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 modelsMost applications in urban or regional ozone modelingUsed for planning (e.g., SIP, search for control strategies)Similar in many aspectsComparison Comparative study of two ozone episodes in the

eastern US commissioned by Ohio EPA (June 1997)

UAM and CAMx

Results: small differences

CAMx

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

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

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