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Air Dispersion Modeling Guidelines

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Air Dispersion Modeling Guidelines Air Quality Modeling Guidelines for Arizona Air Quality Permits PREPARED BY: FACILITIES EMISSIONS CONTROL SECTION AIR QUALITY DIVISION ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY November 1, 2019 TABLE OF CONTENTS 1 INTRODUCTION.......................................................................................................... 1 1.1 Overview of Regulatory Modeling ........................................................................... 1 1.2 Purpose of an Air Quality Modeling Analysis .......................................................... 2 1.3 Authority for Modeling ............................................................................................. 3 1.4 Acceptable Models.................................................................................................... 3 1.5 Overview of Modeling Protocols and Checklists ..................................................... 4 1.6 Overview of Modeling Reports ................................................................................ 5 2 LEVELS OF MODELING ANALYSIS SOPHISTICATION .................................. 5 2.1 Screening Models or Screening Techniques ............................................................. 6 2.1.1 Screening Models for Near-Field Assessments ................................................. 6 2.1.2 Screening Techniques for Long-Range Transport Assessments ....................... 7 2.2 Refined Modeling ..................................................................................................... 8 2.2.1 AERMOD .......................................................................................................... 9 2.2.2 Photochemical Grid Models .............................................................................. 9 3 MODELING ANALYSIS FEATURES ..................................................................... 10 3.1 Modeling Worst-Case Scenarios............................................................................. 10 3.1.1 Emissions Profiles ............................................................................................ 11 3.1.2 Load Analyses .................................................................................................. 12 3.1.3 Emission Caps .................................................................................................. 12 3.2 Modeling Emissions Inventory ............................................................................... 13 3.3 Types of Sources ..................................................................................................... 13 3.3.1 Point Sources ................................................................................................... 13 3.3.2 Volume Sources ............................................................................................... 14 3.3.3 Area Sources .................................................................................................... 15 3.3.4 Line Sources ..................................................................................................... 16 3.3.5 Road Emission Sources .................................................................................... 16 3.3.6 Flares ................................................................................................................ 18 3.3.7 Open Pit Sources .............................................................................................. 19 3.3.8 Pseudo Point / Non-Standard Point Source ..................................................... 19 3.3.9 Buoyant Line Sources ...................................................................................... 20 3.3.10 Emission Point Collocation ............................................................................ 21 3.4 Ambient Air Boundary ........................................................................................... 21 3.4.1 Definition of General Public ............................................................................ 22 3.4.2 Public Access ................................................................................................... 22 3.4.3 Ambient Air Boundary Determination ............................................................ 23 3.5 Modeling Coordinate Systems ................................................................................ 24 3.6 Receptor Networks.................................................................................................. 24 3.7 Rural/Urban Classification ...................................................................................... 26 3.8 Meteorological Data................................................................................................ 28 3.8.1 Representativeness of Meteorological Data ..................................................... 28 3.8.2 NWS Meteorological Data ............................................................................... 29 3.8.3 Site-Specific Meteorological Data ................................................................... 30 3.8.4 Prognostic Meteorological Data ...................................................................... 32 3.8.5 Surface Characteristic ...................................................................................... 33 i 3.9 Building Downwash and GEP Stack Height .......................................................... 34 3.10 Background Concentrations .................................................................................. 35 3.10.1 Background Concentration Determination .................................................... 35 3.10.2 Model Nearby Sources ................................................................................... 37 3.10.3 Site-Specific Ambient Air Monitoring .......................................................... 38 3.11 Modeled Design Concentrations ........................................................................... 38 4 ADEQ PERMITTING JURISDICTION AND CLASSIFICATIONS ................... 41 4.1 Air Quality Permitting Jurisdiction in Arizona ....................................................... 41 4.2 Modeling for Permits and Registration ................................................................... 44 4.2.1 Classes of Permits and Registration ................................................................. 44 4.2.2 Modeling Requirements for Permits ................................................................ 45 5 MODELING REQUIREMENTS UNDER MINOR NSR PROGRAM ................. 47 5.1 Modeling Demonstration for Attainment Pollutants............................................... 48 5.2. Modeling Demonstration for Nonattainment Pollutants ........................................ 49 6 MODELING REQUIREMENTS FOR PSD SOURCES ......................................... 51 6.1 NAAQS Analyses for Pollutants That Do Not Trigger PSD .................................. 51 6.2 Overview of PSD Modeling Procedures ................................................................. 51 6.2.1 NAAQS Modeling Inventory ........................................................................... 53 6.2.2 Increment Modeling Inventory ........................................................................ 54 6.2.3 Additional Impact Analyses ............................................................................. 56 6.2.4 Class I Area Impact Analyses .......................................................................... 57 7 SPECIAL MODELING ISSUES ................................................................................ 59 7.1 Modeling for 1-hour NO2........................................................................................ 59 7.1.1 Emission Rate .................................................................................................. 60 7.1.2 Significant Impact Level .................................................................................. 60 7.1.3 Three-tiered Approach for 1-hour NO2 Modeling ........................................... 60 7.1.4 Determining Background Concentrations ........................................................ 61 7.1.5 In-Stack NO2/NOX Ratio .................................................................................. 64 7.1.6 Treatment of Intermittent Sources ................................................................... 64 7.1.7 Modeling Demonstration with the 1-hour NO2 NAAQS ................................. 65 7.2 Modeling for 1-hour SO2 ........................................................................................ 67 7.2.1 Emission Rate .................................................................................................. 67 7.2.2 Significant Impact Level .................................................................................. 68 7.2.3 Determining Background Concentrations ........................................................ 68 7.2.4 Treatment of Intermittent Sources ................................................................... 69 7.2.5 Modeling Demonstration with the 1-hour SO2 NAAQS ................................. 69 7.3 Modeling for PM2.5 ................................................................................................. 70 7.3.1 Significant Monitoring Concentration and Significant Impact Levels ............ 71 7.3.2 Modeling Primary PM2.5 and Secondarily Formed PM2.5 ................................ 72 7.3.3 Emission Inventories ........................................................................................ 75 7.3.4 Background Concentration .............................................................................
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