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Community Multiscale Air Quality Model US EPA CMAQ Website: (


CMAQ is an active open-source development project of the U.S. EPA's Office of Research and Development that consists of a suite of programs for conducting air quality model simulations. CMAQ is supported by the CMAS Center: (

CMAQ combines current knowledge in atmospheric science and air quality modeling with multi-processor computing techniques in an open-source framework to deliver fast, technically sound estimates of ozone, particulates, toxics, and acid deposition.

CMAQ version 5.3.3 Overview:

CMAQv5.3.3 is a minor update to CMAQv5.3 that includes multiple bug fixes. These updates include restoration of windowing capability, allowing users to provide gridded input files which were larger in horizontal extent than the simulated domain. This release also includes a new version of the WRF-CMAQ coupled system with a streamlined build process. Users of WRF-CMAQ are strongly encouraged to try the latest version. Additionally, MCIP users should note that starting with this release we are aligning the version numbering between CMAQ and MCIP, i.e., the MCIP updates included in this release are labeled MCIPv5.3.3.

New features in CMAQ version 5.3 include:

  • Simplified emissions scaling
  • Improved representation of natural aerosols
  • Expanded capability for ecological applications
  • Stream-lined CMAQ-ISAM and CMAQ-STM
  • Updates to pre-processors including ICON, BCON and MCIP
  • Enhanced scientific complexity with faster run times
  • Fully revised User's Guide and tutorials
  • Additional updates are documented in the Release Notes

Getting the CMAQ Repository

This CMAQ Git archive is organized with each official public release stored as a branch on the main USEPA/CMAQ repository. The most recently released version of the the model will always be on the branch called 'main'. To clone code from the CMAQ Git archive, specify the branch (i.e. version number) and issue the following command from within a working directory on your server:

git clone -b main CMAQ_REPO

CMAQ Repository Guide

Source code and scripts are organized as follows:

  • CCTM (CMAQ Chemical Transport Model): code and scripts for running the 3D-CTM at the heart of CMAQ.
  • DOCS: Release notes for the release version of CMAQ, CMAQ User's Guide, developers guidance, and short tutorials.
  • PREP: Data preprocessing tools for important input files like initial and boundary conditions, meteorology, etc.
  • POST: Data postprocessing tools for aggregating and evaluating CMAQ output products (e.g. Combine, Site-Compare, etc)
  • UTIL: Utilities for generating code and using CMAQ (e.g. chemical mechanism generation)


Release Notes and code documentation are included within this repository (they are version-controlled along with the code itself).

CMAQ Test Cases

Benchmark/tutorial data for each CMAQ release version are available from the CMAS Data Warehouse. The input and output files are stored on Google Drive with metadata organized through Dataverse. CMAQv5.3.2 comes with new input and output benchmark data for July 1-2, 2016 over the Southeast US (links provided below). The input datasets for these two days are identical to those released with v5.3.1 except for the addition of a grid mask file for the United States: As a result, there is no need for users who have already downloaded the v5.3.1 Southeast benchmark input data to download the v5.3.2 files unless they need the grid mask file for running the new ISAM test case or to test out regional emissions scaling with DESID. The Southeast benchmark output data for v5.3.2 is slightly different from what was released with v5.3 as described in the CMAQv5.3.2 Rlease Notes FAQ.

CMAQ Version Data Type Domain Simulation Dates Dataverse DOI
v5.3 Input CONUS Jan 1 - Dec 31, 2016
v5.3, v5.3.1, v5.3.2, v5.3.3 Input Southeast US July 1 - 14, 2016
v5.3, v5.3.1 Output Southeast US July 1 - 14, 2016
v5.3.2 Output Southeast US July 1 - 2, 2016
v5.3.3 Output Southeast US July 1 - 2, 2016

Code updates to CMAQv5.3.3

Several code updates were made available between CMAQv5.3.3 and CMAQv5.4. Although these are not official CMAQ releases, users may wish to utilize these code updates and bugfixes to improve the performance of their CMAQv5.3.3 simulations. The list of tagged updates for CMAQv5.3.3 are available on the CMAQ Wiki.

Previous CMAQ Versions

The following release versions of CMAQ are currently available on GitHub. DOI values from Zenodo can be used when referencing a specific version.

User Support

EPA Disclaimer

The United States Environmental Protection Agency (EPA) GitHub project code is provided on an "as is" basis and the user assumes responsibility for its use. EPA has relinquished control of the information and no longer has responsibility to protect the integrity, confidentiality, or availability of the information. Any reference to specific commercial products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply their endorsement, recommendation or favoring by EPA. The EPA seal and logo shall not be used in any manner to imply endorsement of any commercial product or activity by EPA or the United States Government.