ALL4's Dan Dix presented at the 23rd Virginia Environmental Symposium about 1-Hour SO2 Implementation Modeling. Dan's presentation consisted of a summary of the NAAQS, an update on NAAQS implementation, NAAQS modeling demonstration approach, and a summary of ambient SO2 monitoring.

1. 1-Hour SO2 NAAQS
Implementation Modeling
Dan P. Dix
23rd Virginia Environmental Symposium
April 11, 2012

2. Agenda
 Summary of NAAQS
 NAAQS Implementation Updates
 Dispersion Modeling Basics
 NAAQS Modeling Demonstration
Approach
 Ambient SO2 Monitoring
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3. About ALL4
 Environmental consulting firm
 Founded 2002 – currently 30+ employees
 Offices in Kimberton, PA and Columbus, GA
 Specialize in air quality consulting:
• Complex air permitting and strategy development
• Air dispersion modeling
• Ambient air quality monitoring
 Dispersion modeling as a company-wide initiative
 www.all4inc.com
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4. National Ambient Air
Quality Standards
(NAAQS)

5. NAAQS Background
 “Backdrop” of the Clean Air Act
 States design their SIPs and enforce and
implement their regulations to meet the
NAAQS
 Air quality construction permit programs are
designed around NAAQS compliance
• PSD: Maintaining NAAQS attainment
• NNSR: Getting into NAAQS attainment
 NAAQS reevaluated every 5 years
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6. NAAQS Summary
Averaging Historic Revised NAAQS
Pollutant Primary/Secondary
Period NAAQS (µg/m3) (µg/m3)
1-Hour Primary 40,000 10,000
CO
8-Hour Primary 10,000 40,000
Ozone 8-Hour Primary/Secondary 75 ppb Withdrawn
Pb 3-Month Rolling Primary/Secondary 1.5 0.15
PM10 24-Hour Primary/Secondary 150 150
24-Hour Primary/Secondary 65 35
PM2.5
Annual Primary/Secondary 15 15
1-Hour Primary N/A 188
NO2
Annual Primary/Secondary 100 100
1-Hour Primary N/A 196
3-Hour Secondary 1,300 1,300
SO2 24-hour Primary 365 Revoked
Annual Primary/Secondary 80 Revoked
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7. Attainment/Nonattainment Designations
 U.S. EPA philosophy on the SO2 NAAQS
implementation process:
• Proposed NAAQS – designations based on
ambient monitoring data
• Final NAAQS – designations based primarily
on air quality modeling data
 Shift to reliance on air quality modeling
will become a critical issue for individual
facilities
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8. NAAQS
Implementation
Updates

9. SO2 NAAQS Implementation
 NAAQS Implementation Schedule:
• June 2011: Initial state nonattainment
recommendations to U.S. EPA (most counties were
“unclassifiable”)
• June 2012: EPA to finalize attainment status (most
states will still be “unclassifiable” or attainment)
• June 2013: Maintenance SIP submittals including
individual facility modeling to achieve compliance
with the NAAQS
• August 2017: Full NAAQS compliance in all areas
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10. Implementation Update
 Draft guidance for states to evaluate
designations using AERMOD was released on
September 22, 2011
 Most states are currently reviewing the U.S. EPA
guidance and crafting their plans
 States or facilities conducting modeling?
 U.S. EPA indicated at 10th Conference on Air
Quality Models that final guidance will not be
released this year due to the scope of comments
made.
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11. SO2 Maintenance SIP Submittals
 U.S. EPA: Revising PSD/NNSR programs to include
new NAAQS is not sufficient. Five components are
required:
• “Attainment Emission Inventory”
• Maintenance Demonstration
• Control Strategy
• Contingency Plan
• Verification of Continued Attainment
 Maintenance SIP will list enforceable 1-hour emission
limits (August 2017)
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12. SO2 NAAQS Implementation
 State SIPs will be based on AERMOD dispersion
modeling for the following individual facilities (by
order of priority):
• SO2 Actual Emissions > 100 tons per year
• SO2 PTE > 100 tons per year
• Smaller facilities “with a potential to cause or
contribute” to a NAAQS violation
 States are considering other options based on
population
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13. SO2 NAAQS Implementation
 Legal challenges ongoing:
• Science behind NAAQS levels
• Approach of using modeling
 Under the current approach, if states don’t
perform modeling, U.S. EPA will through
Federal Implementation Plan (FIP)
 Some states don’t have the resources to
complete evaluations and don’t think U.S.
EPA does either.
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14. SO2 NAAQS Implementation
 What are other States doing?
• Maine - >100TPY Actual, Protocols due June 30, 2012, and final
analysis due December 31, 2012.
• Lake Michigan Air Directors Consortium (LADCO) has developed
Protocol for states to follow.
 Wisconsin, Michigan, Minnesota, Indiana, and Illinois included.
 >100 TPY PTE, facilities given option to complete themselves or
have state complete.
 Michigan were due December 31, 2011.
 Minnesota completed March 12, 2012.
• Nebraska – Power plants have joined to conduct modeling themselves
and conducting tracer study.
• Missouri – Facilities conducting modeling due by April 2012.
• Connecticut - >15TPY PTE, conducted by State by July 2012.
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15. Dispersion Modeling
Basics and Inputs

16. AERMOD Process
Hourly Wind Speed
Hourly Wind Direction
Hourly Ambient
Temperature
Land Use Patterns Predicted Ground Level
Topography Ambient
Concentrations (µg/m3)
Building Dimensions for all averaging times
Stack Dimensions
Exhaust Velocity
Exhaust Temperature
Emission Rates
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17. Air Quality Modeling Steps
1. Emission Inventory
2. Meteorological Data
(AERMET/AERSURFACE)
3. Terrain Data (AERMAP)
4. Building Downwash (BPIPPRM)
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18. Emission Inventories
 Short-term (1-hour) emission rates
 Potential to be used as permit limits
 Intermittent emission units (e.g., emergency
generators, intermittent emission scenarios such as
startup/shutdown operations or alternative fuels)
• Latest guidance indicates following form of
standard as guideline for what to include (i.e., 99th
percentile (4th highest))
 Stack characteristics (height, temperature, velocity,
diameter, location)
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19. Meteorological Data
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20. Meteorological Data
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21. Meteorological Data
 5 years of National Weather Service data
 Minimum of 1 year of onsite data
 Surface characteristics and topography
surrounding the facility should be similar to
(representative of) those surrounding the
meteorological station
 If no representative meteorological data are
available, SO2 implementation guidance
suggests possibility of using AERSCREEN (with
agency approval)
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22. Terrain Data
 “Ambient Air”
 “that portion of the
atmosphere, external to
buildings, to which the
general public has access”
or “the air everywhere
outside of a contiguous plant
property to which public
access is precluded by a
fence or other effective
physical barrier”
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23. Building Downwash
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24. Building Downwash
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25. NAAQS Modeling
Demonstration
Approach

26. Full NAAQS Evaluation
 Includes facility and other local facilities
 Any modeled emission rates should be
acceptable as a 1-hour permit limit with
the appropriate margin for compliance
 Considerations for accounting for
emissions during startup and shutdown
 Emergency unit considerations
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27. Local Sources
 NAAQS evaluation must include sources
that result in a “significant concentration
gradient” in the vicinity of the facility
 Same emission rate considerations apply
for local sources (although permit limit
concerns wouldn’t apply)
 State agency typically dictates which local
sources to include in evaluation
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28. NAAQS Modeling Strategy
 Start with an evaluation of each individual
emission source
 Each source will have different factors that
drive resulting ambient concentrations
 The cumulative ambient concentration
from all sources (plus background) will be
evaluated against the NAAQS
 Evaluate each source against the NAAQS
as a first step
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29. NAAQS Modeling Strategy
 Big picture factors that will drive ambient
concentrations for individual sources:
• Elevated emission rates
• Stack velocity (orientation of release and
flowrate)
• Stack temperature (plume buoyancy)
• Stack height versus surrounding terrain
• Surrounding buildings and structures (i.e.,
building downwash)
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30. Hypothetical Modeling Examples
 Modeling of a hypothetical facility with the
following SO2 emission sources:
• Process SO2 source
• Fuel oil combustion SO2 source
• Backup engine source
 NAAQS modeling evaluation is based on
SO2 potential-to-emit
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31. Hypothetical Facility Terrain
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32. “Process” SO2 Source
 SO2 Emission Rate: 240 lb/hr (CEMS)
 Stack Height: 290 feet
 Stack Diameter: 16.5 feet
 Exhaust Temp: 350 °F
 Exhaust Flow: 230,000 acfm
 Elevated emission rate, buoyant source,
tall stack (taller than the tallest buildings at
the facility)
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33. Process SO2 Source Impacts
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34. Process SO2 Source Impacts
 Highest impacts in complex terrain far from
facility
 Wind speed doesn’t match location of elevated
concentrations
 Impacts occur during periods of atmospheric
stability and low mixing heights (typically early
morning, low wind speed conditions)
 High concentrations due partially to the
limitations of the AERMOD dispersion model
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35. Combustion SO2 Source
 SO2 Emission Rate: 20 lb/hr (AP-42)
 Stack Height: 60 feet
 Stack Diameter: 2 feet
 Exhaust Temp: 225 °F
 Exhaust Flow: 16,000 acfm
 Buoyant source, short stack (shorter than
the tallest buildings at the facility)
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36. Combustion SO2 Source Impacts
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37. Combustion SO2 Source Impacts
 Elevated concentrations are closer to the
facility
 Building downwash effects have a
noticeable impact on ambient
concentrations
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38. Engine SO2 Source
 SO2 Emission Rate: 3 lb/hr (Vendor)
 Stack Height: 10 feet
 Stack Diameter: 1.3 feet
 Exhaust Temp: 935 °F
 Exhaust Flow: Horizontal Discharge
 Horizontal discharge, short stack
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39. Engine SO2 Source Impacts
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40. Engine SO2 Source Impacts
 Elevated ambient concentrations at the
facility fenceline for two reasons:
• Low stack height (10 feet)
• No plume buoyancy due to horizontal
discharge
 Ambient air considerations become very
important (i.e., public access)
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41. Modeling Refinements
 “Process” SO2 Emission Source:
• Stack height increase is technically and
economically infeasible
• Raw materials are fixed due to product
and consumer demand
• Upgrades to the scrubber could achieve
control: ~30% more control (~170 lb/hr)
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42. Process SO2 Source Impacts (Before)
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43. Process SO2 Source Impacts (After)
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44. Modeling Refinements
 Combustion SO2 Emission Source:
• Stack height increase is technically and
economically infeasible
• Fuel oil firing is desirable due to cost savings
considerations
• Raw materials to the source bring inherent
scrubbing capacity: 50 to 65% based on
previous studies
• 50% inherent scrubbing brings emission rate
to 10 lb/hr (justify through testing)
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45. Combustion SO2 Source Impacts (Before)
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46. Combustion SO2 Source Impacts (After)
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47. Modeling Refinements
 Engine SO2 Emission Source:
• Simplest fix is to change the stack
discharge orientation from horizontal to
vertical
• No changes to the vendor-guaranteed
emission rate of the engine
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48. Engine SO2 Source Impacts (Before)
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49. Engine SO2 Source Impacts (After)
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50. Cumulative Concentrations
 The facility must cumulatively comply with
the NAAQS
 Addressing each individual source helps
as a first cut
 This scenario still exceeds the 1-hour
NAAQS for SO2 when the sources are
taken cumulatively
 Haven’t even considered ambient
background concentrations
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51. Modeling Strategies
 Emissions Strategies
• Actual Distribution of Emissions
• Evaluate adequacy of emission limits
• Evaluate emissions control options
• Evaluate alternate fuels and fuel specifications
• Evaluate alternate raw material
 Facility Fence Line Strategies
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52. Modeling Strategies
 Stack/Exhaust Strategies:
• Combined source exhausts
• Co-located exhaust points to increase
buoyancy
• Turn horizontal stacks vertical
• Increase stack heights
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53. Modeling Strategies
 Temporal pairing approach
 Plume transport time
 Surrounding surface characteristics
 Wind speed monitor thresholds
 Mechanical mixing height
considerations
 Alternative models (e.g., CALPUFF)
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54. Modeling Strategies
 Use of PTE emissions and AERMOD can
over estimate concentrations
 Know issues with certain terrain and
meteorological conditions
 Consider Ambient SO2 Monitoring to
compare to AERMOD results
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55. Ambient SO2
Monitoring

56. Ambient SO2 Monitoring
 What’s involved in conducting an ambient
SO2 Monitoring program?
• Who should consider?
• Equipment
• Sighting Considerations
• Pros/Cons
• Cost
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57. Ambient SO2 Monitoring
 Who Should Consider?
• Facilities that have conducted modeling with
unfavorable results, however:
 Recommend conducting exploratory
monitoring to assess conditions first.
 If favorable work with state to develop a
approved monitoring plan.
 Who Should Not Consider?
• Facilities that have conducted modeling with
favorable results.
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58. Ambient SO2 Monitoring Equipment
 Thermo 43i – Pulsed Fluorescence SO2
Analyzer
 Thermo 146i – Multigas Calibrator
 Thermo 111 – Zero Air Supply
 Air Compressor
 SO2 Calibration Cylinder Gas
 Climate Controlled Shelter
 Co-located Meteorological Tower
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59. Ambient SO2 Monitoring
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60. Ambient SO2 Monitoring
 How do you decide where to site an
ambient SO2 monitor?
• Typically sighted using air dispersion
modeling (i.e., AERMOD).
• Should Consider multiple monitors if
possible.
 Up-wind, down-wind, and other “hot
zones” (i.e., building downwash)
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61. Ambient SO2 Monitoring Pros
 Pros
• Collection of monitoring data below the SO2
NAAQS.
• Monitoring data could be used to discount air
quality modeling results.
• Potentially avoid need for permit limits,
pollution controls, fuel restrictions, or shutting
down operations.
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62. Ambient SO2 Monitoring Cons
 Cons
• Collection of monitoring data above the SO2
NAAQS.
• Potential changes to SO2 NAAQS SIP
maintenance process.
• Time involved.
• Cost
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63. Ambient SO2 Monitoring
 Engineering
• $8K – $15K
 Equipment Cost
• $75K – $100K
 Installation Cost
• $25K – $50K
 Operational Cost (Quarterly assurance, data collection
and review)
• $25K – $75K
 Potential partnering opportunities with “neighbors” to split
cost.
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64. Final Thoughts
 States developing their modeling plans now
 States will reach out to request information and/or modeling
 Be involved with the SIP process:
• Provide states with good information
• Conduct your own modeling (either for the state or in
parallel with the state)
 Avoid surprises (new limits) at the end of the SIP process
 Consider collection of ambient SO2 monitoring data
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65. Questions?
Dan Dix
ddix@all4inc.com
(610) 933-5246 x18
2393 Kimberton Road
PO Box 299
Kimberton, PA 19442
All4 Inc.
www.all4inc.com
www.enviroreview.com
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