Strategies to deal with monitored exceedances when AERMOD can’t be used

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Strategies to Deal with
Monitored Exceedances When
AERMOD Can’t be Used
Ron Petersen, PhD, CCM Sergio Guerra, PhD
Cell: 970 690 1344 Cell: 612 584 9595
rpetersen@cppwind.com guerra@cppwind.com
CPP, Inc.
2400 Midpoint Drive, Suite 190
Fort Collins, CO 80525
www.cppwind.com @CPPWindExperts

Overview
• Monitored SO2 concentrations exceed the new 1-hour SO2
NAAQS at nearby Water Tower Monitor (WTM)
• Monitored design concentration is 151 ppb (2009-2011)
relative to 75 ppb NAAQS; background is about 8 ppb
• For attainment, maximum hourly SO2 concentration needs
to be reduced by at least 55%
• AERMOD is showing compliance at the monitoring station
with predicted concentrations a factor of two lower than
monitored
• Rhinelander Mill Boiler Stack S09 has been identified as the
primary contributor

Rhinelander Mill and Monitor
Looking Northeast SO2 Monitor
Stack S09
Corner Vortex Problem

Rhinelander Mill and Critical Features
Cyclone Boiler(S09)
Stack Height
63 m
207 ft
Boiler
Building
38 m
125 ft
Looking South

Monitored SO2 Concentrations for 2009
Highest concentrations for wind speeds around 5 m/s for 200 degree wind direction
(toward Water Tower monitor)

AERMOD
Corner Vortex Issue
• Current building wake equations do
not account for corner vortex
• Corner vortex causes higher
concentrations than currently
predicted in AERMOD due to
increased downdraft and plume rise
suppression
• AERMOD and PRIME downwash
model do not even have input for
approach flow relative to building
corners – model assumes flow
toward broad side of buildings and
is totally oblivious to corner effects

Corner Vortex Issues – EPA Research
Note increased effect for 45º approach flow 

Possible Solutions
• Reduce emission rate by 50% based on monitored
results >> not a good solution
• Extend stack to formula GEP stack height of 75 m
plus emission control: how do you determine since
AERMOD doesn’t work?
• Extend stack to actual GEP stack height plus emission
control if needed: how to determine since AERMOD
doesn’t work?

Issues for Consideration
• Two problems for consideration:
– The need to find a tool other than AERMOD to correlate
reductions in SO2 emissions from the Mill to SO2
concentrations at the Water Tower monitor to show
compliance with the 1-hour SO2 standard, and
– The need to develop a site-specific GEP stack height given
the topography of the Mill and monitor and the excessive
downwash caused by the corner vortex.
• Fluid modeling in a wind tunnel using HYWINMOD allows for
correlation of mill emissions to monitor results, as well as
development of site-specific GEP determination.

Overall Plan
• Determine actual GEP stack height using wind
tunnel modeling
• Demonstrate compliance for final design
configuration
– HYWINMOD (CPP model utilizing output from wind tunnel +
AERMOD) >> complete but EPA approval pending
– AERMOD w/o downwash plus wind tunnel downwash factor
>> likely approval soon
10

GEP Study Plan
• Test protocol developed and reviewed by WDNR and
EPA – tentatively approval received
• Constructed scale model (1:240) and setup
• Wind tunnel testing – documentation tests
• Wind tunnel testing – GEP stack height tests
– Tests with buildings present
– Tests without building present
• Specify the GEP stack height (40% and NAAQS test)
• Report submission and approval – January, 2015
11

40 CFR 51.110 (ii) Defines GEP stack
height to be the greater of:
• 65 meters;
• the formula height (Hb+1.5 L), or
– For a 40 m cube, GEP = 100 m > 65 m!!!
• The height determined by a wind tunnel
modeling study – Will be taller than the
formula!!
– Up to 3.25 times the building height versus 2.5 for the
formula
– Typically 2 times the nearby terrain height

GEP Stack Height Criteria for Wind
Tunnel
• 40% maximum concentration difference
with and without the buildings or terrain
• With buildings in Max Concentration must
exceed NAAQS or PSD increment
• Easy test since approved wind tunnel
method does not include plume
buoyancy.

Example 1
• Kennecott Smelter
mid 80s
• 1200 ft stack
justified as GEP
using wind tunnel
modeling

Example 2:
• Titus Generating Station, Schuylkill River about 3 km south of
Reading, Pennsylvania
• 175 m stack height justified as GEP using wind tunnel
modeling, 1995
175m
100m
65m

Basic Wind Tunnel Modeling
Methodology
•Specify model
operating conditions
•Construct scale model
(3D printing)
•Install model in wind
tunnel and measure
desired quantity

Source Parameters
Stack
Height
Source Source Above Exit Exit Volume Exit
Description ID Base Diameter Temp. Flow Rate Velocity
(m) (m) (K) (m3
/s) (m/s)
S09 - Maximum Load S09 max 62.09 2.13 430.4 47.23 13.25
S09 - Nominal Load S09 nom 62.09 2.13 422.0 34.21 9.60
S09 - Minimum Load S09 Mmin 62.09 2.13 422.0 26.50 7.44

Wind Tunnel Testing
1:240 Scale Model Installed in Wind
Tunnel

Measure Ground-level Concentrations
Tracer
from stack
Max ground-level concentrations measured versus x

Measure Ground-level Concentrations
Data taken until good fit and max
obtained
Automated Max GL Concentration Mapper

Buildings in
Buildings out

Plume rise with and without the building
Buildings in
Buildings Out
CORNER VORTEX EFFECT

All GEP Testing Results

GL Concentration Profile W and W/O Buildings at 90 m
GEP Stack Height
90 m stack height,
190 degree WD,
8 m/s wind speed

Final Result
Actual GEP = 90 m
Formula GEP = 75 m
Creditable GEP = 90 m > formula > 65 m

NAAQS Compliance Demonstration Using
HYWINMOD
• Test protocol development and approval
• HYWINMOD validation
• Surface Roughness
– 0.49 m for Water Tower Direction
– 0.25 m for Airport
• Scale model setup and instrumentation
• Wind tunnel testing of final design configuration for S09
• HYWINMOD analysis to demonstrate compliance at monitor
and at least 55% reduction in concentrations from baseline
emission conditions
• Report submission – approval pending

HYWINMOD
• CPP developed a practical method where wind
tunnel modeling can be used to predict hourly
concentrations for all stabilities and can account for
plume buoyancy
• Previously validated against EPA database: Bowline
Point
• Will account for corner vortex
Wind tunnel
predicted
concentration
(neutral)
Data post
processing
and
correction
Hourly concentrations
incl. plume buoyancy
for all stabilities

HYWINMOD Validation
Rhinelander Mill WT Monitor
HYWINMOD
AERMOD
”Raw” wind tunnel
prior to HYWINMOD
processing 

HYWINMOD Results
4th highest max daily SO2
concentration (μg/m3)
Description/Source Configuration
Maximum
Load
Scenario
Nominal
Load
Scenario
Minimum
Load
Scenario*
5-year
average
5-year
average
5-year
average
Supporting Information
1-hour NAAQS NAAQS 196.5 196.5 196.5
Water Tower Monitor SO2 Design Value
(2009-2011) Co,DV (WTM) 395.6 395.6 395.6
Estimate Design Value Based on
HYWINMOD Scaling Plus BG at 90 m
GEP Stack Height
Cp,DV
(WTM,GEP,S09)+
BG
136.8 152.4 195.7
% Emission Reduction Required -52% -34% 0%

AERMOD Compliance Demonstration
• Run AERMOD w/o building downwash in approved
manner
• Use wind tunnel determine downwash factor, R, to
adjust emission rate
• R is a only a function of wind speed
R = 1 @ <= 2 m/s
R = 1.5 @ 10.8 m/s

AERMOD Emission Factor to
account for downwash

AERMOD Compliance Demonstration
• Protocol prepared: reviewed and approved by
agency
• Report submitted: approval should be
forthcoming this month.

Ron Petersen, PhD, CCM Sergio A. Guerra, PhD
rpetersen@cppwind.com sguerra@cppwind.com
Mobile: +1 970 690 1344 Mobile: + 612 584 9595
CPP, Inc.
2400 Midpoint Drive, Suite 190
Fort Collins, CO 80525
+ 970 221 3371
www.cppwind.com @CPPWindExperts
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Strategies to deal with monitored exceedances when AERMOD can’t be used

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