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
Horizontal
Advection




Vertical
transport
VH – Horizontal wind vector
 - Net vertical entrainment rate
h – Layer interface height
K – Turbulent exchange coefficient
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)
…
Source: CAMx User’s Guide by ENVIRON
From lookup
table generated
by Photolysis
Preprocessor
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
Case1:
VOC/NOx=
10:1
Source: CAMx User’s Guide by ENVIRON
CAMx
Case2:
Initial
VOC/NOx=
20:1
Source: CAMx User’s Guide by ENVIRON
CAMx
Case 3:
Initial
VOC/NOx=
5:1
Source: CAMx User’s Guide by ENVIRON
Session 9, Unit 18
Final Review