What YOU Need to Know About the 1-hour NAAQS Implementation Process
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This document provides an overview and summary of the implementation process for the new 1-hour National Ambient Air Quality Standards (NAAQS) for sulfur dioxide. It discusses the schedule for state implementation plans, outlines how states will use air quality modeling to determine attainment designations, and provides examples of how facilities may conduct dispersion modeling to demonstrate compliance. The webinar also covers the basics of air quality modeling including emission inventories, meteorological data, terrain, and building downwash inputs. Finally, it demonstrates modeling approaches through a hypothetical example facility and discusses strategies facilities can consider to refine their modeling.
What YOU Need to Know About the 1-hour NAAQS Implementation Process
- 1. What YOU Need to Know About the 1-hour NAAQS Implementation Process Dan P. Dix Colin T. McCall November 17, 2011 An All4 Inc. Webinar Brought to you by EnviroReviewTM
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- 3. Agenda Summary of NAAQS NAAQS Implementation Updates Dispersion Modeling Basics and Inputs NAAQS Modeling Demonstration Approach 3
- 4. 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 4
- 5. National Ambient Air Quality Standards (NAAQS)
- 6. 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 6
- 7. NAAQS Summary Historic NAAQS Revised NAAQS Pollutant Averaging Period (µg/m3) (µg/m3) 1-Hour 40,000 40,000 CO 8-Hour 10,000 10,000 Ozone 8-Hour 75 ppb Withdrawn Pb 3-Month Rolling 1.5 0.15 PM10 24-Hour 150 150 24-Hour 65 35 PM2.5 Annual 15 15 1-Hour N/A 188 NO2 Annual 100 100 1-Hour N/A 196 3-Hour 1,300 1,300 SO2 24-hour 365 Revoked Annual 80 Revoked 7
- 8. 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 8
- 9. NAAQS Implementation Updates
- 10. 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 (including air quality modeling for individual facilities) • August 2017: Full NAAQS compliance in all areas 10
- 11. SO2 NAAQS Monitoring Data 11
- 12. Implementation Update 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 need to decide: • Modeling now for nonattainment designations • Model after June 2012 for the June 2013 maintenance SIP States or facilities conducting modeling? 12
- 13. 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) 13
- 14. 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 14
- 15. 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 15
- 16. Dispersion Modeling Basics and Inputs
- 17. 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 17
- 18. Air Quality Modeling Steps 1. Emission Inventory 2. Meteorological Data (AERMET/AERSURFACE) 3. Terrain Data (AERMAP) 4. Building Downwash (BPIPPRM) 18
- 19. 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) 19
- 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) 21
- 22. Terrain Data “Ambient Air” Public access must be restricted in some way (e.g., fence, security guard) in order for onsite receptors to be disregarded in the modeling analysis 22
- 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 26
- 27. Modeled Emission Rate Examples Combination Boiler SO2 modeling: • Bark: > 97% of the annual heat input to the boiler • Boiler fires 3% sulfur residual oil as a backup fuel • Annual NAAQS modeling: 0.025 lb/MMBtu x Annual Heat Input • 1-hour NAAQS modeling: 3.14 lb/MMBtu at the oil firing capacity of the boiler Do we have the appropriate exhaust information (e.g., temperature, flowrate) to model the oil firing scenario? 27
- 28. Modeled Emission Rate Examples Power Boiler SO2 Modeling: • Fires fuel oil and natural gas • Current emission limit: 24-hour limit; compliance demonstrated using a CEMS • Evaluate the impact of using the 24-hour emission limit as a modeled 1-hour emission rate • One year of CEMS data: rare hourly exceedances of the 24-hour limit, but they do occur • Operations need to be managed more tightly to ensure compliance with a 1-hour limit, flexibility is lost 28
- 29. Modeled Emission Rate Examples Low-Odor Recovery Furnace: • Typical operations: < 5 ppm SO2 during black liquor solids firing • Startup scenario: 2% sulfur fuel oil • Do we need to account for startup emissions and exhaust characteristics of the recovery furnace? • U.S. EPA has given states flexibility; decision will depend on the state agency • No bright line for the annual startup/shutdown duration that is said to significantly contribute to the distribution of 1-hour daily maximum concentrations 29
- 30. 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 30
- 31. 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 31
- 32. 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) 32
- 33. Hypothetical Modeling Example 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 33
- 35. “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) 35
- 36. Process SO2 Source Impacts 36
- 37. 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 37
- 38. 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) 38
- 39. Combustion SO2 Source Impacts 39
- 40. Combustion SO2 Source Impacts Elevated concentrations are closer to the facility Building downwash effects have a noticeable impact on ambient concentrations 40
- 41. 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 41
- 42. Engine SO2 Source Impacts 42
- 43. 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) 43
- 44. 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) 44
- 45. Process SO2 Source Impacts (Before) 45
- 46. Process SO2 Source Impacts (After) 46
- 47. 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) 47
- 48. Combustion SO2 Source Impacts (Before) 48
- 49. Combustion SO2 Source Impacts (After) 49
- 50. 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 50
- 51. Engine SO2 Source Impacts (Before) 51
- 52. Engine SO2 Source Impacts (After) 52
- 53. 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 53
- 54. Modeling Strategies Emissions Strategies Actual Distribution of Emissions • Evaluate adequacy of emission limits • Evaluate emissions control options • Evaluate alternate fuels and fuel specifications Facility Fence Line Strategies 54
- 55. Modeling Strategies Stack/Exhaust Strategies: • Combined source exhausts • Co-located exhaust points to increase buoyancy • Turn horizontal stacks vertical • Increase stack heights 55
- 56. Modeling Strategies Temporal pairing approach Plume transport time Surrounding surface characteristics Wind speed monitor thresholds Mechanical mixing height considerations Alternative models (e.g., CALPUFF) 56
- 57. 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 57
- 58. Questions? We will follow up with questions submitted during the presentation that were not answered Please feel free to e-mail or call us with additional questions and we will follow up with you 58
- 59. Questions? Dan Dix Colin McCall ddix@all4inc.com cmccall@all4inc.com (610) 933-5246 x18 (706) 221-7688 x14 2393 Kimberton Road 5900 River Road PO Box 299 Suite 500 Kimberton, PA 19442 Columbus, GA 31904 All4 Inc. www.all4inc.com www.enviroreview.com 59