1 / 35

A Brief Introduction to CMAQ

A Brief Introduction to CMAQ. Serena H. Chung BioEarth Working Group 1 Seminar May 21, 2012. Outline. Chemical Transport Models (CTMs) CMAQ Model Components CMAQ Output Parallel Programming in CMAQ WRF and CMAQ Linkages. Chemical Transport Models (CTMs). Transport:

milica
Download Presentation

A Brief Introduction to CMAQ

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A Brief Introduction to CMAQ Serena H. Chung BioEarth Working Group 1 Seminar May 21, 2012

  2. Outline • Chemical Transport Models (CTMs) • CMAQ Model Components • CMAQ Output • Parallel Programming in CMAQ • WRF and CMAQ Linkages

  3. Chemical Transport Models (CTMs) • Transport: • Same physics as numerical weather model, but different numerical methods are needed • Chemistry • Focuses on criteria pollutants which negatively affect human health • Ozone (O3): plant stresser  ecosystem impact • Particular Matter (PM) in air quality community or aerosols in climate science community • Consists of hundreds if not thousand of chemical species • Climate impact: scatter and absorb radiation; affects cloud formation • NOx (=NO + NO2): most of which eventually deposits as nitrate  ecosystem impact • SO2 : forms, sulfate aerosol, contributes to acidification ecosystem impact • Mercury and other air toxics

  4. Chemical Transport Model Equation • Solves for species concentration Cs using mass conservation equation for each grid cell and time step: • Input or derived from numerical weather model (e.g., WRF, MM5) • Wind fields: u, v, w • Eddy diffusivity (turbulent diffusion) coefficients: Kx=Ky, Kz • Temperature, Pressure, (& Radiation Fields): • To calculate reaction rates • Emissions rate can also be temperature and/or light dependent • Clouds & Precipitation: • Aqueous-phase reactions • Removal rate by wet deposition • Dry deposition velocities vd,s, where Ds = vd,s Cs,layer 1 emission chemical reaction horizontal advection vertical advection horizontal diffusion change in concentration vertical diffusion deposition

  5. Chemical Mechanisms HNO3 PAN ● OH hn • A chemical mechanism is a condensed set of chemical reactions • Chosen to represent conditions of interest, .e.g, O3 in polluted environment, stratospheric O3 • Example - University of Leeds Master Chemical Mechanism • Thousands of species and >10,000 chemical reactions • Options in CMAQ v5.0 • CB05: ~72 species, ~187 reactions • SAPRC99: ~88 species, ~144 reactions • SAPRC07: ~150 species, ~413 reactions DMS or VOC O3 ● HNO3 NO NO2 NO3 N2O5 O3 H2O NO2 + Aer ● ● RO2 or HO2 Atmospheric Deposition NOx (NO+NO2) Nitrogen cycle in the troposphere is tightly coupled to O3 & aerosol chemistry R can be lots of stuff with carbon and hydrogen atoms

  6. Aerosol Size Distribution Typical Urban Conditions Number Distribution Volume Distribution Based on Whitby, Atmos. Environ., 1978

  7. Aerosol Size Distribution & Composition Typical Urban Conditions Number Distribution Volume Distribution Based on Whitby, Atmos. Environ., 1978

  8. Aerosol Size Distribution Typical Urban Conditions Number Distribution Volume Distribution Based on Whitby, Atmos. Environ., 1978

  9. Aerosol Size Distribution Typical Urban Conditions Number Distribution Volume Distribution Based on Whitby, Atmos. Environ., 1978

  10. 2.5 mm 10 mm Aerosol Size Distribution:Number vs Surface vs Volume Number • Number • Affects the number of cloud droplets that form • Surface Area • Affects the amount of radiation that is scatter or absorbed • Volume • Portional to mass, used by the National Ambient Air Quality Standards (NAAQS) • PM10 & PM2.5 standards designed to distinguish coarse and fine particles. Surface Area Volume Figure 7.6 Seinfeld & Pandis

  11. Aerosol Size Representations • No size representation, simulate only aerosol mass • Use few lognormal distributions (e.g, CMAQ uses 3), each characterized by • Total particle number concentrations • Median diameter • Geometric standard deviation • Use sectional bins • Track aerosol mass only, or • Track aerosol number and mass • Mixtures • Internally mixed – all particles within a bin or lognormal distribution have the same chemical composition • Externally mixed – each particle contains one “species”, so species are not mixed • Combination of the two • Effective number of species Neff for sectional bins with number and mass:Neff = (1 + Nspecies)NmixtureNbin Nspecies = ~ 20Nmixture = 1-5 Nbin = 4-30

  12. Chemical Tranport Model • Operator splitting -- the equation is split into parts and solved separately: • vertical diffusion, emission, & dry deposition • horizontal advection • vertical advection • horizontal diffusion • cloud processes (includes aqueous chemistry) • gas-phase chemistry • aerosol chemistry emission chemical reaction horizontal advection vertical advection horizontal diffusion change in concentration vertical diffusion deposition

  13. Horizontal Discretization in CMAQ AIRPACT-3 Example: 12-km x 12-km grids in Lambert Conformal Conic Projection Arakawa C Grid vi,j+1 j+1 Ci,j,s ui+1,j North j East Dy j-1 i-1 i i+1 Dx

  14. Vertical Discretization in CMAQ WRF Example: Terrain-Following, Hydrostatic Pressure Grid where Ph = hydrostatic pressure Pressure at model top: pht ~ 10,000 Pa (~ 15 km) ~30-40 levels with first layer height at ~ 40 m wi,k+1 Ci,k,s ui+1,j k+1 k Up East Dh k-1 i-1 i i+1 Figure not to scale Adapted from Figure 2.1 of Skamarock et al., 2008 Dx

  15. Vertical Discretization AIRPACT-4 Example

  16. CMAQ Grid Cell in 3-Dimension wi,j,k+1 vi,j+1,k ui+1,j,k ui,j,k • Air density • Temperature • Pressure • Water mixing ratios (vapor, rain, snow, ice) • Gas- and aerosol-phase chemical species mixing ratios vi,j/2,k wi,j,k Up North East

  17. Why does CMAQ take so long to run? • The nature of chemical transport models: • Gas phase: ~ 100 chemical species • Particle phase: ~20 species, 3-16 size bins  effectively ~60-320 species minimum • ODEs governing the chemical reactions: • Nonlinear • Stiff -- eigenvalues of Jacobian : negative; min/max ratio is ~ 109 Figure from Gustafason et al. (2005) (http://www.mmm.ucar.edu/wrf/users/workshop/WS2005/presentations/sessions8/4-Gustafson.pdf

  18. Model Time Steps • WRF: • Physics: recommendation is 6 seconds per km of Dx, i.e., 72 seconds for 12-km x 12-km grids • Radiation: recommendation is 1 minute per km of Dx, i.e., 12 minutes for 12-km x 12-km grids • CMAQ: • Synchronization between all processes: ~ 1-3 min • Adaptive time step within each process

  19. CMAQ Model Components http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  20. CMAQ Model Components • Meteorological fields from a numerical weather model • Usually MM5 or WRF, though other models can also be used Meteorology Example of Layer 1 Temperature and Wind Fields from WRF http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png http://www.atmos.washington.edu/mm5rt

  21. CMAQ Model Components • Converts WRF or MM5 output files into CMAQ-ready files • Calculates/diagnoses parameters not provided by WRF (e.g., Monin-Obukhov length) • Calculates dry deposition velocities (depends on land-use type and turbulence characteristics) • Keeps the same horizontal grid cell size • Collapses WRF layers into fewer layers if desired http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  22. CMAQ Model Components Emissions: Various models/processors, e.g., Transportation Industrial Residential Power Plants Fire Biogenic etc http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  23. CMAQ Model Components • Initial Conditions: • Usually from a previous run • Only ~ 2-3 days for spin-up required http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  24. CMAQ Model Components • Boundary Conditions Using: • “Idealized’ profile, • Results from a coarser, bigger domain CMAQ simulation, or • Results of global CTMs http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  25. CMAQ Model Components • Photolysis Rate Calculations • Using look-up table for clear-sky conditions and adjusted “online” based on cloud conditions http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  26. CMAQ Model Components Solves http://www.airqualitymodeling.org/cmaqwiki/index.php?title=File:Figure5-1.png

  27. CMAQ Output • Hourly, 3-dimensional concentrations (.e.g, parts per billion or mg m-3) of chemical species • Hourly accumulated wet and dry deposition (.e.g, kg ha-1 hr-1) for relevant species • netCDF files • same as WRF, but different conventions for date/time • read/write easier with use of Models-3 I/O API library • Examples: • http://lar.wsu.edu/airpact • http://lar.wsu.edu/airpact/gmap/testC.html

  28. CMAQ Output : AIRPACT Example • Lots of stuff at: • AIRPACT-3: http://lar.wsu.edu/airpact • AIRPACT-4: http://lar.wsu.edu/airpact/gmap/testC.html 12-km, Surface-Layer, Hourly Concentrations of Secondary Organic Aerosl (SOA)

  29. CMAQ Output: Vertical Distribution AIRPACT-4 Output for 10AM PST on Feb 23, 2011 O3 Concentation

  30. Parallel Progamming in CMAQ • Distributed Memory using Message Passing Interface (MPI) (WRF supports OpenMP and MPI) • Divide and conquer by horizontal domain decomposition • Similar to WRF, but specifics are different • For I/O, each processor gets the data for its subdomain by extracting the data from the full domain. However, only one processor is responsible for writing to the output data files; thus, gathering full domain data is required before writing 14 15 12 13 8 9 10 11 4 5 6 7 2 3 0 1

  31. WRF-CMAQ Soft Link Static Geographical Data GEOGRID METGRID Emission Models UNGRIB Global Data MCIP Geographical & Large-scale Meteorological Data Interpolated to simulation grids ICON REAL CCTM BCON Initial & Boundary Conditions JPROC WRF Meteorological Fields

  32. Coupled WRF-CMAQ Static Geographical Data GEOGRID METGRID Emission Models Global Data UNGRIB Geographical & Large-scale Meteorological Data Interpolated to simulation grids MCIP REAL Initial & Boundary Conditions ICON WRF call aqprep call cmaq_driver call feedback_read CCTM Meteorological Fields BCON JPROC Speciated Aerosol Size Distributions, & O3 Concentrations

  33. WRF-CMAQ Domains CMAQ_COL_DIM delta_x CMAQ_ROW_DIM CMAQ Domain 5 columns Max CMAQ Domain 5 rows delta_y WRF Domain Adapted from Figure 2 of Wong et al., Geosci. Model Dev., 2012

  34. Coupled WRF-CMAQ Computaional Performance Table 1 of Wong et al., Geosci. Model Dev., 2012 Table 2 of Wong et al., Geosci. Model Dev., 2012 Based on 24-hour simulations for a 12-km eastern US domain

  35. Some resources • http://cmaq-model.org • http://cmascenter.org/ • Seinfeld, J.H. and S.N. Pandis, Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley & Sons, 2006. • Jacob, D.J., Introduction to Atmospheric Chemistry, Princeton University Press, 1999. • Jacobson, M.Z., Fundamentals of Atmospheric Modeling, Cambridge University Press, 1999

More Related