CMAQ (Community Multiscale Air Quality)

pollutantConcentration

change

horizontal advection vertical

advection

horizontaldispersion vertical

diffusion

chemical reaction

deposition(wet & dry)

emission

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

Ci

tu

Ci

x v

Ci

yw

Ci

z

xkx

Ci

x

y

kyCi

y

z

kzCi

z

R D S

Gas-phase species: Ozone, volatile organic compounds (VOCs), ammonia, reactive nitrogen, etc

Aerosol-phase species: Sulfate, nitrate, ammonium, organics, etc

Gas-phase chemistry mechanism: SAPRC99 or CB-05

Aerosol dynamics: 3 log-normal size distributions

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 Inputs and Outputs

Emission Models:MEGAN, BlueSky, SMOKE, etc

WRF

CMAQ

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

& LULC information

LULC Data, Anthropogenic Emission Inventory,

Fire Data

Gridded & Speciated Hourly Emission Rates

ChemicalBoundaryConditions

Gridded, hourly ambient concentrations

and deposition rates

• AIRPACT-3 Forecast Link• N Deposition Rates

CMAQ Output Examples

December 2010 Nitrogen Deposition

Coupled WRF-CMAQ

WRF CMAQ

AQPREPPrepares virtual CMAQ-compatible

input meteorological files

Aerosol Optical Properties,Cloud Condensation Nuclei

Ozone

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)

Coupler

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

• 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• 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 Spatial and Temporal Resolutions

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

• Various versions–Visual Basic/Python/ArcGIS– Fortran version compatible with CMAQ –Online version built in WRF-Chem

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