Jump to main content.


Model Report

Community Multiscale Air Quality Model

Last Revision Date: 11/16/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Community Multiscale Air Quality Model
Model Overview/Abstract:
The U.S. EPA developed the Community Multiscale Air Quality (CMAQ) system to apply a “one atmosphere” multiscale and multi-pollutant modeling approach based mainly on the “first principles” description of the atmosphere. The multiscale capability is supported by the governing diffusion equation in a generalized coordinate system that handles many map projections and vertical coordinate systems, a scheme that maintains dynamic consistency with the upstream (i.e., off-line) meteorology model, and a nesting approach. The multi-pollutant (i.e., tropospheric ozone, acid deposition, particulates, air toxics, mercury, nitrogen loading, and visibility) capability is provided by the generalized chemistry mechanism description, general numerical solver, and comprehensive description of gaseous and aqueous chemistry and modal aerosol dynamics. Input emission data sets for CMAQ are estimated using the SMOKE emissions modeling and processing system. Typical retrospective model applications have employed as input three-dimensional descriptions of prevalent meteorological conditions simulated by the MM5 and Weather Research and Forecasting (WRF) meteorological models, while air quality forecast applications have linked the CMAQ model with the National Weather Service’s operational North American Mesoscale (NAM) model.

Keywords: Air quality modeling, ozone, particulate matter, air toxics, mercury, visibility, meteorological modeling.
Model Technical Contact Information:
Rohit Mathur, Atmospheric Modeling Division, NERL/ORD, mathur.rohit@epa.gov, (919) 541-1483 Developer Contact

Rohit Mathur, Atmospheric Modeling Division, NERL/ORD, mathur.rohit@epa.gov, (919) 541-1483

Jonathan Pleim, Atmospheric Modeling Division, NERL/ORD, pleim.jon@epa.gov, (919) 541-1336

Shawn Roselle, Atmospheric Modeling Division, NERL/ORD, roselle.shawn@epa.gov, (919) 541-7699

Kenneth Schere, Atmospheric Modeling Division, NERL/ORD, schere.kenneth@epa.gov, (919) 541-3795

Model Homepage: http://www.epa.gov/asmdnerl/CMAQ/cmaq_model.html
Substantive Changes from Prior Version: The development and enhancement of the CMAQ modeling system is a continuous process. Major public releases of the model are conducted on a frequent basis. The next major public release of the CMAQ model is scheduled for September 2008. Brief description of substantive model enhancements and changes can be found in release notes available at: http://www.epa.gov/amdweb95/CMAQ/index.html

A history of model releases is available at:http://www.cmascenter.org/download/release_calendar.cfm?temp_id=99999exit EPA

Plans for further model development: Modeling capabilities will be extended to smaller scales to address residual non-attainment in urban areas. Also, the 2-way coupled WRF-CMAQ system will be an important tool for regional climate modeling research. Specific areas of model development research include: meteorological modeling, land-surface and PBL modeling, gas phase mechanisms and solvers, cloud dynamics and aqueous chemistry, photolysis rates and radiative transfer model improvements, aerosol modeling, transport and diffusion, Lagrangian modeling approaches, and on-line integration of meteorology and atmospheric chemistry.

User Information Back to Top
Technical Requirements
Computer Hardware
Unix/Linux platform (single processor, or multi-processor), 2 Ghz chip speed or better, 1Gb memory per processor; Unix/Linux clusters (8 CPUs is typical); or IBM-SP supercomputer
Compatible Operating Systems
RedHat Linux, IBM AIX (Unix), for example
Other Software Required to Run the Model
netCDF, IOAPI libraries
Download Information
The latest version of CMAQ and SMOKE is available for download from the Community Modeling and Analysis System website: http://www.cmascenter.org/exit EPA

Meteorological models: http://www.mmm.ucar.edu/mm5/exit EPA
http://www.wrf-model.org/index.php exit EPA

Using the Model
Basic Model Inputs
Hourly (or finer temporal resolution) gridded meteorological data from either MM5 or WRF meteorological model; processed through CMAQ’s Meteorology-Chemistry Interface Processor (MCIP)

Hourly (or finer temporal resolution) gridded Emissions data from SMOKE emissions modeling system (including biogenic and anthropogenic source emissions of CO, NO, NO2, VOCs, SO2, NH3, and particulate matter)

Initial gridded chemical concentrations and hourly or static lateral boundary concentrations

Basic Model Outputs
Hourly three-dimensional grid of estimated air trace gas concentrations (e.g., ozone, NO, NO2), and fine particulate matter (PM2.5 and its size-distributed chemical constituents). Hourly two-dimensional gridded wet and dry deposition amounts of chemical species, and gridded atmospheric visibility. Temporal resolution of output can be defined by user.
User Support
User's Guide Available?
User's documentation, scripts, and example tutorials may be found on the CMAQ model download site. exit EPA and the CMAQ model home page.

User information can also be obtained from the Models-3 CMAQ listserver. Please subscribe at:
http://lists.unc.edu/read/all_forums/subscribe?name=m3list exit EPA

Availability of User Support
Tutorials, training courses and user support for CMAQ and related products can be found at the CMAS website: http://www.cmascenter.orgexit EPA
User Qualifications
Users should have familiarity with air quality modeling principles, UNIX/LINUX platforms, and scientific programming.

Model Science Back to Top
Problem Identification
Scientifically credible models that synthesize our current understanding of the atmospheric physical and chemical processes that regulate the fate of a variety of primary and secondary air pollutants are needed to assist in formulation of air quality management plans and environmental policy decisions. CMAQ is a comprehensive atmospheric chemistry-transport model that simulates the spatial distributions of a variety of atmospheric pollutants (ozone and other photooxidants, acidic species, mercury, air toxics, and size-distributed and chemically-speciated fine particulate matter) from local to hemispheric spatial scales over hourly to annual temporal scales. The model also estimates atmospheric deposition of a variety of airborne species as well as visibility impairment associated with particulate matter air pollution. Applications of the model have guided formulation of air quality management plans as well as in providing short-term forecast guidance on air quality conditions.
Summary of Model Structure and Methods
The CMAQ modeling system has been designed to approach air quality as a whole by including state-of-the-science capabilities for modeling multiple air quality issues, including tropospheric ozone, fine particles, acid deposition, and visibility degradation. In this way, the development of CMAQ involves the scientific expertise from each of these areas and combines the capabilities to enable a community modeling practice. CMAQ was also designed to have multi-scale capabilities so that separate models were not needed for urban and regional scale air quality modeling.

The target grid resolutions and domain sizes for CMAQ range spatially and temporally over several orders of magnitude. With the temporal flexibility of the model, simulations can be performed to evaluate longer term pollutant climatologies as well as short term transport from localized sources. With the model's ability to handle a large range of spatial scales, CMAQ can be used for urban and regional scale model simulations. By making CMAQ a modeling system that addresses multiple pollutants and different spatial scales, CMAQ has a "one atmosphere" perspective that combines the efforts of the scientific community. Improvements will be made to the CMAQ modeling system as the scientific community further develops the state-of-the-science.

Model Evaluation
CMAQ model evaluations have been conducted for a variety of time periods and pollutant species. The model is continuously being evaluated using data from operational routine monitoring networks for ozone and fine particulate matter in the U.S. Diagnostic evaluations are conducted using surface and aloft observed data from intensive field studies, such as the 2006 Texas Air Quality Study, 2004 ICARTT study, the Southern Oxidants Study and the Supersites intensives. Additional details on model evaluation activities can be found at: http://www.epa.gov/asmdnerl/ModelEvaluation/index.html

The CMAQ user community also performs detailed evaluation and verification against observations as well as sensitivity and uncertainty analysis. The results from these are presented at the annual CMAS meeting; presentation and extended abstracts can be found at: http://www.cmascenter.org/conference.cfmexit EPA

Also see: Special issue on Model Evaluation: Evaluation of Urban and Regional Eulerian Air Quality Models, Atmospheric Environment, Volume 40, Issue 26, August 2006.

Key Limitations to Model Scope
CMAQ is a deterministic model. Thus, some discrepancies in comparing grid-average values with point measurements should be expected.

Majority of the current regional application involve 12 km horizontal resolution grids while urban scale applications typically use 1-4 km resolutions. Finer scale applications would require enhancements in the representation of turbulent transport in the model.

The accuracy of CMAQ predictions is also intricately linked to the accuracy and resolution of the input meteorological and emission data sets.

Local Navigation

Jump to main content.