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Community Multiscale Air Quality (CMAQ) Model

Community Multiscale Air Quality (CMAQ) Model. Sarav Arunachalam. CMAQ Basics. CMAQ designed under the community modeling paradigm: Modular Multiscale One-atmosphere Portable Accessible

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Community Multiscale Air Quality (CMAQ) Model

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  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. PM2.5Species 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

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