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CMAQ (Community Multiscale Air Quality). A 3-D chemical transport model that sovles the mass conservation equation:. horizontal advection. horizontal dispersion. chemical reaction. emission. vertical advection. pollutant Concentration change. vertical diffusion. deposition

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Cmaq community multiscale air quality
CMAQ (Community Multiscale Air Quality)

A 3-D chemical transport model that sovles the mass conservation equation:
















(wet & dry)

Cmaq spatial temporal resolutions
CMAQ Spatial & Temporal Resolutions

  • Temporal Resolution:

    • Takes input at hourly time time steps

    • Runs at sub-hourly time steps (adaptive)

    • Provides output of hourly concentrations & deposition rates

  • Vertical Resolution:

    • Typically 20-35 layers from the surface to ~15km with more layers concentrated near the surface

  • Spatial Resolution follows WRF, but domain is smaller than WRF

    • Examples:

      • 36-km for continental US: 94 x 140 = 13,169 grid cells per layer

      • 12-km for California: 285 x 315 = 89,775 grid cells per layer

      • 12-km for PNW: 95x 95 = 9,025 grid cells per layer

      • 1-km for an urban area

    • Can be nested (following WRF)

CMAQ Spatial Resolution Example

12-km grids over the PNW

CMAQ Inputsand Outputs

Gridded hourly

P, T, U, V, W, Q, R, precip

& LULC information

LULC Data, Anthropogenic Emission Inventory,

Fire Data


Emission Models:

MEGAN, BlueSky, SMOKE,etc





Gridded & Speciated Hourly Emission Rates

Gridded, hourly ambient concentrations and deposition rates

CMAQOutput Examples

  • AIRPACT-3 Forecast Link

  • N Deposition Rates

December 2010 Nitrogen Deposition

Coupled WRF-CMAQ

Aerosol Optical Properties,

Cloud Condensation Nuclei






Prepares virtual CMAQ-compatible input meteorological files

  • Feedbacks between Air Quality and Meteorology:

  • Aerosol scattering & absorption effects on shortwave radiation (using CAM option) and photolysis

  • Aerosol impact on cloud microphysics

  • Ozone impact on longwave radiation (using RRTMG option)

Cmaq architecture etc
CMAQ Architecture, etc

  • Runs in linux/unix environment:

    • …..

  • Language

    • 99% Fortran (Intel or PGI compiler)

    • < 1%C

  • File format

    • netCDF, though different convention than WRF

  • cvs for version control

Cmaq applications
CMAQ Applications

  • Daily air-quality forecast

  • Visibility reduction

  • Impact of climate change on air quality

  • Impact of air quality on meteorology (coupled WRF-CMAQ)

The megan model
The MEGAN model

  • MEGAN estimates emissions of non-methane biogenic volatile organic compounds (BVOC) using geo-gridded, species and vegetation density-dependent emission factors (EF) for various BVOC. These EFs represent average emission rates for a given geographic area under standard temperature and light conditions.

  • Emission rates are computed using actual light and temperature data for a model domain and time period to simulate the effect of deviations of these factors from standard conditions on emissions. The EF (Ɛ) is also multiplied by dimensionless coefficients which simulate the effects of leaf age (Ɣage), within-canopy conditions (ƔCE), and soil moisture (ƔSM) on emissions.

Megan inputs and outputs
MEGAN Inputs and Outputs

  • Input

    • Vegetation species distribution and density information

    • LAI

    • Temperature

    • Radiation

    • Soil Moisture

  • Output

    • Biogenic VOC emissions

    • Working on N2O and CH4 emission rates

Megan architectures etc
MEGAN Architectures, etc

  • Various versions

    • Visual Basic/Python/ArcGIS

    • Fortran version compatible with CMAQ

    • Online version built in WRF-Chem

Megan applications
MEGAN Applications

  • Provides input for global and regional air-quality/chemical transport models

    • Impact of biogenic VOC on ozone formation

    • Impact of BVOC on secondary organic aerosol formation

    • Biosphere-Atmosphere Exchange