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Session 9, Unit 17 UAM and CAMx. UAM and CAMx. UAM - U rban A irshed M odel Currently available versions: UAM-V 1.24 UAM-V 1.30 Available from Systems Applications International (SAI) CAMx - C omprehensive A ir quality M odel with e x tension Version 3.00 Available from ENVIRON.

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uam and camx
UAM and CAMx
  • UAM - Urban Airshed Model
    • Currently available versions:
      • UAM-V 1.24
      • UAM-V 1.30
      • Available from Systems Applications International (SAI)
  • CAMx - Comprehensive Air quality Model with extension
    • Version 3.00
    • Available from ENVIRON
uam and camx1
UAM and CAMx
  • Multi-scale, three dimensional photochemical grid models
  • Most applications in urban or regional ozone modeling
  • Used for planning (e.g., SIP, search for control strategies)
  • Similar in many aspects
  • Comparison
    • Comparative study of two ozone episodes in the eastern US commissioned by Ohio EPA (June 1997)
uam and camx2
UAM and CAMx
  • Results: small differences
slide5
CAMx
  • Grid model
  • Processes modeled in each grid cell volume
    • Emission
    • Dispersion
    • Chemical reactions
    • Removal (wet and dry)
slide6
CAMx
  • Fundamental equation – Eulerian continuity equation for each chemical species
      • VH – Horizontal wind vector
      •  - Net vertical entrainment rate
      • h – Layer interface height
      • K – Turbulent exchange coefficient

Vertical transport

Horizontal Advection

Turbulent diffusion

slide7
CAMx
  • Nested Grid
    • Coarse grid to cover a region
    • Fine grid to model details of urban areas
  • Plume-in-Grid (PiG)
    • Track individual plumes of large sources in grid cell using Lagrangian module until the plume grow large enough to be adequately represented in the grid model (otherwise, pollutants are considered to be distributed uniformly within a grid cell)
slide8
CAMx
  • PiG illustration

Source: CAMx User’s Guide by ENVIRON

slide9
CAMx
  • Ozone Source Apportionment Technology (OSAT)
    • Track contributions to ozone concentration in a grid cell by source category or region
    • Make evaluation of NOx and VOC controls easy
slide10
CAMx
  • Chemical reactions
    • Five sets of chemical mechanisms based on the Carbon Bond Mechanism version 4 (CBM-IV) or the SAPRC97 mechanism
    • Large number of reactions in each mechanism
      • CBM-IV: 96 reactions
      • SAPRC97: 184 reactions
slide11
CAMx
  • Example (SAPRC97)

From lookup table generated by Photolysis Preprocessor

Source: CAMx User’s Guide by ENVIRON

slide12
CAMx
  • Solved using numerical integration
    • Consumes largest portion of CPU time
    • “Adaptive-hybrid” approach results in ten-fold speedup in chemical solution (factor of 3-4 for overall model)
    • Chemical Mechanism Compiler (CMC) – automatically generate FORTRAIN code for the chemistry solver for selected chemical mechanism (CMC is for internal use, not distributed with CAMx)
slide13
CAMx
  • Photolysis
    • TUV ratiative transfer and photolysis model developed by NCAR
    • Multi-dimensional lookup tale of photolytic rates by surface albedo, total ozone column, haze turbidity, altitude, and zenith angle
    • The photolytic rates can be adjusted by cloud cover
slide14
CAMx
  • Decoupled Direct Method (DDM)
    • For sensitivity analysis
    • Wider applicability than OSAT
slide15
CAMx
  • Data requirements
    • Run control file
    • Chemistry parameters file
    • Photolysis rate file
    • Albedo/haze/ozone file (AHO file)
    • Top concentration file
    • Land use file
    • Met files (height/pressure, wind, temp.,water vapor, cloud cover, rainfall, & diffusivity)
    • Files for initial & boundary conditions
    • Source files

Source: CAMx User’s Guide by ENVIRON

slide16
CAMx
  • Running CAMx
    • Compile source code (specify computer platform)
slide17
CAMx
  • Computer resource requirements

Source: CAMx User’s Guide by ENVIRON

slide18
CAMx

Case1: Initial VOC/NOx=10:1

  • Evaluation of control strategy

Source: CAMx User’s Guide by ENVIRON

slide19
CAMx

Case1: VOC/NOx=10:1

Source: CAMx User’s Guide by ENVIRON

slide20
CAMx

Case2:

Initial VOC/NOx=20:1

Source: CAMx User’s Guide by ENVIRON

slide21
CAMx

Case 3: Initial VOC/NOx=5:1

Source: CAMx User’s Guide by ENVIRON