CMAQv5.0

The Community Multiscale Air Quality (CMAQ) model is an active open-source development project of the U.S. EPA that consists of a suite of programs for conducting air quality model simulations. CMAQ combines current knowledge in atmospheric science and air quality modeling, multi-processor computing techniques, and an open-source framework to deliver fast, technically sound estimates of ozone, particulates, toxics and acid deposition.

For further information please visit the EPA website for the CMAQ system: www.epa.gov/cmaq

CMAQv5.0 System Updates

• Incorporated ISORROPIAv2 to explicitly represent Ca²⁺, K⁺, and Mg²⁺, species abundant in sea-salt and soil dust.
• Incorporated the “mosaic approach”, an option to output the dry deposition flux for the different land-use categories within a grid cell.
• Two-way coupling to enable feedback of aerosol direct radiative effects on WRF simulated dynamics and subsequent impacts on simulated air quality through modification of atmospheric ventilation, changes in rainfall, thermal reactions, and temperature and wind-speed dependent emission rates of primary species.
• Introduced the namelist option to manage model species and centralize the specification of various attributes of modeled chemical species.

New Features and Processes in v5.0

• Incorporated in-line photolysis module to represent effects of scattering and absorbing aerosols on photolysis rate modulation and atmospheric photochemistry regulating the formation of secondary air pollutants.
• Incorporated impacts of varying surface albedo (function of wavelength, land-use, and time) on photolysis rates. Enabled representation of effects of reflection from snow surface and consequently improved applicability of the model for winter-time conditions simulation of winter-time O₃ in the Western States.
• Speciated PM_other into primary ammonium (NH₄⁺), sodium (Na⁺), chloride (Cl^-), selected trace elements (Mg, Al, Si, K, Ca, Ti, Mn, and Fe), and non-carbon organic mass (NCOM). This speciation allowed for detailed characterization of the species, processes, and emission sector contributions to the model bias in primary and consequently total PM.
• Incorporated representation of NO_x emissions from lightning.
• Incorporated detailed representation of bi-directional exchange of NH₃ and Hg. Inclusion of bidirectional exchange significantly reduced bias in annual NHx wet deposition.
• First implementation of on-line coupling between CMAQ and WRF enabling dynamical and chemical calculations at finer time-steps that are needed for the application of CMAQ at smaller horizontal grid cells.