Complying with EPA's Guidance for SO2 Designations

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Complying with EPA’s Guidance for SO2
Designations
PNWIS
November 6, 2015
Sergio A. Guerra, PhD – CPP Inc.

Outline
• Background and Overview and Options (To
model or to monitor)
• Summary of SO2 Designation Schedule
• Advanced Modeling Techniques
– Equivalent Building Dimensions (EBD)
– Emission Variability Processor (EMVAP)
– 50th Percentile Background

Background
• August 5, 2013- EPA issued first round of
SO2 Designations.
• Three lawsuits were filed against EPA for
not designating all portions of the
country by the June 2013 deadline.
• March 2, 2015- Court ordered EPA to
complete remaining SO2 designations.

Background
• March 20, 2015- The Updated Guidance for
SO2 Area Designations was released by EPA.
• August 10, 2015- EPA releases the Final Data
Requirements Rule for 1-hr SO2 NAAQS.

Round 1
Areas Associated with 2009-2011 Monitored
Violations.
• 7/25/2013: EPA promulgates final SO2 area
designations for 29 nonattainment areas.
• 10/04/2013: Effective Date.

Round 2
Areas Associated with 68 Power Plants & New
Monitored Violations.
• 9/18/2015: States may submit updated
recommendations and supporting information for
area designations to EPA.
• 1/22/2016: EPA notifies states concerning any
intended modifications to their recommendations
(120-day letters).
• By 7/2/2016: EPA promulgates final SO2 area
designations.

Round 3
Modeled Areas and Areas w/o Monitors
• 1/13/2017: States submit air quality modeling
results for selected areas (per SO2 DRR).
• By 9/1/2017: EPA notifies states of any
intended modification to their
recommendations.
• By 12/31/2017: EPA promulgates final SO2
area designations.

Round 4
New Monitored Areas/All Remaining Areas
• 1/1/2017: States begin to operate new
monitoring network.
• 5/1/2020: States certify 2019 monitoring data
to calculate the 2017-2019 design value.
• By 9/2/2020: EPA notifies states about any
intended modification to their
recommendation (120-day letters).
• 12/31/2020: EPA promulgates final SO2 area
designations.

What Does All This Mean?
Large SO2 sources have two options:
1) Dispersion Modeling
2) Ambient Monitoring
Preferred option is modeling however this can
be challenging because of conservative nature
of model.

Modeling Softballs
December 2013 Modeling TAD:
• Use of actual instead of allowable emissions
(i.e., PTE) to assess violations of the standard.
• Use of 3 years of meteorological data instead
of 5.
• Receptor placement only in locations where
monitor could be placed.
• Use of actual stack height instead of GEP stack
height.

Advanced Modeling Techniques
Areas Advanced Modeling
Techniques
Traditional Modeling
Technique
Building dimensions
used for downwash
Equivalent Building
Dimensions (EBD)
Use of Building Profile Input
Program for PRIME (BPIP-
PRM)
Variable emissions Use EMVAP to account
for variability
Assume continuous
maximum emissions
Background
Concentrations
Combine AERMOD’s
concentration with the
50th % observed
Tier 1: Combine AERMOD’s
concentration with max. or
design value (e.g., 99th %
observed for SO2)
Tier 2: Combine predicted
and observed values based
on temporal matching (e.g.,
by season or hour of day).

Equivalent Building Dimensions

Building Dimension Inputs & BPIP
• BPIP uses building footprints and tier heights
• Combines building/structures
• All structures become one single rectangular solid for each wind
direction and each source
• BPIP dimensions may not characterize the source accurately and may
result in unreasonably high predictions

PRIME
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
• Developed for specific
building dimensions
• When buildings outside of
these dimensions, theory falls
apart

Refinery Structures Upwind
- Horizontal flow
Solid BPIP Structure Upwind
No Structures
Streamlines for Lattice Structures
Should be Horizontal

BPIP Diagnostic Tool
http://www.cppwind.com/what-we-do/air-permitting/bpip-diagnostic-tool
CPP determines Equivalent Building Dimensions (EBD) and provides them
to consultant for use in the dispersion modeling analysis.

BPIP Diagnostic Tool
http://www.cppwind.com/what-we-do/air-permitting/bpip-diagnostic-tool

Long Buildings with Wind
at an Angle
Figure created in BREEZE® Downwash Analyst
BREEZE is a registered trademark of Trinity Consultants, Inc.

• Equivalent Building Dimensions” (EBDs) are the dimensions
(height, width, length and location) that are input into
AERMOD in place of BPIP dimensions to more accurately
predict building wake effects
• Guidance originally developed when ISC was the preferred
model –
– EPA, 1994. Wind Tunnel Modeling Demonstration to Determine
Equivalent Building Dimensions for the Cape Industries Facility,
Wilmington, North Carolina. Joseph A. Tikvart Memorandum, dated
July 25, 1994. U.S. Environmental Protection Agency, Research
Triangle Park, NC
• Determined using wind tunnel modeling
• How does EBD Improve Accuracy? Watch video
What is EBD?

How to Use EBD for Regulatory Purposes?
 Step 1: Develop a protocol outlining the EBD study
 Step 2: Submit EBD protocol for approval to regulatory agency. Also need to
involve Model Clearinghouse
 Step 3: Perform wind tunnel testing
 Step 4: Use building geometry from EBD study in AERMOD
 Step 5: Submit final report for agency review and approval

Current Status Regulatory Status of EBD
From 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.”
• Memo stressed that these wind tunnel studies are source
characterization studies not subject to alternative modeling requirements
Other
• EPA has acknowledged the limitation of BPIPPRM derived parameters for
some cases1,2
1. Roger Brode’s (EPA) comments at 9th Modeling Conference
http://www3.epa.gov/ttn/scram/9thmodconf/9thmc_bpip-prime_workgroup.pdf
2. Roger Brode’s (EPA) comments at 10th Modeling Conference
http://www3.epa.gov/ttn/scram/10thmodconf/presentations/1-9-Brode_10thMC_AERMIC_Update_03-13-2012.pdf

Summary of Approved Projects
• 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 original guidance for AERMOD/PRIME
applications
– Hawaiian Electric (Approved), Region 9, 1998
– Mirant Power Station (Approved), Region 3, 2006
– Cheswick Power Plant (Approved), Region 3, 2006
– Radback Energy (Protocol Approved), Region IX, 2010
– Chevron 1 (Approved), Region 4, 2012
– Chevron 2 (Approved), Region 4, 2013
– Chevron 3 (In process), Region 4, 2015

Monte Carlo Approach
• Pioneered by the Manhattan Project scientists in 1940’s
• Technique is widely used in science and industry
• EPA has approved this technique for risk assessments
• Used by EPA in the Guidance for 1-hour SO2 Nonattainment
Area SIP Submissions (2014)

Emission Variability Processor
• Assuming fixed peak 1‐hour emissions on a continuous basis will
result in unrealistic modeled results
• Better approach is to assume a prescribed distribution of emission
rates
• EMVAP assigns emission rates at random over numerous iterations
• The resulting distribution from EMVAP yields a more representative
approximation of actual impacts
• Incorporate transient and variable emissions in modeling analysis
• EMVAP uses this information to develop alternative ways to
indicate modeled compliance using a range of emission rates
instead of just one value

Background Concentrations

Siting of Ambient Monitors
According to the Ambient Monitoring Guidelines for Prevention of Significant
Deterioration (PSD):
The existing monitoring data should be representative of three types of area:
1) The location(s) of maximum concentration increase from the proposed source or
modification;
2) The location(s) of the maximum air pollutant concentration from existing sources;
and
3) The location(s) of the maximum impact area, i.e., where the maximum pollutant
concentration would hypothetically occur based on the combined effect of existing
sources and the proposed source or modification. (EPA, 1987)
U.S. EPA. (1987). “Ambient Monitoring Guidelines for Prevention of Significant
Deterioration (PSD).”EPA‐450/4‐87‐007, Research Triangle Park, NC.

Wildfires in 2015
NASA’s Earth Observatory
http://earthobservatory.nasa.gov

24-hr PM2.5 Santa Fe, NM Airport
Background Concentration and Methods to Establish Background Concentrations in Modeling.
Presented at the Guideline on Air Quality Models: The Path Forward. Raleigh, NC, 2013.
Bruce Nicholson

Probability of Two Unusual Events
Happening at the Same Time

Combining 99th Percentile
Pre and Bkg (1-hr SO2)
99th percentile is 1st rank out of 100 days = 0.01
P(Pre ∩ Bkg) = P(Pre) * P(Bkg)
= (1-0.99) * (1-0.99)
= (0.01) * (0.01)
= 0.0001 = 1 / 10,000 days
Equivalent to one exceedance every 27 years!
= 99.99th percentile of the combined distribution

Proposed Approach to Combine
Modeled and Monitored Values
• Combining the 99th %(for 1-hr SO2) monitored
concentration with the 99th % predicted
concentration is too conservative.
• A more reasonable approach is to use a
monitored value closer to the main
distribution (i.e., the median).
Evaluation of the SO2 and NOX offset ratio method to account for secondary PM2.5 formation
Sergio A. Guerra, Shannon R. Olsen, Jared J. Anderson
Journal of the Air & Waste Management Association
Vol. 64, Iss. 3, 2014

Combining 99th Pre and 50th Bkg
50th Percentile is 50th rank out of 100 days = 0.50
P(Pre ∩ Bkg) = P(Pre) * P(Bkg)
= (1-0.99) * (1-0.50)
= (0.01) * (0.50)
= 0.005 = 1 / 200 days
Equivalent to 1.8 exceedances every year
= 99.5th percentile of the combined distribution
Evaluation of the SO2 and NOX offset ratio method to account for secondary PM2.5 formation
Sergio A. Guerra, Shannon R. Olsen, Jared J. Anderson
Journal of the Air & Waste Management Association
Vol. 64, Iss. 3, 2014

Advanced Model Input Analysis
Solutions
• Emission Variability
Processor (EMVAP)
• Evaluation of
background
concentrations
EM Magazine, December 2014
Guerra, S.A. “Innovative Dispersion Modeling
Practices to Achieve a Reasonable Level
of Conservatism in AERMOD Modeling
Demonstrations.” EM Magazine, December 2014.

Case Study: Three Cases Evaluated
1. Using AERMOD by assuming a constant
maximum emission rate (current modeling
practice)
2. Using AERMOD by assuming a variable
emission rate
3. Using EMVAP to account for emission
variability

Three Cases Used to Model Power Plant
Input parameter Case 1 Case 2 Case 3
Description of
Dispersion
Modeling
Current
Modeling
Practices
AERMOD with
hourly
emission
EMVAP
(500 iterations)
SO2 Emission
rate (g/s)
478.7
Actual hourly
emission rates
from CEMS
data
Bin1: 478.7
(5.0% time)
Bin 2: 228.7
(95% time)
Stack height
(m)
122
Exit
temperature
(degrees K)
416
Diameter (m) 5.2
Exit velocity
(m/s)
23

Results of 1-hour SO2 Concentrations
Case 1
(µg/m3)
Case 2
(µg/m3)
Case 3
(µg/m3)
Dispersion
Modeling
Current
Modeling
Practices
AERMOD
with hourly
emission
EMVAP
(500
iterations)
H4H 229.9 78.6 179.3
Percent of
NAAQS
117% 40% 92%

St. Paul Park 436 Ambient Monitor

Positively Skewed Distribution
http://www.agilegeoscience.com

Histogram of 1-hr SO2 Observations
Innovative Dispersion Modeling Practices to Achieve a Reasonable Level of Conservatism in AERMOD Modeling Demonstrations.
Sergio A. Guerra
EM Magazine, December 2014.

Concentrations at Different Percentiles
St. Paul Park 436 monitor (2011-2013)
Percentile µg/m3
50th 2.6
60th 3.5
70th 5.2
80th 6.1
90th 9.6
95th 12.9
98th 20.1
99th 25.6
99.9th 69.5
99.99th 84.7
Max. 86.4

Case 3 with Three Different Backgrounds
Case 3 with
Max. Bkg
(µg/m3)
Case 3 with
99th % Bkg
(µg/m3)
Case 3 with
50th % Bkg
(µg/m3)
H4H 179.3 179.3 179.3
Background 86.4 25.6 2.6
Total 265.7 204.9 181.9
Percent of
NAAQS
135.6% 104.5% 92.8%

Conclusion
Current regulatory practices in dispersion modeling lead
to unrealistically high predicted concentrations.
• Source characterization techniques such as wind tunnel
generated building dimensions can mitigate downwash
overpredictions.
• Probabilistic methods to account for emission variability
can help achieve more realistic concentrations.
• Use of 50th % monitored concentration is statistically
conservative when pairing it with the 99th % predicted
concentration.

Conclusion
These Advanced Modeling Techniques are:
• Protective of the NAAQS,
• Provide a reasonable level of conservatism,
• In harmony with probabilistic nature of 1-hr standards

Thank You!
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

Complying with EPA's Guidance for SO2 Designations

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