1. Effects of Sub-Grid Scale Terrain upon CAMx Air Quality Simulation Carlie J. Coats, Jr., M. Talat Odman, and Saswati Datta
Problem Statement
Model Implementation
Terrain Analysis
See accompanying poster presentation for air quality analysis
Acknowledgements
This work was funded under the Central California Ozone Study’s request for proposals, “Improve Conservation of Mass Module in Air Quality Models”.
The statements and conclusions of this report are those of the Investigator, and not necessarily those of the California Air Resources Board, the San Joaquin Valleywide Air Pollution Study Agency, or its Policy Committee, their employees or their members. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products.

2. Problem Statement
Meteorology models do violence to the underlying terrain by “smoothing” (at least 3 dx), so even grid scale terrain has errors.
Systematic temperature biases require re-running emissions
Meteorological laminar-flow assumptions do violence to surface exchanges in variable terrain.
Effects most important under stable (e.g., nocturnal) conditions – unstable mixing ameliorates these effects
For CAMx: parameterize effects of sub-grid scale terrain (this talk; see accompanying poster presentation by Saswati Datta)‏
Emissions: both surface-based and plume-based
Dry Deposition

3. Terrain for CCOS 4KM Domain MM5-Smoothed vs True-Mean from USGS 30” DEM: Note enhanced detail and variability

4. Model Implementation for CCOS/CAMx
Terrain pre-processor PENFRAC
Computes 3D variables TFRAC, the fraction of each grid cell in contact with each of the 3-D model layers, PENFRAC: cumulative terrain penetration.
New CAMx module LPEN_MOD encapsulates
Optional reading of TFRAC (otherwise TFRAC confined to Layer 1)‏
Layer collapse from MM5 to CAMx
Stack height adjustment
Nest interaction
Routines DIFFUS, EMISS, PLUMERIS optionally use TFRAC to allocate surface effects in the vertical.
Discovered mass inconsistency for dry deposition in DIFFUS
Improved 8-PE parallel efficiency from 30% to 95%, just to finish the project.

5. Grid Scale MM5 Terrain Height Error

6. CCOS-Domain Terrain Variability Range of terrain height for 30” DEM in each 4KM grid cell Max is 2071 meters!

7. CCOS-Domain Terrain Variability Standard Deviation of 30” DEM in each 4KM grid cell. Max is 551 meters.

8. CCOS Domain MM5 Layer Structure
Layer 1 top ~ 20 m above ground
Layer 4 top ~ 100 m...
Layer 10 top ~ 300 m...
Layer 20 top ~ 900 m...
Simple-Z maximum terrain penetration: 22 layers, ~ 1000 M.

9. Layer 1 TFRAC

10. Layer 2 Cumulative Terrain Penetration

11. Layer 5 Cumulative Terrain Penetration

12. Layer 10 Cumulative Terrain Penetration

13. Layer 15 Cumulative Terrain Penetration