_from_natural_sources

To enable online emissions again, do the inverse of the steps listed above.

Sea salt debromination

In Zhu et al. [2018], the authors present a mechanistic description of sea salt aerosol debromination. This option was originally enabled by in GEOS-Chem 13.4.0, but was then changed to be an option (disabled by default) due to the impact it had on ozone concentrations.

Further chemistry updates to GEOS-Chem have allowed us to re-activate sea-salt debromination as the default option in GEOS-Chem 14.2.0 and later versions. If you wish to disable sea salt debromination in your simulations, edit the line in HEMCO_Config.rc indicated below.

107     SeaSalt                : on  SALA/SALC/SALACL/SALCCL/SALAAL/SALCAL/BrSALA/BrSALC/MOPO/MOPI
    # ... Preceding options omitted ...
    --> Model sea salt Br-     :       true    # <== false deactivates sea salt debromination
    --> Br- mass ratio         :       2.11e-3

Photolysis

Particulate nitrate photolysis

A study by Shah et al. [2023] showed that particulate nitrate photolysis increases GEOS-Chem modeled ozone concentrations by up to 5 ppbv in the free troposphere in northern extratropical regions. This helps to correct a low bias with respect to observations.

Particulate nitrate photolysis is turned on by default in GEOS-Chem 14.2.0 and later versions. You may disable this option by editing the line in geoschem_config.yml indicated below:

photolysis:
  activate: true
  # .. preceding sub-sections omitted ...
  photolyze_nitrate_aerosol:
    activate: true   # <=== false deactivates nitrate photolysis
    NITs_Jscale_JHNO3: 100.0
    NIT_Jscale_JHNO2: 100.0
    percent_channel_A_HONO: 66.667
    percent_channel_B_NO2: 33.333

You can also edit the other nitrate photolysis parameters by changing the appropriate lines above. See the Shah et al [2023] reference for more information.

Wet deposition

Luo et al 2020 wetdep parameterization

In Luo et al. [2020], the authors introduced an updated wet deposition parameterization, which is now incorporated into GEOS-Chem as a compile-time option. Follow these steps to activate the Luo et al 2020 wetdep scheme in your GEOS-Chem simulations.

Create a run directory for the type of simulation that you wish to use.
- CAVEAT: Make sure your simulation uses at least one species that can be wet-scavenged.
Navigate to the build folder within the run directory.

Then type the following:

$ cmake .. -DLUO_WETDEP=y
$ make -j
$ make install