diff --git a/.gitignore b/.gitignore
index 5aaa6e46e98..e21d4ad68e6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -213,3 +213,9 @@ versions/run.ver
 
 # jcb checkout and symlinks
 ush/python/jcb
+
+
+specs/
+.specify/
+.github/agents/
+.github/prompts/
\ No newline at end of file
diff --git a/changelog.md b/changelog.md
new file mode 100644
index 00000000000..10a593bc744
--- /dev/null
+++ b/changelog.md
@@ -0,0 +1,69 @@
+# Changelog
+
+All notable changes to global-workflow will be documented in this file.
+
+This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+- CATChem interactive atmospheric chemistry for GCAFS via a new `APP=ATMC`
+  option (atmosphere + CATChem), mirroring the existing `ATMA`
+  (atmosphere + GOCART) forecast-only workflow:
+  - `dev/workflow/setup_expt.py` accepts `--app ATMC` for GCAFS.
+  - `dev/parm/config/gcafs/config.base.j2` recognizes `ATMC`, exports a
+    `CHEM_MODEL` selector (`none`/`gocart`/`catchem`), and widens the EnKF
+    APP suffix strip to `+([WAC])`.
+  - `dev/parm/config/gcafs/config.aero.j2` adds `CATCHEM_CONFIG` (default
+    `gcafs_aero`) and `CATCHEM_CONFIG_DIR`, mirroring `NEXUS_CONFIG`.
+  - `dev/parm/config/gcafs/config.fcst.j2` passes `--catchem` to `config.ufs`
+    and selects `FCSTEXEC="ufs_model_gcafs_catchem.x"` when
+    `CHEM_MODEL="catchem"`.
+  - `dev/parm/config/gcafs/config.ufs` parses `--catchem`, setting
+    `cplchm=".true."`, `cplcat=".true."`, and `chm_model="catchem"` while
+    reusing the `ufs.configure.atmaero` template.
+  - `ush/parsing_ufs_configure.sh` renders `chm_model`/`cplcat` into the UFS
+    configure file; `ush/parsing_namelists_fv3.sh` renders `cplcat` into
+    `global_control.nml`.
+  - `ush/forecast_predet.sh` and `ush/forecast_postdet.sh` gain
+    `CATCHEM_predet`, `CATCHEM_rc`, `CATCHEM_postdet`, and `CATCHEM_out`:
+    the CATChem runtime YAML set (`CATChem_config/species/emissions/
+    field_mapping_${CATCHEM_CONFIG}.yaml`) is copied and renamed into `DATA`
+    under the fixed names the CATChem NUOPC cap expects
+    (`CATChem_new_config.yml`, `CATChem_species.yml`, `CATChem_emission.yml`,
+    `CATChem_field_mapping.yml`), `ExtData` is linked from
+    `AERO_INPUTS_DIR`, and `catchem*` diagnostics are copied to
+    `$COM/model/chem/history`.
+  - `dev/scripts/exglobal_forecast.sh` branches the chemistry steps onto the
+    CATChem functions when `cplcat=".true."`.
+  - `parm/archive/chem.yaml.j2` archives `{{ CHEM_MODEL }}*` history and
+    `parm/archive/master_gcafs.yaml.j2` includes the `chem` tarball for
+    `CHEM_MODEL == "catchem"` (GCAFS ATMA archiving is unchanged).
+  - `dev/scripts/exgfs_aero_init_aerosol.py` uses
+    `parm/chem/catchem/catchem_tracer.list` when `CHEM_MODEL == "catchem"`.
+  - `dev/scripts/exglobal_prep_emissions.py` validates the selected CATChem
+    emissions configuration set when `CHEM_MODEL == "catchem"`.
+  - Build support: `sorc/build_opts.yaml` adds the `gcafs_catchem_model`
+    entry (`./build_ufs.sh -a CATCHEM -e gcafs_catchem_model.x`) to the GCAFS
+    system; `sorc/build_ufs.sh` registers the `COMPILE_ID`;
+    `sorc/link_workflow.sh` links `exec/ufs_model_gcafs_catchem.x`.
+  - Docs: `docs/source/user_guide/setup.rst`, `gcafs.rst`, and `clone.rst`
+    describe the `ATMC` option.
+  - CI: `dev/ci/cases/pr/C96_gcafs_catchem_cycled.yaml` adds an `APP=ATMC`
+    cycled GCAFS case (modeled on `C96_gcafs_cycled_noDA.yaml`), registered
+    in the hera/gaeac6/ursa/derecho matrices of `dev/ci/gitlab-ci-hosts.yml`.
+
+### Changed
+
+- `sorc/ufs_model.fd` pinned to ufs-weather-model
+  `6dc36481b6d1347f3c5332905ad48e7e9da8675e`, the first revision exposing the
+  `CATCHEM` application (`-DAPP=CATCHEM`) and the `cplcat` entry in
+  `global_control.nml.IN`.
+
+### Compatibility
+
+- No behavior change for existing `APP=ATMA`/`ATM`/`S2S*` configurations: the
+  GOCART code paths, GCAFS archive contents, and NEXUS/fire emissions
+  preprocessing are untouched; all new logic is gated on `APP=ATMC` /
+  `CHEM_MODEL=="catchem"` / `cplcat==".true."`.
diff --git a/dev/ci/cases/gcafsv1/C96_gcafs_cycled_noDA_dev_catchem.yaml b/dev/ci/cases/gcafsv1/C96_gcafs_cycled_noDA_dev_catchem.yaml
new file mode 100644
index 00000000000..e6240427cd3
--- /dev/null
+++ b/dev/ci/cases/gcafsv1/C96_gcafs_cycled_noDA_dev_catchem.yaml
@@ -0,0 +1,23 @@
+experiment:
+  net: gcafs
+  mode: cycled
+  pslot: {{ 'pslot' | getenv }}
+  app: ATMC
+  resdetatmos: 96
+  comroot: {{ 'RUNTESTS' | getenv }}/COMROOT
+  expdir: {{ 'RUNTESTS' | getenv }}/EXPDIR
+  icsdir: {{ BASE_IC }}/C96C48/20250808
+  idate: 2021122012
+  edate: 2021122200
+  nens: 0
+  interval: 0
+  start: cold
+  yaml: {{ HOMEglobal }}/dev/ci/cases/yamls/gcafs_cycled_noDA_defaults_dev.yaml
+
+workflow:
+  engine: rocoto
+  rocoto:
+    maxtries: 2
+    cyclethrottle: 3
+    taskthrottle: 25
+    verbosity: 2
diff --git a/dev/ci/cases/pr/C96_gcafs_catchem_cycled.yaml b/dev/ci/cases/pr/C96_gcafs_catchem_cycled.yaml
new file mode 100644
index 00000000000..f375a6e4ade
--- /dev/null
+++ b/dev/ci/cases/pr/C96_gcafs_catchem_cycled.yaml
@@ -0,0 +1,28 @@
+experiment:
+  net: gcafs
+  mode: cycled
+  pslot: {{ 'pslot' | getenv }}
+  app: ATMC
+  resdetatmos: 96
+  comroot: {{ 'RUNTESTS' | getenv }}/COMROOT
+  expdir: {{ 'RUNTESTS' | getenv }}/EXPDIR
+  icsdir: {{ BASE_IC }}/C96C48/20250808
+  idate: 2021122012
+  edate: 2021122100
+  nens: 0
+  interval: 12
+  start: cold
+  yaml: {{ HOMEglobal }}/dev/ci/cases/yamls/gcafs_cycled_noDA_defaults_ci.yaml
+
+skip_ci_on_hosts:
+  - orion
+  - hercules
+  - awsepicglobalworkflow
+
+workflow:
+  engine: rocoto
+  rocoto:
+    maxtries: 2
+    cyclethrottle: 3
+    taskthrottle: 25
+    verbosity: 2
diff --git a/dev/parm/config/gcafs/config.base.j2 b/dev/parm/config/gcafs/config.base.j2
index 25b6257f407..2ba58cdfb46 100644
--- a/dev/parm/config/gcafs/config.base.j2
+++ b/dev/parm/config/gcafs/config.base.j2
@@ -164,7 +164,7 @@ shopt -s extglob
 # If a component (WAVES, etc) needs to be turned off by RUN, set it here
 case "${RUN}" in
     enkf*) # Turn off aerosols and waves
-        APP="${APP/%+([WA])}"
+        APP="${APP/%+([WAC])}"
         ;;
     *)     # Keep app unchanged
         ;;
@@ -234,6 +234,9 @@ case "${APP}" in
   ATMA)
     DO_AERO="YES"
     ;;
+  ATMC)  # Atmosphere + CATChem interactive chemistry
+    DO_AERO="YES"
+    ;;
   ATMW)
     export DO_COUPLED="YES"
     export DO_WAVE="YES"
@@ -262,6 +265,19 @@ case "${APP}" in
     ;;
 esac
 
+# Chemistry model selector: none (default), gocart (ATM*A apps), catchem (ATMC)
+case "${APP}" in
+  ATMC)
+    export CHEM_MODEL="catchem"
+    ;;
+  *A)
+    export CHEM_MODEL="gocart"
+    ;;
+  *)
+    export CHEM_MODEL="none"
+    ;;
+esac
+
 # Aerosol forecasts and analyses may be RUN-dependent
 if [[ "${DO_AERO}" == "YES" ]]; then
   if [[ ${aero_anl_runs} =~ ${RUN} ]]; then
diff --git a/dev/parm/config/gcafs/config.fcst.j2 b/dev/parm/config/gcafs/config.fcst.j2
index e0e7805c538..90067d17ef5 100644
--- a/dev/parm/config/gcafs/config.fcst.j2
+++ b/dev/parm/config/gcafs/config.fcst.j2
@@ -25,7 +25,11 @@ if [[ "${DO_WAVE}" == "YES" ]]; then
     string="${string} --ww3 ${waveGRD}"
 fi
 if [[ "${DO_AERO_FCST}" == "YES" ]]; then
-    string="${string} --gocart"
+    if [[ "${CHEM_MODEL}" == "catchem" ]]; then
+        string="${string} --catchem"
+    else
+        string="${string} --gocart"
+    fi
 fi
 # We are counting on $string being multiple arguments
 # shellcheck disable=SC2086
@@ -78,7 +82,11 @@ export esmf_logkind="ESMF_LOGKIND_MULTI_ON_ERROR" #Options: ESMF_LOGKIND_MULTI_O
 
 export FORECASTSH="${SCRglobal}/exglobal_forecast.sh"
 #export FORECASTSH="${SCRglobal}/exglobal_forecast.py"  # Temp. while this is worked on
-export FCSTEXEC="ufs_model_gcafs.x"
+if [[ "${CHEM_MODEL}" == "catchem" ]]; then
+    export FCSTEXEC="ufs_model_gcafs_catchem.x"
+else
+    export FCSTEXEC="ufs_model_gcafs.x"
+fi
 
 #######################################################################
 # Model configuration
diff --git a/dev/parm/config/gfs/config.aero.j2 b/dev/parm/config/gfs/config.aero.j2
index e4f958ae44f..23fd5b08800 100644
--- a/dev/parm/config/gfs/config.aero.j2
+++ b/dev/parm/config/gfs/config.aero.j2
@@ -228,5 +228,21 @@ export NEXUS_DO_CAMS=.false. # Use CAMS global emissions
 # Enables time-varying scaling when CAMS is active.
 export NEXUS_DO_CAMSTEMPO=.true. # Use CAMS temporal emissions
 
-#================================================================================
-echo "END: config.aero"
+#================================================================================# 4. CATChem settings
+#===============================================================================
+# CATChem is an interactive atmospheric chemistry model coupled to FV3 through
+# its own NUOPC cap (chm_model='catchem'). Runtime configuration is provided as
+# a set of four YAML files (config, species, emissions, field mapping) that are
+# staged into the DATA directory under fixed names before the forecast runs.
+
+# CATChem configuration set (selects the *_<CATCHEM_CONFIG>.yaml bundle under
+# parm/chem/catchem). Options: gcafs_aero (default)
+#---------------------------------------------------------------------------------------------------
+export CATCHEM_CONFIG="{{ CATCHEM_CONFIG | default('gcafs_aero') }}"
+
+# Directory containing the CATChem runtime YAML sets. The selected config set is
+# resolved by filename suffix, e.g. CATChem_config_${CATCHEM_CONFIG}.yaml.
+#---------------------------------------------------------------------------------------------------
+export CATCHEM_CONFIG_DIR="${PARMglobal}/chem/catchem"
+
+#===============================================================================echo "END: config.aero"
diff --git a/dev/parm/config/gfs/config.ufs b/dev/parm/config/gfs/config.ufs
index 43c1e6ed4ba..8164a69c801 100644
--- a/dev/parm/config/gfs/config.ufs
+++ b/dev/parm/config/gfs/config.ufs
@@ -17,6 +17,7 @@ if (( $# <= 1 )); then
     echo "--cice6 500|100|025"
     echo "--ww3 gwes_30m|glo_025|glo_100|glo_200|glo_500|mx025|uglo_100km"
     echo "--gocart"
+    echo "--catchem"
 
     exit 1
 
@@ -27,6 +28,7 @@ skip_mom6=true
 skip_cice6=true
 skip_ww3=true
 skip_gocart=true
+skip_catchem=true
 skip_mediator=true
 
 # Loop through named arguments
@@ -55,6 +57,9 @@ while (( $# > 0 )); do
     "--gocart")
       skip_gocart=false
       ;;
+    "--catchem")
+      skip_catchem=false
+      ;;
     *)    # unknown option
       echo "FATAL ERROR: Unknown option: ${key}, ABORT!"
       exit 1
@@ -648,6 +653,18 @@ if [[ "${skip_gocart}" == "false" ]]; then
   model_list="${model_list}.aero"
 fi
 
+# CATChem specific settings
+# CATChem couples through its own NUOPC cap (chm_model='catchem') but reuses the
+# atmaero configure template: cplcat=true implies cplchm=true (the chemistry PETs
+# are the same as the GOCART/aerosol PETs), so the model_list suffix stays .aero.
+if [[ "${skip_catchem}" == "false" ]]; then
+  source "${EXPDIR}/config.aero"
+  export cplchm=".true."
+  export cplcat=".true."
+  export chm_model="catchem"
+  model_list="${model_list}.aero"
+fi
+
 # Set the name of the UFS (previously nems) configure template to use
 # Default ufs.configure templates for supported model configurations
 # WW3 restart field variable is different for slow vs fast loop.  Add  WW3_RSTFLDS="ice" for slow loop variables based on coupling scheme.
diff --git a/dev/scripts/exgfs_aero_init_aerosol.py b/dev/scripts/exgfs_aero_init_aerosol.py
index c4a887b2997..c92cc1678f5 100755
--- a/dev/scripts/exgfs_aero_init_aerosol.py
+++ b/dev/scripts/exgfs_aero_init_aerosol.py
@@ -57,8 +57,9 @@
 tracer_file_pattern = "{file_base}/{timestamp}fv_tracer.res.{tile}.nc"
 # Name of restart dycore file (time when restart is valid)
 dycore_file_pattern = "{file_base}/{timestamp}fv_core.res.nc"
-# Text list of tracer names to copy
+# Text list of tracer names to copy (selected from CHEM_MODEL at runtime)
 tracer_list_file_pattern = "{parm_gfs}/ufs/gocart/gocart_tracer.list"
+catchem_tracer_list_file_pattern = "{parm_gfs}/chem/catchem/catchem_tracer.list"
 merge_script_pattern = "{ush_gfs}/merge_fv3_aerosol_tile.py"
 n_tiles = 6
 # Maximum number of past cycles to look for for tracer data
@@ -84,11 +85,15 @@ def main() -> None:
     rot_dir = get_env_var("ROTDIR")
     ush_gfs = get_env_var("USHglobal")
     parm_gfs = get_env_var("PARMglobal")
+    chem_model = get_env_var("CHEM_MODEL", fail_on_missing=False) or "none"
 
     # os.chdir(data)
 
     merge_script = merge_script_pattern.format(ush_gfs=ush_gfs)
-    tracer_list_file = tracer_list_file_pattern.format(parm_gfs=parm_gfs)
+    if chem_model == "catchem":
+        tracer_list_file = catchem_tracer_list_file_pattern.format(parm_gfs=parm_gfs)
+    else:
+        tracer_list_file = tracer_list_file_pattern.format(parm_gfs=parm_gfs)
 
     time = datetime.strptime(f"{pdy}{cyc}", "%Y%m%d%H")
     atm_source_path = time.strftime(atm_base_pattern.format(**locals()))
diff --git a/dev/scripts/exglobal_forecast.sh b/dev/scripts/exglobal_forecast.sh
index b00ac6d9fe0..a9f5b5eff84 100755
--- a/dev/scripts/exglobal_forecast.sh
+++ b/dev/scripts/exglobal_forecast.sh
@@ -95,6 +95,7 @@ cpl=${cpl:-.false.}
 cplflx=${cplflx:-.false.} # default off,import from outside source
 cplwav=${cplwav:-.false.} # ? how to control 1-way/2-way?
 cplchm=${cplchm:-.false.} # Chemistry model
+cplcat=${cplcat:-.false.} # CATChem interactive chemistry model
 cplice=${cplice:-.false.} # ICE model
 
 OCNTIM=${OCNTIM:-1800}
@@ -122,7 +123,11 @@ if [[ "${cplice}" == ".true." ]]; then
     CICE_predet
 fi
 if [[ "${cplchm}" == ".true." ]]; then
-    GOCART_predet
+    if [[ "${cplcat}" == ".true." ]]; then
+        CATCHEM_predet
+    else
+        GOCART_predet
+    fi
 fi
 echo "MAIN: Variables before determination of run type loaded"
 
@@ -145,7 +150,11 @@ if [[ "${cplice}" == ".true." ]]; then
     CICE_postdet
 fi
 if [[ "${cplchm}" == ".true." ]]; then
-    GOCART_postdet
+    if [[ "${cplcat}" == ".true." ]]; then
+        CATCHEM_postdet
+    else
+        GOCART_postdet
+    fi
 fi
 echo "MAIN: Post-determination set up of run type finished"
 
@@ -161,7 +170,11 @@ if [[ "${cplice}" == ".true." ]]; then
     CICE_nml
 fi
 if [[ "${cplchm}" == ".true." ]]; then
-    GOCART_rc
+    if [[ "${cplcat}" == ".true." ]]; then
+        CATCHEM_rc
+    else
+        GOCART_rc
+    fi
 fi
 UFS_configure
 echo "MAIN: Name lists and model configuration written"
@@ -202,7 +215,11 @@ if [[ "${cplice}" == ".true." ]]; then
     CICE_out
 fi
 if [[ "${cplchm}" == ".true." ]]; then
-    GOCART_out
+    if [[ "${cplcat}" == ".true." ]]; then
+        CATCHEM_out
+    else
+        GOCART_out
+    fi
 fi
 if [[ "${esmf_profile:-}" == ".true." ]]; then
     CPL_out
diff --git a/dev/scripts/exglobal_prep_emissions.py b/dev/scripts/exglobal_prep_emissions.py
index abd773e0bfa..e0de8a6a4aa 100755
--- a/dev/scripts/exglobal_prep_emissions.py
+++ b/dev/scripts/exglobal_prep_emissions.py
@@ -4,7 +4,7 @@
 # which perform the pre-processing for aerosol emissions
 import os
 
-from wxflow import Logger, cast_strdict_as_dtypedict
+from wxflow import Logger, cast_strdict_as_dtypedict, WorkflowException
 from pygfs import ChemFireEmissions, NEXUSEmissions
 
 
@@ -13,10 +13,61 @@
     level=os.environ.get("LOGGING_LEVEL", "DEBUG"), colored_log=True)
 
 
+def _check_catchem_emissions(config) -> None:
+    """Validate the CATChem emissions configuration set.
+
+    CATChem reads the anthropogenic and fire emission fields from ChemInput
+    (the NEXUS_DIAG.* and FIRE_EMIS_*.nc netCDF files produced below) and maps
+    them onto model tracers through its own runtime emissions YAML, staged as
+    CATChem_emission.yml by CATCHEM_rc().  Confirm the selected emissions set
+    exists so that an unknown CATCHEM_CONFIG fails loudly here rather than at
+    forecast time.
+
+    Parameters
+    ----------
+    config : dict
+        Task configuration from the environment.
+
+    Returns
+    -------
+    None
+
+    Raises
+    ------
+    WorkflowException
+        If the CATChem emissions YAML for the selected config is missing.
+    """
+    catchem_config = config.get('CATCHEM_CONFIG', None)
+    catchem_config_dir = config.get('CATCHEM_CONFIG_DIR', None)
+    if catchem_config is None or catchem_config_dir is None:
+        raise WorkflowException(
+            "CHEM_MODEL is 'catchem' but CATCHEM_CONFIG/CATCHEM_CONFIG_DIR "
+            "are not set; check config.aero sourcing")
+
+    emis_yaml = os.path.join(
+        catchem_config_dir, f"CATChem_emissions_{catchem_config}.yaml")
+    if not os.path.isfile(emis_yaml):
+        raise WorkflowException(
+            f"CATChem emissions configuration not found: {emis_yaml} "
+            f"(CATCHEM_CONFIG='{catchem_config}')")
+
+    logger.info(
+        f"CATChem emissions: species-to-tracer mapping delegated to {emis_yaml}; "
+        "NEXUS/fire preprocessing still produces the ChemInput netCDF fields")
+
+
 if __name__ == '__main__':
 
     # Take configuration from environment and cast it as python dictionary
     config = cast_strdict_as_dtypedict(os.environ)
+
+    # When running with the CATChem chemistry model, the emission species-to-
+    # tracer mapping lives in the staged CATChem emissions YAML rather than the
+    # NEXUS/HEMCO .rc set.  Validate that set up front; the underlying NEXUS and
+    # fire emissions still produce the ChemInput fields CATChem reads.
+    if config.get('CHEM_MODEL', 'none') == 'catchem':
+        _check_catchem_emissions(config)
+
     nxsemis = NEXUSEmissions(config.copy())
     # Instantiate the emissions pre-processing task
     fireemis = ChemFireEmissions(config.copy())
diff --git a/dev/workflow/applications/applications.py b/dev/workflow/applications/applications.py
index 3d0ebc6e36c..f8ea6fa81a5 100644
--- a/dev/workflow/applications/applications.py
+++ b/dev/workflow/applications/applications.py
@@ -197,6 +197,7 @@ def _get_run_options(self, conf: Configuration) -> Dict[str, Any]:
             run_options[run]['do_aero_anl'] = run_base.get('DO_AERO_ANL', False)
             run_options[run]['use_aero_anl'] = run_base.get('USE_AERO_ANL', False)
             run_options[run]['do_aero_fcst'] = run_base.get('DO_AERO_FCST', False)
+            run_options[run]['chem_model'] = run_base.get('CHEM_MODEL', 'none')
 
             if run_base.get('GEFSTYPE', "") == "gefs-real-time":
                 run_options[run]['do_gefs_real_time'] = True
diff --git a/dev/workflow/setup_expt.py b/dev/workflow/setup_expt.py
index 03e15e79449..d4fdbdd8866 100755
--- a/dev/workflow/setup_expt.py
+++ b/dev/workflow/setup_expt.py
@@ -177,7 +177,7 @@ def input_args(*argv):
         If start type is invalid
     """
 
-    ufs_apps = ['ATM', 'ATMA', 'ATMW', 'S2S', 'S2SA', 'S2SW', 'S2SWA']
+    ufs_apps = ['ATM', 'ATMA', 'ATMC', 'ATMW', 'S2S', 'S2SA', 'S2SW', 'S2SWA']
 
     def _validate_interval(interval_str):
         """
diff --git a/docs/source/user_guide/clone.rst b/docs/source/user_guide/clone.rst
index 8e33dc140fa..1b6c80fb69c 100644
--- a/docs/source/user_guide/clone.rst
+++ b/docs/source/user_guide/clone.rst
@@ -189,6 +189,9 @@ Build Options
 +------------+-----------------------------------------------------------+
 | GCAFS      | Non-hydrostatic FV3/GOCART                                |
 +------------+-----------------------------------------------------------+
+| GCAFS      | Non-hydrostatic FV3/CATChem (APP=ATMC; build with         |
+| CATChem    | ./build_ufs.sh -a CATCHEM -e gcafs_catchem_model.x)       |
++------------+-----------------------------------------------------------+
 
 ^^^^^^^^^^^^^^^
 Link components
diff --git a/docs/source/user_guide/gcafs.rst b/docs/source/user_guide/gcafs.rst
index 166af1b77ac..84598f22fc4 100644
--- a/docs/source/user_guide/gcafs.rst
+++ b/docs/source/user_guide/gcafs.rst
@@ -34,6 +34,9 @@ GCAFS can be run using the global-workflow framework. To set up a free-forecast
                 --idate 2023010100 --edate 2023010100 \
                 --resdetatmos 384 --comroot /path/to/com --expdir /path/to/exp
 
+Use ``--app ATMC`` instead of ``--app ATMA`` to run with the CATChem
+interactive chemistry model (see :ref:`gcafs_catchem` below).
+
 Configuration is managed through the standard global-workflow configuration files. GCAFS-specific
 settings are documented in :ref:`gcafs_config`.
 
@@ -109,6 +112,43 @@ The primary configuration file for aerosol settings, containing:
 These settings are processed as Jinja2 templates, allowing for experiment-specific customization
 through template variables like ``{{ NEXUS_CONFIG | default('gocart') }}``.
 
+.. _gcafs_catchem:
+
+-------------------
+CATChem (APP=ATMC)
+-------------------
+
+Selecting ``--app ATMC`` replaces the GOCART chemistry model with CATChem, an
+interactive atmospheric chemistry model coupled to FV3 through its own NUOPC
+cap (``chm_model='catchem'``, ``cplcat=.true.``).  The forecast executable is
+switched to ``ufs_model_gcafs_catchem.x`` (built via
+``./build_ufs.sh -a CATCHEM -e gcafs_catchem_model.x``) and the same aerosol
+forecast tasks (``prep_emissions``, ``aerosol_init``, ``fcst``) are used.
+
+**CATChem settings** (in ``config.aero.j2``):
+
+.. code-block:: bash
+
+   export CATCHEM_CONFIG="gcafs_aero"                # CATChem configuration set
+   export CATCHEM_CONFIG_DIR="${PARMglobal}/chem/catchem"  # Directory holding the YAML sets
+
+The selected configuration set resolves the four runtime YAML files staged
+into the forecast ``DATA`` directory under the fixed names expected by the
+CATChem cap:
+
+.. code-block:: text
+
+   CATChem_config_${CATCHEM_CONFIG}.yaml        -> CATChem_new_config.yml
+   CATChem_species_${CATCHEM_CONFIG}.yaml       -> CATChem_species.yml
+   CATChem_emissions_${CATCHEM_CONFIG}.yaml     -> CATChem_emission.yml
+   CATChem_field_mapping_${CATCHEM_CONFIG}.yaml -> CATChem_field_mapping.yml
+
+The staged ``CATChem_config.yml`` references ``./CATChem_species.yml`` and
+``./CATChem_emission.yml`` relative to ``DATA``, and reads Mie optics tables
+from ``./ExtData/monochromatic/`` (linked from ``AERO_INPUTS_DIR``).
+CATChem diagnostics (``catchem_diag*.nc``) are copied to
+``$COM/model/chem/history`` and archived into ``chem.tar``.
+
 =======================
 Emissions Preprocessing
 =======================
diff --git a/docs/source/user_guide/setup.rst b/docs/source/user_guide/setup.rst
index 835be173b78..8c914dab848 100644
--- a/docs/source/user_guide/setup.rst
+++ b/docs/source/user_guide/setup.rst
@@ -74,6 +74,7 @@ where:
 
      - ATM: atmosphere-only [default]
      - ATMA: atm-aerosols
+     - ATMC: atm-CATChem interactive chemistry (GCAFS)
      - ATMW: atm-wave (currently non-functional)
      - S2S: atm-ocean-ice
      - S2SA: atm-ocean-ice-aerosols
diff --git a/parm/archive/chem.yaml.j2 b/parm/archive/chem.yaml.j2
index 953f9d4f40e..4a6d2df25ab 100644
--- a/parm/archive/chem.yaml.j2
+++ b/parm/archive/chem.yaml.j2
@@ -1,5 +1,5 @@
 chem:
-    {% set head = "gocart" %}
+    {% set head = CHEM_MODEL | default('gocart') %}
     name: "CHEM"
     target: "{{ ATARDIR }}/{{ cycle_YMDH }}/chem.tar"
     required:
diff --git a/parm/archive/master_gcafs.yaml.j2 b/parm/archive/master_gcafs.yaml.j2
index a6fd47520af..04ebdb6a11d 100644
--- a/parm/archive/master_gcafs.yaml.j2
+++ b/parm/archive/master_gcafs.yaml.j2
@@ -35,6 +35,14 @@ datasets:
             - "{{ COMIN_ATMOS_GRIB_1p00 }}/{{ head }}pres_a.1p00.f{{ '%03d' % fhr }}.grib2"
             - "{{ COMIN_ATMOS_GRIB_1p00 }}/{{ head }}pres_a.1p00.f{{ '%03d' % fhr }}.grib2.idx"
             {% endfor %}
+
+# Archive CATChem output (APP=ATMC). GCAFS ATMA/gocart chem history is not
+# archived here to preserve existing behavior; only the CATChem tarball is added.
+{% if CHEM_MODEL is defined and CHEM_MODEL == 'catchem' %}
+{% filter indent(width=4) %}
+{% include "chem.yaml.j2" %}
+{% endfilter %}
+{% endif %}
 # Archive the EXPDIR if requested
 {% if archive_expdir %}
 {% filter indent(width=4) %}
diff --git a/parm/chem/catchem/CATChem_config_gcafs_aero.yaml b/parm/chem/catchem/CATChem_config_gcafs_aero.yaml
new file mode 100644
index 00000000000..767136f727b
--- /dev/null
+++ b/parm/chem/catchem/CATChem_config_gcafs_aero.yaml
@@ -0,0 +1,448 @@
+### CATChem_config.yml: CATChem Runtime configuration options.
+###
+### NOTE: Add quotes around nitrogen oxide ('NO'), because YAML
+### parsers will confuse this with a negative "no" value.
+
+#============================================================================
+# Simulation settings
+#============================================================================
+simulation:
+  name: test
+  start_date: 20240501 0000
+  end_date: 20240501 0100
+  #species_filename: ./Configs/Default/CATChem_species.yml
+  #emission_filename: ./Configs/Default/CATChem_emission.yml
+  species_filename: ./CATChem_species.yml
+  emission_filename: ./CATChem_emission.yml
+  verbose:
+    activate: false
+#============================================================================
+# Grid settings
+#============================================================================
+grid:
+  number_of_levels: 127
+  number_of_soil_layers: 4
+#============================================================================
+# Timesteps settings
+#============================================================================
+timesteps:
+  transport_timestep_in_s: 10
+  chemistry_timestep_in_s: 60
+#============================================================================
+# Diagnostic settings
+#============================================================================
+diagnostics:
+  output:
+    enabled: true
+    directory: "./output"
+    prefix: "catchem_diag"
+    frequency: 3600  #output frequency in seconds; e.g., 3600 for hourly output
+    format: "netcdf" #only format supported now
+    compress_lev: 0 #compress NC file; 0 for no compression, 1-9 for increasing levels of compression (and run time)
+    latlon_output: true #stitch cubed-sphere tiles into a single lat/lon file (only applies when tile count > 1)
+    diag_list: [so2, so4, seas1, seas2, seas3, seas4, seas5, bc1, bc2, oc1, oc2, dust1, dust2, dust3, dust4, dust5]  #list of species to output; empty list for all species
+  collection:
+    enabled: true
+    buffer_size: 1000
+#============================================================================
+# Optics files for Mie
+#============================================================================
+mie:
+  directory: "./ExtData/monochromatic/"  #in running directory after copying from the above directories
+  files:
+    SS: optics_SS.v3_5.nc
+    DU: optics_DU.v15_5.nc
+    BC: optics_BC.v1_5.nc
+    OC: optics_OC.v1_5.nc
+    NI: optics_NI.v2_5.nc
+    SU: optics_SU.v1_5.nc
+#============================================================================
+# RunPhase settings: define process running order
+#============================================================================
+run_phases:
+  test1:
+    description: "Emission and chemistry processes"
+    processes:
+      - seasalt
+      - dust
+      - carbchem
+      - settling
+      - drydep
+      - so4chem
+      - wetdep
+
+#============================================================================
+# Settings for CATChem processes
+#============================================================================
+processes:
+  extemis:
+    activate: true
+    diagnostics: true
+    global_factor: 1.0
+    anthro1:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ChemInput/NEXUS_DIAG.%y4%m2%d2.nc"  # %y4=year, %m2=month, %d2=day
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "P100" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "hourly"
+      diagnostics: true
+      diag_list: [SO2, OC, BC]
+    anthro2:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ChemInput/NEXUS_DIAG.%y4%m2%d2.nc"  # %y4=year, %m2=month, %d2=day
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "P500" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "hourly"
+      diagnostics: true
+      diag_list: [SO2_elev, OC_elev, BC_elev]
+    ship:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ChemInput/NEXUS_DIAG.%y4%m2%d2.nc"  # %y4=year, %m2=month, %d2=day
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "P100" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "hourly"
+      diagnostics: true
+      diag_list: [SO2_ship, OC_ship, BC_ship]
+    bio:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/nexus/MEGAN_OFFLINE_BVOC/v2021-12/MEGAN_OFFLINE_CLIMO_2000_2022_%m2.nc"  # %y4=year, %m2=month, %d2=day
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "none" #biogenic is only at the surface.
+      frequency: "monthly"  #note it is monthly climatology from offline megan for now
+      diagnostics: true
+      diag_list: [isoprene, mtpa]
+    so2_aviation_lto:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_so2.aviation_lto.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_lto" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [so2_aviation]
+    so2_aviation_cds:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_so2.aviation_cds.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_cds" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [so2_aviation]
+    so2_aviation_crs:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_so2.aviation_crs.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_crs" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [so2_aviation]
+    oc_aviation_lto:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_oc.aviation_lto.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_lto" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [oc_aviation]
+    oc_aviation_cds:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_oc.aviation_cds.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_cds" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [oc_aviation]
+    oc_aviation_crs:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_oc.aviation_crs.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_crs" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [oc_aviation]
+    bc_aviation_lto:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_bc.aviation_lto.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_lto" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [bc_aviation]
+    bc_aviation_cds:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_bc.aviation_cds.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_cds" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [bc_aviation]
+    bc_aviation_crs:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/sfc/HTAP/v2.2/htap-v2.2.emis_bc.aviation_crs.x3600_y1800_t12.2010.nc4"
+      format: "netcdf"
+      gridded: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "aviation_crs" #options: none, P100, P500, Ppbl, aviation, aviation_lto, aviation_cds, aviation_crs
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [bc_aviation]
+    point: #not used for now
+      activate: true
+      scale_factor: 1.0
+      topfraction: -1.0
+      source_file: "INPUT/PT.nc"
+      format: "netcdf"
+      gridded: false
+      frequency: "hourly"
+      lat_name: "LATITUDE"
+      lon_name: "LONGITUDE"
+      plume_rise: "sofiev"
+      stack_diameter:    STKDM
+      stack_height:      STKHT
+      stack_temperature: STKTK
+      stack_velocity:    STKVE
+      diagnostics: true
+      diag_list: [NO, SO2, POC, PSO4]
+    gmi:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/PIESA/L127/A2_ACCMIP_gmic_MERRA_oh_h2o2_no3.x144_y91_z127_t14.%y4.nc"
+      format: "netcdf"
+      gridded: true
+      is_2d: false
+      apply_method: "replace"
+      reverse_vertical: true
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "none"
+      frequency: "monthly" # 14 months (Dec+Jan padding); time-coord matching selects the right slice
+      diagnostics: true
+      diag_list: [oh, h2o2]
+    dms:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/MERRA2/sfc/DMSclim_sfcconcentration.x360_y181_t12.Lana2011.nc4"
+      format: "netcdf"
+      gridded: true
+      is_2d: true
+      apply_method: "replace"
+      regrid_method: conserve
+      time_interpolation: linear
+      lat_name: "latitude"
+      lon_name: "longitude"
+      vertical_dist: "none"
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [conc]
+    volcano:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/nexus/VOLCANO/v2021-09/so2_volcanic_emissions_CARN_v202005.degassing_only.rc"
+      format: "volcano"      # triggers the point-source reader + 3D injector
+      gridded: false
+      frequency: "static"     # "daily" if seperated by day
+      diagnostics: false     #current will all be zeros
+      diag_list: [SO2]
+    fire:
+      activate: true
+      scale_factor: 0.7778
+      topfraction: -1.0
+      source_file: "ChemInput/FIRE_EMIS_%y4%m2%d2.nc"  # %y4=year, %m2=month, %d2=day
+      format: "netcdf"
+      gridded: true
+      is_2d: true
+      regrid_method: conserve
+      time_interpolation: linear
+      use_oc_fbb: true
+      diurnal_bb: true
+      lat_name: "lat"
+      lon_name: "lon"
+      vertical_dist: "Ppbl"
+      frequency: "daily"
+      plume_rise: "sofiev"
+      diagnostics: true
+      diag_list: [SO2,OC,BC]
+    dust:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/FENGSHA/FENGSHA_2022_NESDIS_inputs_10km_v3.2.nc"
+      format: "netcdf"
+      gridded: true
+      regrid_method: neareststod
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      is_2d: true
+      apply_method: "replace"
+      frequency: "static"
+      diagnostics: true
+      diag_list: [clayfrac,sandfrac,uthres,sep]
+    fengsha:
+      activate: true
+      scale_factor: 1.0
+      source_file: "ExtData/FENGSHA/FENGSHA_2022_NESDIS_inputs_10km_v4.nc"
+      format: "netcdf"
+      gridded: true
+      regrid_method: neareststod
+      time_interpolation: linear
+      lat_name: "lat"
+      lon_name: "lon"
+      is_2d: true
+      apply_method: "replace"
+      frequency: "monthly"
+      diagnostics: true
+      diag_list: [albedo_drag]
+  seasalt:
+    activate: true
+    diagnostics: true
+    diag_species: []
+    scheme: 'geos12'
+    gong97:
+      scale_factor: 1.0
+      weibull_flag: false
+    gong03:
+      scale_factor: 1.0
+      weibull_flag: false
+    geos12:
+      scale_factor: 1.0
+      weibull_flag: false
+  dust:
+    activate: true
+    diagnostics: true
+    diag_species: []
+    scheme: 'fengsha'
+    fengsha:
+      alpha: 0.20
+      gamma: 1.0
+      drylimit_factor: 1.2
+      moist_correction_factor: 1.0
+      kvhmax: 0.0002
+      drag_option: 1
+      horizflux_option: 1
+      moist_option: 1
+      distribution_option: 1
+    ginoux:
+      Ch_DU: [0.07, 0.07, 0.07, 0.07, 0.07]
+  drydep:
+    activate: true
+    diagnostics: true
+    diag_species: [so2, so4, seas1, seas3, seas5, oc1,oc2,bc1,bc2,dust1, dust3, dust5]
+    gas_scheme: 'wesely'
+    aero_scheme: 'gocart'
+    wesely:
+      scale_factor: 1.0
+    gocart:
+      scale_factor: 1.0
+      resuspension: false
+      dust_resuspension_only: true   # default
+    zhang:
+      scale_factor: 1.0
+  wetdep:
+    activate: true
+    diagnostics: true
+    diag_species: [so2, so4, seas1, seas3, seas5, oc1,oc2,bc1,bc2,dust1, dust3, dust5]
+    scheme: 'jacob'
+    jacob:
+      scale_factor: 1.0       #washout scale for all species
+      radius_threshold: 0.05
+      so4_gocart_resusp: true #sulfate-only GOCART-style resuspension
+      so4_washout_eff: 0.3 #sulfate-only below-cloud washout efficiency (1.0=unchanged); reduce to cut excess SO4 washout
+  settling:
+    activate: true
+    diagnostics: true
+    diag_species: [so4, seas1, seas3, seas5, oc1,oc2,bc1,bc2,dust1, dust3, dust5]
+    scheme: 'gocart'
+    gocart:
+      scale_factor: 1.0 #not doing anything for now since we cannot edit gocart2g module
+      simple_scheme: true  #read in mie data for wet particles if true; otherwise calculate particles wet swelling internally
+      swelling_method: 2    # 1 for Fitzgerald 1975; 2 for Gerber 1985 if simple_scheme is false
+      correction_maring: false  #correction settling velocity following Maring et al, 2003 for both simple and non-simple schemes
+      maring_dust_only: true  #apply Maring correction to dust only (true) or all species (false)
+  so4chem:
+    activate: true
+    diagnostics: true
+    diag_species: [so2, so4]  #only msa, so2 and so4 for gocart now
+    scheme: 'gocart'
+    gocart:
+      update_so2: true #whether to update SO2 concentration based on chemical production/loss
+  carbchem:
+    activate: true
+    diagnostics: true
+    diag_species: [oc1,oc2,bc1,bc2]  #no brown carbon for now
+    scheme: 'gocart'
+    gocart:
+      time_days_hydrophobic_to_hydrophilic: 2.5  # Rate of conversion of hydrophobic to hydrophilic [days]
\ No newline at end of file
diff --git a/parm/chem/catchem/CATChem_emissions_gcafs_aero.yaml b/parm/chem/catchem/CATChem_emissions_gcafs_aero.yaml
new file mode 100644
index 00000000000..bc3b26626a7
--- /dev/null
+++ b/parm/chem/catchem/CATChem_emissions_gcafs_aero.yaml
@@ -0,0 +1,283 @@
+anthro1:
+  #NO:
+  #  long_name: "Nitrogen Oxide"
+  #  units: "kg/m2/s"
+  #  scale: [1.0]
+  #  map: ["NO"]   #double check upper or lower case
+  SO2:
+    long_name: "Sulfur Dioxide"
+    units: "kg/m2/s"
+    scale: [0.97, 0.045] #1-0.03; 0.03*96/64
+    map: ["so2", "so4"]
+  OC:
+    long_name: "Organic Carbon"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9] #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+  BC:
+    long_name: "Black Carbon"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2] #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+anthro2:
+  SO2_elev:
+    long_name: "Sulfur Dioxide at Elevated Levels"
+    units: "kg/m2/s"
+    scale: [0.97, 0.045] #1-0.03; 0.03*96/64
+    map: ["so2", "so4"]
+  OC_elev:
+    long_name: "Organic Carbon at Elevated Levels"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9] #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+  BC_elev:
+    long_name: "Black Carbon at Elevated Levels"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2] #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+ship:
+  SO2_ship:
+    long_name: "Sulfur Dioxide from Ships"
+    units: "kg/m2/s"
+    scale: [1.0]
+    map: ["so2"]
+  SO4_ship:
+    long_name: "Sulfate from Ships"
+    units: "kg/m2/s"
+    scale: [1.0]
+    map: ["so4"]
+  OC_ship:
+    long_name: "Organic Carbon from Ships"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9] #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+  BC_ship:
+    long_name: "Black Carbon from Ships"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2] #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+fire:
+  SO2:
+    long_name: "Sulfur Dioxide from Biomass Burning"
+    units: "kg/m2/s"
+    scale: [1.0]
+    map: ["so2"]
+  OC:
+    long_name: "Organic Carbon from Biomass Burning"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9]  #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+  BC:
+    long_name: "Black Carbon from Biomass Burning"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2]  #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+so2_aviation_lto:
+  so2_aviation:
+    long_name: "Sulfur Dioxide from Aviation LTO"
+    units: "kg/m2/s"
+    scale: [1.0]
+    map: ["so2"]
+oc_aviation_lto:
+  oc_aviation:
+    long_name: "Organic Carbon from Aviation LTO"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9] #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+bc_aviation_lto:
+  bc_aviation:
+    long_name: "Black Carbon from Aviation LTO"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2] #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+so2_aviation_cds:
+  so2_aviation:
+    long_name: "Sulfur Dioxide from Aviation CDS"
+    units: "kg/m2/s"
+    scale: [1.0]
+    map: ["so2"]
+oc_aviation_cds:
+  oc_aviation:
+    long_name: "Organic Carbon from Aviation CDS"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9] #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+bc_aviation_cds:
+  bc_aviation:
+    long_name: "Black Carbon from Aviation CDS"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2] #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+so2_aviation_crs:
+  so2_aviation:
+    long_name: "Sulfur Dioxide from Aviation CRS"
+    units: "kg/m2/s"
+    scale: [1.0]
+    map: ["so2"]
+oc_aviation_crs:
+  oc_aviation:
+    long_name: "Organic Carbon from Aviation CRS"
+    units: "kg/m2/s"
+    scale: [0.9, 0.9] #0.5 x 1.8; 0.5 is the fraction of OC that is hydrophobic/hydrophilic; 1.8 is the scaling factor from OC to POM
+    map: ["oc1", "oc2"]
+bc_aviation_crs:
+  bc_aviation:
+    long_name: "Black Carbon from Aviation CRS"
+    units: "kg/m2/s"
+    scale: [0.8, 0.2] #There is no 1.8 factor for BC
+    map: ["bc1", "bc2"]
+bio:
+  limo:
+    long_name: "Limonene"
+    units: "kg/m2/s"
+    scale: [0.09]
+    map: ["oc2"]     #0.05 x 1.8; Note: biogenic terpenes are assumed to be emitted as hydrophilic OC with 5% conversion rate
+  isoprene:
+    long_name: "Isoprene"
+    units: "kg/m2/s"
+    scale: [0.054]
+    map: ["oc2"]     #0.03 x 1.8; Note: biogenic isoprene is assumed to be emitted as hydrophilic OC with 3% conversion rate
+  mtpa:
+    long_name: "Monoterpene alpha-Pinene"
+    units: "kg/m2/s"
+    scale: [0.09]
+    map: ["oc2"]     #0.05 x 1.8; Note: biogenic terpenes are assumed to be emitted as hydrophilic OC with 5% conversion rate
+  mtpo:
+    long_name: "Monoterpene other"
+    units: "kg/m2/s"
+    scale: [0.09]
+    map: ["oc2"]     #0.05 x 1.8; Note: biogenic terpenes are assumed to be emitted as hydrophilic OC with 5% conversion rate
+  #PEC:
+  #  long_name: "Primary Elemental Carbon"
+  #  units: "kg/m2/s"
+  #  scale: [0.8, 0.2] # 0.8/0.2 is the fraction of hydrophobic/hydrophilic; 1.8 is not used for BC
+  #  map: ["bc1", "bc2"]
+  #PSO4:
+  #  long_name: "Primary Sulfate"
+  #  units: "kg/m2/s"
+  #  scale: [1.0]
+  #  map: ["so4"]    #will be changed to SO4 later
+gmi:
+  oh:
+    long_name: "Hydroxyl Radical"
+    units: "mol/mol"
+    scale: [1.0]
+    map: ["oh"]
+  h2o2:
+    long_name: "Hydrogen Peroxide"
+    units: "mol/mol"
+    scale: [1.0]
+    map: ["h2o2"]
+  no3:
+    long_name: "Nitrate Radical"
+    units: "mol/mol"
+    scale: [1.0]
+    map: ["no3"]
+dms:
+  conc:
+    long_name: "Dimethyl Sulfide"
+    units: "nmol/l"
+    scale: [1.0]
+    map: ["dms_in"]
+volcano:
+  SO2:
+    long_name: "Volcanic Sulfur Dioxide (degassing)"
+    units: "kg/m2/s"
+    scale: [2.0]   # file rate is kg S/s; 2.0 = fMassSO2/fMassSulfur (64/32) -> kg SO2/s
+    map: ["so2"]
+dust:
+  clayfrac:
+    long_name: "Clay Fraction"
+    units: "1"
+    scale: [1.0]
+    map: ["MET_CLAYFRAC"]
+  sandfrac:
+    long_name: "Sand Fraction"
+    units: "1"
+    scale: [1.0]
+    map: ["MET_SANDFRAC"]
+  sep:
+    long_name: "Sediment Supply Map"
+    units: "1"
+    scale: [1.0]
+    map: ["MET_SSM"]
+  uthres:
+    long_name: "Friction Velocity Threshold"
+    units: "m/s"
+    scale: [1.0]
+    map: ["MET_USTAR_THRESHOLD"]
+fengsha:
+  albedo_drag:
+    long_name: "Drag Partition"
+    units: "1"
+    scale: [1.0]
+    map: ["MET_RDRAG"]
+# point:
+#   NO:
+#     long_name: "Nitrogen Oxide"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["NO"]
+# fire:
+#   NO:
+#     long_name: "Nitrogen Oxide"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["NO"]
+#   FRP:
+#     long_name: "Fire Radiative Power"
+#     units: "1"
+#     scale: [1.0]
+#     map: []
+# dust:
+#   DU1:
+#     long_name: "Dust Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["dust1"]
+#   DU2:
+#     long_name: "Dust Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["dust2"]
+#   DU3:
+#     long_name: "Dust Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["dust3"]
+#   DU4:
+#     long_name: "Dust Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["dust4"]
+#   DU5:
+#     long_name: "Dust Species Coarse Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["dust5"]
+# seasalt:
+#   SeaS1:
+#     long_name: "Seasalt Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["seas1"] ##dummy mapping here for test only
+#   SeaS2:
+#     long_name: "Seasalt Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["seas2"]
+#   SeaS3:
+#     long_name: "Seasalt Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["seas3"]
+#   SeaS4:
+#     long_name: "Seasalt Species Fine Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["seas4"]
+#   SeaS5:
+#     long_name: "Seasalt Species Coarse Mode"
+#     units: "kg/m2/s"
+#     scale: [1.0]
+#     map: ["seas5"]
\ No newline at end of file
diff --git a/parm/chem/catchem/CATChem_field_mapping_gcafs_aero.yaml b/parm/chem/catchem/CATChem_field_mapping_gcafs_aero.yaml
new file mode 100644
index 00000000000..2fa2a4ce6c4
--- /dev/null
+++ b/parm/chem/catchem/CATChem_field_mapping_gcafs_aero.yaml
@@ -0,0 +1,269 @@
+import_fields:
+  - standard_name: "inst_temp_levels"
+    catchem_var: "T"
+    dimensions: 3
+    units: "K"
+    optional: false
+  # RH is intentionally NOT imported. Upstream/develop derives RH internally
+  # from T, QV, PMID (met_utilities::relative_humidity), and the C++ core uses
+  # the identical formula. Importing a host RH here would override the
+  # derivation and diverge hydrophilic swelling (settling/wetdep) from the
+  # legacy baseline. Keep RH derived to preserve numerical parity.
+  - standard_name: "inst_geop_interface"
+    catchem_var: "Z"
+    dimensions: 3
+    vertical_axis: "interface"
+    units: "m"
+    optional: false
+  - standard_name: "inst_geop_levels"
+    catchem_var: "ZMID"
+    dimensions: 3
+    units: "m"
+    optional: false
+  - standard_name: "inst_pres_interface"
+    catchem_var: "PEDGE"
+    dimensions: 3
+    vertical_axis: "interface"
+    units: "Pa"
+    optional: false
+  - standard_name: "inst_pres_levels"
+    catchem_var: "PMID"
+    dimensions: 3
+    units: "Pa"
+    optional: false
+  - standard_name: "inst_zonal_wind_levels"
+    catchem_var: "U"
+    dimensions: 3
+    units: "m/s"
+    optional: false
+  - standard_name: "inst_merid_wind_levels"
+    catchem_var: "V"
+    dimensions: 3
+    units: "m/s"
+    optional: false
+  - standard_name: "inst_cloud_frac_levels"
+    catchem_var: "CLDF"
+    dimensions: 3
+    units: "1"
+    optional: false
+  - standard_name: "inst_rainfall_amount"
+    catchem_var: "PRECLSC"
+    dimensions: 2
+    units: "m"
+    optional: false
+  - standard_name: "inst_convective_rainfall_amount"
+    catchem_var: "PRECCON"
+    dimensions: 2
+    units: "m"
+    optional: false
+  - standard_name: "inst_zonal_wind_height10m"
+    catchem_var: "U10M"
+    dimensions: 2
+    units: "m/s"
+    optional: false
+  - standard_name: "inst_merid_wind_height10m"
+    catchem_var: "V10M"
+    dimensions: 2
+    units: "m/s"
+    optional: false
+  - standard_name: "inst_friction_velocity"
+    catchem_var: "USTAR"
+    dimensions: 2
+    units: "m/s"
+    optional: false
+  - standard_name: "inst_land_sea_mask"
+    catchem_var: "LWI"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_temp_height_surface"
+    catchem_var: "TS"
+    dimensions: 2
+    units: "K"
+    optional: false
+  - standard_name: "inst_pres_height_surface"
+    catchem_var: "PS"
+    dimensions: 2
+    units: "Pa"
+    optional: false
+  - standard_name: "inst_temp_height2m"
+    catchem_var: "T2M"
+    dimensions: 2
+    units: "K"
+    optional: false
+  - standard_name: "inst_spec_humid_height2m"
+    catchem_var: "QV2M"
+    dimensions: 2
+    units: "kg/kg"
+    optional: false
+  - standard_name: "inst_sensi_heat_flx"
+    catchem_var: "HFLUX"
+    dimensions: 2
+    units: "w/m2"
+    optional: false
+  - standard_name: "inst_laten_heat_flx"
+    catchem_var: "EFLUX"
+    dimensions: 2
+    units: "w/m2"
+    optional: false
+  - standard_name: "inst_net_sw_flx"
+    catchem_var: "SWGDN"
+    dimensions: 2
+    units: "w/m2"
+    optional: false
+  - standard_name: "inst_aerodynamic_conductance"
+    catchem_var: "CMM"
+    dimensions: 2
+    units: "s/m"
+    optional: false
+  - standard_name: "inst_surface_roughness"
+    catchem_var: "Z0"
+    dimensions: 2
+    units: "m"
+    optional: false
+  - standard_name: "inst_pbl_height"
+    catchem_var: "PBLH"
+    dimensions: 2
+    units: "m"
+    optional: false
+  - standard_name: "height"
+    catchem_var: "ORO"
+    dimensions: 2
+    units: "m"
+    optional: true
+    advertise: true
+  - standard_name: "canopy_moisture_storage"
+    catchem_var: "WCA"
+    dimensions: 2
+    units: "m3"
+    optional: true
+    advertise: true
+  - standard_name: "inst_canopy_resistance"
+    catchem_var: "RCA"
+    dimensions: 2
+    units: "s/m"
+    optional: true
+    advertise: true
+  - standard_name: "surface_cell_area"
+    catchem_var: "AREA_M2"
+    dimensions: 2
+    units: "m2"
+    optional: false
+  - standard_name: "surface_snow_area_fraction"
+    catchem_var: "FRSNO"
+    dimensions: 2
+    units: "frac"
+    optional: false
+  - standard_name: "ice_fraction_in_atm"
+    catchem_var: "FRSEAICE"
+    dimensions: 2
+    units: "frac"
+    optional: false
+  - standard_name: "leaf_area_index"
+    catchem_var: "LAI"
+    dimensions: 2
+    units: "m2/m2"
+    optional: false
+  # FV3 exposes green vegetation fraction as ``vfrac``.  Keep the host
+  # exchange name here and translate it to the mechanism-independent CATChem
+  # met-state key below; the NUOPC cap uses this YAML mapping at runtime.
+  - standard_name: "inst_vegetation_area_frac"
+    catchem_var: "GVF"
+    dimensions: 2
+    units: "frac"
+    optional: false
+  - standard_name: "ocean_fraction"
+    catchem_var: "FROCEAN"
+    dimensions: 2
+    units: "frac"
+    optional: false
+  - standard_name: "vegetation_type"
+    catchem_var: "DLUSE"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "lake_fraction"
+    catchem_var: "FRLAKE"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_surface_soil_wetness"
+    catchem_var: "GWETTOP"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_ice_nonconv_tendency_levels"
+    catchem_var: "PFILSAN"
+    dimensions: 3
+    # UFS supplies nlev levels.  Preserve the upstream CATChem cap's
+    # nlev+1 interface layout by copying those values into entries 1:nlev
+    # and repeating the final host value at entry nlev+1.
+    vertical_axis: "level_to_interface"
+    units: "kg/m2/s"
+    optional: false
+  - standard_name: "inst_liq_nonconv_tendency_levels"
+    catchem_var: "PFLLSAN"
+    dimensions: 3
+    vertical_axis: "level_to_interface"
+    units: "kg/m2/s"
+    optional: false
+  - standard_name: "soil_type"
+    catchem_var: "DSOILTYPE"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_soil_moisture_content"
+    catchem_var: "SOILM"
+    dimensions: 3
+    vertical_axis: "soil_layer"
+    units: "m3/m3"
+    optional: false
+  - standard_name: "temperature_of_soil_layer"
+    catchem_var: "SOILT"
+    dimensions: 3
+    vertical_axis: "soil_layer"
+    units: "K"
+    optional: true
+    advertise: true
+  - standard_name: "inst_up_sensi_heat_flx"
+    catchem_var: "HFLUX_UP"
+    dimensions: 2
+    units: "w/m2"
+    optional: true
+    advertise: true
+  - standard_name: "inst_tracer_mass_frac"
+    catchem_var: "chem"
+    dimensions: 4
+    # Match upstream: specific humidity is supplied by the host-owned sphum
+    # tracer, rather than through a competing rank-3 meteorology import.
+    host_tracer_name: "sphum"
+    host_tracer_var: "QV"
+    units: "1"
+    optional: false
+
+export_fields:
+  - standard_name: "inst_tracer_mass_frac"
+    catchem_var: "chem"
+    dimensions: 4
+    units: "1"
+    optional: false
+  - standard_name: "inst_tracer_diag_aod"
+    catchem_var: "AOD"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_tracer_diag_coszens"
+    catchem_var: "coszens"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_tracer_diag_jo3o1d"
+    catchem_var: "jo3o1d"
+    dimensions: 2
+    units: "1"
+    optional: false
+  - standard_name: "inst_tracer_diag_jno2"
+    catchem_var: "jno2"
+    dimensions: 2
+    units: "1"
+    optional: false
\ No newline at end of file
diff --git a/parm/chem/catchem/CATChem_species_gcafs_aero.yaml b/parm/chem/catchem/CATChem_species_gcafs_aero.yaml
new file mode 100644
index 00000000000..88467a8e682
--- /dev/null
+++ b/parm/chem/catchem/CATChem_species_gcafs_aero.yaml
@@ -0,0 +1,327 @@
+### CATChem_species.yml: CATChem Runtime Species Configuration
+###
+### NOTE: Add quotes around nitrogen oxide ('NO'), because YAML
+### parsers will confuse this with a negative "no" value.
+
+# species (gas dey dep set to false to test GOCART only for now):
+- name: so2
+  __description: Sulfur dioxide
+  __is_gas: true
+  __is_drydep: true
+  __is_wetdep: true
+  __dd_f0: 0.0
+  __dd_hstar: 1.0e+5
+  molecular weight [kg mol-1]: 64.04e-3
+  __dd_DvzAerSnow: 0.03
+  __dd_DvzMinVal_snow: 0.2
+  __dd_DvzMinVal_land: 0.3
+  __viscosity: 0.0 #dummy value
+  #This is Luo's scheme for SO2 but adopted here
+  __henry_k0: 1.22
+  __henry_cr: 3100.0
+  __wd_retfactor: 5.0e-2
+  __wd_LiqAndGas: true
+  __wd_convfacI2G: 6.17395e-1
+  __wd_rainouteff: [1.0, 0.0, 1.0]
+  __wd_reevap_frac: 1.0  #GOCART resuspends full re-evaporated fraction (GEOS-Chem/Luo default 0.5)
+- name: h2o2
+  __description: Hydrogen peroxide
+  __is_gas: true
+  __is_drydep: false   #turn off for now due to climatology reading from GOCART inputs.
+  __is_wetdep: true
+  __is_advected: false
+  __dd_f0: 1.0
+  __dd_hstar: 5.0e+7
+  molecular weight [kg mol-1]: 34.02e-3
+  __viscosity: 0.0 #dummy value
+  __henry_k0: 8.3e+4
+  __henry_cr: 7400.0
+  __wd_retfactor: 5.0e-2
+  __wd_LiqAndGas: true
+  __wd_convfacI2G: 4.36564e-1
+- name: oh
+  __description: Hydroxyl radical
+  __is_gas: true
+  __is_advected: false
+  molecular weight [kg mol-1]: 17.01e-3
+- name: no3
+  __description: Nitrate radical
+  __is_gas: true
+  __is_photolysis: true
+  __is_advected: false
+  molecular weight [kg mol-1]: 62.01e-3
+- name: so4       #This is to match CMAQ name to use the restart file. so4 is used in GEOS-Chem.
+  __description: sulfate
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 96.06e-3
+  __radius: 0.35
+  __density: 1700.0
+  __dd_DvzAerSnow: 0.03
+  __dd_DvzMinVal_snow: 0.01
+  __dd_DvzMinVal_land: 0.01
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __wd_rainouteff: [1.0, 0.0, 1.0]
+  __wd_reevap_frac: 1.0  #GOCART resuspends full re-evaporated fraction (GEOS-Chem/Luo default 0.5)
+  __mie_name: SU
+- name: dms
+  __description: Dimethyl sulfide
+  molecular weight [kg mol-1]: 62.13e-3
+  __radius: 0.0
+  __is_gas: true   #gocart treat it as a gas without dry and wet deposition
+  __is_dust: false
+  __is_aerosol: false
+  __is_drydep: false
+  __henry_k0: 0.48
+  __henry_cr: 3100.0
+  __mie_name: SU
+- name: dms_in
+  __description: Dimethyl sulfide in ocean water (climatology for emissions calculation)
+  __is_advected: false
+  molecular weight [kg mol-1]: 62.13e-3
+  __radius: 8.7e-2
+- name: msa
+  __description: methanesulphonic acid
+  __is_aerosol: true   #gocart treat it as a gas, but we treat it as aerosol
+  __is_drydep: true
+  __is_wetdep: true
+  __radius: 0.35
+  __density: 1700.0
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  __dd_DvzAerSnow: 0.03
+  __dd_DvzMinVal_snow: 0.01
+  __dd_DvzMinVal_land: 0.01
+  molecular weight [kg mol-1]: 96.10e-3
+  __wd_rainouteff: [1.0, 0.0, 1.0]
+  __mie_name: SU
+- name: bc1
+  __description: BC1
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 12.01e-3    #gocart is 180 g/mol but it seems not used in gocart processes. So we go with GC
+  __radius: 0.35   #gocart is 0.35; GC is 0.087
+  __density: 1800.0
+  __dd_DvzAerSnow: 0.03
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __wd_rainouteff: [0.0, 0.0, 0.0]
+  __t_chem_loss: -1.0  #Rate of chemical destruction of carbon species [days]; Note -1 (any negative value) means carbon loss is turned off by default.
+  __mie_name: BC
+- name: bc2
+  __description: BC2
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 12.01e-3    #gocart is 180 g/mol but it seems not used in gocart processes. So we go with GC
+  __radius: 0.35   #gocart is 0.35; GC is 0.087
+  __density: 1800.0
+  __dd_DvzAerSnow: 0.03
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __t_chem_loss: -1.0  #Rate of chemical destruction of carbon species [days]; Note -1 (any negative value) means carbon loss is turned off by default.
+  __mie_name: BC
+- name: oc1
+  __description: OC1
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 12.01e-3    #gocart is 180 g/mol but it seems not used in gocart processes. So we go with GC
+  __radius: 0.35   #gocart is 0.35; GC is 0.087
+  __density: 1800.0
+  __dd_DvzAerSnow: 0.03
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __wd_rainouteff: [0.0, 0.0, 0.0]
+  __t_chem_loss: -1.0  #Rate of chemical destruction of carbon species [days]; Note -1 (any negative value) means carbon loss is turned off by default.
+  __mie_name: OC
+- name: oc2
+  __description: OC2
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 12.01e-3    #gocart is 180 g/mol but it seems not used in gocart processes. So we go with GC
+  __radius: 0.35   #gocart is 0.35; GC is 0.087
+  __density: 1800.0
+  __dd_DvzAerSnow: 0.03
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __t_chem_loss: -1.0  #Rate of chemical destruction of carbon species [days]; Note -1 (any negative value) means carbon loss is turned off by default.
+  __mie_name: OC
+- name: dust1
+  __long_name: dust1
+  __description: dust1
+  __lower_radius: 0.1
+  __upper_radius: 1.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 29.00e-3
+  __radius: 0.73
+  __density: 2500.
+  __is_dust: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [0.8, 0.8, 0.8]
+  __mie_name: DU
+- name: dust2
+  __long_name: dust2
+  __description: dust2
+  __lower_radius: 1.0
+  __upper_radius: 1.8
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 29.00e-3
+  __radius: 1.4
+  __density: 2650.
+  __is_dust: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [0.8, 0.8, 0.8]
+  __mie_name: DU
+- name: dust3
+  __long_name: dust3
+  __description: dust3
+  __lower_radius: 1.8
+  __upper_radius: 3.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 29.00e-3
+  __radius: 2.4
+  __density: 2650.
+  __is_dust: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [0.8, 0.8, 0.8]
+  __mie_name: DU
+- name: dust4
+  __long_name: dust4
+  __description: dust4
+  __lower_radius: 3.0
+  __upper_radius: 6.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 29.00e-3
+  __radius: 4.5
+  __density: 2650.
+  __is_dust: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: DU
+- name: dust5
+  __long_name: dust5
+  __description: dust5
+  __lower_radius: 6.0
+  __upper_radius: 10.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 29.00e-3
+  __radius: 8.0
+  __density: 2650.
+  __is_dust: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: DU
+- name: seas1
+  __long_name: seas1
+  __description: seas1
+  __lower_radius: 0.03
+  __upper_radius: 0.1
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 31.40e-3  #GEOS-Chem is 31.40; gocart is 58 but it seems not used in gocart processes. So we go with GC
+  __radius: 0.079
+  __density: 2200.
+  __is_seasalt: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: SS
+- name: seas2
+  __long_name: seas2
+  __description: seas2
+  __lower_radius: 0.1
+  __upper_radius: 0.5
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 31.40e-3  #GEOS-Chem is 31.40; gocart is 58
+  __radius: 0.316
+  __density: 2200.
+  __is_seasalt: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: SS
+- name: seas3
+  __long_name: seas3
+  __description: seas3
+  __lower_radius: 0.5
+  __upper_radius: 1.5
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 31.40e-3  #GEOS-Chem is 31.40; gocart is 58
+  __radius: 1.119
+  __density: 2200.
+  __is_seasalt: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: SS
+- name: seas4
+  __long_name: seas4
+  __description: seas4
+  __lower_radius: 1.5
+  __upper_radius: 5.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 31.40e-3  #GEOS-Chem is 31.40; gocart is 58
+  __radius: 2.818
+  __density: 2200.
+  __is_seasalt: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: SS
+- name: seas5
+  __long_name: seas5
+  __description: seas5
+  __lower_radius: 5.0
+  __upper_radius: 10.0
+  __dd_f0: 0.0
+  __dd_hstar: 0.0
+  molecular weight [kg mol-1]: 31.40e-3  #GEOS-Chem is 31.40; gocart is 58
+  __radius: 7.772
+  __density: 2200.
+  __is_seasalt: true
+  __is_aerosol: true
+  __is_drydep: true
+  __is_wetdep: true
+  __wd_rainouteff: [1.0, 1.0, 1.0]
+  __mie_name: SS
\ No newline at end of file
diff --git a/parm/chem/catchem/catchem_tracer.list b/parm/chem/catchem/catchem_tracer.list
new file mode 100644
index 00000000000..dfb29d31263
--- /dev/null
+++ b/parm/chem/catchem/catchem_tracer.list
@@ -0,0 +1,18 @@
+so2
+so4
+dms
+msa
+bc1
+bc2
+oc1
+oc2
+dust1
+dust2
+dust3
+dust4
+dust5
+seas1
+seas2
+seas3
+seas4
+seas5
diff --git a/parm/fetch/gcafs_ATMC_gdas-anl.yaml.j2 b/parm/fetch/gcafs_ATMC_gdas-anl.yaml.j2
new file mode 120000
index 00000000000..606412bb892
--- /dev/null
+++ b/parm/fetch/gcafs_ATMC_gdas-anl.yaml.j2
@@ -0,0 +1 @@
+gcafs_ATMA_gdas-anl.yaml.j2
\ No newline at end of file
diff --git a/sorc/build_opts.yaml b/sorc/build_opts.yaml
index e0a08d9b723..edc8d22500d 100644
--- a/sorc/build_opts.yaml
+++ b/sorc/build_opts.yaml
@@ -34,6 +34,7 @@ systems:
     - "gefs_ww3_prepost"
   gcafs:
     - "gcafs_model"
+    - "gcafs_catchem_model"
     - "nexus"
     - "gsi_utils"
 build:
@@ -71,6 +72,12 @@ build:
     walltime: "00:40:00"
     memory: "40G"
 
+  gcafs_catchem_model:
+    command: "./build_ufs.sh -a CATCHEM -e gcafs_catchem_model.x"
+    cores: 12
+    walltime: "00:40:00"
+    memory: "40G"
+
   upp:
     command: "./build_upp.sh"
     cores: 8
diff --git a/sorc/build_ufs.sh b/sorc/build_ufs.sh
index 835de9ae801..43a41e8b884 100755
--- a/sorc/build_ufs.sh
+++ b/sorc/build_ufs.sh
@@ -58,6 +58,7 @@ case "${EXEC_NAME}" in
     "gefs_model.x") COMPILE_ID=2 ;;
     "sfs_model.x") COMPILE_ID=3 ;;
     "gcafs_model.x") COMPILE_ID=4 ;;
+    "gcafs_catchem_model.x") COMPILE_ID=5 ;;
     *)
         echo "Unsupported executable name: ${EXEC_NAME}"
         exit 1
diff --git a/sorc/link_workflow.sh b/sorc/link_workflow.sh
index b696b4fb3f7..4616c12953f 100755
--- a/sorc/link_workflow.sh
+++ b/sorc/link_workflow.sh
@@ -415,6 +415,14 @@ for sys in "${model_systems[@]}"; do
     fi
 done
 
+# CATChem GCAFS executable (built via "./build_ufs.sh -a CATCHEM -e gcafs_catchem_model.x")
+if [[ -s "ufs_model_gcafs_catchem.x" ]]; then
+    rm -f "ufs_model_gcafs_catchem.x"
+fi
+if [[ -f "${HOMEglobal}/sorc/ufs_model.fd/tests/gcafs_catchem_model.x" ]]; then
+    safe_link_or_copy "${HOMEglobal}/sorc/ufs_model.fd/tests/gcafs_catchem_model.x" "ufs_model_gcafs_catchem.x"
+fi
+
 # WW3 pre/post executables
 declare -a ww3_exes=("ww3_grid" "ww3_prnc" "ww3_outp" "ww3_gint" "ww3_grib")
 declare -A wave_systems
diff --git a/sorc/ufs_model.fd b/sorc/ufs_model.fd
index f6ca8234186..6dc36481b6d 160000
--- a/sorc/ufs_model.fd
+++ b/sorc/ufs_model.fd
@@ -1 +1 @@
-Subproject commit f6ca8234186f07594b7621e960c3e20d4def8952
+Subproject commit 6dc36481b6d1347f3c5332905ad48e7e9da8675e
diff --git a/ush/forecast_postdet.sh b/ush/forecast_postdet.sh
index ff52ef84d37..9cd731ae5df 100755
--- a/ush/forecast_postdet.sh
+++ b/ush/forecast_postdet.sh
@@ -1030,6 +1030,94 @@ GOCART_out() {
     fi
 }
 
+CATCHEM_rc() {
+    echo "SUB ${FUNCNAME[0]}: Staging CATChem runtime configuration files"
+
+    # Link directory containing the chemistry input dataset (ExtData), if provided.
+    # CATChem reads Mie optics tables from ./ExtData/monochromatic/ (see the
+    # 'mie.directory' key in CATChem_config.yml).
+    if [[ -n "${AERO_INPUTS_DIR}" ]]; then
+        ${NLN} "${AERO_INPUTS_DIR}" "${DATA}/ExtData"
+        status=$?
+        if [[ ${status} -ne 0 ]]; then
+            exit "${status}"
+        fi
+    fi
+
+    # Stage the selected CATChem configuration set under the fixed names expected
+    # by the CATChem NUOPC cap and by CATChem_config.yml itself:
+    #   - the cap hardcodes 'CATChem_new_config.yml' and 'CATChem_field_mapping.yml'
+    #   - the config file references './CATChem_species.yml' and './CATChem_emission.yml'
+    local -a catchem_src=(
+        "CATChem_config_${CATCHEM_CONFIG}.yaml"
+        "CATChem_species_${CATCHEM_CONFIG}.yaml"
+        "CATChem_emissions_${CATCHEM_CONFIG}.yaml"
+        "CATChem_field_mapping_${CATCHEM_CONFIG}.yaml"
+    )
+    local -a catchem_dst=(
+        "CATChem_new_config.yml"
+        "CATChem_species.yml"
+        "CATChem_emission.yml"
+        "CATChem_field_mapping.yml"
+    )
+
+    local idx
+    for idx in "${!catchem_src[@]}"; do
+        if [[ ! -r "${CATCHEM_CONFIG_DIR}/${catchem_src[idx]}" ]]; then
+            err_exit "FATAL ERROR: CATChem configuration file '${CATCHEM_CONFIG_DIR}/${catchem_src[idx]}' not found (CATCHEM_CONFIG='${CATCHEM_CONFIG}'), ABORT!"
+        fi
+        cpreq "${CATCHEM_CONFIG_DIR}/${catchem_src[idx]}" "${DATA}/${catchem_dst[idx]}"
+    done
+}
+
+CATCHEM_postdet() {
+    echo "SUB ${FUNCNAME[0]}: Pre-cleaning CATChem output files"
+
+    # CATChem diagnostics (prefix 'catchem_diag' per CATChem_config.yml) cannot
+    # overwrite existing files, so remove any pre-existing output in COM.
+    local outfile
+    for outfile in "${COMOUT_CHEM_HISTORY}"/catchem*; do
+        if [[ -e "${outfile}" ]]; then
+            rm -f "${outfile}"
+        fi
+    done
+}
+
+CATCHEM_out() {
+    echo "SUB ${FUNCNAME[0]}: Copying output data for CATChem"
+
+    # CATChem writes diagnostics into the output directory configured in
+    # CATChem_config.yml ('directory: "./output"', relative to DATA).
+    local diag_dir="${DATA}/output"
+    if [[ ! -d "${diag_dir}" ]]; then
+        diag_dir="${DATA}"
+    fi
+
+    # Build MPMD cmdfile to copy CATChem output files in parallel
+    local cmdfile="${DATA}/cmdfile_catchem_out"
+    rm -f "${cmdfile}"
+
+    local outfile
+    for outfile in "${diag_dir}"/catchem*; do
+        if [[ -e "${outfile}" ]]; then
+            echo "cpfs ${outfile} ${COMOUT_CHEM_HISTORY}/$(basename "${outfile}")" >> "${cmdfile}"
+        fi
+    done
+
+    if [[ -s "${cmdfile}" ]]; then
+        if [[ ! -d "${COMOUT_CHEM_HISTORY}" ]]; then
+            echo "INFO: Directory ${COMOUT_CHEM_HISTORY} does not exist, creating..."
+            mkdir -p "${COMOUT_CHEM_HISTORY}"
+        fi
+
+        "${USHglobal}/run_mpmd.sh" "${cmdfile}" && true
+        export err=$?
+        if [[ ${err} -ne 0 ]]; then
+            err_exit "run_mpmd.sh failed to copy CATChem output files!"
+        fi
+    fi
+}
+
 # shellcheck disable=SC2178
 CMEPS_postdet() {
     echo "SUB ${FUNCNAME[0]}: Linking output data for CMEPS mediator"
diff --git a/ush/forecast_predet.sh b/ush/forecast_predet.sh
index 7d31a3ec2f2..20643baa44c 100755
--- a/ush/forecast_predet.sh
+++ b/ush/forecast_predet.sh
@@ -769,3 +769,16 @@ GOCART_predet() {
     # a subsequent PR to fix this properly.
     ${NLN} "${COMIN_CHEM_INPUT}" "${DATA}/ChemInput"
 }
+
+# shellcheck disable=SC2034
+CATCHEM_predet() {
+    echo "SUB ${FUNCNAME[0]}: CATChem before run type determination"
+
+    # FHMAX gets modified when IAU is on, so keep original value for CATChem output
+    GOCART_MAX=${FHMAX}
+
+    # Stage the prepared chemistry input (emissions) when available
+    if [[ -d "${COMIN_CHEM_INPUT}" ]]; then
+        ${NLN} "${COMIN_CHEM_INPUT}" "${DATA}/ChemInput"
+    fi
+}
diff --git a/ush/parsing_namelists_fv3.sh b/ush/parsing_namelists_fv3.sh
index ff17b0c485b..afaa0191cc0 100755
--- a/ush/parsing_namelists_fv3.sh
+++ b/ush/parsing_namelists_fv3.sh
@@ -291,6 +291,7 @@ FV3_namelists() {
     local DO_SKEB=${do_skeb:-".false."}
     local FRAC_GRID=${FRAC_GRID:-".true."}
     local CPLCHM=${cplchm:-".false."}
+    local CPLCAT=${cplcat:-".false."}
     local CPLFLX=${cplflx:-".false."}
     local CPLICE=${cplice:-".false."}
     local CPLWAV=${cplwav:-".false."}
diff --git a/ush/parsing_ufs_configure.sh b/ush/parsing_ufs_configure.sh
index c8bb0643060..9a93e9e38d7 100755
--- a/ush/parsing_ufs_configure.sh
+++ b/ush/parsing_ufs_configure.sh
@@ -101,7 +101,8 @@ UFS_configure() {
 
     if [[ "${cplchm}" = ".true." ]]; then
 
-        local chm_model="gocart"
+        local chm_model="${chm_model:-gocart}"
+        local cplcat="${cplcat:-.false.}"
         local chm_petlist_bounds="0 $((CHMPETS - 1))"
         local chm_omp_num_threads="${CHMTHREADS}"
         local coupling_interval_sec="${CPL_FAST}"