Guidance for Air Dispersion Modeling San Joaquin Valley Air Pollution Control District Draft Prepared by Leland Villalvazo, Ester Davila, and Glenn Reed Special Thanks to Dr. Jesse Thé Of Lakes Environmental Software TABLE OF CONTENTS GUIDANCE FOR AIR DISPERSION MODELING................................................................................5 1. INTRODUCTION...........................................................................................................................5 2. APPLICATION OF MODELS.........................................................................................................5 2.1 Modeling Overview........................................................................................................5 2.2 Preferred Models...........................................................................................................5 2.2.1 AERMOD ...................................................................................................................6 2.2.2 ISCST3 and ISC-PRIME Overview ............................................................................7 2.2.3 SCREEN3 Overview ..................................................................................................8 2.3 ISC and AERMOD Model Comparison .........................................................................9 2.4 Alternative Models.........................................................................................................9 2.5 Model Validations........................................................................................................10 3. A TIERED APPROACH FOR ASSESSING COMPLIANCE WITH AIR STANDARDS & GUIDELINES...................................................................................................................................11 4. MODEL INPUT DATA .................................................................................................................12 4.1 Comparison of Screening and Refined Model Requirements .....................................12 4.1.1 SCREEN3 Air Dispersion Modeling .........................................................................13 4.1.2 AERMOD Air Dispersion Modeling...........................................................................14 4.1.3 ISC-PRIME Air Dispersion Modeling........................................................................15 4.2 Regulatory and Non-Regulatory Option Use...............................................................16 4.5 Defining Sources.........................................................................................................17 4.5.1 Selection, Description and Parameters ....................................................................17 4.5.2 Source Grouping ......................................................................................................24 4.5.3 Special Considerations ............................................................................................24 4.5.4 Variable Emissions...................................................................................................26 4.5.5 Plant Shutdowns and Start-Ups ...............................................................................27 4.6 Building Impacts..........................................................................................................28 4.6.1 Good Engineering Practice (GEP) Stack Heights and Structure Influence Zones....28 4.6.2 Defining Buildings ....................................................................................................30 4.7 Multiple Pollutants .......................................................................................................32 4.7.1 Standard Approaches to Modeling Multiple Pollutants from Multiple Sources .........32 4.7.2 Unitized Emission Rate and Summation Concepts ..................................................33 5. GEOGRAPHICAL INFORMATION INPUTS................................................................................34 5.1 Comparison of Screening and Refined Model Requirements .....................................34 5.2 Coordinate System......................................................................................................34 5.2.1 Local ........................................................................................................................34 5.2.2 UTM .........................................................................................................................35 5.3 Terrain.........................................................................................................................35 5.3.1 Terrain Concerns in Short-Range Modeling.............................................................35 5.3.2 Flat and Complex Terrain.........................................................................................35 5.3.3 Criteria for Use of Terrain Data ................................................................................36 5.3.4 Obtaining Terrain Data.............................................................................................36 5.3.5 Preparing Terrain Data for Model Use .....................................................................36 5.4 Land Use Characterization..........................................................................................37 5.4.1 Wind Direction Dependent Land Use .......................................................................40 5.4.2 Mixed Land Use Types ............................................................................................41 5.4.3 Seasonal Land Use Characterization.......................................................................41 5.4.4 Standard and Non-Default Surface Characteristics..................................................41 2 of 101 08/06 Rev 1.2 5.4.5 Defining Urban and Rural Conditions.......................................................................41 6. METEOROLOGICAL DATA ........................................................................................................43 6.1 Comparison of Screening and Refined Model Requirements .....................................43 6.2 Preparing Meteorological Data for Refined Modeling..................................................43 6.2.1 Hourly Surface Data.................................................................................................43 6.2.2 Mixing Height and Upper Air Data............................................................................44 6.2.3 AERMET and the AERMOD Model..........................................................................45 6.2.4 PCRAMMET and the ISC Models ............................................................................45 6.3 Regional Meteorological Data .....................................................................................46 6.3.1 Pre-Processing Steps ..............................................................................................47 6.3.2 Availability and Use of District Meteorological Data .................................................48 6.4 Data Assessment: Reliability, Completeness and Representativeness ......................49 6.5 Expectations for Local Meteorological Data Use.........................................................49 7. RECEPTOR LOCATIONS...........................................................................................................50 7.1 Receptor Types...........................................................................................................50 7.1.1 Cartesian Receptor Grids.........................................................................................50 7.1.2 Polar Receptor Grids................................................................................................50 7.1.3 Multi-Tier Grids.........................................................................................................51 7.1.4 Fenceline Receptors ................................................................................................52 7.1.5 Discrete & Sensitive Receptors................................................................................52 7.2 Minimum Receptor Requirements for Capturing and Assessing Maxima ...................53 7.2.1 Polar Grid.................................................................................................................53 7.2.2 Cartesian Grid ..........................................................................................................54 8. OTHER MODELING CONSIDERATIONS...................................................................................55 8.1 Explanation for Alternative Model Use ........................................................................55 8.2 Use of Modeled Results in Combination with Monitoring Data....................................56 8.3 Information for Inclusion in a Modeling Assessment ...................................................56 9. GLOSSARY OF TERMS .............................................................................................................57 APPENDIX A:..................................................................................................................................60 1.0 Permit Health Risk Assessments ...........................................................................60 1.1 Exposure Duration Adjustment...............................................................................60 1.2 Food Grade Products and Pre-Cleaned Material ...................................................60