CMAQ v6.0 Release (October 2026)

CMAS Center Announcements
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Announcing the release of CMAQ version 6.0 (October 2026)

CMAQ URL: www.epa.gov/cmaq

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The U.S. EPA and the Community Modeling and Analysis System (CMAS) Center are pleased to announce the release of CMAQ version 6.0. This new version includes many new features and improvements, including:

New chemistry

  • Implementation of particle nitrate photolysis improves overall representation of ozone concentrations, especially on high ozone days
  • Addition of heterogeneous sulfur chemistry improves representation of particulate matter in cold, dark conditions
  • Improvements in the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) version 3, including the addition of chlorine chemistry and updated reactions for semivolatile organic compounds

Major advancements in windblown dust estimates

  • Dramatic improvement of windblown dust emissions for NLCD40 land-use specification address high bias in dust estimates from earlier CMAQ versions.
  • New satellite-based global vegetation dataset accounts for the effect of previously underestimated brown vegetation and further improves dust estimates for many regions in the US and Northern Hemisphere.

Improvements to source apportionment tools, CMAQ-ISAM and CMAQ-DDM3D

  • Tagged source apportionment modeling via CMAQ-ISAM is now compatible with the most up-to-date chemistry in CRACMM2, CRACMM3, CRACMM3M, and CRACMM3HAPS.
  • Sensitivity-based source apportionment via DDM3D is now more robust after instabilities from heterogenous chemistry have been resolved. In addition, CMAQ-DDM3D now supports the STAGE dry deposition module.

New customization options and simplified user experience

  • The Explicit and Lumped air quality Model Output module (ELMO) version 2 offers:
    • expanded features for gas and deposition species. ELMOv1 focused on support for aerosol species.
    • full flexibility for defining aggregates (e.g., VOC, NOY, NOz, etc.) and assigning them to output files.
    • new chemical and meteorological diagnostic variables available for output. Tutorials are provided to support users in adding custom variables themselves.
    • automatic logging of the composition of aggregate output variables like PM2.5, fine-mode organic aerosol (PMF_OA), total Nitrogen deposition, etc.
    • new support for source apportionment tools, CMAQ-ISAM and CMAQ-DDM3D. For example, source-resolved PM2.5 and NOx may now be output directly. Users no longer have to prescribe manually how to sum source-resolved species together.
  • Two dry deposition modules, STAGE and M3DRY, are now both built into the model executables and may be changed at run-time.

Improved methods for land-surface impacts on deposition, emissions, and dilution

  • The new Soil Emissions of Gases to the Atmosphere (SEGA) module provides a simple, meteorological dependent method to calculate soil NO and HONO emissions for regional to global applications.
  • The resistance to dry deposition of volatile carbon-containing compounds has been increased consistent with their vapor-pressures. This increases VOC and CO concentrations across model applications.
  • Boundary-layer mixing dynamics in stable conditions have been made consistent with upstream meteorological models.
  • Enhanced options for online coupling of CMAQ chemistry to meteorological models. First public release of a unified coupler to support WRF-CMAQ and MPAS-CMAQ in a harmonized framework.

CMAQ Code, Documentation, and User Support

Additional user support, including training courses and other CMAS-supported software products is available through the CMAS Center website: www.cmascenter.org