The Community Multi-scale Air Quality (CMAQ) modeling system is a component of a third generation integrated modeling and analysis framework, Models-3, as formulated by the Atmospheric Modeling Division (AMD) of the NOAA Air Resources Laboratory (ARL) in collaboration with the U.S. EPA’s National Exposure Research Laboratory (NERL). CMAQ models air quality capabilities to understand air borne pollution problems with multiple pollutants and multiple spatial scales.

The CMAQ model has both temporal and spatial flexible scales:

1. Temporal scales allow coverage for both long-term pollutant climate models as well as short term localized transport study, and
2. Spatial scales allow for both urban and regional model simulations of chemical and physical interactions in the atmosphere.

CMAQ was designed to handle scale-dependent meteorological formulations with governing equations expressed in a generalized coordinate system and can accommodate various vertical coordinates and map projections. This approach ensures consistency between CMAQ and the meteorological modeling system used. CMAQ has five interface processors and three types of modeling components defined in CMAQ interface processors and system components.

Specific CMAQ Chemistry Transport Model (CCTM) science modules include the following:

• Horizontal advection (HADV)
• Vertical advection (VADV)
• Mass conservation adjustments for advection processes (ADJON)
• Horizontal diffusion (HDIFF)
• Vertical diffusion (VDIFF)
• Gas-phase chemical reaction solver (CHEM)
• Aqueous-phase reactions and cloud mixing (CLOUD)
• Aerosol dynamics and size distributions (AERO)
• Plume chemistry effects (PING)
• Aerosol deposition velocity estimation
• Photolytic rate computation
• Process analysis