Community Multiscale Air Quality (CMAQ) Model

1
Community Multiscale Air Quality (CMAQ) Model
Sarav Arunachalam
2
CMAQ Basics

• CMAQ designed under the community modeling
  paradigm
• Modular
• Multiscale
• One-atmosphere
• Portable
• Accessible
• Can model from urban (few km) to regional
  (hundreds of kilometers) to inter-continental
  (thousands of kilometers) scales of transport
• Tropospheric O3, acid deposition, visibility,
  particulate matter, toxics, mercury
• Requires inputs from emissions and meteorology
  models, initial and boundary conditions
• CMAQ Chemical Transport Model preprocessors

3
Pollutants Treated

• Gas Phase (O3 and precursors)
• Carbon Bond 2005 (CB05)
• Statewide Air Pollution Research Center 99
  (SAPRC99)
• Aerosol Treatment
• PM2.5, PM10, Visibility
• Toxic Species
• Formaldehyde, Acetaldehyde, 1,3-Butadiene,
  Acrolein, Naphthalene, Toluene, Xylene, Mercury

4
Atmospheric Diffusion Equation (ADE)

• ADE represents mass balance in which emissions,
  transport, diffusion, chemical reaction and
  removal processes are represented by

Several assumptions included above
5
ADE (..Contd.)

• where,
• i chemical species, i  (where i  1, 2, N )
  
• Ci pollutant concentration of species, i
• u, v, w horizontal and vertical wind speed
  components f (x, y, z, t )
• KH, KV horizontal and vertical turbulent
  diffusion coefficients f (x, y, z, t )
• Ri rate of formation of i by chemical
  reactions f ( C1, C2, .., Ci, .. CN)
• S emission rate of all precursors
• Li net rate of removal of pollutant i by
  surface uptake processes f (x, y, z, t )

6
3-D Box Representation
7
Numerical Solution of Partial Differential
Equations (PDEs)

• E.g. Model Application with 100 Columns X 100
  Rows X 25 Layers 250,000 grid-cells
• CB-IV Chemical Mechanism with 79 species and 94
  reactions
• Number of differential equations to be solved
  simultaneously per model output time step
  250,000 X 79 19,750,000
• For 1 day, ODEs 19.75 X 24 474 million
• For 1 month, ODEs 19.75 X 24 X 30 14.22
  billion
• For 1 year, ODEs 19.75 X 24 X 365 173
  billion

8
PM Treatment in CMAQ

• Particle size distribution represented as the
  superposition of three lognormal
  subdistributions, called modes
• Aitken mode (up to 0.1 microns) (typically for
  fresh particles)
• Accumulation mode (0.1 2.5 microns) (typically
  for aged particles)
• Coarse mode (2.5 10 microns)
• PM10 is the sum of all three modes
• Predict particle number, total surface area,
  total mass for each mode
• Primary Components
• AORG_P (Primary organic aerosol)
• AEC (Primary elemental carbon)
• A25 (Unspeciated fine PM/dust)
• Secondary Components
• ASO4 (Sulfate aerosol)
• ANH4 (Ammonium aerosol)
• ANO3 (Nitrate aerosol)
• AORG_S (Secondary organic aerosol)

Ref Binkowski et al, JGR 2003
Ref Binkowski et al, JGR 2003
9
PM2.5 Species in CMAQ

• ASO4J Accumulation mode sulfate mass
• ASO4I Aitken mode sulfate mass
• ANH4J Accumulation mode ammonium mass
• ANH4I Aitken mode ammonium mass
• ANO3J Accumulation mode nitrate mass
• ANO3I Aitken mode aerosol nitrate mass
• AORGAJ Accumulation mode anthropogenic secondary
  organic mass
• AORGAI Aitken mode anthropogenic secondary
  organic mass
• AORGPAJ Accumulation mode primary organic mass
• AORGPAI Aitken mode primary organic mass
• AORGBJ Accumulation mode secondary biogenic
  organic mass
• AORGBI Aitken mode biogenic secondary biogenic
  organic mass
• AECJ Accumulation mode elemental carbon mass
• AECI Aitken mode elemental carbon mass
• A25J Accumulation mode unspecified anthropogenic
  mass
• A25I Aitken mode unspecified anthropogenic mass

10
Calculating PM2.5 from CMAQ Model Species

• ASO4 ASO4J ASO4I
• ANH4 ANH4J ANH4I
• ANO3 ANO3J ANO3I
• AORG_P AORGPAJ AORGPAI
• AORG_S AORGAJ AORGAI AORGBJ AORGBI
• AEC AECJ AECI
• A25 A25J A25I
• PM25 ASO4 ANH4 ANO3 AORG_P AORG_S AEC
  A25

11
What is PM10?

• PM10 is not a single chemical species, but
  composed of multiple chemical species, of
  different sizes
• One needs to understand the composition for
  better air quality management

12
CMAQ Modules

• ICON
• Prepare Initial Conditions
• BCON
• Prepare Boundary Conditions
• JPROC
• Prepare photolysis rates
• MCIP
• Meteorology-Chemistry Interface Preprocessor
• CCTM
• CMAQ Chemistry Transport Model

13
Other Input Processors for CMAQ

• Sparse Matrix Operator Kernel Emissions (SMOKE)
  Modeling system to prepare emissions inputs for
  CMAQ
• Mesoscale Meteorological Model (MM5) or Weather
  Research Forecast (WRF) model to prepare
  meteorological inputs

14
CMAQ Applications

• Global community of CMAQ users
• Scientific investigations
• Air Quality Management
• International (Trans-continental transport)
• National (Rulemakings by the U.S. EPA)
• State/Regional (State Implementation Planning) to
  address nonattainment issues

15
CMAS User Community
16
Key References

• Byun and Ching, 1999
• Byun and Schere, Applied Mechanics Reviews, 2006
• Binkowski et al, JGR, 2003
• Foley et al, Atmos. Chem. Physics, 2010
• Otte et al, Atmos. Chem. Physics, 2010
• More comprehensive list on CMAS website

17
Questions?

• Visit http//www.cmascenter.org for more
  information
• Model download with benchmark datasets
• Hands-on Training
• Online help desk
• Annual Users Conference in Chapel Hill