Technical Support Document EPA’s 2011 National-scale Air Toxics Assessment 2011 NATA TSD December 2015 Office of Air Quality, Planning, and Standards Research Triangle Park North Carolina 27711 EPA’s National-scale Air Toxics Assessment This page intentionally left blank. ii EPA’s National-scale Air Toxics Assessment This page intentionally left blank. iii EPA’s National-scale Air Toxics Assessment This page intentionally left blank. iv EPA’s National-scale Air Toxics Assessment Contents List of Exhibits ......................................................................................................................................... viii Common Acronyms and Abbreviations .................................................................................................... x 1 Background and Introduction ............................................................................................................... 1 1.1 The Purpose of this Document ......................................................................................................... 1 1.2 What NATA Is ................................................................................................................................. 2 1.3 The History of NATA ...................................................................................................................... 3 1.4 How States and EPA Use NATA Results ........................................................................................ 4 1.5 How NATA Results Should Not Be Used ....................................................................................... 5 1.6 The Risk Assessment Framework NATA Uses ............................................................................... 6 1.7 The Scope of NATA ........................................................................................................................ 7 1.7.1 Sources of Air Toxic Emissions that NATA Addresses ....................................................... 8 1.7.2 Stressors that NATA Evaluates............................................................................................. 8 1.7.3 Exposure Pathways, Routes, and Time Frames for NATA ................................................ 10 1.7.4 Receptors that NATA Characterizes ................................................................................... 11 1.7.5 Endpoints and Measures: Results of NATA ....................................................................... 11 1.8 Model Design ................................................................................................................................. 12 1.8.1 The Strengths and Weaknesses of the Model Design ......................................................... 14 2 Emissions ............................................................................................................................................... 17 2.1 Sources of Emissions Data ............................................................................................................. 17 2.1.1 Developing NATA Emissions from the 2011 NEI ............................................................. 19 2.1.2 Categorization of the NATA Emissions in the NATA Output Data ................................... 23 2.1.3 Modifications to NEI Emissions Data ................................................................................ 25 2.1.4 2011 NATA Emissions: CMAQ versus HEM-3 ................................................................. 27 2.2 Emissions Preparation for CMAQ ................................................................................................. 29 2.2.1 Emission Inventories and Approaches: CMAQ .................................................................. 29 2.2.2 Emissions Processing Steps and Ancillary Data ................................................................. 38 2.3 Emissions Preparation for HEM-3 ................................................................................................. 52 2.3.1 Overview of Differences in Emissions Processing Between CMAQ and HEM- 3 .......................................................................................................................................... 52 2.3.2 HEM Run Groups ............................................................................................................... 55 2.3.3 Point Excluding Airports .................................................................................................... 58 2.3.4 Point: Airports ..................................................................................................................... 64 2.3.5 Nonpoint HEM Run Groups: NP10m and NPOtherLow .................................................... 69 2.3.6 Nonpoint HEM Run Groups: CMVs .................................................................................. 70 2.3.7 Nonpoint HEM Run Groups: RWC .................................................................................... 70 2.3.8 Nonroad HEM Run Group .................................................................................................. 72 2.3.9 Onroad HEM Run Groups: Light Duty and Heavy Duty ................................................... 73 2.4 Source Groups ................................................................................................................................ 75 2.5 Uncertainties in Emissions/Emissions Processing ......................................................................... 77 2.6 Summary ........................................................................................................................................ 78 3 Air Quality Modeling & Characterization ......................................................................................... 79 3.1 Hybrid Model Description ............................................................................................................. 79 3.1.1 Overview ............................................................................................................................. 79 3.1.2 Treatment of Species ........................................................................................................... 81 v EPA’s National-scale Air Toxics Assessment 3.1.3 Meteorological Processing .................................................................................................. 81 3.1.4 Emissions Processing Overview ......................................................................................... 82 3.1.5 Initial and Boundary Conditions ......................................................................................... 82 3.1.6 Source Attribution ............................................................................................................... 82 3.2 Treatment of Non-hybrid Air Toxics and Areas Outside the CONUS .......................................... 83 3.2.1 Background Concentrations ................................................................................................ 83 3.3 Model Evaluation ........................................................................................................................... 86 3.3.1 Overview ............................................................................................................................. 87 3.3.2 Observations ....................................................................................................................... 87 3.3.3 Model Performance Statistics ............................................................................................. 88 3.3.4 Hybrid Evaluation ............................................................................................................... 89 3.3.5 Non-hybrid Evaluation ...................................................................................................... 103 3.4 Summary ...................................................................................................................................... 105 4 Estimating Exposures for Populations ............................................................................................. 107 4.1 Estimating Exposure Concentrations ........................................................................................... 107 4.2 About HAPEM ............................................................................................................................ 107 4.3 HAPEM Inputs and Application .................................................................................................. 108 4.3.1 Data on Ambient Air Concentrations ................................................................................ 109 4.3.2 Population Demographic Data .......................................................................................... 109 4.3.3 Data on Population Activity .............................................................................................. 109 4.3.4 Microenvironmental Data ................................................................................................. 110 4.4 Exposure Factors .......................................................................................................................... 112 4.5 Quality Assurance in Exposure Modeling ................................................................................... 113 4.6 Summary ...................................................................................................................................... 113 5 Characterizing Effects