Transcript AERMOD/AERSURFACE

Meteorological Site
Representativeness and
AERSURFACE Issues
Margaret Valis
Leon Sedefian
Outline
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AERSURFACE Review
Met Site Representativeness Case Study
AERSURFACE Issues
Summary
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
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
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
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.
Representativeness Case Study:
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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
Surface Roughness (m)
AERSURFACE Roughness Estimates
for ALB Airport and Case Study Facility
1
0.8
0.6
ALB
Facility
0.4
0.2
0
1
2
3
4
5
6
7
Sector
8
9
10 11 12
AERSURFACE Weighting Issue
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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:
+
Comparison of Zo for Different
Sector Choices
WINTER
Season
Direction
0-30
30-60
60-90
Zo (12 sect)
Zo(3 sect)
0.146
0.141
0.131
0.125
0.152
90-120
120-150 150-180 180-210 210-240 240-270 270-300 300-330 330-360
0.194
0.189
0.224
0.028
0.72
0.155
0.154
0.167
0.171
0.194
SPRING
Season
Direction
0-30
30-60
60-90
Zo (12 sect)
Zo(3 sect)
0.17
0.185
0.187
0.176
0.195
90-120
120-150 150-180 180-210 210-240 240-270 270-300 300-330 330-360
0.25
0.214
0.268
0.055
0.11
0.177
0.191
0.206
0.209
0.232
SUMMER
Season
Direction
0-30
30-60
60-90
Zo (12 sect)
Zo(3 sect)
0.192
0.213
0.213
0.226
0.225
90-120
120-150 150-180 180-210 210-240 240-270 270-300 300-330 330-360
0.285
0.231
0.288
0.066
0.124
0.187
0.206
0.224
0.227
0.255
AUTUMN
Season
Direction
0-30
30-60
60-90
Zo (12 sect)
Zo(3 sect)
0.189
0.204
0.199
0.219
0.218
90-120
120-150 150-180 180-210 210-240 240-270 270-300 300-330 330-360
0.279
0.229
0.282
0.056
0.113
0.183
0.199
0.215
0.219
0.249
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. 2001 comparisons also highlight that 2001 developed
categories do not reflect presence of trees that were accounted for in 1992
NLCD
AERSURFACE Land Use
Misclassification Issue
Low Density Residential (pink) found in area between runway
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.