1. Meteorological Site Representativeness and AERSURFACE Issues
Margaret Valis
Leon Sedefian

2. Outline AERSURFACE Review Met Site Representativeness Case Study
AERSURFACE Issues
Summary

3. Review
AERMOD designed to accept same meteorological data as ISCST3: NWS surface and upper air data
AERMOD also designed to accept more robust on-site meteorological data, including multi-level profiles of wind, temperature and turbulence
However, more advanced boundary layer algorithms in AERMOD require user-specified surface characteristics:
Albedo
Bowen ratio
Surface roughness
Sensitivity to surface characteristics is one of the main implementation issues with AERMOD

4. Review
AERSURFACE is a tool designed to assist with determining surface characteristics data (albedo, Bowen ratio & surface roughness) for use in AERMET and/or AERSCREEN
Initial version of AERSURFACE was released on SCRAM on January 11, 2008
AERSURFACE is not currently considered part of the AERMOD regulatory modeling system

5. AERSURFACE(08009) Design
Revisions to calculating area-weighted averages for surface roughness: Inverse-distance weighting to adjust for increased width/area of sector with distance
Revisions to calculation methods: Averaging ln(zo) for surface roughness (= geometric mean)
Revisions to default domain/distances:1km radius for roughness
Geometric mean for Bowen ratio, arithmetic mean for albedo
10x10km domain for Bowen ratio and albedo –no sector or distance dependency

6. Notes from AERMOD Implementation Guide (dated Jan. 9, 2008)
The degree to which predicted pollutant concentrations are influenced by surface parameter differences between the application site and the meteorological measurement site depends on the nature of the application (i.e., release height, plume buoyancy, terrain influences, downwash considerations, design metric, etc.).
If the reviewing agency is uncertain as to the representativeness of a meteorological measurement site, a site-specific sensitivity analysis may be needed in order to quantify, in terms of expected changes in the design concentration, the significance of the differences in each of the surface characteristics.

7. Representativeness Case Study:
Nearest NWS station is Albany,
located about 25 km north of the
facility
Figure shows 10x10km domain for
Bowen ratio and albedo, and 1km
radius for roughness
Aerial photos and 1992 NLCD plots
for each site are also provided
Estimates of surface roughness,
albedo and Bowen ratio based on
AERSURFACE are provided for
1992 and 2001 NLCD

15. AERSURFACE Weighting Issue
If AERSURFACE (08009) is run for a location that is very close to the center of a
land cover cell, the sector average Zo may be skewed if Zo for the land cover
category of this cell is significantly different than the other land cover types
within the sector (e.g. forest versus grasslands) due to inverse distance
weighting; will be addressed in next version.
Met tower location:+
Land cover cell center:+

16. Comparison of Zo for Different Sector Choices

17. Potential AERSURFACE Issues
Uncertainties regarding ASOS met station locations –a key AERSURFACE input
Use of erroneous station locations in AERSURFACE could invalidate results
NLCD categories (both 1992 and 2001) are not ideal for estimating roughness at airports
1992 Commercial/Industrial/Transportation category includes runways, as well as terminal buildings and parking garages; spans full range of roughness values
2001 “Developed” categories also cover runways to buildings, plus grassy areas around runways (“Developed, Open Space” in 2001, formerly “Urban/Recreational Grasses” in 1992)
Recent 1992 vs comparisons also highlight that 2001 developed categories do not reflect presence of trees that were accounted for in 1992 NLCD

18. AERSURFACE Land Use Misclassification Issue
Low Density Residential (pink) found in area between runway

19. Summary
Should consider the issue of met data representativeness in the full context of a project and not as just a “roughness length” issue.
The profiling of wind, temperature and turbulence from met site is a connected, but separate issue. Each land use parameter should be reviewed to determine its appropriateness.
Blind application of AERSURFACE/land use data can lead to errors not detected otherwise.