PRIME2: Model Evaluations

Sergio Guerra, PhD | GHD
Ron Petersen, PhD, CCM | Petersen Research and Consulting
EUEC 2019, San Diego CA
February 26, 2019
PRIME2 Model Evaluation
-AERMOD 18081
-AERMOD D18227_ORD
-AERMOD D18227_PRM2

Objectives
PRIME2 Subcommittee was formed to:
• Establish a mechanism to review, approve
and implement new science into the model
for this and future improvements
• Provide a technical review forum to improve
the PRIME building downwash algorithms

Next Steps: Implementation
Model
Improvements
Submitted to
EPA
AERMOD with
PRIME2 and
ORD Switches
EPA
releases
New PRIME2
as Alpha
option
App W
Sec
3.2.2
reqs.
EPA
releases
PRIME2 as
Beta
option
Notice of
proposed
rulemaking
(NPRM)
New PRIME is
released as
default
regulatory
option
Alpha option needs to meet the alternative refined model requirements in App W, Section 3.2.2 before it
can become a Beta option. These requirements include:
1-Model has received a scientific peer review;
2-Model can be demonstrated to be applicable to the problem on a theoretical basis;
3-The data bases to perform analysis are available and adequate;
4-Appropriate performance evaluations show model is not biased toward underestimation; &
5-A protocol on methods and procedures to be followed has been established

Why a New Downwash Model?
• AERMOD’s PRIME algorithm based on research carried out before
2000
• Original theory based on a limited number of building dimensions
and building types
• Theory is not suitable for porous, streamlined, wide or elongated
structures
• Theory based on theoretical assumptions that can be improved

Background
• Industry funding obtained in 2016 and early 2017 to
carry out PRIME2 research
• Initial results presented at EPA’s 2016 Regional, State,
and Local Modelers’ Workshop
http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2016/Pre
sentations/1-14_CPP_AERMOD-PRIME-Next-Generation_Downwash_Model.pdf
• Journal article documenting flaws in downwash theory
was published in JAWMA, August 2017
https://www.tandfonline.com/doi/full/10.1080/10962247.2017.1279088
• 2017 EPA Releases White Papers
• EPA ORD has been doing building downwash research and has
made some improvements to PRIME

New equation documented
https://doi.org/10.1016/j.jweia.2017.11.027 PRIME2 Model Evaluation

Update AERMOD
AERMOD Fortran Files Modified
PRIME.f
Where all building downwash
calculations are carried out
Calc1.f
Where approach wind
conditions come from
Modifications
• New Zeff
• New Ueff, SWeff, SVeff
• New U30, SW30 and
SV30 for input to new
equation
Modifications
• New turbulence equation
• New wind speed equation
Recompile and Create
AERMOD/PRIME2
7 PRIME2 Model Evaluation

Key Features of PRIME2
• Lateral turbulence enhancement in the wake is less than vertical
turbulence enhancement (currently PRIME has them identical)
• Wake effects decrease as approach roughness increases
• Wake effects for streamlined structures are reduced
• Building wake effects decay rapidly back to ambient levels above the
top of the building versus the current theory that has these effects
extending up to 3 building heights
• The approach turbulence and wind speed is calculated at a more
appropriate height versus the current theory where half the wake
height at 15 building heights downwind of the building is used

EPA ORD AERMOD/PRIME
Modifications
Current PRIMEThree ORD model enhancements
1. Fix mismatch in plume vertical spread
at transition between cavity and far
wake.
2. Use effective wind speed, Ueff, for
primary plume versus stack height for
concentration calculations
3. Adjust cap on ambient turbulence from
0.06 to 0.07. No effect on PRIME2.
Fix 1
Current PRIME
Ueff at Stack Top
Fix 2
@ (Hp+RecH)/2
RecH) = 0
Hp

PRIME2 Switches
PRIME2Ueff defines the height used to compute effective
parameters Ueff, Sweff, Sveff and Tgeff at plume height and at 30
m.
PRIME2UTurb enables enhanced calculations of turbulence and
wind speed
Streamline defines the set of constants for modeling all structures
as streamlined. If omitted, rectangular building constants are used.

ORD Switches
PRIMEUeff controls the heights for which the wind speed is
calculated for the main plume concentrations.
• Average between plume height and receptor height recommended in ORD
version
• Default is current method in AERMOD, stack height wind speed.
PRIMETurb adjusts the vertical turbulence intensity, wiz0 from 0.6
to 0.7.
PRIMECav modifies the cavity calculations
If no switch applied, current AERMOD methodology used.

Case Study Evaluation
Conducted for the following four cases:
• Arconic (formerly Alcoa )- Davenport, IA
• Mirant Potomac River Generating Station- Alexandria, VA
• Basic American Foods- Blackfoot, ID
• Oakley Generating Station- Oakley, CA
The evaluation compares the following averages for each case:
• 1-hour (H1H)
• 24-hr (H1H)
• Annual

Arconic- Davenport, IA (formerly Alcoa)
Met data: Davenport, IA met data, 2010-2014 from IDNR (http://www.iowadnr.gov/Environmental-Protection/Air-
Quality/Modeling/Dispersion-Modeling/Meteorological-Data).
Q Stack Height Stack Temp. Stack Vel. Stack Diam. Height of BPIP Cont. Bdg.
g/s m K m/s m m
S_349 1.94 21.34 310.93 17.82 2.46 16.7-17.5
Stack

Arconic – Summary Results in µg/m3
Arconic 349 w BPIP H1H
Average 18081 D18227-ORD D18227-PRM2
H1H
1-hr 172.7 166.0 95.9
24-hr 30.0 26.8 19.7
Annual 3.0 4.5 1.0

Arconic H1H Comparisons for 1-hr, 24-hr and
Annual Averages
172.7
30.0
3.0
166.0
26.8
4.5
95.9
19.7
1.0
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
200.0
1-hr 24-hr Annual
Q(µg/m3)
Arconic 349 w BPIP H1H
18081 D18227-ORD D18227-PRM2

Arconic Q-Q Plots

Arconic: BPIP inputs ran with AERMOD v18081

Arconic: BPIP inputs ran w AERMOD vD18227_ORD

Arconic: BPIP inputs ran w AERMOD vD18227_PRM2

Mirant Potomac River Generating Station,
Alexandria, VA
Met data: Reagan Airport, VA original 1992 met data reprocessed with AERMETv18081.
g/s m K m/s m m
BS4 1 48.2 303.71 18.42 2.44 35.3
Stack

Mirant – Summary Results in µg/m3
Mirant BS4 w BPIP H1H
H1H
1-hr 21.1 32.3 26.7
24-hr 6.9 11.5 7.6
Annual 0.6 1.1 0.3

Mirant H1H Comparisons for 1-hr, 24-hr and
Annual Averages
21.1
6.9
0.6
32.3
11.5
1.1
26.7
7.6
0.3
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
1-hr 24-hr Annual
Q(µg/m3)
Mirant BS4 w BPIP H1H
18081 D18227-ORD D18227-PRM2

Mirant Q-Q Plots

Mirant: BPIP inputs ran with AERMOD v18081

Mirant: BPIP inputs ran
with AERMOD vD18227_ORD

Mirant: BPIP inputs ran with
AERMOD vD18227_PRM2

Basic American Foods, Blackfoot, ID
Met data: On-site met data from the Blackfoot Met Tower operated by the Idaho National Laboratory and
supplemented with data from the Pocatello Regional Airport, 2002-2006.

Basic American Foods, Blackfoot, ID
Met data: On-site met data from the Blackfoot Met Tower operated by the Idaho National Laboratory and
supplemented with data from the Pocatello Regional Airport, 2002-2006.
g/s m K m/s m m
EU_24 0.13 12.65 359.26 12.44 0.76
EU_25 0.06 12.65 338.71 5.76 0.91
EU_26 0.13 12.65 359.26 12.44 0.76
EU_31 0.12 12.65 344.26 14.57 1.04
EU_32 0.05 12.60 338.71 10.52 0.79
EU_33 0.05 12.60 327.59 11.34 0.61
Stack
7.0

BAF – Summary Results in µg/m3
BAF EU24-27& EU31-33 w BPIP H1H
H1H
1-hr 451.3 611.6 350.7
24-hr 146.0 152.7 119.1
Annual 48.8 51.1 35.4

BAF H1H Comparisons for 1-hr, 24-hr and
Annual Averages
451.3
146.0
48.8
611.6
152.7
51.1
350.7
119.1
35.4
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
1-hr 24-hr Annual
Q(µg/m3)
BAF EU24-27& EU31-33 w BPIP H1H
18081 D18227-ORD D18227-PRM2

BAF Q-Q Plots

BAF: BPIP inputs ran with AERMOD v18081

BAF: BPIP inputs ran

BAF: BPIP inputs ran with
AERMOD vD18227_PRM2

Oakley Generating Station, Oakley, CA
Met data: Metro Oakland International Airport, CA met data for years 2009-2013. Downloaded from CARB
(https://www.arb.ca.gov/toxics/harp/metfiles2.htm).
g/s m K m/s m m
EU_31 1 47.41 362.00 22.26 5.59 31.7
Stack

Oakley GS – Summary Results in µg/m3
Oakley GS Tur1 w BPIP H1H
H1H
1-hr 1.4 1.6 4.3
24-hr 0.4 0.4 0.8
Annual 0.1 0.1 0.1

Oakley GS H1H Comparisons for 1-hr, 24-hr and
Annual Averages
1.4
0.4
0.1
1.6
0.4
0.1
4.3
0.8
0.1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1-hr 24-hr Annual
Q(µg/m3)
Oakley GS Tur1 w BPIP H1H
18081 D18227-ORD D18227-PRM2

Oakley GS Q-Q Plots

Oakley: BPIP inputs ran with AERMOD v18081

Oakley: BPIP inputs ran

Oakley: BPIP inputs ran with
AERMOD vD18227_PRM2

Results
• Performance of version D18227-PRM2 is inconsistent
• Predicted values are lower than the base case for Arconic and BAF with
small differences for Mirant (except for annual which has PRIME2
significantly lower).
• The base case predictions are lower than the ones from the D18227-
ORD and D18227-PRM2 versions for the Oakley case.

Results
• In general, version D18227-ORD produces higher concentrations
than AERMOD 18081.
• The primary reason for this is that the ORD version uses the wind speed
at the average between plume centerline height and receptor height to
calculate concentrations versus stack height in AERMOD.
• PRIME2’s theory does not depend on the wake height but rather the
building height, width, length and position relative to the stack.

Future Areas of Improvements
• PRIME streamline
• PRIME plume rise
• Height used to calculate turbulence
• BPIP-PRM
• Cavity plume amplification problem

Conclusions
• PRIME2 includes a superior theory to account for building
downwash effects for rectangular and streamlined structures.
• Inconsistencies may be due to other parts of the model
• Work from EPA ORD complements the work performed by PRIME2.
• Plan is to continue EPA collaboration to address model
improvements to AERMOD related to building downwash.

Sergio A. Guerra, PhD Ron Petersen, PhD, CCM
sergio.guerra@ghd.com rpetersen@petersenresearch.com
Office: + 720 974 0935 Mobile:+1 970 690 1344

www.ghd.com

PRIME2: Model Evaluations

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