The 2013 EPA Draft SO2 NAAQS Designations Modeling Technical Assistance Document states that an accurate characterization of the modeled facility is critical. The document also says that that if the building information is not accurate, downwash will not be accurately accounted for in AERMOD. This presentation will discuss two generic facilities, one with a 31 m high long narrow solid building and a single stack that is 1.5 times the building height. The second facility has two 50 m high porous structures located near a single stack of the same height. Accurate building information was assembled for these two facilities and input into BPIP. The BPIP AERMOD input file was analyzed and the following problems were found: 1) building widths and/or lengths outside the range of AERMOD theory; and 2) the porous structures were assumed to be solid. In spite of inputting accurate site information, BPIP generated building dimensions for AERMOD input will not result in accurate predictions. Consequently, an EPA “Source Characterization” study was conducted where “Equivalent Building Dimensions” were defined that more accurately model the dispersion for these two sites. AERMOD was then run using the original BPIP determined inputs and the refined inputs based on a more accurate “Source Characterization.” With refined BPIP inputs, the maximum 1-hr concentrations decreased by factors of 2 to 3.5 Due to the stringent nature of the 1-hr NAAQS, clearly a more accurate source characterization study should be high on the list of refined modeling options.

1. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
IMPLICATIONS OF ACCURATE SOURCE CHARACTERIZATION
ON PERMITTING FOR THE 1-HR AND 24-HR NAAQS
Ron Petersen, PhD, CCM
CPP, Inc.
1415 Blue Spruce Drive
Fort Collins, CO 80525
rpetersen@cppwind.com
Cell: 970 690 1344

2. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Outline
• What is source characterization?
• The forgotten but important factor – building dimensions
• Where BPIP inputs are a problems
• Example applications of AERMOD with better inputs
(EBD)
• Impact of better inputs (i.e., accurate source
characterization)

3. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Source Characterization
2013 EPA Draft SO2 NAAQS Designations Modeling Technical
Assistance Document
Common considerations
• Stack height and location, stack parameters, emission
rates, in-stack ratios, urban versus rural, etc.
Often Overlooked (2 to 8 Reduction in Predicted
Design Value)
• “If stack locations and building information are
not accurate, downwash will not be
accurately accounted for in AERMOD.”
• Building dimension inputs are critical!!!

4. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Building Dimension Inputs & BPIP
 BPIP uses building footprints
and tier heights
 Combines buildings
 All structures become one
single rectangular solid for
each wind direction and
each source
 BPIP dimensions may not
characterize the source and
may give the wrong answer.
BPIP Input

5. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
AERMOD’s Building Downwash Algorithm
• Used EPA wind
tunnel data base and
past literature
• Developed analytical
equations for cavity
height, reattachment,
streamline angle,
wind speed and
turbulence

6. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
AERMOD’s Building Downwash Algorithm
Only valid for certain
building sizes
• W/H 1 to 4
• L/H = 0 to 4
• Assumes all
buildings are solid
and rectangular

7. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Building Dimension Inputs AERMOD Needs to
Work
The building shape
and position that
match the theory in
AERMOD.
BPIP will often not
do this.
Streamline figures from: Snyder, W.H. and R.E. Lawson, Jr.: Wind Tunnel Measurements of Flow Fields in the Vicinity
of Buildings; 8th Joint Conference on Appl. of Air Poll. Met. With A&WMA; AMS, Boston, MA, 1994; pp. 244-250

8. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
• Example BPIP Problems
PW facility (blue), BPIP building dimensions (red) for stack S-344 (red) and
envelope of the building cavity calculated by PRIME (yellow) for a) a wind
direction of 90 degrees; and b) a wind direction of 140 degrees.
)
BPIP Building Dimensions:
H = 17 m
L/H = 53
W/H = 34
BPIP Building Dimensions:
H = 17 m
L/H = 23
W/H = 63
a)
b)
BPIP Building Dimensions:
H = 17 m
L/H = 23
W/H = 63
BPIP Input in RED
Site Plan and BPIP Result

9. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Solution - Use EBD in Place of BPIP Dimensions
• Equivalent Building Dimensions” (EBDs) are the
dimensions that are input into AERMOD in place of BPIP
dimensions to more accurately predict building wake
effects
• Determined using wind tunnel modeling
9

10. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Current Regulatory Status of EBD
October 24, 2011 Model Clearinghouse Review of EBD for AERMOD
• “.. any EBD studies being considered should be
discussed with the appropriate reviewing authority as
early in the process as possible and that the Model
Clearinghouse should also be engaged as early as
possible.”
• …. these wind tunnel EBD studies are classified
as “source characterization studies.”
• Roger Brode and George Bridgers, EPA Model
Clearinghouse, receptive for those cases where
AERMOD with BPIP inputs is not working – 2013 EPA
R/S/L Modelers Workshop.

11. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Basic Wind Tunnel Modeling Methodology
•Obtain source/site data
•Construct scale model
– 3D Printing
•Install model in wind
tunnel and measure
Cmax versus X

12. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Measure Ground-level Concentrations
Tracer
from stack
Max ground-level concentrations measured versus x

13. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Measure Ground-level Concentrations
Data taken until good fit and max
obtained
Automated Max GL Concentration Mapper

14. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
EBD Used to Reduce Predicted AQ Impacts on Residential
Tower downwind of Mirant Power Station, Alexandria, VA
Residential Tower

15. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Find EBD that gives same Max GL Concentration
Profile as with Site Structures
=
- Input EBD Into AERMOD for wind directions of concern
- AERMOD predicted impacts decreased by more than a
factor of two.
Mirant Power Station – Approved Study, Region 3
Wind Tunnel Testing Conducted with Site Structures and
with EBD

16. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
AECOM (David Shea) Conducted Field Study That
Validated use of EBD – see AWMA 2007 papers

17. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Example Application
Very wide/narrow building
Stack height: 47 m
Building height: 31 m
Property line in Red
Emission rate: 1 g/s
AERMOD RESULTS
Five years of met data

18. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Maximum Hourly Impact at Fenceline

19. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
BPIP Input Analysis
• W and L values > 5 times Hb for
many wind directions (see red
shading)
• AERMOD will overpredict for these
wind directions
• Past EBD studies and theory show
that Lmax and Wmax ≤ 4 Hb.
• New BPIP input generated using this
criterion
• Input filed provided to modeling
consultant to re-run AERMOD
Flow Wind BUILDHGT BUILDWID BUILDLEN
Vector Direction Hb W L XBADJ YBADJ Hb: W: L
(Deg.) (Deg.) (m) (m) (m) (m) (m)
0 180 31.09 88.64 304.03 -144.87 -58.28 1.0 2.9 9.8
10 190 24.99 30.53 11.47 -7.79 -18.85 1.0 1.2 0.5
20 200 24.99 30.76 12.48 -4.99 -18.91 1.0 1.2 0.5
30 210 31.09 98.96 301.7 -115.52 -46.9 1.0 3.2 9.7
40 220 31.09 148.5 284.64 -99.38 -40.06 1.0 4.8 9.2
50 230 31.09 193.52 258.94 -80.23 -31.99 1.0 6.2 8.3
60 240 31.09 232.67 225.36 -58.63 -22.96 1.0 7.5 7.2
70 250 31.09 264.74 184.94 -35.26 -13.22 1.0 8.5 5.9
80 260 31.09 288.77 138.9 -10.81 -3.08 1.0 9.3 4.5
90 270 31.09 304.03 88.64 13.97 7.14 1.0 9.8 2.9
100 280 31.09 310.04 35.68 38.32 17.16 1.0 10.0 1.1
110 290 31.09 309.59 46.42 29.12 26.65 1.0 10.0 1.5
120 300 31.09 301.7 98.96 -2.58 35.33 1.0 9.7 3.2
130 310 31.09 284.64 148.5 -34.19 42.94 1.0 9.2 4.8
140 320 31.09 258.94 193.52 -64.77 49.24 1.0 8.3 6.2
150 330 31.09 225.36 232.67 -93.38 54.05 1.0 7.2 7.5
160 340 31.09 184.94 264.74 -119.15 57.21 1.0 5.9 8.5
170 350 31.09 138.9 288.77 -141.3 58.64 1.0 4.5 9.3
180 360 31.09 88.64 304.03 -159.16 58.28 1.0 2.9 9.8
190 10 24.99 30.53 11.47 -3.68 18.85 1.0 1.2 0.5
200 20 24.99 30.76 12.48 -7.49 18.91 1.0 1.2 0.5
210 30 31.09 98.96 301.7 -186.18 46.9 1.0 3.2 9.7
220 40 31.09 148.5 284.64 -185.26 40.06 1.0 4.8 9.2
230 50 31.09 193.52 258.94 -178.71 31.99 1.0 6.2 8.3
240 60 31.09 232.67 225.36 -166.73 22.95 1.0 7.5 7.2
250 70 31.09 264.74 184.94 -149.68 13.22 1.0 8.5 5.9
260 80 31.09 288.77 138.9 -128.09 3.08 1.0 9.3 4.5
270 90 31.09 304.03 88.64 -102.6 -7.14 1.0 9.8 2.9
280 100 31.09 310.04 35.68 -74 -17.16 1.0 10.0 1.1
290 110 31.09 309.59 46.42 -75.54 -26.65 1.0 10.0 1.5
300 120 31.09 301.7 98.96 -96.39 -35.33 1.0 9.7 3.2
310 130 31.09 284.64 148.5 -114.31 -42.94 1.0 9.2 4.8
320 140 31.09 258.94 193.52 -128.75 -49.24 1.0 8.3 6.2
330 150 31.09 225.36 232.67 -139.29 -54.05 1.0 7.2 7.5
340 160 31.09 184.94 264.74 -145.59 -57.21 1.0 5.9 8.5
350 170 31.09 138.9 288.77 -147.47 -58.64 1.0 4.5 9.3
BPIP Dimensions
Aspect Ratio

20. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
BPIP Input Analysis – Zoom In
Flow Wind BUILDHGT BUILDWID BUILDLEN
Vector Direction Hb W L XBADJ YBADJ Hb: W: L
(Deg.) (Deg.) (m) (m) (m) (m) (m)
0 180 31.09 88.64 304.03 -144.87 -58.28 1.0 2.9 9.8
10 190 24.99 30.53 11.47 -7.79 -18.85 1.0 1.2 0.5
20 200 24.99 30.76 12.48 -4.99 -18.91 1.0 1.2 0.5
30 210 31.09 98.96 301.7 -115.52 -46.9 1.0 3.2 9.7
40 220 31.09 148.5 284.64 -99.38 -40.06 1.0 4.8 9.2
50 230 31.09 193.52 258.94 -80.23 -31.99 1.0 6.2 8.3
60 240 31.09 232.67 225.36 -58.63 -22.96 1.0 7.5 7.2
70 250 31.09 264.74 184.94 -35.26 -13.22 1.0 8.5 5.9
80 260 31.09 288.77 138.9 -10.81 -3.08 1.0 9.3 4.5
90 270 31.09 304.03 88.64 13.97 7.14 1.0 9.8 2.9
100 280 31.09 310.04 35.68 38.32 17.16 1.0 10.0 1.1
110 290 31.09 309.59 46.42 29.12 26.65 1.0 10.0 1.5
120 300 31.09 301.7 98.96 -2.58 35.33 1.0 9.7 3.2
BPIP Dimensions
Aspect Ratio

21. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Estimated EBD values
• Estimated values to right used to
modify AERMOD input file
• AERMOD re-run with these
building dimension inputs
• AERMOD results below show
wind tunnel study likely to help
significantly
AERMOD Building Dimension
Inputs 1-hour 24-hour annual
BPIP 15.19 8.20 0.89
Screening EBD Values 9.68 5.05 0.19
AERMOD Maximum predicted
concentration (μg/m3
)
Flow Wind BUILDHGT BUILDWID BUILDLEN
Vector Direction Hb W L XBADJ YBADJ Hb: W: L
(Deg.) (Deg.) (m) (m) (m) (m) (m)
0 180 31.09 88.64 124.36 -144.87 -58.28 1.0 2.9 4.0
10 190 24.99 30.53 11.47 -7.79 -18.85 1.0 1.2 0.5
20 200 24.99 30.76 12.48 -4.99 -18.91 1.0 1.2 0.5
30 210 31.09 98.96 124.36 -115.52 -46.9 1.0 3.2 4.0
40 220 31.09 124.36 124.36 -99.38 -40.06 1.0 4.0 4.0
50 230 31.09 124.36 124.36 -80.23 -31.99 1.0 4.0 4.0
60 240 31.09 124.36 124.36 -58.63 -22.96 1.0 4.0 4.0
70 250 31.09 124.36 124.36 -35.26 -13.22 1.0 4.0 4.0
80 260 31.09 124.36 124.36 -10.81 -3.08 1.0 4.0 4.0
90 270 31.09 124.36 88.64 13.97 7.14 1.0 4.0 2.9
100 280 31.09 124.36 35.68 38.32 17.16 1.0 4.0 1.1
110 290 31.09 124.36 46.42 29.12 26.65 1.0 4.0 1.5
120 300 31.09 124.36 98.96 -2.58 35.33 1.0 4.0 3.2
130 310 31.09 124.36 124.36 -34.19 42.94 1.0 4.0 4.0
140 320 31.09 124.36 124.36 -64.77 49.24 1.0 4.0 4.0
150 330 31.09 124.36 124.36 -93.38 54.05 1.0 4.0 4.0
160 340 31.09 124.36 124.36 -119.15 57.21 1.0 4.0 4.0
170 350 31.09 124.36 124.36 -141.3 58.64 1.0 4.0 4.0
180 360 31.09 88.64 124.36 -159.16 58.28 1.0 2.9 4.0
190 10 24.99 30.53 11.47 -3.68 18.85 1.0 1.2 0.5
200 20 24.99 30.76 12.48 -7.49 18.91 1.0 1.2 0.5
210 30 31.09 98.96 124.36 -186.18 46.9 1.0 3.2 4.0
220 40 31.09 124.36 124.36 -185.26 40.06 1.0 4.0 4.0
230 50 31.09 124.36 124.36 -178.71 31.99 1.0 4.0 4.0
240 60 31.09 124.36 124.36 -166.73 22.95 1.0 4.0 4.0
250 70 31.09 124.36 124.36 -149.68 13.22 1.0 4.0 4.0
260 80 31.09 124.36 124.36 -128.09 3.08 1.0 4.0 4.0
270 90 31.09 124.36 88.64 -102.6 -7.14 1.0 4.0 2.9
280 100 31.09 124.36 35.68 -74 -17.16 1.0 4.0 1.1
290 110 31.09 124.36 46.42 -75.54 -26.65 1.0 4.0 1.5
300 120 31.09 124.36 98.96 -96.39 -35.33 1.0 4.0 3.2
310 130 31.09 124.36 124.36 -114.31 -42.94 1.0 4.0 4.0
320 140 31.09 124.36 124.36 -128.75 -49.24 1.0 4.0 4.0
330 150 31.09 124.36 124.36 -139.29 -54.05 1.0 4.0 4.0
340 160 31.09 124.36 124.36 -145.59 -57.21 1.0 4.0 4.0
350 170 31.09 124.36 124.36 -147.47 -58.64 1.0 4.0 4.0
Estimated EBD using Max Width and Length Criteria of 4 times the Height
Aspect Ratio

22. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
AERMOD Results With Wind Tunnel EBD
Very wide/narrow building
Stack height: 47 m
Building height: 31 m
Property line in Red
Emission rate: 1 g/s
AERMOD RESULTS
Five years of met data
AERMOD Building Dimension
Inputs 1-hour 24-hour annual
BPIP 15.19 8.20 0.89
Wind Tunnel EBD 3.99 1.88 0.18
Reduction Factor 3.80 4.37 4.93
AERMOD Maximum predicted

23. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Stack at Industrial Facility
Stack height = 27 m
Q = 1 g/s
Building height = 17 m
Building width and/or length > 200 m
5 years of meteorological data
AERMOD RESULTS
SHORT LARGE BUILDING
Building Input 1-hr 3-hr 24-hr annual
BPIP 129.1 101.7 38.2 4.0
Wind Tunnel EBD 27.3 17.8 7.9 0.5
Reduction Factor 4.7 5.7 4.8 7.9
Maximum concentration (ug/m3
)

24. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
BPIP
Max = 38.2 ug/m3
EBD
Max = 8.1ug/m3
AERMOD Contours: 24-hr max

25. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Stack height: 45 m
Structure height: 61 m
Emission rate: 1 g/s
Five years of met data
Stack
AERMOD Results
Lattice Structure
Building
Input 1-hour 24-hour annual
BPIP 23.21 5.51 0.37
Wind Tunnel EBD 7.72 2.36 0.11
Reduction Factor 3.01 2.33 3.51
Maximum Concentration Results

26. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
FACTOR of 4 to 8
reduction when EBD used
Short building with a large foot print
FACTOR of 2 to 4
reduction when EBD used
Hyperbolic cooling towers
Typical AERMOD Overprediction
Factors When Using BPIP Inputs

27. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Typical AERMOD Overprediction
Factors When Using BPIP Inputs
FACTOR of 2 to 5
reduction when EBD used
Very Wide/Narrow Buildings
FACTOR of 2 to 3.5
reduction when EBD used
Lattice Structures

28. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Result of Accurate Building Dimension
Source Characterization
• More accurate
concentration
estimates
• Estimates that are 2
to 8 times lower for
appropriate cases
Short/wide/long
Streamlined
Wide
Lattice

29. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
Questions?
Ron Petersen, Ph.D., CCM
CPP, Inc
rpetersen@cppwind.com
970 690 1344

30. EUEC 2015, San Diego, CAWind Engineering and Air Quality Consultants
EBD Background
• Several studies conducted and approved using original guidance for
ISC applications
• Amoco Whiting Refinery, Region 5, 1990
• Public Service Electric & Gas, Region 2, 1993
• Cape Industries, Region 4, 1993
• Cambridge Electric Plant, Region 1, 1993
• District Energy, Region 5, 1993
• Hoechst Celanese Celco Plant, Region 3, 1994
• Pleasants Power, Region 3, 2002
• Studies conducted using AERMOD
• Hawaiian Electric (Approved), Region 9, 1998
• Mirant Power Station (Approved), Region 3, 2006
• Cheswick Power Plant (Approved), Region 3, 2006
• Alcoa (Not Approved), Region 7, 2010
• Chevron (Approved), Region 4, 2012