Session 9, Unit 17 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 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 CAMx Results: small differences

CAMx Grid model Processes modeled in each grid cell volume Emission Dispersion Chemical reactions Removal (wet and dry)

CAMx Fundamental equation – Eulerian continuity equation for each chemical species  V H – Horizontal wind vector   - Net vertical entrainment rate  h – Layer interface height  K – Turbulent exchange coefficient Horizontal Advection Vertical transport Turbulent diffusion

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)

CAMx PiG illustration Source: CAMx User’s Guide by ENVIRON

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

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

CAMx Example (SAPRC97) … From lookup table generated by Photolysis Preprocessor Source: CAMx User’s Guide by ENVIRON

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)

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

CAMx Decoupled Direct Method (DDM) For sensitivity analysis Wider applicability than OSAT

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

CAMx Running CAMx Compile source code (specify computer platform)

CAMx Computer resource requirements Source: CAMx User’s Guide by ENVIRON

CAMx Evaluation of control strategy Source: CAMx User’s Guide by ENVIRON Case1: Initial VOC/NOx= 10:1

CAMx Source: CAMx User’s Guide by ENVIRON Case1: VOC/NOx= 10:1

CAMx Source: CAMx User’s Guide by ENVIRON Case2: Initial VOC/NOx= 20:1

CAMx Source: CAMx User’s Guide by ENVIRON Case 3: Initial VOC/NOx= 5:1

Session 9, Unit 18 Final Review