Important theoretical issues that significantly affect the accuracy of predicted concentrations subject to downwash effects have been identified in AERMOD/PRIME. These issues have prompted a number of industry groups to fund new research aiming at overcoming these shortcomings. The Plume Rise Model Enhancements (PRIME) building downwash algorithms1 (Schulman et al. 2000) in AERMOD2 are being updated to address some of the most critical limitations in the current theory. These enhancements will incorporate the latest advancements related to building downwash effects. The technical aspects of these enhancements are discussed in more detail in a recent publication "PRIME2: Development and Evaluation of Improved Building Downwash Algorithms for Solid and Streamlined Structures". The updates to the PRIME code include new equations to account for building wake effects that decay rapidly back to ambient levels above the top of the building; reduced wake effects for streamlined structures; and reduced wake effects for high approach roughness. A comparison with field data was conducted with the Bowline Point, Alaska North Slope, Millstone Nuclear Power Station, and the Duane Arnold Energy Center databases. A new experimental BPIP-PRM version is also discussed.

1. Sergio Guerra, PhD | GHD
Ron Petersen, PhD, CCM | CPP
June 28, 2018
PRIME2 Model Evaluation
A&WMA's 111th Annual Conference &
Exhibition, Hartford, CT

2. Outline
1. Brief Summary of Downwash Summit
2. Field Evaluation
3. BPIP-PRM
PRIME2 Model Evaluation

3. Key Takeaways from 2/16/18 Workshop
• EPA OAQPS confirmed that the PRIME2 updates can be included as an Alpha
option in a future model release. EPA expects the next release to happen by
the end of 2018.
• Review from OAQPS before release would take between 3-4 months, but will
depend on workload.
• EPA OAQPS prefers that the PRIME2 and ORD updates be implemented
separately in the model; e.g., PRIME2-A and PRIME2-B updates.
• Requirements from App W Section 3.2.2 would be needed before an Alpha
version becomes Beta.
• Updating BPIPPRM to reduce exaggeration of building footprint for angular
approaches to buildings is a top need for OAQPS and ORD.
• EPA ORD will continue to investigate and develop new formulation to deal with
rotated elongated buildings (lateral shift and effect of corner vortices).
PRIME2 Model Evaluation

4. Next Steps by CPP in 2018 – In Progress
Convert PRIME2 into an alpha version of PRIME
• Add the necessary commenting
• Need to use EPA’s current code and add PRIME2 enhancements as
options.
• Add switches for height of wind speed used for concentration
calculations.
• Add switches for Zeff calculation method for approach met conditions
and wake met conditions.
Evaluate PRIME2 against past permitting projects with wind tunnel EBD
studies: Mirant, ALCOA, Basic American Foods, TBD
• Current BPIP with AERMOD/PRIME and AERMOD/PRIME2
• EBD with AERMOD/PRIME and AERMOD/PRIME2
PRIME2 Model Evaluation

5. Field Evaluation
PRIME2 Model Evaluation

6. Bowline Point Field Evaluation for Receptors 1 and 3
Q-Q Plot of Predicted vs. Observed Concs. with BPIP
Values
Model Version
Top 25 Mean
X obs
Top 25 Mean
X predict
Top 25
Pre/Obs
Fractional
Bias
R1&3 AERMODv16216r (ug/m3) 422.17 447.71 1.06 0.06
R1&3 PRIME2v17234a (ug/m3) 422.17 684.51 1.62 0.47
6
PRIME2 Model Evaluation

7. Bowline Point
7
29.6
m
65.2
m
86.9
m
Q (g/s) Hs (m) Ts (K) Vs (m/s) Ds (m)
STACK 0 - 449.3 86.87 358 - 409 7.9 – 30.9 5.72
• Buoyant , SO2 Source
• Hudson River Valley, New York
• 100m met tower
• No turbulence data
• Even split between stable and
unstable hours
• Hourly emissions data
• Full year of data
• 4-Receptors (Recs 1 and 3 used)
7
PRIME2 Model Evaluation

8. Refined BPIP Method Example
Bowline Point
8
PRIME2 Model Evaluation

9. Refined BPIP Method Example: Bowline Point
Merged Tiers
Building
Dimensions
BPIP
(m)
Updated BPIP
(m)
Building
Height(Hb)
65.23 65.23
Building Width (W) 121.95 121.95
Building Length (L) 109.93 35.98
XBADJ -127.62 -97.20
YBADJ -2.47 -2.5
Assumption 1:
Tallest tiers combine
(green bdg)
Assumption 2:
BDG WIDTH (W) is
crosswind width of
merged tier.
Assumption 3:
XBADJ starts at the
upwind edge of the
merged tier
Assumption 4:
BDG LENGTH (L) is
calculated by
dividing the area of
the merged tier by W
9 PRIME2 Model Evaluation

10. Refined BPIP Method Example: Bowline Point
Unmerged Tiers
Building
Dimensions
BPIP
(m)
Updated BPIP
(m)
Building
Height(Hb)
65.23 65.23
Building Width (W) 94.57 49.9
Building Length (L) 130.27 27.65
XBADJ -132.56 -127.90
YBADJ -27.17 -4.0
Assumption 1:
Tallest tiers do not
combine (green bdg)
Assumption 2:
BDG WIDTH (W) is
crosswind width of
unmerged tier.
Assumption 3:
XBADJ starts at the
upwind edge of the
tallest tier
Assumption 4:
BDG LENGTH (L) is
calculated by
dividing the area of
the tallest tier by W
10 PRIME2 Model Evaluation

11. Bowline Point Field Evaluation for Receptors 1 and 3
Q-Q Plot of Predicted vs. Observed Concs. with BPIP
Values
Model Version
Top 25 Mean
X obs
Top 25 Mean
X predict
Top 25
Pre/Obs
Fractional
Bias
R1&3 AERMODv16216r (ug/m3) 422.17 447.71 1.06 0.06
R1&3 PRIME2v17234a (ug/m3) 422.17 684.51 1.62 0.47
11
PRIME2 Model Evaluation

12. Model Version
Top 25 Mean
X obs
Top 25 Mean
X predict
Top 25
Pre/Obs
Fractional
Bias
R1&3 AERMODv16216r (ug/m3) 422.17 237.67 0.56 -0.56
R1&3 PRIME2v17234a (ug/m3) 422.17 535.01 1.27 0.24
Bowline Point Field Evaluation for Receptors 1 and 3
Q-Q Plot of Predicted vs. Observed Concs. with Modified BPIP Values
12
PRIME2 Model Evaluation

13. Q (g/s) Hs (m) Ts (K) Vs (m/s) Ds (m)
STACK 1 39.2 554-584 17-21 3.66
34.0
m
39.2
m
Alaska North Slope Field Study
• Buoyant , SF6 Source
• 33m met tower
• Met data include: ws, wd, temp,
sigma-theta, and sigma-w
• 7 arcs of recs from 50m to 3,000m
• 44 hours during light hours (0900-
1600)
• Stability conditions generally neutral
or slightly stable
• Wind speeds at 33-m level
• Less than 6 m/s for one test
• Between 6 and 15 m/s for four
tests
• More than 15 m/s during three
tests
13

14. Refined BPIP Method
Example
Alaska North Slope
14 PRIME2 Model Evaluation

15. Model Version
Top 25 Mean
X obs
Top 25 Mean
X predict
Top 25
Pre/Obs
Fractional Bias
AERMODv16216r 3.13 3.59 1.15 0.137
PRIME2_17234 3.13 7.58 2.42 0.829
Alaska North Slope Field Evaluation
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values
15 PRIME2 Model Evaluation

16. Building
Dimensions
BPIP
(m)
Updated BPIP
(m)
Building
Height(Hb)
34.0 34.0
Building Width (W) 51.26 51.26
Building Length (L) 55.67 25.81
XBADJ -45.24 -43.70
YBADJ 6.58 6.6
Assumption 1:
Tallest tier combine
(green bdg)
Assumption 2:
BDG WIDTH (W) is
crosswind width of
merged tier.
Assumption 2:
XBADJ starts at the
lee edge of the
merged tier
Assumption 3:
YBADJ is calculated
by dividing the area
of the merged tier by
the width of the
artificially created
building
Refined BPIP Method Example: Alaska North Slope
Merged Tiers
16 PRIME2 Model Evaluation

17. Building
Dimensions
BPIP
(m)
Updated BPIP
(m)
Building
Height(Hb)
34.0 34.0
Building Width (W) 52.98 20.25
Building Length (L) 28.61 25.30
XBADJ -28.7 -28.6
YBADJ -11.79 4.8
Assumption 1:
Tallest tier do not
combine (green bdg)
Assumption 2:
XBADJ starts at the
lee edge of the
merged tier
Assumption 3:
YBADJ is calculated
by dividing the area
of the merged tier by
the width of the
artificially created
building
Refined BPIP Method Example: Alaska North Slope
Unmerged Tiers
17 PRIME2 Model Evaluation

18. Model Version
Top 25 Mean
X obs
Top 25 Mean
X predict
Top 25
Pre/Obs
Fractional Bias
AERMODv16216r 3.13 3.59 1.15 0.137
PRIME2_17234 3.13 7.58 2.42 0.829
Alaska North Slope Field Evaluation
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values
18 PRIME2 Model Evaluation

19. Model Version
Top 25 Mean
X obs
Top 25 Mean
X predict
Top 25
Pre/Obs
Fractional Bias
AERMODv16216r 3.13 2.78 0.89 -0.120
PRIME2_17234 3.13 6.14 1.96 0.648
Alaska North Slope Field Evaluation
Q-Q Plot of Predicted vs. Observed Concs. with Modified BPIP Values
19 PRIME2 Model Evaluation

20. Millstone Nuclear Power Station
(Dominion Millstone Power Station)
Q (g/s) Hs (m) Ts (K) Vs (m/s) Ds (m)
REAC 1 48.3 291 - 297 4.6 – 8.7 2.12
TURB1 1 29.1 292 - 306 10.5 1.4
TURB2 1 29.1 292 - 306 10.5 1.4
TURB3 1 29.1 292 306 10.5 1.4
41.6
m
44.7
m
27.6
m
29.1
m
48.3
m
• Non-buoyant , SF6 Source
• Waterford, Connecticut
• 36-hrs of SF6 emissions, from
48m stack
• 26-hrs of Freon emissions, from
29m stack
• 3 arcs at 350, 800 and 1,500 m
• Met tower with 10-m and 43-m
levels
• Even number of stable and
unstable hours
• Mostly high wind speeds (>7 m/s)
20

21. 21
Millstone Nuclear Power Station
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values

22. 22
Millstone Nuclear Power Station
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values

23. Duane Arnold Energy Center
23.5
m
42.7
m
1
m
23.5
m
45.7
m
Q (g/s) Hs (m) Ts (K) Vs (m/s) Ds (m)
STACK 5 1 45.7 293 – 299 7.4 - 40.8 1.4
STACK 4 1 23.5 294 - 300 0.01 2.12
STACK 1 1 1.0 299 - 303 0.01 1.4
• Non-buoyant , SF6 Source
• Palo, Iowa
• Terrain varies by about 30m
• Two arcs of monitors at 300m and 1000m
• Releases from two rooftops (46-m and
24-m levels) and the ground (1-m level)
• Release hours were 12, 16 and 11 for
46m, 24m, and 1m
• 1-m and 24-m releases were non-
buoyant, non-momentum
• 46-m release was close to ambient, but
had about a 10 m/s exit velocity
• Met data consisted of winds at 10m, 24m,
and 50m.
• Met conditions mostly convective (30 out
of 39 hours), with fairly light wind speeds
23

24. 24
Duane Arnold Energy Center
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values

25. 25
Duane Arnold Energy Center
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values

26. 26
Duane Arnold Energy Center
Q-Q Plot of Predicted vs. Observed Concs. with BPIP Values

27. Additional Evaluations to Consider
• American Gas Association SF6 field study (one of the EPA’s 17
AERMOD evaluation databases) – samplers as close as 50 m
• Wainwright, Alaska NOx database – monitor at 500 m
• Colorado drill rig field study – 12 NOx monitors at about 100 m
• Sheldon Station (Nebraska) – EGU with SO2 DRR monitoring at
about 600 m from stacks
• Other modeling stakeholders are encouraged to conduct and present
their own evaluation studies
PRIME2 Model Evaluation

28. Experimental BPIPPRM from EPA’s ORD
PRIME2 Model Evaluation

29. Wind
L1
L2
BPIP new building length calculation method
New building length = min(L1,L2) = L2
Wind
Example 1
Provided by EPA’s Office of Research and Development

30. Wind
L1
L2
New building length = min(L1,L2) = L1
Example 2
Provided by EPA’s Office of Research and Development

31. Provided by EPA’s Office of Research and Development

32. Provided by EPA’s Office of Research and Development

33. Conclusions
PRIME2 includes a superior theory to account for building downwash
effects for rectangular and streamlined structures.
Benefits from improved theory cannot be fully realized due to
outstanding issues in the model.
Work from EPA ORD complements the work performed by CPP.
Plan is to continue EPA collaboration to address model improvements
to AERMOD related to building downwash.
PRIME2 Model Evaluation

34. Sergio A. Guerra, PhD Ron Petersen, PhD, CCM
sergio.guerra@ghd.com rpetersen@cppwind.com
Office: + 720 974 0935 Mobile:+1 970 690 1344
Questions?
PRIME2 Model Evaluation

35. www.ghd.com
PRIME2 Model Evaluation