Attainment with the New NAAQS and What You Need to Know About Air Dispersion Modeling
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Attainment with the New NAAQS and What You Need to Know About Air Dispersion Modeling



ALL4's Dan Dix presented at the Pennsylvania Chamber Environmental and Energy Conference & Trade Show about the basics of air dispersion modeling and what facilities can do to determine where they ...

ALL4's Dan Dix presented at the Pennsylvania Chamber Environmental and Energy Conference & Trade Show about the basics of air dispersion modeling and what facilities can do to determine where they stand with the NAAQS.



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Attainment with the New NAAQS and What You Need to Know About Air Dispersion Modeling Attainment with the New NAAQS and What You Need to Know About Air Dispersion Modeling Presentation Transcript

  • Attainment with the NewNAAQS and What You Need to Know About Air Dispersion Modeling Dan P. Dix Pennsylvania Chamber Environmental and Energy Conference & Trade Show April 18, 2012
  • Agenda  Summary of NAAQS  PSD Modeling Procedures  NAAQS Implementation Updates  Dispersion Modeling Basics and Inputs  NAAQS Modeling Demonstration Approach2
  • 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  www.all4inc.com3 View slide
  • About ALL4  ALL4’s customized environmental regulatory update service.  Includes concise tabular summary of changes and events in state, local, and/or federal regulations based on previous months environmental activity.  Also Includes a regular consulting call with an environmental expert to discuss how the activities in report impact your business.4 View slide
  • National Ambient Air Quality Standards (NAAQS)
  • 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 years6
  • 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 Revoked7
  • 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 data8
  • PSD Air QualityModeling Analysis
  • PSD Modeling Analysis PSD Significance Pollutant Levels (TPY) CO 100 Pb 0.6 So what happens PM 25 PM10 15 when PSD PM2.5 10 Significance Level NO2 40 SO2 40 are exceeded as H2SO4 10 part of a PSD TRS 10 H2S 10 permit application? VOC 4010
  • SIL Analysis  Project related emission increases are modeled and compared to the Significant Impact Levels (SILs).  A SIL exists for each NAAQS and is used as a screening approach to determine if a full NAAQS and PSD Increment Analysis is required.11
  • SIL Analysis SIL Pollutant Averaging Period (µg/m3) 1-Hour 2,000 CO 8-Hour 500 Pb 3-Month Rolling 1.5 PM10 24-Hour 5 24-Hour 1.2 PM2.5 Annual 0.3 NO2 1-Hour 7.5 1-Hour 7.9 SO2 3-Hour 25 If project related emissions result in predicted concentrations greater than the SIL, a NAAQS and PSD Increment Analysis is required.12
  • NAAQS Analysis  Facility wide PTE emissions must be modeled for any pollutant resulting in project related emissions greater than the SIL.  Local sources within 50 kilometers plus the Significant Impact Area (SIA) must be included.  Background concentrations from representative monitors must be included.  The cumulative impacts from all three must then be compared to the NAAQS.13
  • PSD Increment Analysis  A facility wide emission inventory must be prepared for the actual emission increases that occurred since the major source baseline date (the time at which the first PSD project was completed for an area) and compared to the PSD Increment Levels.  Since these emissions are typically difficult to calculate, conservatively use either the NAAQS (PTE) emission rates or actual emissions from the most recent two years.14
  • PSD Increment Analysis Class I PSD Class II PSD Class III PSD Pollutant Averaging Period Increment Increment Increment (µg/m3) (µg/m3) (µg/m3) 1-Hour None None None CO 8-Hour None None None PM10 24-Hour 8 30 None 24-Hour N/A N/A None PM2.5 Annual N/A N/A None 1-Hour N/A N/A None NO2 Annual 2.5 25 None 1-Hour N/A N/A None SO2 3-Hour 25 512 None15
  • AQRV Analysis  An Air Quality Related Value (AQRV) Analysis must be completed for any Class I area within 300 kilometers of the facility.  The CALPUFF model is used for Class I areas located more than 50 kilometers away.  What is a Class I area? • National parks greater than 6,000 acres that existed before 1977. • Wilderness areas greater than 5,000 acres that existed before 1977 and are operated by the U.S. Forest Service or the U.S. Fish and Wildlife Service.  Q/d Screening Approach16
  • 17
  • NAAQSImplementation Updates
  • 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 areas19
  • Implementation Update  Draft guidance for states to evaluate designations using AERMOD was released on September 22, 2011  Numerous comments received on draft guidance.  On April 12, 2012 Gina McCarthy (U.S. EPA Assistant Administrator) issued a letter to all States stating that modeling demonstrations showing attainment of the standard for areas initially designated “unclassifiable” will no longer be required for the June 2013 SIP Submittals.  Instead U.S. EPA will be conducting “Stakeholder Outreach” in order to discuss a workable approach for implementation of the new standard. 
  • 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)21
  • 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 population22
  • SO2 NAAQS Implementation  Facilities may wish to install on-site meteorological tower, co-located SODAR, and ambient SO2 measurements • Collection of one-year of on-site meteorological data • Collection of 3+ years of measurement data for SO2 NAAQS • Track concurrent hourly SO2 emissions • Evaluate performance of AERMOD or EPA-approved alternative model • Propose modeling approach using evaluation results as guidance23
  • Dispersion Modeling Basics and Inputs
  • 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 Rates25
  • AERMOD Modeling System26
  • Air Quality Modeling Steps 1. Emission Inventory 2. Meteorological Data (AERMET/AERSURFACE) 3. Terrain Data (AERMAP) 4. Building Downwash (BPIPPRM)27
  • 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) for SO2 or 98th percentile (8th highest) for NO2 & PM2.5)  Stack characteristics (height, temperature, velocity, diameter, location)28
  • Meteorological Data29
  • 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)30
  • 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 analysis31
  • Building Downwash32
  • Building Downwash33
  • NAAQS Modeling Demonstration Approach
  • Full NAAQS Evaluation  Includes facility, other local facilities, and background concentrations  Any modeled emission rates should be acceptable as a 1-hour permit limit (for NO2 and SO2) with the appropriate margin for compliance  Considerations for accounting for emissions during startup and shutdown  Emergency unit considerations35
  • Local Sources  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  Typically 50km + Significant Impact Area (SIA)36
  • 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 step37
  • 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)38
  • Hypothetical Modeling Example  Modeling of a hypothetical facility with the following SO2 emission sources: • Process SO2 source • Backup engine source  NAAQS modeling evaluation is based on SO2 potential-to-emit39
  • Hypothetical Facility Terrain40
  • “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)41
  • Process SO2 Source Impacts42
  • 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 model43
  • 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)44
  • 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 stack45
  • Engine SO2 Source Impacts46
  • 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)47
  • 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)48
  • Process SO2 Source Impacts (Before)49
  • Process SO2 Source Impacts (After)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 engine51
  • Engine SO2 Source Impacts (Before)52
  • Engine SO2 Source Impacts (After)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 concentrations54
  • 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 Strategies55
  • Modeling Strategies  Stack/Exhaust Strategies: • Combined source exhausts • Co-located exhaust points to increase buoyancy • Turn horizontal stacks vertical • Increase stack heights56
  • Modeling Strategies  Plume transport time  Surrounding surface characteristics  Wind speed monitor thresholds  Mechanical mixing height considerations  Alternative models (e.g., CALPUFF)57
  • Final Thoughts  PSD Modeling • New 1-hour SO2 and NO2 standards extremely stringent  Conduct modeling for planning purposes  Consider doing through attorney under attorney-client privilege  Your facility could be modeled if another nearby source is conducting PSD modeling  SIP Implementation Modeling • Be involved in U.S. EPA’s Stakeholder Outreach process • Be Aware that Environmental Group are modeling facilities with publically available information • Consider collecting site-specific meteorological and SO2 ambient monitoring data58
  • Questions? Dan Dix (610) 933-5246 x18 2393 Kimberton Road PO Box 299 Kimberton, PA 19442 All4 Inc. www.enviroreview.com59