AtChem2 is a modelling tool for atmospheric chemistry. It is primarily designed to use the Master Chemical Mechanism (MCM, https://mcm.york.ac.uk/MCM), but it can be used with any general set of chemical reactions as long as they are provided in the correct format. The MCM is a near-explicit chemical mechanism which describes the gas-phase oxidation of volatile organic compounds (VOC) in the lower atmosphere.

AtChem2 is open source, under the MIT license.

Please, see the file CITATION.md for information on how to cite the model in publications.

• build/ contains the Python and shell scripts used to compile AtChem2.
• doc/ contains the AtChem2 user manual, with the LaTeX source files, and the poster presented at the ACM 2018 conference.
• mcm/ contains data files related to specific versions of the MCM.
• model/ contains an example directory structure for the chemical mechanism, model configuration, constraints, output, and an example chemical mechanism (in FACSIMILE format). There can be several such directories (with different names).
• obj/ contains the files generated by the Fortran compiler.
• src/ contains the Fortran source files.
• tests/ contains the Testsuite scripts and files.
• tools/ contains shell scripts to install AtChem2 and its dependencies, plotting scripts in various languages, and other utilities.

AtChem2 requires a Fortran compiler (GNU gfortran or Intel ifort), the CVODE (part of SUNDIALS) and openlibm libraries, make, and Python. Compilation of CVODE also requires cmake. Optionally, numdiff, FRUIT, and Ruby are required to run the Testsuite. AtChem2 compiles and runs on Unix/Linux and macOS systems. A working knowledge of the unix shell is required to install and use AtChem2.

The latest stable version of AtChem2 can be downloaded from the Releases page. After installing the required dependencies using the scripts in the tools/install/ directory, copy the file tools/install/Makefile.skel to the Main Directory and rename it Makefile. Set the variables CVODELIBDIR, OPENLIBMDIR and FRUITDIR in Makefile to the paths of CVODE, openlibm and (if installed) FRUIT. To compile the model using the example chemical mechanism, execute the command:

./build/build_atchem2.sh ./model/mechanism.fac

The build script converts the chemical mechanism from the FACSIMILE format (mechanism_test.fac) to a Fortran-compatible format, and generates the shared library mechanism.so in the model/configuration/ directory. After the build process is completed, an executable file called atchem2 is created in the Main Directory.

Set the initial conditions, the required outputs and the other model parameters by editing the files in the model/configuration/ directory. If required, copy the constraint files to the relevant subdirectory in model/constraints/. To run the model with the default configuration, execute the command:

./atchem2

The atchem2 executable accepts several command line arguments to customize the location of the configuration, input and output directories, and of the shared library. More information on AtChem2, and detailed instructions on its installation, configuration and use can be found in the manual (doc/AtChem2-Manual.pdf) and in the GMD paper (see CITATION.md).

The AtChem2 wiki contains a summary of the instructions to install, compile, run and contribute to the development of Atchem2, together with additional information and a list of known issues with the suggested solutions or workarounds.

A containerised version of AtChem2 is available. Currently this is built for release 1.2.2. The container is built on Rocky Linux 8.9 and pre-installs the cvode and openlibm dependencies via their relevant tools/install/install_*.sh scripts.

The image can be downloaded via:

docker pull ghcr.io/wacl-york/atchem2:1.2.2

When running the container, changes to the model (e.g. those made to configurations, constraints and mechanisms) should be in a folder that matches the AtChem2 directory structure. This folder is then mounted as a volume to the container with the name /data_transfer/. The mechanism to use is provided as a positional argument to the image e.g. ./model/my_mech.fac.

my_model_run
└── model
    ├── configuration
    ├── constraints
    └── my_mech.fac

docker run -it --rm -v /path/to/my_model_run:/data_transfer ghcr.io/wacl-york/atchem2:1.2.2 ./model/my_mech.fac

Outputs will be copied to my_model_run/model/output on completion.

Some HPC systems use Singularity / Apptainer instead of Docker as their container engine. This image is compatible with those aswell. The image can be converted to a .sif via:

apptainer pull path/to/image/atchem2.sif docker://ghcr.io/wacl-york/atchem2:1.2.2

apptainer run --bind /path/to/my_model_run/:/data_transfer/ path/to/image/atchem2.sif ./model/my_mech.fac