The HEM4 User's Guide
Instructions for using the Human Exposure Model
for Single and Multiple Facility Exposure and Risk Modeling
Open-Source Version 4.2
with Demographic Assessment Module
and 2020 Census
January 2023
Prepared by:
SC&A Incorporated
•I'SC.A
1414 Raleigh Road, Suite 450
Chapel Hill, NC 27517
Prepared for:
Air Toxics Assessment Group
Health and Environmental Impacts Division
Office of Air Quality Planning & Standards
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
GSA Contract 47QRAA20D002W
BPA 68HERD21A0003
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Disclaimer
The development of HEM4 and this User's Guide has been
funded by the United States Environmental Protection Agency
under contracts EP-D-06-119, EP-W-12-011, and GSA
47QRAA20D002W (BPA 68HERD21A0003) to SC&A Inc.
However, the information presented in this User's Guide does
not necessarily reflect the views of the Agency. No official
endorsement should be inferred for products mentioned in this
document.
HEM4 User's Guide
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Contents
Disclaimer ii
Contents iii
Figures vi
Tables viii
1. Introduction 1
1.1 Organization of the HEM4 User's Guide 1
1.2 Main Features of HEM4 2
1.3 Differences Between HEM4 and 2019 Version of HEM-3 4
1.4 Strengths, Limitations and Uncertainties of HEM4 7
1.5 Requirements for Running HEM4 8
2. Installing HEM4 9
2.1 Downloading the HEM4 Program 9
2.2 Downloading Chemical Health Effects Data 10
2.2.1 Description of Chemical Health Effects Library 10
2.3 Downloading Census Data 12
2.3.1 Description of Census Library 12
2.4 Downloading Meteorological Data 13
2.4.1 Description of Meteorological Library 13
3. Preparing HEM4 Input Files 16
3.1 Overview and General Rules 16
3.2 Facility List Options File 19
3.2.1 Fields in the Facility List Options File 19
3.2.2 Meteorological Station and Period Options 24
3.2.3 Dispersion Environment Options: Rural or Urban 24
3.2.4 Modeling Domain Options 25
3.2.5 Acute Options 28
3.2.6 Deposition and Depletion Options 29
3.2.7 Elevation Option 33
3.2.8 User Receptors Option 34
3.2.9 Building Downwash Option 34
3.2.10 FASTALL Option 34
3.2.11 Emissions Variation Option 35
3.3 HAP Emissions File 35
3.3.1 Pollutant Emissions per Source 36
3.3.2 Percent Particulate for Deposition and Depletion 37
3.4 Emissions Location File 37
3.4.1 Source Types and Parameter Requirements 42
3.4.2 Particle Deposition Method 47
3.5 Additional Input Files 47
3.5.1 Polygon Vertex Input File for Modeling Polygon Emission Sources 47
3.5.2 Buoyant Line Parameter Input File for Modeling Buoyant Line Sources 50
3.5.3 Particle Data Input File for Modeling Particulate Deposition and Depletion 52
3.5.4 Input Files Required for Modeling Vapor Deposition and Depletion 53
3.5.5 Building Dimensions Input File for Modeling Building Downwash 57
3.5.6 User-Defined Receptors File 58
3.5.7 Emissions Variation Input Files 60
3.5.8 Alternate Receptors File 64
3.5.9 Census Update File 66
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3.5.10 Updating the Chemical Unit Risk Estimates and Health Benchmarks Input Files .68
4. Step-by-Step Instructions for Running HEM4 69
4.1 Provide Standard Input Files and Indicate Receptors 71
4.2 Provide Additional Input Files 73
4.3 Provide Deposition and Depletion Input Files 74
4.4 Check HEM4 Log 76
4.5 Summarize Risks 77
4.6 Assess Demographics of Modeled Population 79
4.7 Analyze Outputs 82
4.7.1 HEM4 Outputs 82
4.7.2 Demographic Assessment Outputs 86
4.8 Revise Census Data Option 89
4.9 Error Messages and Failed Runs 89
5. HEM4 Modeling Calculations for Each Facility 94
5.1 Dispersion Modeling 94
5.1.1 Regulatory Default, ALPHA and BETA Options 94
5.1.2 Dilution Factors 95
5.2 Estimating Risks and Hazard Indices 95
5.2.1 Explicit Modeling of Inner Receptors, User Receptors and Polar Receptors 95
5.2.2 Interpolated Modeling of Outer Receptors using the Polar Receptor Network 97
5.2.3 Maximum Individual Risks, Hazard Indices, and Hazard Quotients 98
5.2.4 Maximum Offsite Impacts 98
5.2.5 Contributions of Different Pollutants and Emission Sources 98
5.3 Population Exposures and Incidence 99
5.4 Summarizing Human Health Impacts 101
6. HEM4 Output Files 102
6.1 Facility-Specific Outputs 102
6.1.1 Maximum Individual Risk 102
6.1.2 Maximum Offsite Impacts 104
6.1.3 Risk Breakdown 104
6.1.4 Block Summary Chronic 105
6.1.5 Ring Summary Chronic 106
6.1.6 Source Risk KMZ Image 107
6.1.7 Incidence 108
6.1.8 Cancer Risk Exposure 109
6.1.9 Noncancer Risk Exposure 109
6.1.10 All Inner Receptors 110
6.1.11 All Outer Receptors 110
6.1.12 All Polar Receptors 111
6.1.13 AERMOD Outputs 112
6.1.14 Input Selection Options 114
6.1.15 Acute Maximum Concentrations (Optional) 115
6.1.16 Acute Populated Concentrations (Optional) 115
6.1.17 Acute Breakdown (Optional) 117
6.2 Run Group Outputs 117
6.2.1 Facility Max Risk and HI 117
6.2.2 Facility Cancer Risk Exposure 118
6.2.3 Facility TOSHI Exposure 119
6.2.4 Additional Run Group Outputs 119
7. Risk Summary Reports 120
7.1 Facility-Specific Summaries 120
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7.1.1 Cancer Drivers Summary 120
7.1.2 Hazard Index Drivers Summary 121
7.1.3 Acute Impacts Summary 121
7.1.4 Multipathway Summary 122
7.1.5 Max Concentration Summary 124
7.1.6 Max Risk and HI by Source and Pollutant Summary 124
7.2 Run Group Summaries 125
7.2.1 Max Risk and Hazard Indices Summary 125
7.2.2 Risk Histogram Summary 126
7.2.3 Hazard Index Histogram Summary 127
7.2.4 Incidence Drivers Summary 128
7.2.5 Source Type Risk Histogram Summary 128
8. Demographic Assessment Methodology & Results 130
8.1 U.S. Census Source Data and Demographic Methodology 130
8.2 Discussion of Sample Demographic Results 132
9. Understanding the Risk Results 140
10. Quality Assurance Remodeling 142
11. References 146
12. Appendix A: Sample HEM4 Output Files 149
13. Appendix B: Demographic Assessment Calculations 168
B.1 Total Population Risks 168
B.2 Race, Ethnicity and Age Categories 169
B.3 Level of Education 169
B.4 Poverty Level 170
B.5 Linguistic Isolation 170
B.6 Demographic Defaults 171
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Figures
Figure 1. HEM4 Meteorological Stations 15
Figure 2. Example Orientations of Area Emission Sources for the HEM4 Model 46
Figure 3. HEM4 Title Screen 71
Figure 4. Run HEM4 with U.S. Census Receptors 72
Figure 5. Run HEM4 with Alternate Receptors 72
Figure 6. Confirm HEM4 Run Pop-Up Start Box 73
Figure 7. Provide Additional Input Files 74
Figure 8. Provide Deposition and Depletion Input Files 75
Figure 9. Log Screen 77
Figure 10. Run the Risk Summary Programs 78
Figure 11. Demographic Assessment Screen 80
Figure 12. Sample Demographic Assessment Run Combinations 81
Figure 13. View and Analyze Outputs 82
Figure 14. Hazard Index Drivers File Opened via Spreadsheet App 83
Figure 15. Select Data to Plot Widget 83
Figure 16. Chronic Risk Map shown in Google Earth™ 84
Figure 17. Acute Map View of HTML File 85
Figure 18. Example Graphical Visualization of Incidence by Pollutant and Source Type 86
Figure 19. The Demographic Assessment Bar Graph under "Analyze Outputs" 87
Figure 20. The Demographic Assessment Map of Facilities under "Analyze Outputs" 88
Figure 21. Revise Census Data Screen 89
Figure 22. Sample Google Earth™ Map of Results 108
Figure 23. Sample Cancer Drivers Summary Output 120
Figure 24. Sample Hazard Index Drivers Summary Output 121
Figure 25. Sample Acute Impacts Summary Output (abbreviated) 123
Figure 26. Sample Multipathway Summary Output 123
Figure 27. Sample Max Concentration Summary 124
Figure 28. Sample Max Risk and HI by Source and Pollutant Summary 125
Figure 29. Sample Max Risk Summary Output 126
Figure 30. Sample Risk Histogram Summary Output 127
Figure 31. Sample Hazard Index Histogram Summary Output (Partial) 127
Figure 32. Sample Incidence Drivers Summary Output 128
Figure 33. Sample Sourcetype_Histogram_Sorted RTR Summary Output 129
Figure 34. Sample Demographic Assessment Output: Distribution of Cancer Risk for Racial and
Ethnic Categories 135
Figure 35. Sample Demographic Assessment Output: Proximity and Average Risk Summary
137
Figure 36. Sample Demographic Assessment Output: Population at Risk Summary 138
Figure 37. Sample Demographic Assessment Output: EJ Summary 139
Figure 38. Sample Source_risk.kmz HEM4 Output 143
Figure 39. Sample Maximum Individual Risk HEM4 Output (facility-specific) 149
Figure 40. Sample Maximum Offsite Risk HEM4 Output (facility-specific) 149
Figure 41. Sample Risk Breakdown HEM4 Output (facility-specific, abbreviated) 150
Figure 42. Sample Block Summary Chronic HEM4 Output (facility-specific, abbreviated) 151
Figure 43. Sample Ring Summary Chronic HEM4 Output (facility-specific, abbreviated) 152
Figure 44. Sample Source Risk KMZ Google Earth™ Image (facility-specific) 153
Figure 45. Sample Incidence HEM4 Output (facility-specific, abbreviated) 154
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Figure 46. Sample Cancer Risk Exposure HEM4 Output (facility-specific) 155
Figure 47. Sample Noncancer Risk Exposure HEM4 Output (facility-specific) 155
Figure 48. Sample All Inner Receptors HEM4 Output (facility-specific, abbreviated) 156
Figure 49. Sample All Outer Receptors HEM4 Output file (facility-specific, abbreviated) 157
Figure 50. Sample All Polar Receptors HEM4 Output file (facility-specific, abbreviated) 158
Figure 51. Sample AERMOD.inp file (facility-specific, abbreviated) 159
Figure 52. Sample AERMOD.out file (facility-specific, abbreviated) 160
Figure 53. Sample plotfile. pit output file (facility-specific, abbreviated) 161
Figure 54. Sample maxhour.plt output file (optional facility-specific, abbreviated) 162
Figure 55. Sample Input Selection Options HEM4 Output file (facility-specific, abbreviated) ..163
Figure 56. Sample Acute Maximum Concentrations HEM4 Output file (optional facility specific,
abbreviated) 163
Figure 57. Sample Acute Populated Concentrations HEM4 Output file (optional facility-specific,
abbreviated) 164
Figure 58. Sample Acute Breakdown HEM4 Output file (optional facility-specific) 164
Figure 59. Sample Facility Max Risk and HI HEM4 Output file (for run group, abbreviated) ...165
Figure 60. Sample Facility Cancer Risk Exposure HEM4 Output file (for run group) 165
Figure 61. Sample Facility TOSHI Exposure HEM4 Output file (for run group) 165
Figure 62. Sample All Facility Source Locations Google Earth™ Image (for run group) 166
Figure 63. Sample HEM4 Log Output file (for run group, abbreviated) 167
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Tables
Table 1. Summary of Key Improvements for HEM4.2 versus 2019 HEM-3 6
Table 2. Fields in the Facility List Options Input File (Required) 19
Table 3. Sample Deposition and Depletion Options and Model Results 31
Table 4. Format Guidelines for the HAP Emissions Input File (Required) 35
Table 5. Sample HAP Emissions Input File 36
Table 6. Fields in the Emissions Location Input File (Required) 38
Table 7. Sample Emissions Location Input File 41
Table 8. Format Guidelines for the Polygon Vertex File 48
Table 9. Sample Polygon Vertex File 49
Table 10. Format Guidelines for the Buoyant Line Parameter Input File 51
Table 11. Sample Buoyant Line Parameter Input File 51
Table 12. Format Guidelines for the Particle Data Input File 52
Table 13. Sample Particle Data Input File 53
Table 14. Format Guidelines for Land Use Input File 55
Table 15. Sample Input File for Land Use 55
Table 16. Format Guidelines for Month-to-Seasons Input File 56
Table 17. Sample Month-to-Seasons Input File 56
Table 18. Format Guidelines for the Building Dimensions File 57
Table 19. Sample Building Dimensions Input File 58
Table 20. Format Guidelines for the User-Defined Receptors File 59
Table 21. Sample Input File for User-Defined Receptors 60
Table 22. Format Guidelines for the Emissions Variation Input Files 62
Table 23. Sample Emissions Variation File based on Hour of Day (24 factors) 63
Table 24. Sample Emissions Variation File based on Month (12 factors) 63
Table 25. Sample Emissions Variation File based on Season and Hour of Day (96 factors) ....63
Table 26. Sample Emissions Variation File based on Wind Speed (6 factors) 63
Table 27. Format Guidelines for Alternate Receptors File (CSV) 65
Table 28. Sample Input File for Alternate Receptor Input File 65
Table 29. Format Guidelines for the Census Update File 67
Table 30. Sample Census Update File 67
Table 31. Summary of HEM4 Sample Template Input Files 69
Table 32. Sample List of Error Messages and Causes in HEM4 90
Table 33. Fields Included in the Maximum Individual Risk & Maximum Offsite Impacts Files.103
Table 34. Fields Included in the Risk Breakdown File 105
Table 35. Fields Included in the Block Summary and Ring Summary Chronic Files 107
Table 36. Fields Included in the Incidence File 109
Table 37. Fields Included in the All Inner and All Outer Receptor Files 111
Table 38. Fields included in the All Polar Receptors File 112
Table 39. Fields included in the Acute Chem Max and Acute Chem Pop Files 116
Table 40. Summary of Census Data used for Demographic Groups 132
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1. Introduction
The Human Exposure Model Open-Source Version 4.2 ("HEM4") is a streamlined, but rigorous
tool you can use for estimating ambient concentrations, human exposures and health risks that
may result from air pollutant emissions from complex industrial facilities. HEM4 can be used to
model impacts from a single facility or from multiple facilities located across the United States
(U.S.) and its territories, as well as outside the U.S. anywhere in the world. HEM4 is designed
for use by the U.S. Environmental Protection Agency (EPA), states, local agencies, industry,
and other stakeholders, and is currently used in the Risk & Technology Review (RTR)
assessments by EPA of regulated source categories. In RTR assessments, HEM4 is used to
model emissions and the resulting ambient concentrations from hundreds of facilities, whether
located within close proximity or thousands of miles away from each other. The model then
predicts the potential exposures and inhalation health risks posed by these emissions, including
in zones with combined impacts from multiple nearby facilities. Compared to its predecessor
HEM-3, HEM4 incorporates additional front-end and back-end features and capabilities in the
model platform including: more modeling options, risk summary reports that summarize the
cancer risk and noncancer health impacts from the modeled emissions, browser-based
graphical viewing and analysis tools, and incorporated demographic assessments of the
modeled population to analyze potential environmental justice impacts. HEM4 enables the user
to model air concentrations, risk, and health impacts at U.S. Census block receptors as well as
at user-defined receptors inside or outside the U.S. HEM4 is available for download at
http://www.epa.qov/fera/download-human-exposure-model-hem.
1.1 Organization of the HEM4 User's Guide
This User's Guide is organized into 11 sections plus appendices:
Section
1
HEM4's main features, limitations, and requirements
Section
2
Installation instructions for HEM4 and its data libraries
Section
3
Preparing input files for HEM4 run
Section
4
Step-by-step instructions for running HEM4
Section
5
Calculations performed by HEM4 for each modeled facility
Section
6
Facility-specific outputs
Section
7
Risk summary outputs describing all facilities in run group
Section
8
Demographic assessment results for each facility and for run group
Section
9
Using HEM4's outputs to understand the modeled risk results
Section
10
Quality assurance remodeling
Section
11
References
Appendices
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1.2 Main Features of HEM4
HEM4 performs four main operations: dispersion modeling, estimation of population exposure,
estimation of human health risks, and demographic assessment. For dispersion modeling, the
American Meteorological Society - U.S. EPA Regulatory Model (AERMOD) is run by HEM4 as a
compiled executable program. AERMOD is a state-of-the-science Gaussian plume dispersion
model that EPA prefers for most industrial source modeling applications for air toxics
applications (EPA 2005). AERMOD was developed under the auspices of the American
Meteorological Society - Environmental Protection Agency Regulatory Model Improvement
Committee (AERMIC) as summarized on EPA's AERMOD website. (See
https://www.epa.qov/scram/air-qualitv-dispersion-modelinq-preferred-and-recommended-
models#aermod for all AERMOD model documentation as well as links to AERMOD's
preprocessors, AERMET, AERMAP, AERSCREEN, AERSURFACE and BPIPPRIM and post-
processor, LEADPOST.)
This version 4.2 of HEM incorporates AERMOD version 22112, which was originally made
available to the public in June 2022 (EPA 2022a, EPA 2022b). AERMOD can model dispersion
of emissions from a wide range of different source types that may be associated with an
industrial source complex (or "facility") including stack sources, area sources, and volume
sources. Additionally, AERMOD is capable of modeling polygon, line, and buoyant line source
types. AERMOD can also model emissions that vary in time or with wind speed, deposition with
or without plume depletion, and other complex plume processes such as building downwash.
HEM4 supplies AERMOD with meteorological data pre-processed by AERMET and required for
AERMOD's dispersion calculations. HEM4's Meteorology Library contains meteorological
("met") data from over 800 observation stations across the continental U.S., Alaska, Hawaii, and
Puerto Rico. Section 2.4 provides information on how to download the met data used by HEM4,
discusses how the met files were processed and the data contained in each, and includes a
national map of the locations for all met stations. HEM4 runs AERMOD as many times as is
necessary to address the gaseous and particulate pollutants emitted from each modeled facility.
AERMOD outputs annual average ambient concentrations at discretely modeled receptor
locations, through the simulation of hour-by-hour dispersions from the emission sources into the
surrounding atmosphere.
For U.S. emission sources, after running AERMOD for dispersion modeling, HEM4 estimates
population exposure and human health risks by drawing on additional data libraries that are
provided with the model, including a U.S. Census Library and a Chemical (Pollutant) Health
Effects Library. The Census Library of census block internal point ("centroid") locations and
populations provides the basis of human exposure calculations. The model includes location
and population data from the 2020 U.S. Census. HEM4 draws upon the Census Library to
identify all census block locations within the study domain as defined by the default modeling
radius around each facility or a radius that you specify. The Census Library includes locations
and populations, elevations, and controlling hill heights for all the approximately 5.8 million
populated blocks tabulated in the 2020 U.S. Census (Census 2022a). Section 2.3 provides
information on how to download the census data and discusses the data contained in HEM4's
Census Library.
Alternatively, HEM4 can model without the U.S. Census Library by using Alternate Receptors
that the user can provide within the U.S. or anywhere in the world.
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HEM4 uses the Chemical Health Effects Library of pollutant unit risk estimates (UREs) and
reference concentrations (RfCs) to calculate population cancer risks and noncancer health
hazards, respectively. These UREs and RfCs are based on the latest values recommended by
the EPA for hazardous air pollutants (HAP) and other toxic air pollutants. More information on
how EPA uses these dose-response values in risk assessments, including the source for these
values, is provided on EPA's Dose-Response Assessment webpage (EPA 2021a) and in
Section 2.2.
Using the air concentration results from AERMOD in combination with the data supplied by
HEM4's Census and Chemical Health Effects Libraries, HEM4 estimates cancer risks and
noncancer health hazards ("risks") resulting from inhalation exposure at census block locations
and at other receptor locations that you may specify. Unlike the previous HEM-3 version of the
model, HEM4 can also be used outside the U.S. to predict concentrations and risk at receptors
specified by the user surrounding emission sources anywhere in the world. The predicted risk
estimates are generally conservative with respect to the modeled emissions because they are
not adjusted for attenuating exposure factors (such as indoor/outdoor concentration ratios, daily
hours spent away from the residential receptor site, and years of lifetime spent living elsewhere
than the current residential receptor site).
HEM4 computes cancer risks using the EPA's UREs for HAP and other toxic air pollutants. The
resulting estimates reflect the risk of developing cancer for an individual breathing the ambient
air at a given receptor site 24 hours per day over a 70-year lifetime. HEM4 estimates noncancer
health hazards or "risks" using hazard quotients (HQs) and hazard indices for 14 target organs
and systems. The HQ for a given pollutant and receptor site is the ratio of the ambient
concentration of the pollutant to the RfC at which (and below which) no adverse noncancer
health effects are expected. The chronic hazard index (HI) for a given target organ is the sum of
HQs for substances that affect that organ. HEM4 computes target organ-specific hazard indices
(TOSHIs) for the following 14 organ systems: the respiratory system; the liver; the neurological
system; developmental effects; the reproductive system; the kidneys; the ocular system; the
endocrine system; the hematological system; the immunological system; the skeletal system;
the spleen; the thyroid; and whole body effects. Like the cancer risk estimates, noncancer
hazard indices are not adjusted for attenuating exposure factors and are therefore considered
conservative estimates.
Optionally, HEM4 can estimate acute (short-term, such as hourly) concentrations for each
pollutant and receptor site, including the location of the maximum acute concentration for each
pollutant emitted from the facility. In addition, the model outputs a listing of the associated acute
benchmarks for each pollutant at or below which certain acute adverse effects are not expected.
From these acute concentrations and benchmarks, the ratio of the maximum acute
concentration to the associated benchmark is computed to determine the maximum acute HQ
for each pollutant of concern. Acute noncancer HQs, like chronic noncancer TOSHIs and cancer
risk are conservative estimates in HEM4. Section 2.2.1 discusses the terms URE, RfC, HQ, HI
and TOSHI in more detail.
HEM4 estimates the predicted lifetime cancer risk, chronic noncancer TOSHIs, annual
concentrations, and (optionally) acute concentrations at every receptor location, and identifies
receptor locations where the impact is highest. For these locations, the model gives the
concentrations of the modeled pollutants emitted from each emission source driving the overall
cancer risks, chronic TOSHIs, and acute impacts. The model also estimates the number of
people exposed to various cancer risk levels and TOSHI levels as a result of the modeled
emissions.
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HEM4 provides these results for each individual modeled facility and also consolidates facility-
specific results into output files that provide results for all modeled facilities as a group. HEM4's
post-processors, the risk summary programs, produce additional outputs of combined and
summarized results that are useful in capturing the risk and health hazards, as well as the
pollutant and emission source drivers of these impacts, for a group of modeled facilities as a
whole (e.g., an entire source category of facilities modeled under the EPA's RTR program).
HEM4 provides a browser-based option of viewing all the summarized results in graphical form,
including an interactive map of the facilities modeled, pie and bar charts of overall cancer
incidence, population risks, and pollutant and source risk drivers, and an interactive table of the
main results for each facility.
Finally, when modeling with U.S. Census receptors, HEM4's Demographic Assessment module
can be used to link the modeled population in each facility domain - including cancer and
noncancer risk estimates for that population - to demographic information from the Census'
American Community Survey (ACS) on race and ethnicity, age, poverty status, educational
attainment, and linguistic isolation (Census 2022b). HEM4 also provides these demographic
data at the county, state, and nationwide levels for comparison. The Demographic Assessment
module thereby allows for the identification of potentially disproportionate cancer and noncancer
risks posed by the modeled emissions to certain demographic groups within the modeled
population. HEM4 also provides an interactive browser-based option for viewing each modeled
facility's demographic results in comparison to other modeled facilities, and in comparison to the
county, state, and nationwide demographic breakdowns.
1.3 Differences Between HEM4 and 2019 Version of HEM-3
HEM was originally developed as a screening tool for exposure assessment in the 1980s (EPA
1986). The original model was upgraded to run in a Windows™ environment, eventually called
HEM-3, and regularly improved and re-released by EPA in several HEM-3 versions over the
years, including most recently in 2007, 2014, 2017 and 2019. HEM4 is written in the open-
source software language Python™, while HEM-3 is written in the FoxPro® language, last
published by Microsoft® in 2007 and now unsupported. HEM4 version 4.1 was originally
released to the public in September 2021. This version 4.2 ("HEM4.2") includes the same
capabilities and features as version 4.1 but updates the Census data from the 2010 Decennial
to the 2020 Decennial population data, the ACS demographic data from 2015-2019 to 2016-
2020 five-year averages, and AERMOD to the latest version 22112 released in June 2022.
Compared to HEM-3, HEM4 includes additional modeling and analysis capabilities, improved
and streamlined user interfaces, as well as enhanced graphical output capabilities, as listed
below.
• HEM4 bases model selection options primarily on the data in your input files, rather than
on responses to user interface questions, which is less prone to user error.
• HEM4 performs consistency checks on your input files and includes more specific and
instructive error messages, to aid you in rectifying any errors or inconsistencies in your
input files before the model run begins.
• HEM4 can model impacts anywhere in the world with user-provided "alternate
receptors", in addition to U.S. Census block receptors.
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HEM4 (version 4.2) includes the 2020 Decennial Census population data and the 2016-
2020 five-year average ACS demographic data.
• HEM4 includes an integrated processor to change the U.S. Census database you use to
model by zeroing out block populations, moving blocks, and/or deleting blocks.
• HEM4 (version 4.2) includes a more precise determination of the dispersion
environment, rural or urban, based on the Census 2020 population density surrounding
each facility. The previous method was based on coarser Census 2010 urbanized areas.
• HEM4 includes meteorological data based primarily on 2019 observations.
• HEM4 will default to using the full year of selected met data, but you may instead model
with a specified period of met data by indicating a start and end date and even hour.
• HEM4 allows you to specify the exact location of the facility center or use the center
location calculated by the model.
• HEM4 allows you to specify polar ring distances or use the polar ring locations
calculated by the model.
• HEM4 allows you to choose Method 1 or Method 2 for particle deposition. Method 2
requires less knowledge of the particle size distribution of your emissions compared to
Method 1, which requires a detailed particle size input file.
• HEM4 allows you to choose a different acute high value for each facility (e.g., maximum,
99th percentile, 98th percentile), rather than modeling each facility with the same
maximum acute value.
• HEM4 incorporates buoyant line updates including modeling of multiple buoyant line
source groups, each with different parameters, for a given facility.
• HEM4 includes the Risk Summary Report programs (previously called the RTR
Summary Programs) integrated into the model itself, rather than as an add-on suite of
programs.
• HEM4's Risk Summary Reports are enhanced. The HI Histogram output accounts for all
14 TOSHIs (not just three). The Incidence Drivers output is now sorted in descending
order of pollutant-specific incidence and includes the pollutant's percentage contribution
to total incidence. The Source Type Risk Histogram output includes the maximum
overall risk histogram and incidence for all modeled facilities in your run group, in
addition to the histogram and incidence specific to each source type.
• In addition to spreadsheet output files, HEM4 includes enhanced capabilities for
visualization and analysis of outputs, including browser-based interactive tables, graphs,
and mapping options.
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• HEM4 includes an integrated Demographic Assessment module, which allows you to
assess the demographics of the people within user-specified proximities to modeled
emissions and the demographics of the people at risk from the modeled emissions.
• In addition to the enhancements listed above, HEM4 has maintained all the capabilities
of the 2019 HEM-3 version, which included numerous enhancements compared to the
previous versions.
These HEM4.2 enhancements in comparison to the 2019 version of HEM-3 are listed below in
Table 1.
Table 1. Summary of Key Improvements for HEM4.2 versus 2019 HEM-3
Model Feature
HEM4.2
2019 HEM-3
Software language
Written in open-source
Python™ language
Written in Microsoft FoxPro®
language, now unsupported
Minimal user interface
Model options based primarily
on data in input files; less prone
to user error
Model options based on input
files as well as responses to
user interface questions;
more prone to user error
Error messages
Input file inconsistency checks
are automatically made prior to
model run with more specific
and instructive error messages
to aid user in correcting errors
pre-run
Error messages were not
specific enough and did not
capture many input file
inconsistencies prior to runs
Receptor enhancement and
flexibility
Modeling can occur anywhere
in the world because users can
specify alternate populated
receptors in lieu of U.S. Census
blocks
Only U.S. modeling was
possible because U.S.
Census receptor data was
required for any model run
Census data update
Includes the 2020 Decennial
population data and 2016-2020
ACS demographics
Included the 2010 Decennial
population data only
Census database revisions
Census blocks may be revised
or removed using an integrated
processor
Census database could not
be edited by user
Rural versus Urban
dispersion
Based on a more precise
determination of the 2020
population density surrounding
each facility
Based on a coarser
determination using Census
2010 urbanized areas
Meteorological data update
Includes met data based on
2019 observations primarily
Included met data based on
2014-2016 observations
Meteorological Period
Options
Period start and end fields
allow you to specify exactly
what met period HEM4 should
instruct AERMOD to use for
your modeling run, down to the
year, month, day and even hour
HEM-3 always used the
default annual period of met
data
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Model Feature
HEM4.2
2019 HEM-3
Facility center
User may specify the location
of the facility center
The facility center was always
calculated by model based on
source locations
Polar ring distances
User may specify polar ring
distances or use defaults
Polar ring distances were set
by default only
Particle deposition
User can choose AERMOD's
Method 1 or 2 to model particle
deposition. Method 2 requires
less particle data.
Particle deposition was
always modeled via
AERMOD Method 1, which
requires detailed particle size
distribution data
Acute high value
User can specify a different
percentile to use as the acute
high value for each facility
The same maximum value
had to be used for every
facility in the modeling run
Buoyant line update
User can specify different
parameters for the modeling of
multiple buoyant line
sources/groups per facility
Only one set of average
parameters for a buoyant line
source were allowed
Risk Summary programs
Risk Summary Programs are
integrated into HEM4
RTR Summary Programs
were a separate executable
Risk Summary report
enhancements
The HI Histogram output
accounts for all 14 TOSHIs.
The Incidence Drivers output is
sorted in descending order of
pollutant-specific incidence and
includes the pollutant's
percentage contribution to total
incidence. The Source Type
Risk Histogram output includes
the maximum overall histogram
for the run group.
HEM-3 accounted for only 3
TOSHIs in the HI Histogram
output. HEM-3's Incidence
Drivers output was unsorted
and did not include the
percentage that each
pollutant contributes to the
total incidence. HEM-3's
Source Type Risk Histogram
did not include the maximum
overall column for the run.
Graphical outputs
Browser-based interactive
tables, graphs, and mapping
options for visualization and
analysis of outputs, in addition
to spreadsheet output files
Graphical output options were
not available in HEM-3
Demographic Assessment
The Demographic Assessment
module allows evaluation of the
demographics surrounding
modeled emissions, including
demographic-specific risk.
HEM-3 did not include an
integrated way to assess
demographics of the
communities surrounding
modeled emissions.
1.4 Strengths, Limitations and Uncertainties of HEM4
HEM4 is designed to perform detailed and rigorous analyses of chronic and acute air pollution
risks for populations located near industrial emission sources. The model was previously
updated with the goal of simplifying the running of AERMOD without sacrificing any of
AERMOD's strengths. In keeping with this goal, you can specify complex emission source
configurations, including point sources for stacks, area and volume sources for fugitive
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emissions, obliquely oriented area sources for roadways, line sources for airport runways,
buoyant line sources for roof vents, and polygon sources for a variety of area source shapes
including entire census blocks and tracts. The model identifies all receptors located near each
facility, including census blocks (if in the U.S.) and alternate receptors. You can also specify the
locations of individual houses, schools, facility boundaries, monitors, or other user-defined
receptors to model. HEM4/AERMOD can account for impacts of terrain, building downwash
effects, pollutant deposition and plume depletion, and temporally varying emissions. HEM4 also
analyzes multiple pollutants concurrently, with the capability of including particulate and
gaseous pollutants in the same model run.
However, HEM4's framework has some limitations and incorporated uncertainties. As noted
earlier, HEM4's concentrations are estimated using AERMOD and subject to AERMOD's
uncertainties and limitations. While AERMOD is considered state-of-the-science for Gaussian
plume dispersion (not considering secondary air pollutant formation), like all air pollutant
dispersion models, AERMOD is subject to uncertainties as described more on EPA's AERMOD
webpage (See studies and support documents listed under "Model Supporting Documents" on
https://www.epa.gov/scram/air-quality-dispersion-modeling-preferred-and-recommended-
models). HEM4 also incorporates the uncertainties associated with its dose response estimates.
Pollutant UREs for cancer, RfCs for noncancer HI, and benchmarks for acute health effects are
subject to uncertainties as described more on EPA's Dose-Response Assessment webpage
(EPA 2021a). Another limitation of HEM4 is that when modeling with census block receptors in
the U.S. the model estimates pollutant concentrations and risks for the block centroid, as
defined by the U.S. Census Bureau. Values calculated for this internal point are not
representative of the range of values over the entire block, and may not represent where most
people reside within a block. Furthermore, these values do not account for the movement of
people from their home census blocks to other census blocks, due to commuting or other daily
activities. In addition, as previously noted, HEM4 calculates outdoor concentrations of air
pollutants. These concentrations do not account for indoor sources of pollution, or the reduction
of outdoor pollution in conditioned indoor air.
HEM4 performs several tests on user input data—including ensuring consistency of input files
and some parameters—before using AERMOD to calculate air pollution impacts. However,
there are some potential problems users may introduce to their input files that HEM4 may not
detect in these initial tests (e.g., using numerical values for inputs that correspond to units other
than what HEM4/AERM0D expects, such as feet instead of meters). To avoid this, carefully
review the model input guidelines to make sure that the contents and format of your input files
meet these guidelines before launching HEM4.
1.5 Requirements for Running HEM4
You can use HEM4 on any Windows™-based personal computer running Wndows XP™ or
later. The HEM4 executable package is approximately 1.2 Gb in size once it has been
uncompressed from the zip file. Disk space requirements for running HEM4 will depend on the
number of census and meteorological files that you use. To model an individual facility, the
model requires, at minimum, 10 megabytes (MB) of disk space for a small facility and 1 to 2
gigabytes (GB) for a large, complex facility. Furthermore, disk space requirements can be 10 to
20 times larger (than 2 GB) for complex facilities located in densely populated urban areas (i.e.,
with many receptors), depending on the modeling options you choose. The full census and
meteorological libraries that you can download in addition to the model require about 3.3 GB of
space. The HEM4 model also will need a minimum of 8 GB of random-access memory (RAM).
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Once installed, you can use HEM4 to model risks and exposures for any location in the U.S. or
around the world, and for a wide range of emission source configurations.
For each model analysis, you should provide emission rates for all HAP and emission source
locations in the form of Excel™ spreadsheet files. HEM4 requires separate estimates of
emission rates of each pollutant, from each emission source, for each facility to be modeled.
The model also requires detailed information on each emission source, including location,
release height, emission velocity and temperature for point (stack) sources, and the
configuration of non-point emission sources (e.g., area sources which emit with negligible
velocity at ambient temperature). You will be able to design the model receptor network around
each facility to be modeled via an input spreadsheet file. You can also use an optional
spreadsheet file to provide the dimensions of buildings near emission sources, for use in
computing building downwash effects. When modeling particulate emissions, you can use an
optional spreadsheet file to provide particle size information and deposition parameters. If you
opt to model dry deposition of gaseous emissions, you will need to provide additional
spreadsheet input files describing the land use and vegetation surrounding the facility. You will
be prompted to indicate the location of your input spreadsheet files through user input screens,
which are discussed in more detail in Section 4, Step-by-Step Instructions for Running HEM4.
This user's guide is designed to provide all the information you will need to run HEM4. However,
some of the options for running HEM4 draw on advanced features of AERMOD. If unfamiliar
with the AERMOD dispersion model, you may need to refer to EPA's AERMOD documentation
(available at https://www.epa.gov/scram/air-guality-dispersion-modeling-preferred-and-
recommended-models#aermod.) in order to develop some of the inputs needed for HEM4 (EPA
2022a, EPA 2022b). This is particularly true for some of the more complex modeling options,
such as plume deposition and depletion, building downwash, temporal and wind speed emission
variations, and complex source configurations.
2. Installing HEM4
This section provides instructions for downloading and installing the HEM4 model and required
data libraries from the EPA's HEM Download Page.
2.1 Downloading the HEM4 Program
The HEM4 model is available from EPA's HEM Download webpage at
http://www.epa.gov/fera/download-human-exposure-model-hem. This site includes general
installation instructions, including hardware and software requirements, as well as links to
download and install HEM4 and its associated data libraries. Download the HEM4 zip install
package under "Software available for download." HEM4 can be installed anywhere on your PC
and the root folder is not required to be named HEM4. However, for the purposes of this
User's Guide, it is assumed the root folder will be named "HEM4". HEM4 is started by
running the executable file ending in ".exe". Note: The HEM4 source code is available on
github.com/USEPA/HEM4.
In addition to user-supplied inputs describing the nature and location of the emissions
(discussed in Section 3.1), HEM4 relies upon several data libraries that supply other required
inputs for a modeling run. To complete the installation of HEM4, download the following data
libraries:
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• the Chemical Health Effects Library, a.k.a. "Toxicity Value Files" containing the
hazardous air pollutant (HAP) specific dose response values and benchmark values for
affected organs. Note: upon installation, HEM4's resources folder will include a Dose
Response Library and Target Organ Endpoints table, but check this HEM Download
webpage, as well as EPA's Dose-Response Assessment webpage (EPA 2021a),
regularly for future updates to these files;
• the Census Library containing nationwide files that provide the population numbers and
terrain elevation data surrounding a facility location (based on the 2020 Census); and
• the Meteorological Library containing met station files (a surface and profile file for each
station) with data for over 800 stations nationwide.
You will find links to these data libraries on the HEM Download Page. The following sections
provide instructions for downloading these files, along with a brief description of each of these
data libraries.
2.2 Downloading Chemical Health Effects Data
HEM4 uses a chemical health effects library of pollutant unit risk estimates (UREs) and
reference concentrations (RfCs) to calculate risks for cancer and noncancer health hazards,
respectively. To download these values, click on the "Toxicity Value Files" link on EPA's HEM
Download Page (http://www.epa.gov/fera/download-human-exposure-model-hem). Before
initiating a modeling run, check for updated versions of these files on the HEM Download Page.
When updated files become available, copy these into the "resources" folder under the HEM4
directory that you selected during installation. Be sure to unzip the files and verify they are
located in the specified folder when finished. The folder for chemical health effects data is
"HEM4\resources."
2.2.1 Description of Chemical Health Effects Library
For each pollutant or HAP, the Chemical Health Effects Library includes the following
parameters, where applicable and available:
• URE for cancer;
• RfC for chronic noncancer health effects;
• reference benchmark concentration for acute health effects; and
• target organs affected by the pollutant (for chronic noncancer effects).
These parameters are based on the EPA's database of recommended dose response values for
HAP (EPA 2021a), which is updated periodically, consistent with continued research on these
parameters. The URE represents the upper-bound excess lifetime cancer risk estimated to
result from continuous exposure to an agent (HAP) at a concentration of 1 microgram per cubic
meter (|jg/m3) in air. For example, if the URE is 1.5 x 10"6 per |jg/m3, then 1.5 excess cancer
cases are expected per 1 million people, if all 1 million people were exposed daily for a lifetime
to 1 microgram of the pollutant in 1 cubic meter of air. UREs are considered plausible upper
limits to the true value; the true risk is likely to be less but could be greater (EPA 2022c).
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The RfC is a concentration estimate of a continuous inhalation exposure to the human
population that is likely to be without an appreciable "risk" of deleterious noncancer health
effects during a lifetime including to sensitive subgroups such as children, asthmatics, and the
elderly. No adverse effects are expected to result from exposure if the ratio of the potential
exposure concentration to the RfC, defined as the hazard quotient (HQ), is less than or equal to
one (1). Note that the uncertainty of the RfC estimates can span an order of magnitude. (EPA
2022c). Target organs are those organs (e.g., kidney) or organ systems (e.g., respiratory) which
may be impacted by chronic noncancer health effects from exposure to the pollutant in question.
The hazard index (HI) is the sum of hazard quotients for substances that affect the same target
organ or organ system, also known as the target organ specific hazard index (TOSHI). HEM4's
chemical health effects library includes target organs for estimating 14 TOSHIs:
• Respiratory HI;
• Liver HI;
• Neurological HI;
• Developmental HI;
• Reproductive HI;
• Kidney HI;
• Ocular HI;
• Endocrine HI;
• Hematological HI;
• Immunological HI;
• Skeletal HI;
• Spleen HI;
• Thyroid HI; and
• Whole Body HI.
The reference concentrations for acute health effects include both "no effects" reference levels
for the general public such as the California Reference Exposure Levels (RELs), and
emergency response levels, such as Acute Exposure Guideline Levels (AEGLs) and
Emergency Response Planning Guidelines (ERPGs). A more in-depth discussion of the
development and use of the health reference values may be found in the EPA's Air Toxics Risk
Assessment Library (EPA 2020), available for download at http://www.epa.qov/fera/risk-
assessment-and-modeling-air-toxics-risk-assessment-reference-library.
You can add pollutants and associated health effect values, as needed, to the two Excel™
spreadsheets comprising HEM4's Chemical Health Effects Library, the Dose Response
Library file and the Target Organ Endpoints file. These files are located in HEM4's resources
folder:
• HEM4\resources\Dose_Response_Library.xlsx; and
• HEM4\resources\Target_Organ_Endpoints.xlsx.
The Dose Response Library file includes a listing of HAP and other toxic pollutants and the
various URE values, RfC values, and acute benchmark values associated with these pollutants.
The Target Organ Endpoints file includes a listing of HAP and other toxic pollutants and the
organ(s) or organ system(s) that may be impacted with chronic noncancer health effects, by
exposure to these pollutants above the RfC level.
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Note that each pollutant you list in your facility-specific input files (discussed in Section
3.1) needs to be included and match exactly (the spelling of) a pollutant name in HEM4's
Dose Response Library file. The Target Organ Endpoints file need not contain every pollutant
listed in your inputs. You should ensure, however, that every pollutant in your input files that has
chronic noncancer health effects associated with it - and that you wish to model as such - has
an RfC value in the Dose Response Library file and is also listed in the Target Organ Endpoints
file, with the impacted organs and organ systems checked. Note: Only pollutants with RfC
values need to be listed in the Target Organ Endpoints file.
2.3 Downloading Census Data
You will need census files for the region or regions you wish to model. You can obtain
nationwide files from the 2020 Census on the HEM Download Page
(http://www.epa.gov/fera/download-human-exposure-model-hem) of EPA's FERA website.
Nationwide files are provided on a state-by-state basis in JavaScript Object Notation format
(.json). HEM4 will access census files to cover the area within 50 kilometers of each facility you
are modeling. Multiple states may be needed to model a particular facility if the facility is located
within 50 kilometers of a state boundary.
Download, unzip and copy the nationwide census files into the "census" folder under the HEM4
folder you selected during installation. Once unzipped, check to be sure that these files are now
located in the specified folders when finished. The census folder is "HEM4\census". Do not
delete the Census_key.json file (HEM4\census\Census_key.json). This file is required for HEM4
modeling runs.
2.3.1 Description of Census Library
The HEM4 Census Library includes census block identification codes, locations, populations,
elevations, and controlling hill heights for the over 5.8 million populated census blocks identified
in the 2020 Census. The location coordinates reflect an internal point selected by the Census
Bureau to be roughly in the center of the block. For complex shapes, the internal point may not
be in the geographic center of the block, but they are still referred to as "centroids" in this guide.
Locations and population data for census blocks in the 50 states and Puerto Rico are extracted
from the U.S. Census Bureau website for Census 2020 (Census 2022a).
HEM4's census database includes elevation and controlling hill height data, in addition to the
population and location data supplied by the Census Bureau. The AERMOD terrain
preprocessor program, AERMAP (EPA 2018a), was used to estimate the elevation and hill
height of each populated census block in the U.S., including Alaska, Hawaii, Puerto Rico, and
the Virgin Islands. The controlling hill height values are used for flow calculations within
AERMOD. The elevation data contained within the 2020 Census files were derived from the
United States Geological Survey National Elevation Dataset (NED) at a resolution of 1 arc
second, or about 30 meters (USGS 2022). HEM4 uses these block elevations to estimate the
elevation of each nearby polar grid receptor and the elevation of each source, if the user does
not provide source elevations, as discussed later in this guide.
The HEM4 Census Library also includes the locations for over 120,000 schools and 700
monitors. School location data are for schools spanning pre-kindergarten through high school,
and is available for both public and private schools (NCES 2022a, NCES 2022b). You can
obtain monitoring locations from the Air Toxics Data Ambient Monitoring Archive of the Ambient
Monitoring Technology Information Center (AMTIC) (EPA 2018b). Note: The precision of the
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latitude/longitude location of these monitors varies and, in some cases, is precise to only two
decimal places (roughly ± 600 meters), making comparison with HEM4 modeling results
inexact.
In addition to the above Decennial Census data (Census 2022a), demographic data from the
U.S. Census' American Community Survey (Census 2022b) is also required by HEM4 for the
Demographic Assessment module. You do not need to separately download the ACS data, as it
is already included in HEM4's "resources" folder within the HEM4 executable in two large files
named "acs.csv" and "acs-levels.csv". The demographic data used by the Demographic
Assessment module is discussed in Section 8 and in Appendix B.
2.4 Downloading Meteorological Data
HEM4 requires meteorological information for AERMOD to use for dispersion modeling, and you
can obtain nationwide meteorological data files from the HEM Download Page
(http://www.epa.gov/fera/download-human-exposure-model-hem). Each set of meteorological
files contains surface data and upper air data and is named beginning with the abbreviation for
the state in which the station is located. Generally, the closest set of stations will be most
representative of the meteorology in the modeling domain. However, there are several
situations where a different combination of meteorological stations will be more representative.
For instance, if the modeling domain is located on the Gulf of Mexico, a surface station near the
Gulf may be more representative than an inland station, even if there is a closer inland station.
Download the nationwide meteorological files from the HEM Download Page into the "MetData"
subfolder of HEM4's "aermod" folder, and unzip the met files. After unzipping, verify they are
located in the MetData subfolder of the aermod folder ("HEM4\aermod\MetData"). AERMOD
uses two files for each met station and these files have extensions of SFC (surface data) and
PFL (profile data).
Note that when you download the HEM4 model (as described in Section 2.1), the installation
package will place an Excel™ spreadsheet named "metlib_AERMOD.xlsx" in your
"HEM4\resources" folder. This spreadsheet lists all the SFC and PFL met stations that are
provided in the nationwide meteorological data files (those available on the HEM Download
Page on the date you download the model). You may edit this spreadsheet to include additional
met station files, but you must provide the new met station data as both SFC and PFL files in
your "HEM4\aermod\MetData" folder. Be careful that the SFC and PFL file names match the
new rows you have added to the metlib_AERMOD.xlsx spreadsheet in your resources folder.
You may also edit rows in this spreadsheet or delete met station entries entirely. (A Python error
message will be displayed when you initiate a model run, if HEM4 cannot locate the
metlib_AERMOD.xlsx spreadsheet in your resources folder.)
2.4.1 Description of Meteorological Library
AERMOD requires surface and upper air meteorological data that meet specific format
requirements. HEM4 includes a library of meteorological data from National Weather Service
(NWS) observation stations. The current HEM4 AERMOD Meteorological Library includes over
800 nationwide locations, depicted in Figure 1.
EPA meteorologists obtained calendar year 2019 Integrated Surface Hourly Data (ISHD) for
approximately 800 Automated Surface Observation System (ASOS) stations
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(http://www.nws.noaa.gov/asos/) spanning the entire US, as well as Puerto Rico and the US
Virgin Islands, from the National Centers for Environmental Information (NCEI) (formerly, the
National Climatic Data Center (NCDC)). The AERMOD meteorological processor, AERMET
(EPA 20226) and its supporting modeling system (AERSURFACE and AERMINUTE) were used
to process the meteorological data.
To estimate the boundary layer parameters required by AERMOD, AERMET requires hourly
surface weather observations (which may include hourly values calculated from 1-minute data)
and the full (i.e., meteorological variables reported at all levels) twice-daily upper air soundings.
The surface and upper air stations are paired to produce the required input data for AERMOD.
To support AERMET, ASOS 1-minute data for each surface station were obtained from NCEI in
a DSI 6405 format. Further, upper air sounding data for the same time period for over 80
observation sites were obtained from the National Oceanic & Atmospheric Administration
(NOAA) Earth System Research Laboratory's (ESRL) online Radiosonde Database (see
http://www.esrl.noaa.gov/raobs/General lnformation.html). These datasets were produced by
ESRL in Forecast Systems Laboratory (FSL) format.
AERMET Processing
Utilizing the AERMET meteorological data pre-processor, and the ASOS surface and FSL upper
air stations, surface and profile files for input into AERMOD were generated nationwide. The
surface stations were paired with representative upper air stations by using the upper air station
closest to each surface station. The AERSURFACE tool was used to estimate the surface
characteristics for input into AERMET utilizing land cover data surrounding the surface station.
In addition, the AERMINUTE pre-processor was used to process 1-minute ASOS wind data for
input into AERMET. The following provides more detail regarding the pre-processors, AERMET
and AERMINUTE, used to generate the AERMOD meteorological data.
• AERMET Options: Version 19191 used to process ASOS site data; surface data in NCEI
TD-3505 (ISHD) format; upper air data in FSL (all levels, tenths m/s) format; used the
ADJ_U* non-Default BETA option to adjust the friction velocity (u* or ustar) for low wind
speed stable conditions.
• AERMINUTE Options: Version 15272 used for 1-minute ASOS data in TD-6405 format
where available.
The surface files were examined for completeness. If more than 10 percent of the
meteorological data were missing within the 2019 calendar year for a station, the next previous
calendar year of meteorological data that was considered complete was used for that station in
the HEM4 meteorological database. In all, 838 met station pairs were found suitable and are
included in the HEM4 meteorological library, as depicted in Figure 1. Of these 838 met stations,
791 stations contain 2019 met data, while the rest are 2016 through 2018.
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Figure 1. HEM4 Meteorological Stations
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3. Preparing HEM4 Input Files
This section explains how to prepare the required and optional user-supplied input files for
HEM4. In addition to the instructions provided in this section regarding how to set up your input
files, especially for more advanced modeling options, it is important to review the AERMOD
documentation for further guidance (EPA 2022a, EPA 2022b).
3.1 Overview and General Rules
HEM4 requires a series of Excel™ spreadsheet files to specify the emissions and configuration
of the facilities (or facility) you are modeling. HEM4 accepts all recent Microsoft Excel™
versions using the xlsx spreadsheet format (e.g., Excel 2007 and later). It should be noted that
Excel 2007/2010, 2013, 2016, and 2019 versions have a 1,048,576-row capacity (and 16,384-
column capacity).
To use HEM4 to calculate ambient pollutant concentrations (using AERMOD), you will need the
following three files at minimum:
• a Facility List Options file, which is the primary driver of the model run listing the facilities
to be modeled and specifying the model run parameters and options;
• an Emissions Location file, which provides emission source locations and configurations
for the facilities being modeled; and
• a HAP Emissions file, which provides the names and amounts of the pollutants emitted
from each emission source at the modeled facilities.
You may also need the following additional input files, depending on the options you choose to
use in your modeling run.
• a Polygon Vertex file - this file is required if one (or more) of your sources is configured
as a polygon; it specifies the location of the polygon(s) by providing coordinates of the
vertices. Note: this file is not needed for area sources.
• a Buoyant Line Parameter file - this file is required if one (or more) of your sources is a
buoyant line; it defines the parameters for a group or groups of buoyant line sources
(with each group containing one or more buoyant lines) including average parameter
values for building length, building height, building width, line source width, building
separation (between the individual lines within a group) and buoyancy parameter.
• a Building Dimensions file - this file is required to model building downwash effects; it
describes building dimensions or other obstructions near emission sources that would
produce wake effects. Note: your Facility List Options file must indicate the facilities to
be modeled with building downwash effects.
• An Emissions Variation file - this file provides emission rate factors for individual
sources for one or more of the facilities you specify and is required to model temporally-
varying emissions (e.g., emissions reflecting diurnal, weekly, monthly, and seasonal
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variations) or emissions driven by wind speed variations. Note: your Facility List Options
file must indicate the facilities containing the sources to be modeled with emissions
variations.
• a Particle Data file - this file is required to model particulate deposition; it specifies the
particle size distribution for various size ranges.
• the Gas Parameter file (included in HEM4's resources folder) - this file is required to
model gaseous deposition; it specifies the parameters needed for modeling dry and/or
wet deposition of gaseous (vapor) pollutants including diffusion coefficients, cuticular
resistance and Henry's Law coefficients. Note: defaults are provided by the model
automatically, but you should provide pollutant-specific parameters if available by editing
the Gas_param.xlsx file as discussed in Section 3.5.4.
• a Land Use and Month-to-Seasons files - these two files are required to model dry
deposition of gaseous pollutants; they describe the land use and vegetative land cover
surrounding emission source(s) for facilities listed in the files.
• a User-Defined Receptors file - this file specifies the locations of additional discrete
receptors and is required if you want HEM4 to compute pollutant concentrations and
risks at locations you specify (e.g., houses, schools, or other sites near a facility), in
addition to U.S. census block receptors. Note: your Facility List Options file must indicate
the facilities to be modeled with user receptors.
• an Alternate Receptor file - this file is required if you wish to use receptors other than
U.S. Census block centroids in your modeling run and instead provide your own list of
receptors for modeling within the U.S. or anywhere in the world; the file specifies the ID,
location, elevation, hill height and population of the alternate receptors to be modeled.
These files are described in more detail below in Sections 3.2 through 3.5. In addition to the
above list of input files, you can optionally revise the census database using a Census Update
input file (as described below in Section 3.5.9) and revise the chemical health effect input files -
the dose response values and target organ assumptions - used in the model (as described
below in Section 3.5.10).
HEM4 will prompt you to provide the input files required for your model run by opening up
Browse lines that allow you to identify the name and location on your computer of each required
input file. Directly inputting data from spreadsheets avoids having to retype the emission rates
and other calculated parameters. However, this method of input has its drawbacks. Notably,
HEM4 will not run successfully unless you have formatted the input files exactly as specified in
the format guidelines. This section describes general rules you should follow to avoid common
mistakes. To make formatting easier, specific formatting requirements are exemplified in sample
input files, which are provided in the default "HEM4\lnputs" folder. Note: If this is your first
time running HEM4, it is highly recommended that you first run the model with the
sample input files provided, as practice, and to confirm that HEM4 installed properly on
your computer. Most of the sample input files are run-ready, except for certain more advanced
emissions variation input files with "template" in their file name (which instead provide
instructions for entering your own values before using them in a model run).
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General Rules for Input Files
• Use a separate Excel™ workbook for each input file. Ensure your Microsoft Office™
Trust Center settings allow your Excel version to be fully opened and operational (i.e.,
not in protected view only).
• Use only one input file worksheet per workbook.
• Match columns with the format specified for the input file. You can use the sample
input files and substitute actual data for the sample data. Delete any extra lines of
sample data.
• Do not insert columns between data columns. HEM4 will read these, including any extra
hidden columns, as data.
• Use the number of header rows indicated in the sample input files (included with the
HEM4 download) at the top of each spreadsheet file for all required and optional input
files.
• Do not include text in numerical data fields (for instance "<0.001"). HEM4 may read
these fields as 0s (zeroes) or may accept only a portion of the number.
• For location coordinates, HEM4 will accept latitudes and longitudes in decimal degrees
as well as Universal Transverse Mercator (UTM) coordinates. The maximum precision
HEM4 uses for latitude and longitude decimal degrees is 5 places after the
decimal. (HEM4 will convert latitudes/longitudes to UTMs for use in AERMOD.) You
must enter coordinates in the World Geodetic System of 1984 (WGS84) format.1 The
1983 North American Datum (NAD83) and the WGS84 are identical for most
applications, so no conversion is needed if using coordinates based on NAD83.
However, if coordinates are based on the 1927 North American Datum (NAD27)
geographic system format, they would need to be converted to WGS84 before being
used in HEM4.
• Match the units used for parameters, such as emission rates and stack parameters,
with the units given in the file's format guidelines provided in the following sections
(for example: meters/second, meters, tons/year, etc.). The required units are also
indicated in parentheses in the header rows of the sample input files which are included
in the "Inputs" folder of the model.
• The length and decimal places indicated in the format guidelines for each field in the
various input files is, in most cases, the suggested length based on HEM4's internal
rounding conventions. For the Source ID field, however, it should be noted that
AERMOD does not accept Source IDs longer than 8 characters.
1 WGS84, NAD83 and NAD27 are different world reference frames (a.k.a. geographic systems) that are
used as the basis for projected coordinate systems like UTMs. HEM4 uses WGS84. For more information
see https://www.nqa.mil/ProductsServices/GeodesvandGeophvsics/PaqesAA/orldGeodeticSvstem.aspx
and https://qisqeoqraphv.com/wqs84-world-qeodetic-svstem/.
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3.2 Facility List Options File
The Facility List Options Excel™ file is the primary driver specifying the parameters and options
of the modeling run and is required for any HEM4 run. This file is an enhanced version of the
Facility List Options file used in Multi HEM-3, with new columns allowing for additional features
and several columns re-arranged for more intuitive grouping of fields. The Facility List Options
file contains one row for every facility that will be run with the various modeling options listed as
columns for each facility row. If you use all default modeling options, the only field
requiring input is the Facility ID. All other fields have defaults which are employed when the
field in the Facility List Options file is left blank.
3.2.1 Fields in the Facility List Options File
Table 2 shows the fields included in the Facility List Options file. These fields are columns in the
actual Facility_List_Options.xlsx input file that you must provide to HEM4, and each row in the
actual file is for a different facility, as identified by the Facility ID. The rows in Table 2 are shown
in the same column order required by HEM4 in the input file. (For a sample template, see
HEM4_Facility_List_Options.xlsx in your HEM4 inputs folder.) The options listed in Table 2 are
described in more detail following the table.
Table 2. Fields in the Facility List Options Input File (Required)
Field
Default Setting
(if field left blank)
Description of Facility List Options Field
Facility ID
(FacilitylD)
You must enter an alphanumeric string identifying the facility
being modeled. This field is mandatory; all other fields have
default values when blank.
Met Station
(met_station)
Met station selected
by model as closest
to the facility
The name of the meteorological surface station (e.g.,
NAME02.SFC) to be used by AERMOD when modeling
each facility. The met station closest to facility is chosen
unless you specify a name.
Rural/Urban
(rural_urban)
HEM4 determines
when using U.S.
Census block
receptors; HEM4
defaults to rural for
alternate receptors
Used to set the type of dispersion environment for
AERMOD. "R" indicates rural land use surrounding the
facility; "U" indicates urban land use. If left blank when
modeling using U.S. Census block receptors, HEM4 will
determine the population density in a circular area centered
on the facility center within a radius of 3 km, based on the
2020 Census. When using alternate receptors instead of
U.S. Census block receptors, a blank in this column will
cause HEM4 to default to a rural dispersion environment.
Urban Population
(urban_pop)
Defaults to 50,000
people if left blank,
but only used and
needed if "U"
specified in
Rural/Urban field
If you indicate "U" for urban land use (in Rural/Urban field
above), then you should provide the model with the urban
population size, otherwise leave blank. Note: If you specify
"U" in the Rural/Urban field but provide no urban population
value in this field, HEM4 will use a default urban population
of 50,000 people. If you leave the Rural/Urban field blank,
then HEM4 will calculate the urban population as needed.
Max distance
(max_dist)
50,000 meters
The outside max radius of the modeling domain in meters
(must be > the modeling distance and < 50,000 meters).
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Field
Default Setting
(if field left blank)
Description of Facility List Options Field
Modeling distance
(model_dist)
3,000 meters
The cutoff distance (in meters) for individual modeling of
ambient impacts at census blocks; beyond this distance
ambient impacts are interpolated rather than explicitly
modeled. Note: For polygon source types, set the modeling
distance > the largest distance across the polygon.
Radials
(radials)
16
The number of radials in the polar receptor network
emanating from the facility center (must be > 4).
Circles
(circles)
13
The number of concentric circles in the polar receptor
network, centered on the facility center (must be > 3).
Overlap distance
(overlap_dist)
30 meters
The distance (in meters) between an emissions source and
a census block or alternate receptor within which you do not
want the receptor to be considered as a point of maximum
exposure/risk, because it might be on facility property.
Must be an integer value > 1 meter and < 500 meters.
First ring distance
(ringl)
If left blank,
calculated by HEM4
to be just outside the
source locations, but
not less than 100 m
from facility center
The distance to the first ring (circle) of the polar network as
measured from the facility center. You can override the
default distance calculated by HEM4 to fit the size and
shape of the facility properties to be modeled.
Facility Center
If left blank,
calculated by HEM4
based on the source
locations in the
emissions location
input file
You can enter the facility center location in this field to
override HEM4's (default) location. Enter as a comma
separated list that should start with either "U" (if using UTM
coordinates) or"L" (if using lat/lon coordinates). The list
should contain two values if L for latitude followed by
longitude (e.g., L, 35.91,-78.89) or three values if U for
northing, easting and UTM zone number with hemisphere
(e.g., U, 3975044, 690891, 17N). Hemisphere is S or N and
defaults to N if omitted.
Ring Distances
HEM4 will
automatically place
13 polar rings
(circles) by default
You can override HEM4's placement of polar rings (circles)
by specifying a list of distances in this field. Enter a comma
separated list that contains at least 3 values representing the
distance in meters for each polar ring from the facility center.
The distances entered must be > 0 and <= 50,000 meters,
and the values must be increasing (e.g.,
100,500,1000,5000,10000,50000).
Acute
(acute)
N
Entering "Y" directs HEM4 to calculate short-term (acute)
concentrations for that facility. If left blank or "N" is entered,
acute impacts are not estimated in the model run.
Hours
(hours)
1-hour
The short-term (acute) averaging period that AERMOD will
use for ambient concentrations, for that facility. The
averaging period options are: 1, 2, 3, 4, 6, 8, 12 and 24-
hours. The default is 1-hour.
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Field
Default Setting
(if field left blank)
Description of Facility List Options Field
Acute Multiplier
(multiplier)
10
The acute multiplier applied to the average annual emission
rate and used to approximate the short-term emission rate
(e.g., 10 times the rate entered in the HAP Emissions file).
Note: HEM4 also assumes that this short-term rate can
occur at the same time as the worst-case meteorological
conditions. Two-decimal precision is accommodated;
minimum value is 1.00
High Value
(high_value)
Maximum acute
value is used as the
high value when this
field is left blank
This field indicates which acute concentration to report as
the high acute value in the outputs, for each facility. If you
wish to use a value other than the maximum (e.g., the 98th or
99th percentile), then enter the value in this field. The number
you enter must be an integer and is calculated based on the
number of hourly values in the modeled run. For example, if
you want the 98th percentile acute value used from a data
set of 8,760 hourly values (in one year), then enter 175 in
this field, which is the truncated product of 0.02 x 8760.
Similarly, if you want to use the 99th percentile acute value,
then enter 87 in the text box, which is the truncated product
of 0.01 x8760. The default acute high value (if this field is
left blank) is the maximum modeled acute concentration.
Deposition
(dep)
N
Deposition is not modeled by default; entering "Y" generally
directs the model to calculate deposition in the model run
(particle, vapor, or both as designated below) and provide
the deposition flux in the output files. However, you can also
enter "Y" in this field to produce separate particle and vapor
(rather than the standard combined) concentrations in the
outputs, even when not calculating deposition; see pdep and
vdep fields below. You may model deposition with or without
plume depletion. Note that you cannot model deposition/
depletion for any facility that contains a buoyant line.
Depletion
(depl)
N
Depletion is not modeled by default; entering "Y" directs the
model to deplete the plume by the calculated deposition flux.
Note: You may enter "Y" here even if you chose "N" for
deposition; in that case the model will internally calculate
deposition flux to deplete the plume but will not provide the
deposition flux values in the output files. (This option saves
space if you do not need the deposition flux.) Note that you
cannot model deposition/depletion for any facility that
contains a buoyant line.
Particle
Deposition
(pdep)
NO
The value "WD" directs the model to incorporate both wet
and dry deposition for particles. Use "WO" for wet only
particle deposition; use "DO" for dry only particle deposition;
use "NO" (or leave blank) if not modeling deposition of
particles and you do not need particle concentrations.
Alternatively, enter "CO" for concentration only, if you want
particle concentrations provided in the outputs but do not
need deposition modeled for particles. If you enter WD, WO
or DO in this field for a given facility (or facilities), then HEM4
will prompt you to provide a particle size input file for that
facility (or facilities), if you are using Method 1 for deposition.
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Field
Default Setting
(if field left blank)
Description of Facility List Options Field
(pdep), continued
NO
Note that you cannot model deposition/ depletion for any
facility that contains a buoyant line.
Particle Depletion
(pdepl)
NO
The value "WD" directs the model to incorporate both wet
and dry depletion of particles from the plume. Use "WO" for
wet only particle depletion; use "DO" for dry only particle
depletion; use "NO" (or leave blank) if not modeling depletion
of particles from the plume. If you enter WD, WO or DO in
this field for a given facility (or facilities), then HEM4 will
prompt you to provide a particle size input file for that facility
(or facilities), if you are using Method 1 for deposition. Note
that you cannot model deposition/depletion for any facility
that contains a buoyant line.
Vapor (gaseous)
Deposition
(vdep)
NO
The value '"WD" directs the model to incorporate both wet
and dry vapor deposition of pollutants; use "WO" for wet only
vapor deposition; use "DO" for dry only vapor deposition; use
"NO" (or leave blank) if not modeling deposition of vapor
pollutants and you do not need vapor concentrations.
Alternatively, enter "CO" for concentration only, if you want
vapor concentrations provided in the outputs but do not need
deposition modeled for vapor/gases. If you entered WD or
DO in this field, HEM4 will prompt you to provide a land use
input file and a month-to-seasons input file, which are
needed for dry deposition/depletion modeling. Note that you
cannot model deposition/depletion for any facility that
contains a buoyant line.
Vapor (gaseous)
Depletion
(vdepl)
NO
The value "WD" directs the model to incorporate both wet
and dry depletion of vapor pollutants from the plume. Use
"WO" for wet only vapor depletion; use "DO" for dry only
vapor depletion; use "NO" (or leave blank) if not considering
depletion of vapor pollutants from the plume. If you entered
WD or DO in this field, HEM4 will prompt you to provide a
land use input file and a month-to-seasons input file, which
are needed for dry deposition/depletion modeling. Note that
you cannot model deposition/depletion for any facility that
contains a buoyant line.
Elevations
(elev)
Y
Elevations of receptors are accounted for by default;
entering an "N" excludes elevations from the model run.
User receptors
(user_recpt)
N
Enter "Y" to include user receptors in the modeling run, for
each facility. User receptors are not included by default.
Note: if you are modeling using user receptors, HEM4 will
prompt you for a separate user receptor input file.
Building
Downwash
(bldg_dw)
N
Enter "Y" in this field for each facility containing point
sources for which you wish to model downwash over a
nearby building. Building downwash is not included by
default. If you are modeling building downwash, HEM4 will
prompt you for a separate input file that must contain
building dimension information, for (applicable point sources
in) each facility marked with a "Y" in this column. Note that
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Field
Default Setting
(if field left blank)
Description of Facility List Options Field
(bldg_dw),
continued
N
building downwash may only be modeled with vertical point
(P), capped point (C), and horizontal point (H) source types.
FASTALL
(fastall)
N
Entering "Y" directs HEM4 to use AERMOD's control option
FASTALL for modeling that facility, which conserves model
run time by simplifying AERMOD's dispersion algorithms.
FASTALL is not used by default. Note that you cannot use
FASTALL for any facility that contains a buoyant line.
Emissions
Variation
(emiss_var)
N
Entering "Y" indicates that you want to vary the emissions of
one or more sources at this facility. This field allows the
application of variations to the emission inputs from specific
sources by different user-supplied time scales (e.g., by
season, month, hour of day, day of week), or by different
wind speeds (6 ranges). If you enter a "Y" for a given facility,
then HEM4 will prompt you for a separate emissions
variation input file for that facility, and that file must contain
variation factors for at least one source at each facility
marked with a "Y".
Annual
(annual)
Y
Entering an "N" in the annual field indicates that you want
the modeling run to be based on meteorological data from a
period other than an annual period. If you enter an "N" in this
annual field, then you must enter values in the "period_start"
and "period_end" fields (below). Leaving this field blank or
entering a "Y" will cause HEM4/AERMOD to calculate
annual concentration averages using the entire met data file,
which is the default.
Period Start
(period_start)
[Entry required if an
"N" is entered in
Annual field above]
The period_start field indicates the start of the
meteorological period during which AERMOD will run. You
should enter a comma separated list of 3 or optionally 4
values here indicating the year, month, day and (optionally)
hour of when the modeling period should begin. For
example, if you enter 2016,02,11,12 then the model will use
2016 met data starting on February 11th at the 12th hour
(noon) and end on the date and time indicated in the
period_end field. Note that if you do not enter an hour here,
then the model will use hour 1 as the default.
Period End
(period_end)
[Entry required if an
"N" is entered in
Annual field above]
The period_end field indicates the end of the meteorological
period during which AERMOD will run. You should enter a
comma separated list of 3 or optionally 4 values here
indicating the year, month, day and (optionally) hour of when
the modeling period should end. For example, if you enter
2016,06,30,17 then the model will use the met data starting
on the date and time indicated in the previous period_start
field and ending in 2016 on June 30th at the 17th hour (5
pm). Note that if you do not enter an hour here, then the
model will use hour 24 as the default.
Take care when filling out the Facility List Options File, as this file drives and controls
the modeling run. To avoid error, this file must be consistent with your other input files.
For example, if you indicate 100% particles in the Percent Particulate column of your HAP
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Emissions input file and you wish to model deposition and/or depletion, then you cannot choose
to model vapor deposition and/or depletion in this file. In addition, the modeling options you
indicate in the Facility List Options file may require additional input files for modeling. For
example, if you indicate in the Facility List Options file that you would like building downwash
modeled for certain facilities (by entering a "Y" in this field), then one or more point sources at
those facilities must be included in the separate building dimensions input file that HEM4 will
prompt you for. You will also need to provide consistent input files if you marked a "Y" for any
facilities in the user receptor or emissions variations fields. The various modeling options driven
by the Facility List Options file are discussed more in the next sections.
3.2.2 Meteorological Station and Period Options
HEM4's library of meteorological (met) station data is described in Section 2.4.1. By default,
HEM4 chooses the met station closest to the facility to be modeled (i.e., if this field is left blank).
If you do not want HEM4 to choose the closest met station's data to use for your modeling run,
in the meteorological station field (met_station column) of the Facility List Options file, enter the
name of the met surface station you want AERMOD to use when modeling each facility (e.g.,
NC13722.SFC). The names of all stations in the met library can be found in the
metlib_aermod.xlsx file in "HEM4\resources" folder, and the stations' met data can be found in
the "HEM4\aermod\MetData" folder. You can also add your own met station to the
metlib_aermod.xlsx file in the HEM4's resources folder and provide the new met station data as
both SFC and PFL files in your "HEM4\aermod\MetData" folder, as explained in more detail in
Section 2.4.
The other fields related to met data are at the end of the Facility List Options file, on the far-right
side of the spreadsheet, and include "annual", "period_start", and "period_end". These columns,
as noted above in Table 2, allow you to choose to model with a period other than the default
annual period of met data. The period start and period end fields allow you to specify exactly
what met period HEM4 should instruct AERMOD to use for your modeling run, down to the year,
month, day and even hour. The period start and end dates you specify must be included in
the meteorological files being used. If the set of meteorological files you specify, or that
HEM4 chooses, does not cover the dates you specify, AERMOD will generate an error
and that facility will not be modeled. These period options are useful if modeling, for
example, facilities that come on and offline during different parts of a year. The options may also
be helpful in performing analyses to determine what time periods in the year produce the
highest local concentrations and impacts.
It should be noted that the selection of the met station and met period for your modeling run can
have a significant effect on the air concentrations and therefore risk and HI estimates that HEM4
produces. See Table 2 for HEM4's default settings used in the Facility List Options for the met
station and period options.
3.2.3 Dispersion Environment Options: Rural or Urban
The Rural or Urban field (rural_urban column) is used by HEM4 to set the type of dispersion
environment to be used by AERMOD for the modeling of each facility. The EPA provides
guidance on whether to select urban or rural dispersion in its Guideline on Air Quality Models
(Appendix W). That guidance suggests an urban dispersion environment should be used if (1)
the land use is classified as urban for more than 50% of the land within a 3-kilometer radius of
the emission source, or (2) the population density within a 3-kilometer radius is greater than 750
people per square kilometer. AERMOD's handling of urban versus rural dispersion algorithms is
discussed in Section 3 of the AERMOD User's Guide (EPA 2022a), Section 5 of the AERMOD
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Implementation Guide (EPA 2022b), and Section 5.9 of the AERMOD Formulation Document
(EPA_2022e).
If you are modeling using U.S. Census block centroids as receptor locations, by default HEM4.2
will use the population density to determine if a facility should be modeled as urban or rural. To
do so, HEM uses the population of each 2020 Census block centroid within 3 km of the facility
center to determine the population density surrounding each facility. If that population density is
greater than 750 people per square kilometer, HEM will instruct AERMOD to use an urban
dispersion environment; otherwise, rural dispersion will be used by AERMOD. In addition, if
using an urban dispersion environment for modeling, AERMOD requires a population input for
its urban mode, as discussed in Section 5.9 of the AERMOD Formulation Document (EPA
2022e). If you left the rural/urban field blank so that HEM4.2 determines which dispersion
environment to use by default, then you may also leave the urban population field blank. If
HEM4.2 determines that urban is the appropriate dispersion to use for your facility, HEM4.2 will
determine this urban population input by tallying the population out to 20 km in all directions
around each facility center, using the 2020 Census block centroid populations within that 20 km
radius.
If you choose the urban dispersion environment for the model run (rather than leaving this field
blank in the Facility List Options file indicating HEM4.2's default approach described above),
you should specify the population of the urban area surrounding the facility, if known, by
entering it in the urban population column/field (urban_pop) of the Facility List Options file. This
is true whether you are modeling with U.S. Census block receptors or with alternate receptors. If
you choose to model using an urban dispersion environment and do not provide a population,
HEM4.2 will set your urban population column/field (urban_pop) to 50,000 people. As noted
above, AERMOD uses this urban population value in its dispersion algorithms for urban areas.
If you are modeling using alternate receptors instead of census blocks (e.g., outside the U.S.),
ideally you should determine which dispersion environment to use for each facility. If instead
you leave the rural/urban field blank when using alternate receptors, then AERMOD will default
to a rural dispersion environment, resulting typically in more conservative (higher) concentration
predictions.
3.2.4 Modeling Domain Options
You will provide HEM4 the parameters that define each facility's modeling domain in columns E
through L of the Facility List Options file. The modeling domain is circular and centered on each
facility, with a user-specified radius. HEM4 identifies all the receptor locations in the modeling
domain - census blocks for U.S. runs based on the census database, or alternate receptors for
non-census modeling runs. The model then divides the blocks into two groups - inner and outer
receptors - based on their distance from the facility. For the inner group of receptors (closest to
the facility), each census block or alternate receptor location is modeled as a separate receptor
in AERMOD.
Maximum Distance: In column E (max_dist) of the Facility List Options file, enter the maximum
radius in meters to be modeled; this is the radius around each facility of the entire modeling
domain. The maximum distance must be greater than or equal to the "modeling distance"
(discussed next), but not greater than 50,000 meters because, as a Gaussian dispersion model,
AERMOD is not recommended beyond 50 kilometers. If you leave this field blank, HEM4 will
use a default maximum distance of 50,000 meters. The maximum distance is the radius of the
circular study area for which HEM4 will model ambient impacts (at census block centroid
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receptors or alternate receptors, polar grid receptors, and user receptors, as explained below in
this section). The center of this modeling domain is by default the geographical center of each
facility (based on source locations for each facility) you are modeling, but you can change this
center using the "facility center" column K, as discussed below.
Modeling Distance: In column F of the Facility List Options file (model_dist), enter the distance
in meters within which census blocks will be modeled individually. This is the "cutoff distance"
around each facility for explicitly including census block or alternate receptors in the AERMOD
run. Within this radial distance measured from the facility center, AERMOD will model each
census block centroid or alternate receptor explicitly as a receptor. Outside of this radius,
AERMOD will not model the census blocks or alternate receptors directly; ambient impacts at
receptors beyond the modeling distance will be interpolated using dispersion modeling results
from the polar receptor network, described below. If you leave this field blank, HEM4 will by
default use a modeling distance of 3,000 meters. The Modeling Distance may not be greater
than the Maximum Distance (above).
It should be noted that larger values for this cutoff modeling distance will require more time to
model, because the number of receptors requiring explicit AERMOD modeling will be higher.
However, you should set this cutoff value at a large enough distance so that the maximum risk
receptor (discussed in Section 6.1.1) will be modeled individually. This distance will vary
depending on the configuration of the sources but is generally between 1,500 and 2,000 meters.
A typical modeling cutoff distance for larger facilities is 3,000 meters (or 3 km). When modeling
large sources configured as polygons (e.g., U.S. Census tracts), set this modeling cutoff
distance to be greater than the largest distance across the polygon, to ensure discrete modeling
of all census blocks within the polygon.
Radials: In column G of the Facility List Options file (radials), enter the number of radials in the
area to be modeled. The polar grid receptors of the polar network are located at the intersection
of a radial and a polar ring (or "circle", described next). A typical run would include 13 concentric
rings and 12 or 16 radial directions. HEM4 will distribute the radial directions evenly around the
facility. For instance, if you select 16 directions, receptors will be modeled at compass bearings
of 0, 22.5, 45, 67.5, 90, 112.5, 135, 157.5, 180, 202.5, 225, 247.5, 270, 292.5, 315, and 337.5
degrees. If you leave this field blank, by default HEM4 will use 16 radial directions. If you
choose to enter a different number of radials, you must specify at least 4 radials in this field.
Circles (polar rings): In column H of the Facility List Options file (circles), enter the number of
concentric circles (rings) in the polar receptor network around each facility, centered on the
facility center. You must enter at least 3 rings. If you leave this field blank, by default HEM4 will
use 13 rings. Also, HEM4 will calculate by default the inner radius of the polar network, unless
you choose to specify a distance to the first ring (or "Ringl", described below). This model-
calculated first ring distance is based on the location of the emission sources and the facility
center. HEM4 selects the distance that places the first modeling ring just beyond all emission
sources, but not less than 100 meters from the facility center. HEM4 will place the concentric
rings at a logarithmic progression of distances starting at the inner ring distance and ending at
the outer radius of the modeling domain. However, you have the option to specify different ring
distances (than HEM4's calculated distances) in the "ring_dists" column L, described below.
Although the polar grid receptors are used primarily for interpolating risks at census blocks
outside of the modeling cutoff distance, it is important to include some rings close to the facility.
Overlap Distance: In column I of the Facility List Options file (overlap_dist), enter the distance in
meters where source and receptor are considered to be overlapping. This distance must be
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greater than or equal to 1 meter and less than or equal to 500 meters. If you leave this field
blank, HEM4 by default will use an overlap distance of 30 meters, which is approximately equal
to the width of a narrow buffer and a roadway. Within this distance, sources and receptors are
considered to be overlapping, as measured from each source at the facility (e.g., stack, edges
of area and volume sources). This feature is provided to address situations, for example,
wherein U.S. Census blocks are very close to a facility and have complex shapes. In such
cases, the centroid of a census block may be much closer to the facility than the nearest actual
dwelling. (In fact, if a census block surrounds a portion of the facility, the centroid of the block
may be on facility property.) If a receptor falls within this distance, HEM4 will not calculate risks
based on the location of that receptor but will instead assume that the risks associated with the
receptor are the same as the highest predicted value for any receptor that does not overlap
facility property (including polar receptors). An exception to this occurs when modeling polygon
sources. Unlike other sources, when modeling polygons, overlapping of source and receptor is
permitted. This allows the impacts, for example, of a U.S. Census tract modeled as a polygon
source (e.g., mobile source emissions modeled uniformly across a census tract) to be
calculated within the census tract being modeled.
Rinql or First Ring: In column J of the Facility List Options file (ringl), enter the distance in
meters to the first ring (circle) of the polar network for each facility, as measured from the facility
center. As noted above (under "Circles"), if you leave this field blank then HEM4 will calculate
the default value to the first ring to be just outside the source locations, but not less than 100
meters from the facility center. You can override the default distance calculated by the model to
fit the size and shape of the facility properties to be modeled. For example, you should set the
first receptor ring to less than 100 meters (or conversely greater than what HEM4 calculates), if
appropriate to the size and shape of the facility property. Place the nearest polar receptor ring
as close as possible to the facility boundary - this inner radius of the polar network should be
the minimum distance from the facility center that is generally outside of facility property. For
complex or irregularly shaped facilities however, you may find it useful to specify an inner ring
that encroaches on facility property in some directions. Furthermore, you may want to specify a
set of boundary receptors by employing the user-defined receptors file (as described in Sections
3.2.8 and 3.5.6). Note that the first ring distance must be less than the modeling cutoff
distance (entered in column F "model_dist", for explicit modeling of receptors).
Facility Center: In column K of the Facility List Options file (fac_center), you may specify the
facility center location to override HEM4's determination of where the facility center is located. If
you leave this field blank, HEM4 will by default choose the facility center by determining the
geographic center of all emission source locations for that facility in your Emissions Location file
(discussed in Section 3.4). If you wish to specify a different facility center location, then enter its
location in this field as a comma separated list that should start with either "U" (if using UTM
coordinates) or "L" (if using latitude/longitude coordinates). The list should contain two values if
L for latitude followed by longitude (L, 35.91 ,-78.89) or three values if U for northing, easting and
UTM zone number with hemisphere (U, 3975044, 690891, 17N). Hemisphere (S or N) defaults
to N if omitted.
Ring distances: In column L of the Facility List Options file (ring_dists), you may override
HEM4's placement of polar rings (circles) by specifying a list of distances in this field. To do so,
enter a comma separated list that contains at least 3 values representing the distance in meters
for each polar ring from the facility center. The distances entered must be greater than 0 and
less than or equal to 50,000 meters, and the values must be increasing
(e.g.,100,500,1000,5000,10000, 50000). If you leave this field blank, HEM4 will by default place
13 polar rings (circles), as noted above under "Circles".
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A note about the Polar Network: Columns G (radials) and H (circles) of the Facility List Options
file, and optionally columns J (ringl), K (fac_center) and L (ring_dists), define HEM4's polar
network. In addition to modeling ambient impacts at populated receptors (census block
centroids or alternate receptors) within the modeling cutoff distance, HEM4 also uses AERMOD
to model ambient impacts explicitly at polar grid receptors within the polar network. This polar
network extends beyond the modeling cutoff distance to the maximum (outside) radius. The
polar receptor network in HEM4 serves three functions:
(1) to estimate default impacts if one or more U.S. Census block receptor or alternate
receptor locations are inside the overlap cutoff distance;
(2) to evaluate potential acute effects that may occur due to short-term exposures in
unpopulated locations outside the facility boundary; and
(3) to interpolate long- and short-term impacts at receptors (U.S. Census block locations
or alternate receptors) that are within the modeling domain but outside the cutoff
distance for explicit modeling of individual receptors
If modeling with terrain effects (discussed in Section 3.2.7), the elevation of each polar grid
receptor is based on the elevation of nearby individually/explicitly modeled "discrete" receptors
including census blocks, alternate receptors, and user receptors. The maximum elevation of
nearby discrete receptors is assigned to each polar receptor, to ensure terrain effects on
receptor concentrations are conservatively estimated. The importance of the polar network
is discussed further in Section 5.
3.2.5 Acute Options
As introduced in Section 1.2, you can use HEM4 to estimate chronic health risks and, optionally,
acute (short-term) health risks as well. Chronic health risks are estimated based on long-term
average concentrations, as predicted by AERMOD. The time frame of this average is
determined by the number of years covered by the meteorological data file selected for the
model run: the default is generally one year when running AERMOD, although periods other
than one year can be chosen as discussed in Section 3.2.2 above regarding met station and
period options. Acute health risks are based on short-term average exposures such as 1, 2, 3,
4, 6, 8, 12 and 24 hours.
You can choose to model acute health risks using columns M (acute), N (hours), O (multiplier)
and P (high_value) of the Facility List Options file. HEM4 uses what you input in these fields for
each facility to direct AERMOD to model acute concentrations, and then HEM4 uses these
acute concentration predictions by AERMOD to estimate acute health risks. Enter a Y (for "yes")
in column M (acute) to indicate you want HEM4/AERMOD to model short-term/acute
concentrations for that facility. If you leave this field blank then by default HEM4 will not model
acute impacts, regardless of what you put in columns N, O and P. Next, in column N (hours),
enter the short-term/acute averaging period that AERMOD will use for ambient concentrations,
for each facility. The averaging period options are: 1, 2, 3, 4, 6, 8, 12 and 24 hours. If you
entered Y in column M (acute) and leave column N (hours) blank, then HEM4 will by default use
an averaging period of 1 hour.
In column O (multiplier), enter the acute multiplier for each facility. This multiplier is applied to
the average annual emission rate (in tons/year from your HAP Emissions input file, which the
model converts to grams/second); and it is used to approximate the short-term emission rate. If
you entered a Y in column M (acute), but leave this field blank, then by default HEM4 will use a
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multiplier of 10 for that facility (e.g., the default of 10 times the average annual emission rate
entered in the HAP Emissions file might be used to approximate short-term emission spikes).
Regarding short-term spikes, it is important to note that AERMOD applies this short-term rate
over the course of the entire met period chosen (discussed in Section 3.2.2) and the peak
acute value will occur at the same time as the worst-case meteorological conditions.
Therefore, the acute results produced with an appropriate multiplier can be viewed as
conservative estimates. Two-decimal precision is accommodated in the multiplier column O, but
the multiplier entered must be greater than or equal to 1.00.
The highest acute value reported by HEM4 is also impacted by what you enter in column P
(high_value). This field indicates which acute concentration to report as the high acute value in
the outputs, for each facility. If you wish to use a value other than the maximum (e.g., the 98th or
99th percentile), then enter the associated value in this field. The number you enter must be an
integer and is dependent on the number of hourly values in the model run. For example, if you
want the 98th percentile acute value used from a dataset of 8,760 hourly values (in one year),
then enter 175 in this text box, which is the truncated product of 0.02 x 8,760. Similarly, if you
want to use the 99th percentile acute value, then enter 87 in the text box, which is the truncated
product of 0.01 x 8,760. If instead you leave column P (high_value) blank, then HEM4 will by
default report the maximum modeled acute concentration as the "high value".
3.2.6 Deposition and Depletion Options
Deposition and Depletion: Deposition and depletion are not modeled by default by HEM4.
However, depending on the deposition and depletion options you choose in the Facility List
Options file in columns Q through V, HEM4 will (1) calculate and output a deposition flux and (2)
deplete the plume (or not) based on the calculated deposition. Generally speaking, deposition
modeled with plume depletion will reduce the ambient impacts from the emission sources by
removing pollutants from the plume. Air concentrations will be depleted as pollutants are
deposited to the ground. Alternatively, you may choose to calculate the deposition flux, but not
deplete the plume (to allow for non-depleted air concentrations that a standard run would
produce). Deposition without plume depletion will not affect the air concentrations but will
provide a deposition flux in the outputs. Whether you choose to deplete the plume or not, the
modeled deposition flux may be then used as an input to a separate multipathway model such
as the Total Risk Integrated Methodology (TRIM) (EPA 2021b).
Enter a Y (for "yes") in column Q (dep) of your Facility List Options file if you would like
AERMOD to model deposition and HEM4 to output a deposition flux column (in g/m2/y) for all
polar receptors and for the inner discretely modeled receptors.2 Enter a Y in column R (depl) if
you would like AERMOD to model depletion (i.e., deplete the plume based on a calculated
deposition flux). If you enter a Y in both columns Q (dep) and R (depl), then HEM4 will output a
deposition flux column AND deplete the plume. If you enter a Y in only column R (and leave
column Q blank or enter an "N"), then no deposition flux will be provided, but the plume will be
depleted (based on an internally calculated deposition flux). If you do not need the deposition
flux output by the model, this option saves space.
HEM4 uses AERMOD to calculate deposition and depletion effects for particulate matter, vapor
(gaseous) pollutants, or both. The make-up of your emissions - that is, the percentage
particulate and gas - is dictated to HEM4 by your HAP Emissions input file. Specifically, column
2 If you specify a PERIOD average instead of an ANNUAL average of meteorological data, deposition
results will be given in g/m2 instead of g/m2/y.
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E (Fraction emitted as particulate matter [%])in the HAP Emission input file indicates to HEM4
whether your emissions are 100% particle (if column E is populated with 100 for all pollutants),
100% gas (if column E is left blank or populated with 0 for all pollutants), or a mixture of
particles and gas. However, for each facility, you can choose to model deposition and/or
depletion for merely the particulate portion of your emissions (if you have a particulate portion),
the vapor portion of your emissions (if you have a gas portion), or both (if you have both particle
and gas emissions, as indicated in column E of your HAP Emissions input file).
Particle and Vapor Deposition and Depletion Types (Wet and Dry; Wet Only; Dry Only; None): If
you entered "Y" in column Q (dep) and/or R (depl) regarding modeling deposition and/or
depletion, you must also indicate what type of deposition and/or depletion you wish HEM4 to
direct AERMOD to model: wet and dry (WD), dry only (DO), wet only (WO), or none (No or
leave blank). Use columns S (pdep), T (pdepl), U (vdep) and V (vdepl) of your Facility List
Options file to indicate what kinds of deposition and/or depletion you want modeled for
particulates and vapor (gas). In column S (pdep) you should indicate the type of particle
deposition you want modeled, if any. In column T (pdepl), you should indicate the type of
particle depletion you want modeled, if any. Do likewise in columns U (vdep) and V (vdepl) for
the types of vapor deposition and vapor depletion of your pollutants, respectively. See the
AERMOD User's Guide (EPA 2022a) and AERMOD Implementation Guide (EPA 2022b) for a
more detailed discussion of these processes.
You can mix and match the type of deposition and depletion you tell HEM4 to model. For
example, you can direct HEM4 to model wet and dry (WD) deposition, and then deplete the
plume based on those wet and dry (WD) deposition processes. Or you can choose wet and dry
deposition (WD), but then only deplete the plume based on the wet deposition process (WO). In
addition, the "none" option (No or blank) allows you to model deposition for particles (or vapor)
only, while ignoring the vapor (or particle) portion of your emissions, even if your HAP
Emissions file shows a mixture of particles and gas. For example, if you wish HEM/AERMOD to
ignore the vapor portion of your emissions, you can indicate in column S (pdep) and/or column
T (pdepl) what type of deposition and/or depletion (respectively) to model for your particle
emissions (WD, WO or DO) and then leave both column U (vdep) and column V (vdepl) blank or
enter "No". Alternatively, you can choose to model deposition/depletion for either particles or
vapor, while modeling concentrations only (with no deposition/depletion calculated) for the other
portion of your emissions (particle or vapor), as described next.
Concentration Outputs Broken Out into Particle and Vapor: Finally, even if you do not wish to
model deposition/depletion, you can use the deposition fields in the Facility List Options file to
produce separate particle and vapor concentrations in the output files (if you have both particle
and gas emissions, as indicated in column E of your HAP Emissions input file). In other words,
you can direct HEM4/AERMOD merely to produce more detailed concentration outputs,
showing the breakdown of particle and vapor concentration at each receptor location, without
modeling either deposition or depletion. For standard runs modeled without deposition/depletion
(in which columns Q through V are blank), HEM4 combines the particles and gases into one
combined concentration in the output files at each modeled receptor location.3 Alternatively, to
obtain separate "P" and "V" air concentrations for particles and gases individually, you can enter
"Y" in the deposition field (column Q) and "CO" for "concentration only" in the pdep field (column
S) to obtain particle "P" concentrations in the outputs, plus "CO" in the vdep field (column U) to
obtain vapor/gas "V" concentrations in the outputs. Neither deposition nor depletion will be
3 See for example Table 37 in Section 6.1.10 regarding the All Inner Receptors output file, which explains
that a "C" in the field Emission Type means a combined particle/vapor concentration.
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modeled in this case. However, the outputs will show distinct rows for particles ("P") and vapor
("V") at each location, rather than the standard combined ("C") row. To produce concentrations
only in this way, you should leave all depletion fields blank (N or No) in columns R (depl), T
(pdepl) and V (vdepl). Note: Using the CO option, you may also choose to produce particle only
concentrations while ignoring the vapor portion of your emissions, or vice versa.
You can also mix and match deposition/depletion options with this concentration only (CO)
option. For example, you may choose to model deposition (with or without depletion) for the
particle portion of your emissions, but choose to model concentrations only (with no
deposition/depletion processes modeled) for the vapor portion of your emissions. To do this,
enter "Y" in column Q (dep) and "CO" in column U (vdep) for your vapor emissions, plus enter
whatever deposition/depletion options you wish to model for your particle emissions in columns
R (depl), S (pdep), and T (pdepl).
As evident from the discussion in this section, there are numerous deposition, depletion, and
concentration-only options HEM/AERMOD can model, which are initiated by the many
combinations you can enter in columns Q (dep), R (depl), S (pdep), T (pdepl), U (vdep), and V
(vdepl) of your Facility List Options file. To illustrate a few of these options, Table 3 provides a
partial list of some deposition/depletion combinations with their model results.
Table 3. Sample Deposition and Depletion Options and Model Results
Entries in Columns Q - V of the Facility List Options File*
Model Results*
Q: dep
R: depl
S:pdep
T: pdepl
U:vdep
V: vdepl
Y
Y
WD
WD
WD
WD
Deposition flux will be provided,
and the plume will be depleted,
using wet and dry processes for
both particles and gases, for both
deposition and depletion.
Y
Y
WD
WO
WD
DO
Deposition flux will be provided,
and the plume will be depleted,
using wet and dry processes for
particle and gas deposition, but
wet-only processes for particle
depletion and dry-only processes
for gas depletion.
Y
WO
DO
Deposition flux will be provided
with no plume depletion, using wet-
only processes for particles and
dry-only processes for gases.
Y
WD
WD
No deposition flux will be provided
but the plume will be depleted
using both wet and dry processes
for particles and gases.
Y
WD
Deposition flux will be provided
with no plume depletion, using wet
and dry processes for particle
deposition. (No gases modeled)
Y
Y
DO
WO
CO
Deposition flux will be provided,
and the plume will be depleted,
using dry-only processes for
particle deposition and wet-only
processes for particle depletion.
Vapor/gas concentrations will be
provided, but neither deposition nor
depletion will be modeled for
vapor/gases.
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Entries in Columns Q - V of the Facility List Options File*
Model Results*
Q: dep
R: depl
S:pdep
T: pdepl
U:vdep
V: vdepl
Y
WO
No deposition flux will be provided
but the plume will be depleted
using wet-only processes for
gases. (No particles modeled)
Y
WD
CO
Deposition flux will be provided
based on wet and dry processes
for particles, with no depletion of
the plume. In addition, vapor/gas
concentrations will be provided, but
neither deposition nor depletion will
be modeled for vapor/gases.
Y
Y
CO
WD
wo
Deposition flux will be provided
based on wet and dry processes
for gases, and the plume will be
depleted based on wet only
processes for gases. Particle
concentrations will be provided, but
neither deposition nor depletion will
be modeled for particles.
Y
CO
CO
Separate particle and gas
concentrations will be provided in
the outputs, but no deposition or
depletion will be modeled.
Y
CO
Particle concentrations will be
provided in the outputs, but no
deposition or depletion will be
modeled. (No gases modeled)
Y
CO
Vapor concentrations will be
provided in the outputs, but no
deposition or depletion will be
modeled. (No particles modeled)
[The above is merely a partial list of some of the possible deposition/depletion combinations, for
illustration purposes. More variations may be chosen that are not illustrated here.]
*Note: These Model Results will happen if your column entries are consistent with your emissions (e.g.,
you cannot model deposition and/or depletion of particles if your facility's emissions are 0% particulate in
column E of your HAP Emissions file).
Additional Deposition/Depletion Input Files: Depending on the type of deposition and/or
depletion you indicate in columns Q through V for each facility, and depending also on the
method of particle deposition you indicate for each source at these facilities in your Emissions
Location file (discussed in Section 3.4.2), HEM4 will prompt you to provide additional files.
These files are introduced below and described in more detail in Sections 3.5.3 and 3.5.4.
If you want to model deposition and/or depletion of particles in your emissions using Method 1
(described in Section 3.4.2), HEM4 requires a particle data file. This additional input file will
need to contain particle size (diameter) information, mass fraction percentages for each size,
and particle density for each size, for emissions from each source (for which you wish to model
particle deposition and/or depletion using Method 1). The particle data file is described further in
Section 3.5.3.
If you want to model dry deposition and/or depletion of gaseous/vapor pollutants, HEM4
requires a land use input file and a month-to-seasons input file. These additional input files are
needed to describe the land use and vegetation surrounding each facility at which you wish to
model dry only (DO) or wet and dry (WD) deposition and/or depletion of gaseous pollutants, as
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discussed in Section 3.5.4. If you wish to model wet only (WO) deposition and/or depletion of
gaseous pollutants, these additional input files are not needed by HEM4. (These files are also
not needed for 100% particulate emissions.)
Finally, you should check to ensure that the gaseous pollutants in your HAP Emissions file are
included in the Gas Parameter (Gas Param) reference file, described further in Section 3.5.4. If
these pollutants are not included - or if you wish to include different parameter values than the
Gas Parameter file currently uses - you should edit the Gas Parameter file, as discussed in
Section 3.5.4. Otherwise, generic default gas parameter values will be used.
To model deposition/depletion, HEM4 requires additional modeling time compared to a standard
run (with no deposition and/or depletion modeling). Furthermore, HEM4 requires significantly
more time to run if you opt to model deposition and/or depletion and you are also modeling
acute impacts. The exact run time will depend on your source configuration and modeling
domain, but the combination of acute calculations and deposition/depletion will generally
increase run times from a few minutes to over an hour, or more, per facility.
Deposition and plume depletion have more of an effect on ambient concentrations farther from
the facility than these processes do closer to the facility, where the maximum impact generally
occurs. Therefore, if you select the deposition and/or depletion options for a model run, you may
save time by performing two separate runs. For example, you can use the first HEM4 run to
calculate chronic effects and include deposition and plume depletion. You can then use the
second run to calculate acute effects without deposition and depletion.
It should also be noted that HEM4 does not model deposition and/or depletion at census block
and alternate receptors beyond the modeling distance, except at the polar receptors. This
means that deposition and/or depletion is modeled at only the "inner receptors" (discussed in
Section 6.1.10) and the polar receptors. If you need deposition and/or depletion modeled for the
entire modeling domain at all census block or alternate receptors, you should set the modeling
distance equal to the maximum distance. HEM4 will require additional modeling time in this
scenario, compared to using a smaller modeling distance. You may save modeling time by
performing two separate runs, especially if you are also modeling acute impacts.
Note that if a facility listed in your Facility List Options file includes a buoyant line source in your
accompanying Emissions Location file, you cannot model deposition or depletion for that facility.
You may, however, model such a facility as two facilities, one with the buoyant line source[s]
and the other containing the non-buoyant line sources.
3.2.7 Elevation Option
HEM4 includes terrain elevations by default in your modeling run if you leave column W (elev)
blank or enter a "Y" in this field in your Facility List Options file. To exclude terrain elevations in
your modeling run (i.e., to model as flat terrain), enter an "N" in this field for a given facility.
Elevated terrain around the facility can cause local impacts to increase, though impacts will
differ for each set of sources and elevations. It is especially important to include terrain
elevations if the height of receptors around the facility may exceed the height of any stacks at
the facility. Consult the EPA's Guideline on Air Quality Models (also published as Appendix W of
40 CFR Part 51) (EPA 2005) for more explicit directions on when the use of terrain elevations is
recommended. If you choose to include elevations in the model run, you can specify elevations
for each source in the Emissions Location file. If you do not provide elevations in the Emissions
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Location file, HEM4 will calculate source elevations from neighboring census block elevations.
Note: You should provide elevations for every source or for no sources at each facility, as noted
in Section 3.4 regarding the Emissions Location file.
3.2.8 User Receptors Option
If you would like to include additional "user receptors" in your model run for one or more facilities
- in addition to the census block or alternate receptors, enter a "Y" in column X (user_rcpt) of
your Facility List Options file. HEM4 does not include user receptors by default, so if this column
is blank then user receptors will not be included for that facility. If you are modeling impacts at
user receptor locations, HEM4 will prompt you for a separate input file containing the user
receptor information, for each facility marked with a "Y". The user receptor input file is described
in Section 3.5.6.
3.2.9 Building Downwash Option
If you would like to model downwash over a building, which is under or near a point source, then
enter "Y" in column Y (bldg_dw) of your Facility List Options file. HEM4 does not model building
downwash by default, and you should simply leave this field blank if you do not wish to model it
as part of the plume dispersion. If you are modeling building downwash, HEM4 will prompt you
for a separate input file that must contain building dimension information, for applicable point
sources in each facility marked with a "Y" in this column. Note that building downwash may only
be modeled with vertical point (P), capped point (C), and horizontal point (H) source types.
These source types are described in Section 3.4.1 regarding the Emissions Location file. The
building dimension input file is described in more detail in Section 3.5.5.
Under AERMOD's regulatory option, the effects of building downwash should be taken into
account when a building is close enough to impact dispersion from an emission source. Building
downwash will affect dispersion predictions when:
• the stack height is less than either 2.5 times the building height or the sum of the
building height and 1.5 times the building width; and
• the distance between the stack and the nearest part of the building is less than or equal
to five times the lesser of the height or the projected width of the building (EPA 1995, pg.
1-22 and 1-23).
AERMOD incorporates the Plume Rise Model Enhancements (PRIME) algorithms (Schulman
2000) for estimating enhanced plume growth and restricted plume rise for plumes affected by
building wakes (EPA 2022e). A building may impact emissions from multiple sources. To model
the impact of building downwash, HEM4 requires information on the configuration of the building
when viewed from different wind directions, and this information is contained in the building
dimensions input file, described further in Section 3.5.5.
3.2.10 FASTALL Option
To conserve model run time by simplifying the dispersion algorithms used to model a given
facility's emissions, enter a "Y" in column Z (fastall) of your Facility List Options file. HEM4 does
not employ FASTALL by default, so if you leave this field blank AERMOD will use the more
rigorous (non-simplified) dispersion algorithms.
The FASTALL option conserves model runtime by simplifying the AERMOD algorithms used to
represent meander of the pollutant plume. This simplification is achieved by eliminating the
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upwind component of dispersion for point and volume sources, and by reducing the requirement
for uniformity of emissions over the extent of area sources (EPA 2022a). For faster runs, you
may want to select the FASTALL option which includes these plume and source simplifications.
(More information on AERMOD's FASTALL option is available for download at
https://www.epa.qov/scram/air-qualitv-dispersion-modelinq-preferred-and-recommended-
models#aermod.)
Note that if a facility listed in your Facility List Options file includes a buoyant line source in your
accompanying Emissions Location file, you cannot use the FASTALL option for that facility. You
may, however, model such a facility as two facilities, one with the buoyant line source[s] and the
other without. You may also use FASTALL for the other facilities in your Facility List Options file.
3.2.11 Emissions Variation Option
Enter a "Y" in column AA "emiss_var" of your Facility List Options to apply variations to the
emissions from one or more sources at a given facility. You may vary emissions by different
user-supplied time scales (e.g., by season, month, day of week, hour of day), or by different
wind speeds (6 ranges). HEM4 will prompt you for an emissions variation file if you entered "Y"
for one or more facilities, and that file must contain variation factors or scalars for at least one
source at each facility marked with a "Y". The optional Emission Variation input files are
discussed in more detail in Section 3.5.7.
It should be noted that these emission variation factors/scalars will compound the effects of the
acute multiplier (specified in column O "multiplier") on the short-term/acute emission rates used
by AERMOD. For example, whatever numerical factors you supply in an Emission Variations
input file will be multiplied by an acute multiplier of 10 (if the default multiplier is used) to derive
the short-term emission rate. Therefore, if applying hour-of-day emission variation factors, you
may want to set the acute multiplier to 1, unless it is reasonable to assume that the short-term
rate may still exceed the hour-of-day factors by an additional multiple.
3.3 HAP Emissions File
The HAP Emissions Excel™ file, like the Facility List Options file, is required for any HEM4
modeling run. This file includes emissions in tons per year (tpy) for each HAP emitted from
modeled sources, for all facilities listed in the Facility List Options file. Tables 4 and 5 give the
format guidelines for the HAP Emissions file and a sample HAP emissions input file,
respectively.
Table 4. Format Guidelines for the HAP Emissions Input File (Required)
Field
Type
Description
Facility ID
Character
An alphanumeric string identifying the facility being modeled
Source ID
Character
An alphanumeric character string up to 8 characters long. It
must contain at least one alphabetic character and all Source
IDs must match a Source ID used in the Emissions Location file.
Note: AERMOD allows a maximum of 8 characters for the
Source ID; and all Source IDs will be converted to upper case by
AERMOD.
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Field
Type
Description
Pollutant
Character
The pollutant name must correspond to one of the chemical
names listed in the dose response library. (see
Dose_Response_Library.xlsx in the resources folder)
Emission
Amount
Numeric
The emitted amount of the pollutant in tons per year (tpy).
Percent
Particulate
Numeric
The percent of pollutant emitted as particulate. Required if
deposition and/or depletion will be modeled, or if a breakdown
by particulate and vapor is desired in the concentration outputs.
If left blank, defaults to 0% particulate when deposition is
modeled. If deposition is not modeled, this field is ignored by
HEM4.
A sample template is provided in the HEM4 Inputs folder named HEM4_HAP_Emiss.xlsx. The
pollutants emitted per source at each facility are required in every HAP Emissions file and are
discussed in Section 3.3.1. The percent particulate emitted from each source is generally only
required if you are modeling deposition or depletion (see Section 3.2.6) and is discussed in
Section 3.3.2.
Table 5. Sample HAP Emissions Input File
Facility ID
Source ID
Pollutant
Emissions
(tons/year)
Fraction
Emitted as
Particulate
Matter (%)
Fac2-IL
CT0001
Antimony compounds
1.2E-01
100.0
Fac2-IL
CT0001
Chromium (VI) compounds
3.2E-04
100.0
Fac2-IL
CT0001
Mercury (elemental)
4.2E-02
50.0
Fac2-IL
CV0001
Dibenzofuran
1.1E-01
90.0
Fac2-IL
CV0001
Xylenes (mixed)
1.3E+00
0.0
Fac1-NC
SR0001
Benz(a)anthracene
7.3E-06
11.9
Fac1-NC
SR0001
Benzo(a)pyrene
2.5E-08
23.9
Fac1-NC
SR0001
Benzo(b)fluoranthene
2.8E-06
17.8
Fac1-NC
MS0001
Chrysene
3.2E-05
52.3
Fac1-NC
MS0001
Dibenz(a,h)anthracene
3.6E-08
99.3
Fac1-NC
MS0001
lndeno(1,2,3-cd)pyrene
1.1E-07
98.9
Fac1-NC
RW0001
Chromium (VI) compounds
3.8E-05
100.0
Fac1-NC
RW0001
Mercury (elemental)
3.6E-04
50.0
Fac1-NC
RV0001
Nickel compounds
4.8E-03
100.0
3.3.1 Pollutant Emissions per Source
You should include one record (row) for each combination of facility (Facility ID), emission
source (Source ID) and chemical (Pollutant) in your HAP Emissions file. The Source ID is a key
parameter in the HAP Emissions file, because HEM4 uses the Source ID to link the emitted
HAP at that source to other input files, such as the Emissions Location input file (discussed in
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Section 3.4) and other optional input files (discussed in Section 3.5). The Source ID should
provide each source a distinct name, and different sources should have unique Source IDs even
if they will be modeled at the same location. AERMOD requires that the Source ID be
restricted to eight (8) characters (or fewer) and it must consist of all alphanumeric
characters. Do not use spaces at the beginning or in the middle of the Source ID. In addition,
AERMOD converts all letters in the Source ID string to upper case. Therefore, upper and
lowercase characters cannot be discriminated between; so "ABC" and "abc" would be
treated as the same Source ID. While each source should have a unique Source ID, it is
advantageous to group certain types of sources within part of the Source ID. For example, "ST"
could be used in the Source ID to indicate a storage tank and each distinct storage tank could
be given a number (e.g., ST01, ST02). Such grouping is important for certain summary
programs, as discussed in Section 4.5.
Each chemical you name in the HAP Emissions file (under "Pollutant" in the sample shown in
Table 5) must match one of the chemical names listed in the dose response table located in the
HEM4 resources folder. The dose response values are part of HEM4's Chemical Health Effects
Library, described in Section 2.2. If necessary, you can add pollutants to the two Excel™
spreadsheets comprising HEM4's Chemical Health Effects Library: the dose response table and
the target organ endpoints table. Section 3.5.10 explains how to make changes to the Chemical
Health Effects Library. Finally, emission amounts for each HAP emitted from each Source
ID must be expressed in tons/year. Be sure your input files use the correct units.
3.3.2 Percent Particulate for Deposition and Depletion
If you are modeling deposition or depletion, or if you want separate records for particle phase
and vapor phase at each receptor location in the concentration outputs, then you must provide
HEM4 with the breakdown between vapor and particulate matter in the emission inputs. Provide
this breakdown in column E of the HAP Emissions file, expressed as the fraction emitted as
particulate for each emission record (each combination of source and pollutant). For a given
facility, if you are not modeling deposition or depletion, then HEM4 will ignore the field. If you
are modeling deposition or depletion and have left this field blank, then HEM4 assigns the blank
a default value of 0% particulate. Note that if you are modeling deposition or depletion, you will
need additional input files depending on the type of deposition to be modeled, as described in
Section 3.2.6 and Sections 3.5.3 and 3.5.4. (Note: You do not need any additional input files if
you merely want a breakdown of particle and vapor in your outputs.)
3.4 Emissions Location File
The Emissions Location Excel™ file, like the HAP Emissions file and the Facility List Options
file, is required for any HEM4 run. The file includes emission source locations and types (e.g.,
the latitude and longitude of a stack) for all Source IDs listed in the HAP Emissions file, for all
facilities listed in the Facility List Options file. Tables 6 and 7 display the format guidelines for
the fields in the Emissions Location file and a sample file, respectively. A sample template is
provided in the HEM4 Inputs folder named HEM4_Emiss_Loc.xlsx. For each Source ID at every
facility, the Emissions Location file includes the location, source type and required parameters,
as discussed in Section 3.4.1. Additionally, the Emissions Location file includes the particle
deposition method you will identify, for any sources for which you wish to model particle
deposition or depletion, as discussed in Section 3.4.2.
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Table 6. Fields in the Emissions Location Input File (Required)
Field
Type
Source
type(s)*
Description
Facility ID
Character
all
An alphanumeric string identifying the facility being
modeled
Source ID**
Character
all
Source ID is a unique alphanumeric character string up to
8 characters long, with no spaces. It must match exactly
the Source ID in other input files (e.g., the HAP Emissions
file). Note: AERMOD allows a maximum of 8 characters
for the Source ID; and all Source IDs will be converted to
upper case by AERMOD.
Coordinate
system
Character
all
Type of coordinates: L = latitude, longitude; U = UTM.
Base all coordinates on the WGS84 geographic system.
Note: NAD83 and WGS84 are identical for most
applications, but coordinates based on NAD27 need to be
converted to WGS84 before being used in HEM4.
X-coordinate
Numeric
all
UTM east coordinate, in meters (if coordinate system = U)
or decimal longitude (if system = L) of the center of point
or volume sources, the southwest corner of area sources,
the first vertex of polygon sources, or the starting point of
line and buoyant line sources.*** For longitudes, 5 decimal
place accuracy is recommended, corresponding to 1-
meter accuracy.
Y-coordinate
Numeric
all
UTM north coordinate, in meters (if coordinate system =
U) or decimal latitude (if system = L) of the center of point
or volume sources, the southwest corner of area sources,
the first vertex of polygon sources, or the starting point of
line and buoyant line sources. *** For latitudes, 5 decimal
place accuracy is recommended, corresponding to 1-
meter accuracy.
UTM zone
Character
all
UTM zone where the source is located if the coordinate
system = U; leave this field blank if the coordinate system
= L. If using the UTM coordinate system, enter the UTM
Zone from 1 to 60 followed by the hemisphere (S or N).
For example, 17N. If you do not include a hemisphere, will
default to N.
Source type
Character
all
Type of source*: P = vertical point, C = capped point, H =
horizontal point, A = area, V = volume, I (capital "i") =
polygon, N = line, B = buoyant line
Length - x
Numeric
A, N
Length in meters in x-dimension direction for area and line
sources. For area source types, the x direction refers to
the direction before the source is rotated (if it is rotated).
For line source types, enter the width (m), which must be
>= 1 meter.
Length - y
Numeric
A
Length in meters in y-dimension direction for area
sources. This is the length in the y direction before the
source is rotated (if it is rotated).
Angle
Numeric
A
Angle of rotation: blank except for area sources. For area
source tvDes. enter the anale of rotation (from North')
between 0 and 90 degrees. (Defaults to 0 if left blank).
Lateral
Numeric
V
Initial lateral/horizontal dimension (in meters) for volume
sources.
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Field
Type
Source
type(s)*
Description
Vertical
Numeric
V, A, I,
N
Initial vertical dimension (in meters) for volume sources.
Optional for area, polygon & line sources.
Release height
Numeric
V, A, I,
N, B
Height of release (in meters) for area, volume, polygon,
line, and buoyant line sources. Use the height (top) of the
source for area and polygon sources and the vertical
center for volume sources. Note: that for buoyant line
sources, AERMOD requires a minimum release height of
2 meters.
Stack height
Numeric
P, C, H
Release height above ground (in meters) for all point
source types.
Diameter
Numeric
P, C, H
Diameter of stack (in meters) for all point source types.
Velocity
Numeric
P, C, H
Velocity at which emissions are released from the stack
(in meters/second) for all point source types.
Temperature
Numeric
P, C, H
Temperature (in Kelvin) at which emissions exit the stack
for all point source types.
Elevation
Numeric
all
Elevation above sea level in meters at the source location.
Use when modeling terrain effects and user-specified
elevations are desired. This field is optional; HEM4 will
calculate if all source elevations are left blank. Note: if an
elevation value is provided by the user for one or more
sources, any blanks (i.e., non-entries for other source
elevations) will be interpreted by the model as an
elevation of 0 meters; therefore, either enter elevations for
every source or leave all blank.
X-coordinate2
Numeric
N, B
Second X (end) coordinate for line and buoyant line
source types. UTM east coordinate, in meters (if
coordinate system = U) or decimal longitude (if system =
L) of the ending point of line and buoyant line sources.***
For longitudes, 5 decimal place accuracy is
recommended, corresponding to 1- meter accuracy.
Y-coordinate2
Numeric
N, B
Second Y (end) coordinate for line and buoyant line
source types. UTM north coordinate, in meters (if
coordinate system = U) or decimal latitude (if system = L)
of the ending point of line and buoyant line sources.*** For
latitudes, 5 decimal place accuracy is recommended,
corresponding to 1-meter accuracy.
Method Numeric Any but The Method field indicates the type of particle deposition
B AERMOD should use. Enter 1 or leave blank for Method 1
(which is the default); enter 2 for Method 2.
Use Method 1 when greater than 10 percent of the total
particulate mass has a diameter of 10 jjm or larger, or
when the particle size distribution is known. For Method 1,
the source-specific particle size distributions must be
provided in a separate particle data file (described in
Section 3.5.3). Method 2 may be used when the particle
size distribution is not well-known and when a small
fraction (less than 10 percent of the mass) is in particles
with a diameter of 10 jjm or larger. The particle data
required for Method 2 is less specific than Method 1 but
requires that you enter the mass fraction of fine particles
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Field
Type
Source
type(s)*
Description
Method, cont'd
Numeric
Any but
B
and the mass-mean particle diameter for the given source
in the next two fields.
Mass Fraction
Numeric
All,
except
B
The Mass Fraction field refers to the fraction of the particle
mass emitted from this source in the fine particle category
(less than 2.5 microns). Leave this field blank if you are
using Method 1. For Method 2, you should enter a number
between 0 and 1 that is the fraction of particles emitted in
the fine category (a blank will be interpreted as a 1, the
default, meaning that all are emitted as fine particles). For
example, if one-half of the emissions from this source are
fine particles (< 2.5 microns), enter a mass fraction in this
field of 0.50.
Particle
Diameter
Numeric
All,
except
B
The Particle Diameter field is the representative mass-
mean aerodynamic particle diameter in microns emitted
from this source when using Method 2 for particle
deposition (a blank is interpreted as 1 micron, the default).
Leave this field blank for Method 1. For Method 2, enter
the mass-mean particle diameter in microns.
Table Notes:
* Source types for which the parameter is used: all = needed for every source type, A = area, P = vertical point,
C = capped point, H = horizontal point, V = volume, I (capital "i") = polygon, N = line, B = Buoyant line. Note that
currently AERMOD cannot model deposition/depletion for buoyant lines (B), nor can the FASTALL option be used
with buoyant lines. For additional information on these source types, including what additional fields are needed, see
the AERMOD User's Guide at https://www.epa.aov/scram/air-aualitv-dispersion-modelina-preferred-and-
recommended-models#aermod
** If you are modeling deposition or depletion and pollutant properties are known to vary, use a separate record for
each pollutant and source. Therefore, for vapor deposition/depletion modeling, use a unique Source ID for each
pollutant emitted from a given source (e.g., SAMPLE3A for benzene, SAMPLE3B for 1,3-butadiene). Likewise, use a
unique Source ID when modeling particulate deposition or depletion if the particulate properties (size and density
distributions) are known and vary by pollutant, not just source. If you are not modeling vapor deposition/depletion and
the same properties are assumed for all particulates emitted from a source, one Source ID per emission source is
sufficient (e.g., SAMPLE3 for all modeled pollutants from the same source).
*** Start/end coordinates for buoyant line sources generally should be entered in order from West to East, and from
South to North. However, in the case where the buoyant lines are parallel to the Y axis, the order that the lines should
be entered is dependent on which endpoint is entered first, the southern or northern endpoint of the lines. If the
southern endpoint is entered first, the lines should be entered in the order of the eastern most line to the western
most line. If the northern endpoint is entered first, lines should be ordered west to east. Incorrect ordering of these
parameters will result in an AERMOD error stating "Input buoyant line sources not in correct order". See page 3-61 of
the AERMOD User's Guide for more detail (EPA2022a).
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Table 7. Sample Emissions Location Input File
Source Locations & Types
Dimensions & Release Height (non-point sources)
Facility ID
Source ID
Coordinate
system
(U = UTM,
L= latitude/
longitude)
(All source
types)
X-coordinate
Longitude
(decimal)
or UTM East
(m)
(All source
types)
Y-coordinate
Latitude
(decimal) or
UTM North
(m)
(All source
types)
UTM
zone
Source type
(P, C, H =
point,
A = area
V= volume
I = polygon
N = line
B = buoyant
line)
Length in x-
direction
(m)
A & N
sources
(width for N
sources)
Length in y-
direction
(m)
A sources
Angle
(degrees)
A sources
Lateral
Dim.
(m)
V sources
Vertical Dim.
(m)
V sources or
optionally
A, I and N
sources
Release
height
(m)
A, V, I, N
and B
sources
continued
Fac2-IL
CT0001
L
-88.257293
41.480164
P [or C or HI
Fac2-IL
CV0001
L
-88.256715
41.481944
A
130
120
45
2
Fac1-NC
SR0001
L
-78.883686
35.900628
V
20
3
10
Fac1-NC
MS0001
L
-78.888792
35.905920
I
5
Fac1-NC
RW0001
L
-78.888430
35.901810
N
20
50
Fac1-NC
RV0001
U
690891
3975044
17
B
40
Point Source Parameters
Buoyant & Line Endpoints
Particle Deposition Method
...continued
from
above
(Source type
indicated for
reference)
Stack height
(m)
P, C, orH
sources
Stack Diameter
(m)
P, C, orH
sources
Exit Velocity
(m/s)
P, C, orH
sources
Exit
Temperature
(K)
P, C, orH
sources
Elevation
(m)
HEM4 will
calculate if
blank for
every
source
X-coord.2
Longitude
(decimal) or
UTM East
(m)
B & N
sources
Y-coord.2
Latitude
(decimal) or
UTM North
(m)
B & N
sources
Method
(1 or 2;
defaults to 1)
All sources,
except B
Mass
Fraction
(decimal > 0
and < 1 for
Method 2
only)
All sources,
except B
Particle
Diameter
(microns, for
Method 2
only)
All sources,
except B
...(P, C or H)
50
2.8
21.83
322
2
0.04
0.0006
...(A)
¦ ¦¦(V)
...(I)
...(N)
-78.886303
35.902183
...(B)
691291
3975044
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3.4.1 Source Types and Parameter Requirements
Generally, the Emissions Location file should include one record for each individual source
(e.g., stack/point source, area source, line source, buoyant line source) to be modeled, at each
facility. For certain modeling situations, more than one record per source is recommended.4
This record provides information on the location, size, height, and configuration for each source.
You must enter every Facility ID to be modeled in column A of the Emissions Location file. Enter
each Source ID in column B, taking care to match each named Source ID with a corresponding
Source ID in the HAP Emissions file, described in Section 3.3.
Source Locations: In column C "Coordinate system", you can enter source locations as UTM
coordinates, or as latitude and longitude (which HEM4 will convert to UTM coordinates for use
in AERMOD). Complete the coordinate system field for each source record and specify which
coordinates you are entering. Enter "U" for UTM or "L" for latitude and longitude. If using UTM
coordinates, specify the UTM zone (in each emission source record). Enter the location
coordinates for each source in column D "X coordinate, Longitude (decimal) or UTM East (m)"
and in column E "Y coordinate, Latitude (decimal) or UTM North (m)". (The endpoints for line
and buoyant line source types, discussed further below, will be entered is columns S and T.) If
you are using longitudes and latitudes, five decimal places are recommended which
corresponds to an accuracy of roughly 1 meter. See Table 6 above for further specifications for
these fields. You must base all coordinates on the WGS84 geographic system. As noted in
Section 3.1, NAD83 and WGS84 are identical for most applications, so no conversion is needed
if using coordinates based on NAD83. However, if coordinates are based on NAD27, they would
need to be converted to WGS84 before being used in HEM4. There are various commercial
computer programs available that can perform this conversion.
Source Types: Use the source type field in column G to indicate whether the emission source is
a vertical non-capped point source (P), a capped point source (C), a horizontal point source (H),
an area source (A), a volume source (V), a polygon source (I, for upper case "i"), a line source
(N), or a buoyant line source (B)5. For additional information on these source types, including
assumptions used by AERMOD to model their emissions as well as the additional parameters
needed for each, you should consult the AERMOD User's Guide at
https://www.epa.qov/scram/air-qualitv-dispersion-modelinq-preferred-and-recommended-
models#aermod.
Point Sources - Vertical stack. Horizontal stack, and Capped stack: Point source types include
vertical stacks (P), horizontal stacks (H) and capped stacks (C) source types. These point
sources require you to specify the stack height (in meters in column N), the stack diameter (in
meters in column O), the exit velocity (in meters/second in column P), and the exit/release
temperature (in Kelvin in column Q) for the pollutant plume. Although capped and horizontal
4 If modeling deposition or depletion (described in Section 3.2.6) at a facility, and pollutant properties are
known to vary, we recommend you include a separate Source ID record for each pollutant and source—
that is, a unique Source ID—for each pollutant being emitted from the same source. This is generally
recommended for modeling of vapor deposition/depletion and for modeling of particulate deposition/
depletion if the size or density distributions are known for each pollutant (HAPJ and vary for each
pollutant. If you are not modeling deposition/depletion of vapor phase pollutants, and the same particulate
properties are assumed for all pollutants being emitted from a given source, one record per source in the
emissions location input file is sufficient.
5 Note that the current AERMOD version cannot model deposition or depletion for buoyant lines (B), nor
can the FASTALL option in the Facility List Options file be used with buoyant lines.
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stacks (C and H, respectively) require the same user-specified parameters as vertical stacks
(P), AERMOD models these point sources differently than vertical stacks (EPA 2022a, EPA
2022b).
Non-Point Sources: Columns H through N in the Emissions Location file pertain to area (A)
sources, volume (V) sources, polygon (I for capital "i) sources, line (N) sources, and buoyant
line (B) sources. Table 6 above provides guidance on what you should provide in each of these
fields. Fugitive emissions are often modeled as rectangular area (A) sources. A conveyor belt, in
which release temperature is assumed to be ambient and release velocity zero or negligible,
may be simulated as volume (V) sources. A polygon (I) can be used to represent a complex
(non-rectangular) area source with many vertices. A polygon (I) may also be used to represent
an entire U.S. Census tract from which a source is modeled as a uniform emission (e.g., for
mobile sources). Polygon source types require a Polygon Vertex file as an additional input, as
discussed in Section 3.5.1. Line source (N) types can be used to represent roadways and
airport runways and may be used instead of similarly shaped area sources. Unlike point source
types (P, C, or H), area (A), volume (V), polygon (I) and line (N) source types in AERMOD all
assume ambient pollutant release temperatures and zero or negligible pollutant release/exit
velocities.
Buoyant line sources (B), on the other hand, are useful in simulating continuous vents along a
roofline where the emissions, like point sources (P, C or H), are released at elevated (non-
ambient) temperature and with a non-zero release velocity. However, unlike tall stack sources
where the plume can move in all directions without impediment, buoyant line source types
simulate pollutants emitted close to a building's roof where vertical wind shear and building
downwash effects become important. Buoyant line (B) source types require a Buoyant Line
Parameters file as an additional input, as discussed in Section 3.5.2.These non-point source
types are discussed in more detail below.
Area Sources: An area source (A) type represents a rectangular area from which emissions are
released at ambient temperature and with zero or negligible velocity (e.g., fugitive emissions
from a building or tank farm). In AERMOD, area sources can be at ground level, or at a height
above ground level. Specifying a release height (in column M) is optional and defaults to 0. The
default orientation for area sources is with one axis in the north-south direction, but you can
rotate these sources using the "angle" parameter (in column J), which specifies the rotation of
the source from north (in the clockwise direction), to better fit the orientation of the source you
are modeling. The X and Y coordinates you choose (in columns D and E) should reflect the
southwest corner of the area source. The length in the X direction you enter (in column H)
should reflect the length of the area source in the easterly direction, or in the southeasterly
direction if the source is rotated. The length in the Y direction you enter (in column I) should
reflect the length of the area source in the northerly direction, or the northeasterly direction if the
source is rotated. Unlike AERMOD, where 360-degree rotation is allowed, the angle parameter
for HEM4 area sources must be between 0 and 90 degrees. You can use this angle to represent
any possible orientation by switching the X and Y lengths (shown in Figure 2). You can also
optionally enter an initial vertical dimension of the area source (in column L).
Volume Sources: Volume source (V) types - such as multiple vents and conveyor belts - are
specified by a lateral /horizontal dimension (you enter in column K), a vertical dimension (you
enter in column L), and a release height (you enter in column M). Emissions from a volume
source are assumed to be released at ambient temperature and with zero or negligible velocity.
Both the release height (in column M) and the source location coordinates (in columns D and E)
should reflect the center of the source.
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Polygon Sources: You can create a polygon source (I, for capital "i") type to represent a polygon
with 3 sides or many more (up to 20 sides). This source type provides considerable flexibility in
specifying the shape of an area source. You can use a polygon source type to reflect U.S.
Census tract boundaries, for example, when modeling mobile source emissions provided at the
tract level. An associated polygon vertex input file is required when modeling polygon source
types. Section 3.5.1 discusses this in more detail. The shape of the polygon source, as defined
in the Polygon Vertex Input file, is determined by a list of X and Y coordinates representing the
vertices of the polygon. You can order these X and Y coordinates in either a clockwise or
counterclockwise direction. However, the first coordinates entered in the Polygon Vertex Input
file must match the coordinates entered in the emissions location file (in columns D and E) as
the location of the first vertex of the polygon. You can also optionally enter an initial vertical
dimension of the polygon (in column L). Emissions from polygon source types are assumed to
be released at ambient temperature and zero or negligible velocity.
Line Sources: The line source (N) type allows you to specify long, narrow sources, such as
roadways or airport runways. You must enter a start point (in columns D and E) and endpoint of
the line (in columns S and T), as well as the width of the line (a value equal to or greater than 1
meter that you enter in column H). Optionally, you can also specify an initial vertical dimension
(in column L). In this way, the line source can be used as an alternative to a rectangular area
source (A). [Note: According to the AERMOD User's Guide (EPA 2022a) the line source type
utilizes the same routines as the area source type and will give identical results, given the same
inputs.] Like area, volume and polygon source types, emissions from line source types are
assumed to be released at ambient temperature and zero or negligible velocity.
Buoyant Line Sources: Like the line source, for the buoyant line source (B), you must enter the
starting coordinates (in columns D and E) and the end coordinates (in columns S and T).6 The
buoyant line source (B) type was first developed to simulate the transport and diffusion of
emissions from aluminum reduction plants in which some emissions from the reduction process
escape through continuous (rooftop) ridge ventilators (ERT 1980). In general, the buoyant line
source can be used to characterize emissions from a continuous roof vent that spans a portion
or the entire building. Emissions from such buoyant line sources result in enhanced plume rise
(especially from multiple rows of closely spaced emission lines) and the plume is subject to
vertical wind shear and building downwash effects. This source type incorporates an average
buoyancy parameter (in meters4/seconds3) as well as the average building dimensions (in
meters) of the building(s) on which the buoyant line source is located. You must provide HEM4
with these inputs for your buoyant line source type in a Buoyant Line Parameters Input file, as
discussed in Section 3.5.2. It should be noted that AERMOD requires a minimum release height
(in your Emissions Location file) of 2 meters for buoyant line sources. (If you enter a release
height less than 2 meters, AERMOD will change it to 2 meters.) Also, as noted previously, the
current version of AERMOD cannot model deposition or depletion for buoyant lines, nor can the
FASTALL option in the Facility List Options file be used with buoyant lines. For more detailed
6 You may wish to use a series of buoyant lines to represent multiple roof vent lines. AERMOD requires a
strict ordering of these lines to run properly. The start/end coordinates for buoyant line sources generally
should be entered in order from West to East, and from South to North. However, in the case where the
buoyant lines are parallel to the Y axis, the order that the lines should be entered is dependent on which
endpoint is entered first, the southern or northern endpoint of the lines. If the southern endpoint is entered
first, the lines should be entered in the order of the eastern most line to the western most line. If the
northern endpoint is entered first, lines should be ordered west to east. See page 3-61 of the AERMOD
User's Guide for more detail (EPA2022a).
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information regarding the necessary inputs for the buoyant line source type, see the AERMOD
User's Guide (EPA 2022a), as well as documentation for the buoyant line and point source
(BLP) dispersion model (ERT 1980).
Elevation: If you wish to consider terrain impacts in your modeling, you can specify the elevation
above sea level in meters for each emission source. Enter elevations (in column R) for every
source or for no sources; do not enter a partial list, because in that case blanks/non-entries will
be interpreted by the model as a zero (0) elevation if a value is entered for one or more other
sources. If you leave the elevation field blank for all sources, and if you chose to model
elevations in the Facility List Options file, then HEM4 will estimate an elevation for the emission
sources based on the elevations of nearby U.S. Census blocks or alternate receptors. Note that
if you chose not to model elevations in your Facility List Options file, then no elevations will be
considered in the model run including for sources in the Emissions Location file.
HEM4 will model area, volume, polygon, line, and buoyant line sources as flat surfaces, which
can result in strangely located (underground) impacts if the source is located, for example, on a
hillside with varying elevations. To avoid this, either opt to model with no elevations in the
Facility List Options file, or break-up the source into smaller pieces with uniform elevations.
It should also be noted that "release height" (in column M) is different than elevation and
indicates the height above the ground elevation where emissions are released (in which the
ground is set to an elevation above sea level, or not, as discussed in the preceding paragraphs
discussing the elevation field). For point sources, fill in the "stack height" field (in column N) to
designate the release height (for vertical stack, horizontal stack and capped stack source
types). For all other source types (area, volume, polygon, line and buoyant line), you should fill
in the "release height" (in column M) with the source's height above the ground (in meters). If
you leave this field blank, HEM4 will assume the release height is zero (0), meaning at ground
level.
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X-dim= L
Y-dim = S
Angle = 45°
Figure 2. Example Orientations of Area Emission Sources for the HEM4 Model
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3.4.2 Particle Deposition Method
Columns U (Method), V (Massfrac), and W (Partdiam) of the Emissions Location file should only
be filled in if you wish to model particle deposition or depletion using Method 2. If you do not
wish to model particle deposition/depletion or if you wish to use AERMOD's Method 1 to model
particle deposition/ depletion, then leave these fields blank for those sources.
Particle Deposition/Depletion Method: The Method field (in column U) indicates to HEM4 the
type of particle deposition AERMOD should use. As noted above, you should enter 1 or leave
this field blank for Method 1 (which is the default). Method 1 should be used when a significant
fraction (greater than about 10 percent) of the total particulate mass has a diameter of 10 |jm or
larger, or when the particle size distribution is known. The particle size distribution must be
known reasonably well to use Method 1 and these source-specific particle size distributions
must be provided in a separate Particle Data file, as discussed in Section 3.5.3. You should also
leave this field (column U) blank if you are not modeling particle deposition/depletion. Enter 2 in
this field if you wish to model particle deposition or depletion for the given source using
AERMOD's Method 2. Method 2 may be used when the particle size distribution is not well
known and when a small fraction (less than 10 percent of the mass) is in particles with a
diameter of 10 |jm or larger. The particle data required for Method 2 is less detailed than
Method 1 but does require that you enter the mass fraction of fine particles and the mass-mean
particle diameter for the given source in the next two fields.
Mass Fraction for Method 2: The Mass Fraction field (in column V) refers to the fraction of the
particle mass emitted from this source in the fine particle category (less than 2.5 microns).
Leave this field blank if you are using Method 1, or if you are not modeling particle deposition/
depletion at all. For Method 2, you should enter a number between 0 and 1 that is the fraction of
particles emitted in the fine category (a blank will be interpreted by the model as a 1, the default,
meaning that all are emitted as fine particles). For example, if one-half of the emissions from
this source are fine particles (< 2.5 microns), enter a mass fraction in this field of 0.50.
Particle Diameter for Method 2: The Particle Diameter field (in column W) is the representative
mass-mean aerodynamic particle diameter in microns emitted from this source when using
Method 2 for particle deposition (a blank is interpreted by the model as 1 micron, the default).
Leave this field blank for Method 1, or if you are not modeling particle deposition/depletion at all.
For Method 2, enter the mass-mean particle diameter in microns.
3.5 Additional Input Files
In addition to the three required input files (Facility List Option, HAP Emissions, and Emissions
Location) discussed in Sections 3.2, 3.3 and 3.4, other files may be required for your modeling
run depending on (a) what modeling options you chose in the Facility List Options file, (b) what
source types you are modeling in your Emissions Location file, (c) what kinds of receptors you
are modeling with, and/or (d) what changes you may wish to make to HEM4's underlying
databases and resource files. These additional input files are discussed in the next sections.
3.5.1 Polygon Vertex Input File for Modeling Polygon Emission Sources
If your Emissions Location input file contains one or more polygons (source type "I", for capital
"i"), then HEM4 will prompt you for a Polygon Vertex file. This file provides HEM4 with the
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locations of the polygon vertices. Polygons are useful for complex source configurations at a
facility, and for modeling U.S. Census tracts as sources (e.g., for mobile source emissions
modeled uniformly across a tract).
Include a separate record for each vertex of the polygon in the Polygon Vertex file. A polygon
may have any number of vertices (> 3 and < 20). Each record must include information for one
vertex of the polygon. As noted in Section 3.4.1, you can order the X and Y vertex coordinates
in either a clockwise or counterclockwise direction. The first and last vertex must have identical
coordinates, and these coordinates must match the coordinates listed as the location of the first
vertex of the polygon source in your Emissions Location file. The first record for each polygon
source must also include the number of vertices for the polygon and the total area of the
polygon, in meters squared. You can enter coordinates as UTM coordinates, or as longitudes
and latitudes. If using UTM coordinates, you must specify the UTM zone. Base all coordinates
on the WGS84 reference system.
Optionally, you can assign an ID (name) to the polygon. This may be useful, for example, if you
are using the polygon to model a U.S. Census tract. In this case, you may wish to use the U.S.
Census tract ID as the polygon ID and enter it in the last column of the Polygon Vertex file.
Tables 8 and 9 give the format guidelines for the Polygon Vertex file, and a sample Polygon
Vertex file, respectively. A sample template is provided in the HEM4 Inputs folder named
HEM4_polygon_ vertex, xlsx.
Table 8. Format Guidelines for the Polygon Vertex File
Field
Type
Description
Facility ID
Character
An alphanumeric character identifying the facility being
modeled containing the polygon(s)
Source ID
Character
An alphanumeric character string up to 8 characters long, with
no spaces. The Source IDs must be listed as polygon (Type = I,
for caDital "i") source tvDes in the Emissions Location file. Note:
AERMOD allows a maximum of 8 characters for the Source ID;
and all Source IDs will be converted to upper case by
AERMOD.
Coordinate
system
Character
Type coordinates: L = longitude, latitude; U = UTM [WGS84],
X-coordinate
Numeric
UTM east coordinate, in meters (if Coordinate System = U) or
decimal longitude (if System = L). For longitudes, 5 decimal
place accuracy is recommended, corresponding to 1-meter
accuracy.
Y-coordinate
Numeric
UTM north coordinate, in meters (if Coordinate System = U) or
decimal latitude (if System = L). For latitudes, 5 decimal place
accuracy is recommended, corresponding to 1-meter accuracy.
UTM zone
Numeric
If using the UTM coordinate system (U), enter the UTM Zone
from 1 to 60 followed by the hemisphere (S or N). For example,
17N (default hemisphere is N if not specified). If using
longitudes/latitudes, leave this cell blank.
Num of Vertices
Numeric
Number of vertices in the polygon. This number must be 3 or
greater. The upper limit is 20.
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Field
Type
Description
Area
Numeric
Size of area within polygon, in meters squared.
Polygon ID
Character
Optional ID to indicate the name of the polygon (e.g., a U.S.
Census tract is sometimes modeled as a polygon and the
polygon ID may be the U.S. Census tract ID).
Table 9. Sample Polygon Vertex File
Facility ID
Source ID
Coordinate
system
(U = UTM, L
= latitude,
longitude)
Longitude
(decimal) or
UTM East
(m)
Latitude
(decimal) or
UTM North
(m)
UTM
zone
Num of
Vertices
(> 3 and
<20)
Area
(m2)
Polygon
ID
(optional)
Fac1-TX
SAMPLE4
L
-95.3586
29.7674
9
402939.4
Fac1-TX
SAMPLE4
L
-95.3524
29.7685
0
Fac1-TX
SAMPLE4
L
-95.3515
29.7663
0
Fac1-TX
SAMPLE4
L
-95.3533
29.7654
0
Fac1-TX
SAMPLE4
L
-95.3533
29.7622
0
Fac1-TX
SAMPLE4
L
-95.3574
29.7634
0
Fac1-TX
SAMPLE4
L
-95.3582
29.7651
0
Fac1-TX
SAMPLE4
L
-95.3575
29.7661
0
Fac1-TX
SAMPLE4
L
-95.3586
29.7674
0
Fac1-TX
SAMPLE5
L
-95.3512
29.7688
11
710176.8
Fac1-TX
SAMPLE5
L
-95.3524
29.7685
0
Fac1-TX
SAMPLE5
L
-95.3515
29.7663
0
Fac1-TX
SAMPLE5
L
-95.3509
29.7653
0
Fac1-TX
SAMPLE5
L
-95.3533
29.7654
0
Fac1-TX
SAMPLE5
L
-95.3533
29.7622
0
Fac1-TX
SAMPLE5
L
-95.3574
29.7634
0
Fac1-TX
SAMPLE5
L
-95.3582
29.7651
0
Fac1-TX
SAMPLE5
L
-95.3575
29.7661
0
Fac1-TX
SAMPLE5
L
-95.3586
29.7674
0
Fac1-TX
SAMPLE5
L
-95.3512
29.7688
0
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3.5.2 Buoyant Line Parameter Input File for Modeling Buoyant Line Sources
If your Emissions Location input file contains one or more buoyant line sources (source type
"B"), then HEM4 will prompt you for a Buoyant Line Parameter file. Buoyant line source types
are useful in simulating continuous rooftop vents in which emissions are released at non-
ambient (elevated) temperature and non-negligible velocity, as discussed in Section 3.4.1.
Because building downwash effects are especially important with buoyant line source types, the
Buoyant Line Parameter file must provide HEM4 with the length, width, and height of the
building(s) on which the buoyant line source type (e.g., rooftop vent) sits. In addition, the file
must contain the width of the buoyant line source(s), the distance between the buildings (zero
for a solitary buoyant line), and the buoyancy parameter for the buoyant line source(s).
In a previous version of AERMOD, multiple buoyant lines could be modeled but only one set of
"average" parameters for all buoyant lines could be used. The current version of AERMOD
allows you to input multiple buoyant line source groups, with individual parameters for each
group (containing average building dimensions, average line source width and separation, and
average buoyancy parameter). Consequently, HEM4 now allows multiple buoyant line source
groups per facility, with each group containing one or multiple lines. Note that the number of
individual lines associated with a buoyant line source group is unlimited, but each individual
buoyant line may belong to one and only one buoyant line group. (See the AERMOD User's
Guide for further information; EPA 2022a).
The buoyancy parameter of a line source is calculated from an equation based on the line
source length (m) and width (m), the exit/release velocity (m/s), the exit/release temperature (K),
the ambient temperature (K) and the acceleration due to gravity (9.81 m/s2), as presented in
Equation 2-47 on page 2-37 of the Buoyant Line and Point Source Dispersion Model User's
Guide (ERT 1980).7 These parameters should be average values for the array of buoyant
line sources in each group, if more than one parallel buoyant lines are modeled within
the group (EPA 2022a). Provide the following parameters in the Buoyant Line Parameter File:
• Facility ID;
• Buoyant Line Group ID associated with facility;
• Source ID(s) included in buoyant line group (one or more);
• Average Building Length (in meters);
• Average Building Height (in meters);
• Average Building Width (in meters);
• Average Line Source Width, of the individual lines (in meters);
• Average Building Separation, between the individual lines (in meters); and
• Average Buoyancy Parameter (in meters4/seconds3)
Tables 10 and 11 provide the format guidelines for the Buoyant Line Parameter input file and a
sample input file, respectively. A sample template is provided in the HEM4 Inputs folder named
HEM4_buoyant_line_param.xlsx. See also the resources shown in footnote 6 below for helpful
guidance in setting up a buoyant line source.
7 In addition, diagrams detailing buoyant line equation parameters and sample calculations are available
in: Source Characterizations: Buoyant Line Sources, Missouri Department of Natural Resources Air
Pollution Control Program, http://dnr.mo.qov/env/apcp/docs/buovantlinesources10-24-12.pdf on website
http://dnr.mo.gov/env/apcp/permitmodelinq/sourcecharacterizations.htm. November 12, 2013.
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Table 10. Format
Guidelines
for the Buoyant Line Parameter Input File
Field
Type
Description
Facility ID
Character
An alphanumeric character string identifying the facility being
modeled containing the buoyant line(s)
Buoyant Line
Group ID
Character
An alphanumeric character string identifying a buoyant line group.
One or more individual lines may be associated with each buoyant
line group. A facility may have more than one buoyant line group,
although each must have a unique ID. Different facilities may use the
same buoyant line group ID.
Source ID
Character
An alphanumeric character string up to 8 characters long, with no
spaces. The Source ID must be listed as a buoyant line (Type = B)
source tvoe in the Emissions Location file. Note: AERMOD allows a
maximum of 8 characters for the Source ID; and all Source IDs will be
converted to upper case by AERMOD.
Average Building
Length
Numeric
The average length of the building or buildings on which the parallel
buoyant line source types in the group are located (in meters)
Average Building
Height
Numeric
The average height of the building or buildings on which the parallel
buoyant line source types in the group are located (in meters)
Average Building
Width
Numeric
The average width of the building or buildings on which the parallel
buoyant line source types in the group are located (in meters)
Average Line
Source Width
Numeric
The average width of the individual buoyant line source types in the
group (in meters)
Average Building
Separation
Distance
Numeric
The average building separation distance between the (parallel)
individual buoyant lines in the group (in meters)
Average
Buoyancy
Parameter
Numeric
The average buoyancy parameter for the buoyant line emission
plumes (in meters4/seconds3) in the group; See BLP Dispersion
Model documentation (ERT 1980).
Table 11. Sample Buoyant Line Parameter Input File
Facility ID
Buoyant
Line
Group ID
Source ID
Avg
Building
Length
(m)
Avg
Building
Height (m)
Avg
Building
Width (m)
Avg Line
Source
Width (m)
Avg
Building
Separation
(m)
Avg
Buoyancy
(m4/s3)
Fac1-NC
BLG1A
RV01
454.3
16.76
40
5.73
40.95
3335.49
Fac1-NC
BLG1A
RV02
454.3
16.76
40
5.73
40.95
3335.49
Fac1-NC
BLG2A
RV03
220.5
10.50
20
3.25
35.25
3010.25
Fac1-NC
BLG2A
RV04
220.5
10.50
20
3.25
35.25
3010.25
Fac2-IL
BLG1A
RV01
212
25
35
4.50
25
2750.5
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3.5.3 Particle Data Input File for Modeling Particulate Deposition and Depletion
AERMOD can implement dry and wet deposition and plume depletion of both particulate and
vapor emissions (EPA 2022a). This section describes the input file needed for modeling
particulate deposition and/or particulate depletion.
If you indicated in your Facility List Options file that your run will model deposition or depletion of
particulate emissions AND you chose (in your Emissions Location file) to use Method 1 for
particle deposition for one or more sources, then you must provide HEM4 with a separate
Particle Data input file describing the particle size distribution. In this file, include a separate
record for each particle size range emitted by each emission source, for which HEM4/AERMOD
will model particle deposition/depletion using Method 1. Each record must include an average
particle diameter for the size range, the percentage that the size range represents in terms of
the total mass of particulate matter from the given emission source, and the average density of
particles in the size range. The mass percentages must total to 100 for each emission source
(for which you are modeling particle deposition/depletion using Method 1). Tables 12 and 13
provide format guidelines for the Particle Data input file and a sample input file, respectively. A
sample template is provided in the HEM4 Inputs folder named HEM4_particle_data.xlsx.
Table 12. Format Guidelines for the Particle Data Input File
Field
Type
Description
Facility ID
Character
An alphanumeric character string identifying the facility
being modeled
Source ID
Character
The Source ID is a unique alphanumeric character string
up to 8 characters long with no spaces. It must match a
Source ID in the HAP Emissions and Emissions Location
file. Note: AERMOD allows a maximum of 8 characters for
the Source ID; and all Source IDs will be converted to
upper case by AERMOD.
Particle
diameter
Numeric
The average diameter (in |am) for the particle size range
covered by this record.
Mass fraction
Numeric
The percentage (by mass) of particulate matter in this size
range. Must add up to 100% for each Source ID.
Particle
density
Numeric
The average density of the particles in this size range (in
g/cm3).
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Table 13. Sample Particle Data Input File
Particle diameter
Mass fraction
Particle density
Facility ID
Source ID
(|j.m)
(%)
(g/cm3)
Fac1-TX
SAMPLE1
0.50
72.0
1.00
Fac1-TX
SAMPLE1
1.50
8.0
0.75
Fac1-TX
SAMPLE1
2.50
4.0
0.50
Fac1-TX
SAMPLE1
4.00
4.0
1.00
Fac1-TX
SAMPLE1
10.00
12.0
0.35
Fac1-TX
SAMPLE2
0.50
60.0
1.00
Fac1-TX
SAMPLE2
1.50
8.0
0.80
Fac1-TX
SAMPLE2
2.50
4.0
0.15
Fac1-TX
SAMPLE2
4.00
4.0
0.90
Fac1-TX
SAMPLE2
10.00
24.0
1.00
3.5.4 Input Files Required for Modeling Vapor Deposition and Depletion
As described in Section 3.2.6, AERMOD can model dry and wet deposition of both particulate
and vapor (gaseous) emissions and the resulting plume depletion (EPA 2022a). This section
describes the inputs required for modeling vapor deposition and vapor depletion.
Gas Parameter File for Modeling Deposition/Depletion of Vapor Pollutants: To model wet and/or
dry deposition or depletion of vapor pollutants, you must provide HEM4 with the necessary
information to evaluate the scavenging of these pollutants in precipitation and deposition on
vegetation and other surfaces. When modeling any type of vapor deposition or depletion (wet,
dry, or both wet and dry), HEM4 accesses a gas parameter file containing pollutant properties
related to gaseous deposition. Note: The Gas Parameter file is included in HEM4's resources
folder, which is included in the model's installation files; therefore, HEM4 will NOT prompt you
for this file. (The default file pathway is "HEM4\resources\Gas_Param.xlsx".) This file includes
the following four parameters for each pollutant:
• diffusivity in air (Da, in cm2/sec);
• diffusivity in water (Dw, in cm2/sec);
• cuticular resistance to uptake by lipids for individual leaves (rci, in sec/cm); and
• Henry's Law coefficient (H, in Pascal-m3/mol).
Values for these parameters are provided in the Gas Parameter file for 129 pollutants, based on
a study by Argonne National Laboratories (Wesely 2002) and a more recent paper which
compiles Henry's Law coefficients from numerous other sources (Sander 2015). When modeling
a vapor/gaseous pollutant that is not listed in the Gas_Param file, HEM4 uses the following
default parameters:
Da = 0.07 cm2/sec, Dw = 0.7 cm2/sec, rci = 2,000 sec/cm, H = 5.0 Pascal-m3/mol.
These defaults are based on the logarithmic average of parameters for the 129 pollutant
species currently contained in the Gas Parameter file, using one significant figure accuracy. It
should be emphasized that these defaults are averages taken over ranges sometimes in excess
of ten orders of magnitude and may not be appropriate for the pollutants of interest to you.
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You can calculate parameters for additional pollutants and add these to the Gas_Param.xlsx file
or revise the values in the Gas_Param file, as appropriate. For example, you may wish to
estimate parameters for pollutants of interest to you by calculating averages based on the
values in the Gas Parameter file for smaller groups of pollutants in the same chemical family
and of similar molecular weight to your pollutant of interest (e.g., polycyclic aromatic
hydrocarbons, PAHs).
Parameter values for additional pollutant species are available in the literature cited here
(Wesely 2002 and Sander 2015), as well as in EPA's Human Health Risk Assessment Protocol
for Hazardous Waste Combustion Facilities Final Report (dated September 2005 and available
at https://epa-prqs.ornl.gov/radionuclides/2005 HHRAP.pdf). Wesely 2002 also describes a
methodology for estimating cuticular resistance, which is less commonly cited in the literature.
It should be noted that the Gas Parameter Input File is needed only when modeling deposition
(wet, dry, or both wet and dry) of vapor/gaseous pollutants. It is not required to model
deposition (of any type) of particulate emissions.
Land Use and Month-to-Seasons Input Files for Modeling Dry Deposition of Vapor Pollutants
If you chose to model dry (or wet and dry) vapor deposition or dry (or wet and dry) vapor
depletion in your Facility List Options file, then HEM4 will prompt you to provide two additional
input files described in this section. To quantify dry deposition of vapor (gaseous) pollutants to
vegetation, AERMOD requires information on the land use and vegetation surrounding the
emission source. You must provide this information in Excel™ spreadsheets called the land use
and month-to-seasons input files.
Land Use Input File: In the land use input file, you must enter a code characterizing the average
land use for 36 directions from the emission sources (which emit vapor pollutants at a facility
you chose to model dry deposition or dry depletion at), at increments of 10 degrees compass
bearing. Table 14 gives the format guidelines for the land use input file, and Table 15 shows a
sample land use input file. A sample template is provided in the HEM4 Inputs folder named
HEM4_landuse.xlsx.
Month-to-Seasons Input File: You must also provide HEM4 the month-to-seasons input file
containing further information on the typical stage of vegetation in the modeled region during
each month of the year. As the format guidelines in Table 16 show, this file associates each
month with a season code, describing the stage of vegetation ranging from lush midsummer
vegetation to winter snow coverage. Table 17 shows a sample input table for the month-to-
seasons input file. A sample template is provided in the HEM4 Inputs folder named
HEM4_month-to-seasons.xlsx.
Again, it should be noted that the Land Use and Month-to-Seasons input files are required
only if you choose to model dry (or wet and dry) vapor deposition or dry (or wet and dry)
vapor depletion in your Facility List Options file. These files are not required for modeling wet
deposition or depletion of vapor emissions, nor are they required for modeling any kind of (wet
or dry) deposition/depletion of particulate emissions.
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Table 14. Format
Guidelines for Land Use Input File
Field
Type
Description
Facility ID
Character
An alphanumeric character string
identifying the facility being modeled
Direction Sector
1
Numeric
Land use code (value = 1-9) for the
modeling domain at a compass bearing
of 10 degrees from the emission release
point:
1 Urban land, no vegetation
2 Agricultural land
3 Rangeland
4 Forest
5 Suburban areas, grassy
6 Suburban areas, forested
7 Bodies of water
8 Barren land, mostly desert
9 Non-forested wetlands
Direction Sector
n
(n = 2 thru 35)
Numeric
Land use code at a bearing of n * 10
Direction Sector
36
Numeric
Land use code at a bearing of 360
degrees
Table 15. Sample Input File for Land Use
D01
D02
D03
D04
D05
D36
Facility ID
(10°)
(20°)
(30°)
(40°)
(50°)
(360°)
Fac1-NC
1
9
5
5
6
1
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Table 16. Format Guidelines for Month-to-Seasons Input File
Field
Type
Description
Facility ID
Character
An alphanumeric character string identifying the facility being
modeled
January
Numeric
Seasonal category (value = 1-5) for month 1 (January):
1 Midsummer with lush vegetation
2 Autumn with unharvested crop land
3 Late autumn after frost and harvest, or with no snow
4 Winter with snow on ground
5 Transitional spring with partial green coverage or
short annuals
November
Numeric
Seasonal category (value = 1-5) for month 11
December
Numeric
Seasonal category (value = 1-5) for month 12
Table 17. Sample Month-to-Seasons Input File
Facility ID
M01
M02
M03
M04
M05
M12
Fac1-NC
4
4
5
5
1
4
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3.5.5 Building Dimensions Input File for Modeling Building Downwash
If you chose to model building downwash in your Facilities List Options file for one or more
facilities with point source(s), then HEM4 will prompt you for a Building Dimensions input file,
which is required by AERMOD to model building downwash effects. The following parameters
are required in the building dimensions input file:
• building height (keyword=BUILDHGT);
• projected building width perpendicular to the direction of flow (keyword=BUILDWID);
• building length in the direction of flow (keyword=BUILDLEN);
• distance from the stack to the center of the upwind face of the building parallel to the
direction of flow (keyword=XBADJ); and
• distance from the stack to the center of the upwind face of the building perpendicular to
the direction of flow (keyword=YBADJ).
You must provide these parameters for 36 wind directions, at increments of 10 degrees
(compass bearing). Calculate these parameters using the EPA's Building Profile Input Program
for PRIME (BPIPPRM). You can download the BPIPPRM model code and documentation from
the EPA's Support Center for Regulatory Atmospheric Modeling (SCRAM) website at
https://www.epa.qov/scram/air-qualitv-dispersion-modelinq-related-model-support-
proqrams#bpipprm. Table 18 gives the format guidelines for the Excel™ Building Dimensions
input file, and Table 19 shows a sample Excel™ Building Dimensions file. A sample template is
provided in the HEM4 Inputs folder named HEM4_bldg_dimensions.xlsx.
Table 18. Format Guidelines for the Building Dimensions File
Field
(notes)
Type
Description
Facility ID
Character
An alphanumeric character string identifying the facility being
modeled
Pathway
Character
"SO" should always be entered in this field because it
represents a source pathway record, which corresponds to the
code used in the AERMOD input file.
Keyword
Character
Specifies which values are given in this record (row), as
follows:
BUILDHGT = building height
BUILDWID = projected building width perpendicular to the
direction of flow
BUILDLEN = building length in the direction of flow
XBADJ = along-flow distance from the stack to the
upwind face of the building
YBADJ = across-flow distance from the stack to the
upwind face of the building
Source ID
Character
The Source ID is a unique alphanumeric character string up to
8 characters long with no spaces. It must match a Source ID in
the HAP Emissions and Emissions Location file, and building
downwash may only be modeled with vertical point (P), capped
point (C), and horizontal point (H) source types. Note:
AERMOD allows a maximum of 8 characters for the Source ID;
and all Source IDs will be converted to upper case by
AERMOD.
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Field
(notes)
Type
Description
Value 1
(n = 1)
Numeric
Dimension or distance (depending on the Keyword parameter)
viewed from a compass bearing of 10 degrees from north
(clockwise direction) of the emission release point.
Value 2 (n = 2) Numeric Dimension or distance of the building at a bearing of 20
degrees.
Value n
(n = 3 to
Numeric
Dimension or distance of the building at a bearing of [n * 10]
35)
degrees.
Value 36 (n = 36) Numeric Dimension or distance of the building at a bearing of 360
degrees.
Table 19. Sample Building Dimensions Input File
Facility
ID
Pathway
Keyword
Source ID
Value 1
(10°)
Value 2
(20°)
Value 3
(30°)
Value 36
(360°)
Fac1-NC
SO
BUILDHGT
SAMPLE1
26.00
26.00
26.00
26.00
Fac1-NC
SO
BUILDWID
SAMPLE1
111.07
107.16
100.00
111.60
Fac1-NC
so
BUILDLEN
SAMPLE1
128.17
115.85
100.00
136.60
Fac1-NC
so
XBADJ
SAMPLE1
-93.97
-98.48
-100.00
-86.60
Fac1-NC
so
YBADJ
SAMPLE1
55.54
53.58
50.00
55.80
3.5.6 User-Defined Receptors File
If you opted to include user receptors in your Facility List Options file for one or more facilities,
then HEM4 will prompt you for a User Receptors file. HEM4 will automatically calculate ambient
concentrations and resultant cancer risks and noncancer hazard indices for all U.S. Census
blocks or for all alternate receptors within the defined modeling domain. With the User
Receptors file, you can also specify additional receptor sites to model, such as schools, ambient
monitors, residential areas other than the census block's centroid, or facility boundaries.
Specify the locations of these sites in the User Receptors input file, using a separate record to
indicate the location of each user receptor. You must enter locations of each user receptor using
UTM coordinates, or in longitude and latitude. If using UTM coordinates, you must specify the
UTM zone. Base all coordinates on the WGS84 reference system.
If you chose in your Facility List Options file to include elevations in your model run, you can
enter the elevation above sea level for each user receptor. If you leave this field blank in the
User Receptors input file (but did choose to include elevations in your model run in your Facility
List Options file), then HEM4 will assume an elevation for each user receptor based on the
surrounding U.S. Census block elevations or alternate receptor elevations. Specifically, if you
leave the elevation field empty in the User Receptor file for every receptor, then HEM4 will use
the elevation of the closest U.S. Census block or alternate receptor (if not using U.S. Census
blocks in your modeling run). You should enter an elevation for every user receptor, or leave the
elevation field blank for all, to allow HEM4 to provide the elevations. Otherwise, if you enter an
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elevation for some but not all user receptors, HEM4 will assign a 0 value to the receptors you
left blank.
In addition, you may provide hill heights in the User Receptor file, or you may leave the hill
height field blank for HEM4 to calculate these values. AERMOD uses the controlling hill height
for flow calculations. Controlling hill height is defined as the highest elevation that is above a
10% grade from the receptor. [For more information on the use and calculation of controlling hill
heights using an algorithm in AERMAP, the AERMOD terrain processor (EPA 2018a), see
Section 2.3.1.1 If you leave the hill height field blank in the User Receptors file (but did choose to
include elevations in your model run in your Facility List Options file), then HEM4 will assign the
hill height of that user receptor to be the maximum of: 1) the hill height of the closest U.S.
Census block or alternate receptor (if not using U.S. Census blocks in your modeling run), 2) the
elevation of the closest U.S. Census block or alternate receptor, or 3) the user receptor
elevation that you provide. As cautioned above for user receptor elevation, you should enter a
hill height for every user receptor, or leave the hill height blank for all, to allow HEM4 to provide
the hill heights. Otherwise, if you enter a hill height for some but not all user receptors, HEM4
will assign a 0 value to the receptors you left blank.
In the User Receptor file, you must specify a "receptor type code" indicating the type of
receptor. Do not leave this field blank. A code of "P" represents populated-type sites like
houses and other residences, "M" represents ambient monitors, "S" represents schools, and "B"
represents facility boundary sites. You must also name your user receptors, and may use
up to 9 characters. HEM4 will display these names in the output files for ease of reference.
Each user receptor name must be unique. Note: Type M, S, and B receptors are considered
unpopulated and therefore HEM4 will not use M, S, or B receptors as the location of maximum
risk or maximum TOSHI because these maxima are defined as populated (although the
modeled concentrations for all user receptors will be provided in the concentration outputs, as
described in Section 6.1). Only populated type "P" user receptors are considered for sites
of maximum risk or maximum TOSHI.
Tables 20 and 21 give format guidelines for the User Receptors file and a sample input file,
respectively. In addition, a sample template is provided in the HEM4 Inputs folder named
HEM4_user_receptors.xlsx.
Table 20. Format Guidelines for the User-Defined Receptors File
Field
Type
Description
Facility ID
Character
An alphanumeric character string identifying the
facility being modeled
Coordinate system
Character
Type of coordinates: L = longitude, latitude; U = UTM
[WGS84]
X-coordinate
Numeric
UTM east coordinate, in meters (if Coordinate
System = U) or decimal longitude (if System = L). For
longitudes, 5 decimal place accuracy is
recommended, corresponding to 1-meter accuracy.
Y-coordinate
Numeric
UTM north coordinate, in meters (if Coordinate
System = U) or decimal latitude (if System = L). For
latitudes, 5 decimal place accuracy is recommended,
corresponding to 1-meter accuracy.
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Field
Type
Description
UTM zone
Numeric
If using the UTM coordinate system (U), enter the
UTM Zone from 1 to 60 followed by the hemisphere
(S or N). For example, 17N (default hemisphere is N
if not specified). If using longitudes/latitudes, leave
this cell blank.
Elevation*
Numeric
Elevation of the receptor above sea level, in meters.
Optional: HEM4 will calculate if left blank and you are
modeling terrain effects*
Receptor type
Character
Type of receptor: P = populated site (e.g., house);
B = facility boundary; M = monitor, S = school. This
field must be filled in.
Receptor ID
Alpha-numeric
Name of receptor provided by user, containing letters
and numbers, no symbols or spaces. The name you
provide must be 9 characters or less. This name
will be displayed in the outputs. This field must be
filled in.
Hill Height*
Numeric
Hill height scale, in meters. Optional: HEM4 will
calculate if left blank and you are modeling terrain
effects* (You may leave all hill heights blank, even if
you enter elevations for your user receptors in the
elevation field.)
*Note: Fill-in for every receptor or for none. If you enter one or more values, then HEM4 will assign a zero
(0) to any blank values.
Table 21. Sample Input File for User-Defined Receptors
Facility
ID
Location
type
(U - UTM,
L =
latitude/
longitude)
X-
coordinate
(decimal)
or UTM
East
(m)
Y-
coordinate
(decimal)
or UTM
North
(m)
UTM
zone
Elevation
(m)
Receptor type
(P = populated
site, B = facility
boundary, M =
monitor)
Receptor ID
Hill Height
(m)
Fac1
L
-78.88875
35.90016
100
P
Receptl
Fac2
U
560005
441000
16
244
M
Monitor!
3.5.7 Emissions Variation Input Files
If you chose to model emissions variations for one or more facilities in your Facility List Options
file, then HEM4 will prompt you for a separate Emissions Variation input file. AERMOD
computes hourly concentration data based on user-supplied emission inputs. AERMOD also
gives you the option of specifying variable emission rate factors or scalars for individual
sources. You can base these source-specific factors on different temporal scales—such as
season, month, day of the week, and hour of day—or on wind speed.
For HEM4 to calculate temporal or wind speed emissions variations, AERMOD requires
information on the type of variation and the numerical factors to use for each variation. These
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variation types and factors/scalars will be applied to one or more sources at each of the facilities
you indicated in your Facility List Options file. You must supply this information in an Emissions
Variation input file in the form of an Excel™ spreadsheet. It should be noted that, to preserve
the total tons per year (TPY) of emissions you entered for each source-HAP combination
in the HAP Emissions file, the numerical factors/scalars for each source should average
to one (weighted or unweighted average, depending on the variation type). The types of
variations AERMOD can apply include the following (with the HEM4 template file provided in
parentheses, as well as the "n" number of factors):
• SEASON (HEM4_emisvar_season.xlsx)\ emission rates vary seasonally (n=4);
• MONTH (HEM4_emisvar_month.xlsxy. emission rates vary monthly (n=12);
• HROFDY (HEM4_emisvar_hrofdy_template.xlsx): emission rates vary by hour-of-day
(n=24);
HRDOW (HEM4_emisvar_hrdow_template.xlsx)-. emission rates vary by hour-of-day,
and day-of-week [M-F, Sat, Sun] (n=72);
• SEASHR (HEM4_emisvar_seashr_template.xlsx)-. emission rates vary by season and
hour-of-day (n=96);
• HRDOW7 (HEM4_emisvar_hrdow7_template.xlsx): emission rates vary by hour-of-day,
and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=168);
• SHRDOW (HEM4_emisvar_shrdow_template.xlsx)-. emission rates vary by season,
hour-of-day, and day-of-week [M-F, Sat, Sun] (n=288);
• SHRDOW7 (HEM4_emisvar_shrdow7_template.xlsx)-. emission rates vary by season,
hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=672);
• MHRDOW (HEM4_emisvar_mhrdow_template.xlsx): emission rates vary by month,
hour-of-day, and day-of-week [M-F, Sat, Sun] (n=864);
• MHRDOW7 (HEM4_emisvar_mhrdow7_template.xlsx): - emission rates vary by month,
hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=2,016); and
• WSPEED (HEM4_emisvar_wspeed.xlsx): emission rates vary by wind speed (n=6)
(Note: the 6 factors are applied to the wind speed categories used by AERMOD that
have the following default upper bound speeds in m/s of 1.54, 3.09, 5.14, 8.23, 10.8 and
no upper bound). Note: WSPEED is designed to be used for sources where the
emission rate depends on wind speed, such as dust emissions from tilled fields or
storage piles. It should be noted that you will not know the annual emission rate for
these sources in advance without analyzing the distribution of hourly wind speeds in the
meteorological file. But WSPEED can nonetheless be used without analyzing the
meteorological data in advance by calculating the average emissions using just one of
the wind speed categories. These average emissions will then represent a baseline that
can be used in the HAP Emissions input file (as a stand-in for the annual emission rate).
Use a factor of 1.0 for this category in the WSPEED input file, and then calculate the
factor/scalars for the other wind speed categories in relation to this baseline category.
To use the temporal emission variations listed above and not alter your total TPY (entered for
each source-HAP combination in the HAP Emissions file), check to ensure the numerical factors
you assign for each source in the Emissions Variation input file average to one before initiating
your HEM run. Note that variation types based on the type of the day-of-the-week (weekday or
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weekend) - including HRDOW, SHRDOW, and MHRDOW- lend themselves to the use of
weighted averages when constructing factors, based on five weekdays and two weekend days.
Table 22 provides the format guidelines for the Emissions Variation input files. Tables 23, 24,
and 25 provide sample Emissions Variation input files for a sample of the variations AERMOD
can accommodate including: hour of day emission variations (24 factors), monthly emission
variations (12 factors), and both season and hour of day emission variations (96 factors),
respectively. Table 26 provides a sample input file for varying source-specific emissions by wind
speed. It should be noted that HEM4 expects a maximum of 12 factor columns across these
Emissions Variation input spreadsheets (for a total of 15 columns, including the Facility ID,
Source ID and Variation keyword). It should also be noted that although the types of emission
variations described above and the samples provided below are for a single type of emissions
variation, you can also choose to use different variation types for different sources and/or
facilities, within the same input file. The only limitation is that each source can only have a
single type of variation applied in a model run. A template containing multiple emissions
variations in one file is also provided in the HEM4 Inputs folder and is named
HEM4_emisvar_multiple_variations.xlsx. See the AERMOD User's Guide (EPA 2022a) for more
detailed information regarding the temporal and wind speed factors available for varying source-
specific emissions.
Table 22. Format Guidelines for the Emissions Variation Input Files
Field
Type
Description
Facility ID
Character
An alphanumeric character string identifying the facility being modeled
Source ID
Character
The Source ID is a unique alphanumeric character string up to 8
characters long with no spaces. It must match a Source ID in the HAP
Emissions and Emissions Location file. Note: AERMOD allows a
maximum of 8 characters for the Source ID; and all Source IDs will be
converted to upper case by AERMOD.
Variation*
Character
Type of variable emission rates being used (SEASON, MONTH,
HROFDY, HRDOW, SEASHR, HRDOW7, SHRDOW, SHRDOW7,
MHRDOW, MHRDOW7 or WSPEED)*
Factor 1
Character
First factor (scalar) to be applied to emission rate.
Factor 2
Character
Second factor (scalar) to be applied to emission rate.
Factor 3
Character
Third factor (scalar) to be applied to emission rate.
Factor n
Character
nth factor (scalar) to be applied to emission rate.
*Note: Each emission variation type has a set number of "n" factors (or scalars). The number of factors is as
follows: SEASON=4, MONTH=12, HROFDY=24, HRDOW=72, SEASHR=96, HRDOW7=168, SHRDOW=288,
SHRDOW7=672, MHRDOW=864, MHRDOW7=2,016, WSPEED=6. See HEM's template input files for examples
and consult the AERMOD User's Guide for additional information. It should be noted that running AERMOD does
not require the emissions variation factors for a given source to average to one. But when modeling with
HEM/AERMOD, to maintain the total user-provided tons per year of emissions indicated in the HAP
Emissions input file, the numerical factors for the temporally based variations must average to one
(weighted or unweighted, depending on the variation). Otherwise, these numerical factors would change
the total emissions modeled, and not merely distribute that total temporally. (See also discussion above
regarding the WSPEED variation.)
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Table 23. Sample Emissions Variation File based on Hour of Day (24 factors)
Facility
ID
Source
ID
Variation
Hour
factor
(1)
Hour
factor
(2)
Hour
factor
(3)
Hour
factor
(4)
Hour
factor
(5)
Hour
factor
(6)
Hour
factor
(12)
Fac1
SAMPLE1
HROFDY
0.2138
0.1433
1.2928
0.098
0.1342
0.3301
1.4356
(13)
(14)
(15)
(16)
(17)
(18)
(24)
Fac1
SAMPLE1
HROFDY
1.3959
1.2728
0.1079
1.5255
1.5255
1.5519
1.799
Table 24. Sample Emissions Variation File based on Month (12 factors)
Facility ID
Source ID
Variation
JAN
FEB
MAR
APR
MAY
JUN
DEC
Fac1
SAMPLE1
MONTH
0.2138
0.1433
1.2928
0.098
0.1342
0.3301
1.4356
Table 25. Sample Emissions Variation File based on Season and Hour of Day (96 factors)
Season-
Season-
Season-
Season-
Season-
Season-
Season
Season-
Facility
hour
hour
hour
hour
hour
hour
-hour
hour
ID
Source ID
Variation
Factor
Factor
Factor
Factor
Factor
Factor
Factor
Factor
Winter
Winter
Winter
Winter
Winter
Winter
Winter
1
2
3
4
5
6
12
Fac1
SAMPLE1
SEASHR
0.2138
0.1433
1.2928
0.098
0.1342
0.3301
1.4356
Winter
Winter
Winter
Winter
Winter
Winter
Winter
13
14
15
16
17
18
24
Fac1
SAMPLE1
SEASHR
1.3959
1.2728
0.1079
1.5255
1.5255
1.5519
1.799
Spring
Spring
Spring
Spring
Spring
Spring
Spring
1
2
3
4
5
6
12
Fac1
SAMPLE1
SEASHR
1.9045
1.9475
1.4684
1.0435
0.8305
0.6952
0.3979
Spring
Spring
Spring
Spring
Spring
Spring
Spring
13
14
15
16
17
18
24
Fac1
SAMPLE1
SEASHR
0.2138
0.1433
1.2928
0.098
0.1342
0.3301
1.4356
Summer
Summer
Summer
Summer
Summer
Summer
Summer
1
2
3
4
5
6
12
Fac1
SAMPLE1
SEASHR
1.3959
1.2728
0.1079
1.5255
1.5255
1.5519
1.799
Summer
Summer
Summer
Summer
Summer
Summer
Summer
13
14
15
16
17
18
24
Fac1
SAMPLE1
SEASHR
1.9045
1.9475
1.4684
1.0435
0.8305
0.6952
0.3979
Fall
Fall
Fall
Fall
Fall
Fall
Fall
1
2
3
4
5
6
12
Fac1
SAMPLE1
SEASHR
0.2138
0.1433
1.2928
0.098
0.1342
0.3301
1.4356
Fall
Fall
Fall
Fall
Fall
Fall
Fall
13
14
15
16
17
18
24
Fac1
SAMPLE1
SEASHR
0.2138
0.1433
1.2928
0.098
0.1342
0.3301
1.4356
Table 26. Sample Emissions Variation File based on Wind Speed (6 factors)
Facility ID Source ID Variation* Cat. 1 Cat. 2 Cat. 3 Cat. 4 Cat. 5 Cat. 6
Fac1 SAMPLE1 WSPEED 0.2138 0.1433 1.2928 0.098 0.1342 0.3301
*See discussion above regarding the WSPEED variation. If you know and are using the actual annual emission rate
for this source (e.g., storage piles), then these six factors should average to 1.0 for HEM runs. Alternatively, when the
annual emission rate is not known, use the method described above that employs factors relative to a baseline.
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3.5.8 Alternate Receptors File
As noted previously, HEM4 can model based on U.S. Census blocks or based on alternate
receptors you provide. If you check "Use alternate receptors" on the required inputs user
interface (discussed below in Section 4.1), then HEM4 will prompt you for an Alternate Receptor
file, in lieu of using U.S. Census blocks for the model run. This allows you to model with HEM4
anywhere in the world, both within the U.S and outside the U.S.
The Alternate Receptor file must be a CSV file and provide HEM4 with a list of receptor
locations, the type of each receptor (populated "P" or various types of unpopulated receptors,
such as boundary "B" and monitor "M" receptors), and the populations represented by each
receptor. It is important to note that only populated "P" receptors are chosen by HEM4 to be the
sites of maximum risk or hazard index; and only "P" receptors are used by HEM4 in cancer
incidence calculations. This is discussed further below in Sections 5 and 6. Note: For HEM4 to
run using alternate receptors, you must provide population values for every Alternate
Receptor of type "P". The population you provide may be any integer value, 0 or greater.
Even if only one populated Alternate Receptor is missing a value in its population field, HEM4
will not commence the modeling run.
In addition, if you chose in your Facility List Options file to include elevations in your model run,
then you must also provide HEM4 the elevation above sea level for each alternate receptor, as
well as the hill height of each receptor. To model terrain effects, the alternate receptor file must
be filled-in completely for every elevation and hill height. Any blanks in the elevation fields or
hill height fields of the Alternate Receptors file will cause AERMOD to be run in the FLAT
mode with no terrain effects.
AERMOD uses the controlling hill height for flow calculations. Controlling hill height is defined as
the highest elevation that is above a 10% grade from the receptor. For more information on the
use and suggested calculation of controlling hill heights using an algorithm in AERMAP, the
AERMOD terrain processor (EPA 2018c), see Section 2.3.1. It is important to again note that if
you leave any hill height field blank in the Alternate Receptors file, then AERMOD will be run in
the FLAT mode with no terrain effects (even if you opt to include elevations in your model run in
your Facility List Options file and also provide elevations for your alternate receptors).
Alternatively, you can choose to model with the elevation option turned off in your Facility List
Options file. In such a modeling run, you do not need to provide any elevations or hill heights in
the Alternate Receptor file, as HEM4 will model everything on a flat plane.
Tables 27 and 28 give format guidelines for the Alternate Receptors file and a sample input file,
respectively. In addition, a sample template is provided in the HEM4 Inputs folder named
HEM4_alternate_receptors. csv.
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Table 27. Format Guidelines for Alternate Receptors File (CSV)
Field
Type
Sample Value
Description
Receptor ID
Numeric
1
A unique number identifying the Receptor
Type of receptor Character P Type of receptor: P = populated (e.g., house),
B = boundary, M = monitor
Coordinate
Character
L
Type of coordinates: L = longitude, latitude; U =
system
UTM [WGS84]
X-coordinate Numeric -52.74629
UTM east coordinate, in meters (if Coordinate
System = U) or decimal longitude (if System =
L). 5 decimal place precision is recommended
for longitude, corresponding to 1 meter
Y-coordinate
Numeric
47.53796
UTM north coordinate, in meters (if Coordinate
System = U) or decimal latitude (if System = L).
5 decimal place precision is recommended for
latitude, corresponding to 1 meter
UTM zone with
hemisphere
Character
17N
UTM zone where the receptor is located if
Coordinate System = U
Elevation
Numeric
219.7
Elevation of the receptor above sea level, in
meters. Required if you are modeling terrain
effects (i.e., choose to model elevations in the
Facility List Options file)
Hill Height Numeric 219.7
Hill height scale, in meters. Required if you are
modeling terrain effects (i.e., choose to model
elevations in the Facility List Options file)
Population
Numeric
45
Population represented by the alternate
receptor; required by HEM4 for every "P" type
alternate receptor for incidence calculations.
Table 28. Sample Input File for Alternate Receptor Input File
Receptor
ID
Type of
Receptor
(P, B, M)
Coordinate
System
(U = UTM
L =
latitude,
longitude)
X-
coordinate:
Longitude
(decimal) or
UTM East
(m)
Y-
coordinate:
Latitude
(decimal) or
UTM North
(m)
UTM zone
with
hemisphere
Elevation
(m)
Hill Height
(m)
Population
1
B
L
-52.746286
47.53880
219.7
219.7
0
2
P
L
-52.74685
47.54225
219.3
219.3
5
3
P
L
-52.74817
47.53796
220.6
220.6
25
4
P
L
-52.74760
47.53683
262.7
262.7
7
5
M
L
-52.75023
47.53795
263.4
263.4
0
6
P
L
-52.74708
47.53599
292.1
292.1
45
n
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3.5.9 Census Update File
HEM4 provides you the option to change the census file, as discussed below in Section 4.8.
Before you use this option, it should be noted that these changes are permanent to your census
files. For this reason, it is recommended that you save your original census files to a separate
location before using this file to change the official census database provided on EPA's HEM4
webpage.
With the Census Update file, you can:
(1) Zero-out the population of a specific U.S. Census block;
(2) Move a block to a new latitude and longitude location; and/or
(3) Delete a U.S. Census block.
You may wish to Zero-out the population of the block if it is clear no residences are present in
the block. This change will keep the block in the dataset, so concentrations and risks are
modeled, but this receptor will not impact incidence.
You may wish to Move a block to different coordinates that better represent the population.
You may wish to Delete or remove a block from the dataset; for example, because there are no
people living in the block. However, it should be noted that once removed, the block cannot be
added back.
Tables 29 and 30 give format guidelines for the Census Update file and a sample update file,
respectively. In addition, a sample template is provided in the HEM4 Inputs folder named
HEM4_Census_block_update_template.xlsx.
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Table 29. Format Guidelines for the Census Update File
(used to permanently change your U.S. Census files)
Field
Type
Sample Value
Description
Facility ID
Character
Fac2
The Facility ID field in the Census
Update file is optional and may be left
blank. You may wish to use it outside of
HEM4 to track the source of changes.
Run Group
Character
Landfills
The Run Group field in the Census
Update file is optional and may be left
blank. You may wish to use it outside of
HEM4 to track the source of changes.
Block ID
Character
(not numeric)
170010001001003
In this field, enter the 15-digit U.S.
Census block ID. Enter the block ID as
text characters rather than numerals,
because some block IDs have leading
zeroes.
Latitude
Numeric
39.96789
If the Change is a "Move", enter the
Latitude (decimal) of where the block
should be moved. 5 decimal places are
recommended, corresponding to 1-meter
accuracy. You may leave this field blank
for "Zero" and "Delete" changes.
Longitude
Numeric
-91.37989
If the Change is a "Move", enter the
Longitude (decimal) of where the block
should be moved. 5 decimal places are
recommended, corresponding to 1-meter
accuracy. You may leave this field blank
for "Zero" and "Delete" changes.
Change
Character
Move
The potential changes include: Zero,
Move, and Delete
Table 30. Sample Census Update File
Run
Latitude
Longitude
Change
Facility ID
Group
Block ID
(decimal)
(decimal)
Fac1 -TX
Landfills
170010001001003
Zero
Fac1 -TX
Landfills
170010001001009
39.96789
-91.37989
Move
Fac1 -TX
Landfills
170010001001010
Delete
Fac1 -TX
Landfills
370010201001001
Zero
Fac1 -TX
Landfills
370010201001002
36.34567
-79.45678
Move
Fac1 -TX
Landfills
370010201001003
Delete
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3.5.10 Updating the Chemical Unit Risk Estimates and Health Benchmarks Input Files
As discussed in Section 2.2.1, the Chemical Health Effects Library contains chemical health
effects data, including dose response toxicity values. You can make changes to the Chemical
Health Effects Library by editing the Excel™ spreadsheet files that comprise the library—entitled
Dose_Response_Library.xlsx and Target_Organ_Endpoints.xlsx. These files are located in
HEM4's resources folder. You can add new pollutants to these files or edit the values for the
chemicals already in the files. If you want to keep your files consistent with the data EPA uses in
their HAP risk assessments, check for updated toxicity values on EPA's Dose Response
Assessment webpage (EPA 2021a).
When adding new chemical names to the Dose Response Library file, use the same
spelling as used in the HAP emissions input file. The Chemical Abstracts Service (CAS)
number field in the Chemical Health Effects Library is optional. If you do not specify a cancer
URE for a new pollutant, then the URE will be assumed to be 0 (zero) and cancer risks will not
be evaluated for that pollutant. Similarly, if you do not specify a noncancer chronic RfC or acute
benchmark for a new pollutant, HEM4 will not calculate adverse noncancer chronic or acute
health effects, respectively. If a noncancer chronic RfC is indicated in the Dose Response
Library file for a pollutant you add, you must also enter the pollutant in the Target Organ
Endpoints file and indicate what organs or organ systems may be impacted.
For future model runs, to ensure you have the most recent file versions, you should again check
EPA's HEM download webpage (https://www.epa.gov/fera/download-human-exposure-model-
hem) for the date listed next to the "Toxicity Value Files" link. EPA regularly updates these files.
If EPA's update is more recent than the dates shown for the files in HEM4's resources folder,
then download the newer files from EPA's HEM download webpage (from link above) and
replace your outdated Dose Response Library and/or Target Organ Endpoints files. You may
also manually modify the files in your HEM4's resources folder based on updated values from
EPA's HEM download page, or from EPA's Dose Response Assessment webpage (EPA
2021a).
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4. Step-by-Step Instructions for Running HEM4
Before you initiate a HEM4 modeling run8, you should ensure you have the necessary input files
prepared for your specific modeling needs. Section 3 provides detailed descriptions of all HEM4
input files, and sample templates for each are provided in the HEM4 Inputs folder. Table 31
provides a summary of the template files provided in your HEM4 Inputs folder and for what kind
of run each file is needed. In addition to the files listed in Table 31, a HEM4 run requires the
U.S. Census (if not using alternate receptors) and meteorological databases, and the files
located in HEM4's resources folder. These include the Dose_Response_Library.xlsx file, the
Target_ Organ_Endpoints.xlsx file, and, for vapor deposition/depletion, the Gas_Param.xlsx file.
Table 31. Summary of HEM4 Sample Template Input Files
Sample Template Name
Description
When Needed
HEM4 Fac List Options.xlsx
Facility List Options file
Every run
HEM4 HAP Emiss.xlsx
HAP [Pollutant] Emissions file
Every run
HEM4 Emiss Loc.xlsx
Emissions Location file
Every run
H E M4_alte rn ate_rece pto rs. csv
Alternate Receptor file
Required if modeling with alternate
receptors (whether outside or
inside the U.S.) instead of census
block receptors
HEM4_user_receptors.xlsx
User Receptor file
Required if the user receptor
column in the Faclist has a "Y" for
one or more facilities
HEM4_buoyant_line_param.xlsx
Buoyant Line Source Parameter
file
Required if a source in the
Emissions Location file is a buoyant
line
H E M 4_p o ly g o n_ve rtex. x I sx
Polygon Vertex file
Required if a source in the
Emissions Location file is a polygon
HEM4_bldg_dimensions.xlsx
Building Dimensions file
Required if the building downwash
column in the FacList has a "Y" for
one or more facilities
HEM4_particle_data.xlsx
File containing particle size
distribution of emissions per
source
Required if the deposition OR
depletion column has a "Y" AND
Pdep OR Pdepl column in FacList
indicates type, AND if Method 1
(the default) is indicated in
EmissLoc. (HAP Emiss must also
contain particulates)
HEM4_landuse.xlsx
File describing land use
surrounding emissions source
Required if the deposition OR
depletion column has a "Y" AND
Vdep OR Vdepl column in FacList
indicates DO or WD. (HAP Emiss
must also contain gases/vapor)
HEM4_month-to-seasons.xlsx
File describing monthly stage of
vegetation surrounding
emissions source
Required if the deposition OR
depletion column has a "Y" AND
Vdep OR Vdepl column in FacList
indicates DO or WD. (HAP Emiss
must also contain gases/vapor)
HEM4_emisvar_season.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
seasonal variations are desired (4
factors)
8 Note: It is advisable to close and re-start HEM4 between modeling runs, which clears memory for
each new run and avoids potential issues by ensuring a full reset.
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Sample Template Name
Description
When Needed
HEM4_emisvar_month.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
monthly variations are desired (12
factors)
HEM4_emisvar_hrofdy_template.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
hour-of-day variations are desired
(24 factors)
H E M 4_e m i s va r_h rd o w_t e m p 1 ate. xl sx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
hour-of-day + type-of-day (M-F,
Sat, Sun) variations are desired (72
factors)
HEM4_emisvar_seashr_template.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
season + hour-of-day variations are
desired (96 factors)
H E M 4_e m i s va r_h rd o w7_t e m p 1 ate. x 1 sx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
hour-of-day + day-of-week (7)
variations are desired (168 factors);
HEM4_emisvar_shrdow_template.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
season + hour of day + type-of-day
(weekday, Sat, Sun) variations are
desired (288 factors)
H E M 4_e m i s va r_s h rd o w7_te m p 1 ate. x 1 sx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
season + hour-of-day + day-of-
week (7) variations are desired
(672 factors)
HEM4_emisvar_mhrdow_template.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
month + hour-of-day + type-of-day
(weekday, Sat, Sun) variations are
desired (864 factors)
HEM4_emisvar_mhrdow7_template.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
month + hour-of-day + day-of-week
(7) variations are desired (2,016
factors)
HEM4_emisvar_wspeed.xlsx
Emissions Variation file
Required if the Emissions Variation
column in Faclist has a "Y" and
wind speed (m/s) variations are
desired (6 factors)
Finally, to ensure you have the most recent model version, as well as the most recent chemical
health effect (toxicity) values, U.S. Census data, and meteorological data, you should check
EPA's HEM download webpage for updates (https://www.epa.gov/fera/download-human-
exposure-model-hem). EPA updates these files periodically. If EPA's update is more recent than
the version of HEM4 on your computer, then download the newer model version from EPA's
HEM download webpage (from link above) and start the newer model. If the chemical health
effect files (i.e., Dose Response Library file and Target Organ Endpoints file) on EPA's website
are more recent than the ones currently in HEM4's resources folder, then replace the files in
your subfolder with the ones you download from EPA's website. Likewise, check the timestamp
and update your U.S. Census data (in HEM4's "census" subfolder) and the meteorological data
(in HEM4's "aermod" subfolder), as necessary.
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After you have ensured the HEM4 model and integrated databases are up-to-date and you have
prepared the input files for the modeling application, start HEM4 by using Windows File
Explorer™ to navigate to the folder where HEM4 was unzipped and double click on the HEM4
executable file. The HEM4 title screen will be displayed, as shown below in Figure 3. Note that
the buttons near the bottom of the menu bar on the left - the HEM4 USER GUIDE and the
AERMOD USER GUIDE buttons - link to this HEM4 guide (at https://www.epa.gov/fera/risk-
assessment-and-modeling-human-exposure-model-hem'j and to AERMOD's user guide (at
https://www.epa.qov/scram/air-qualitv-dispersion-modelinq-preferred-and-recommended-
models#aermod), respectively, and you should access them whenever you need further
instruction and explanation regarding the inputs or outputs of HEM4, or when troubleshooting a
modeling run issue.
RUN HEM4
SUMMARIZE RISKS
DEMOGRAPHIC ASSESSMENT
\" ANALYZE OUTPUTS
0 log
0 REVISE CENSUS DATA
Q EXIT
Figure 3. HEM4 Title Screen
The RUN HEM4 button at the top of the menu bar on the left will take you to the next screen,
from which you can initiate a model run. As noted above, to view this HEM4 User's Guide or the
AERMOD User's Guide, on this screen or any subsequent screen, click on the buttons near the
bottom of the menu bar. To stop the HEM4 application on any screen, click on the EXIT button
and close the black DOS window (which may remain open after exiting, on some computers.)
4.1 Provide Standard Input Files and Indicate Receptors
On the initial input screen (RUN HEM4) shown below in Figure 4, you must first indicate
whether you will use U.S. Census receptors or alternate receptors for your model run. Within the
U.S., you can use either U.S. Census receptors or alternate receptors that you provide. For
modeling runs outside the U.S., you must use alternate receptors. Figure 4 shows the input
selection buttons for the three required input files: the Facility List Options file, the HAP
Emissions file, and the Emissions Location file. Clicking on each of these buttons will allow you
to browse your computer to select the appropriate file. The Facility List Options file, HAP
Emissions file, and Emissions Location file are described in detail in Sections 3.2, 3.3 and 3.4,
respectively. Note: Depending on the size of your input files, it may take HEM4 several minutes
to load them: wait until the interface indicates each has loaded before attempting to load the
next input file.
Prepared for
Air Toxics Assessment Group
U.S. EPA
Research Tnangle Park. NC 27711
Prepared by
SC&A Incorporated
1414 Raleigh Rd. Suite 450
Chapel Hill, NC 27517
HEM4 User's Guide
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B
ft
SUMMARIZE RISKS
T demographic assessment a use U S Census receptors r Use alternate receptors
analyze outputs Name Run Group (optional)
H LOG ¦
' -ii 1. Please select a Facilities List Options file:
REVISE
CENSUS DATA
-Q 2. Please select a HAP Emissions file
{l 3. Please select an Emissions Location file:
^ HEM4 USER GUIDE
AERMOD USER GUIDE
Q exit
Figure 4. Run HEM4 with U.S. Census Receptors
If you choose to use alternate receptors, then an additional input selection button will appear
near the bottom middle of the screen, as shown in Figure 5, that requires you to browse for and
select an alternate receptor CSV file. (Note: It may take several minutes for your Alternate
Receptor file to upload for modeling. Do not click Next until it has uploaded ) The
Alternate Receptors file is described in Section 3.5.8. As with all modeling runs, for a run using
alternate receptors, you must also browse for and select the Facility List Options, HAP
Emissions, and Emissions Location input files.
e
ft
0
SUMMARIZE RISKS
demographic assessment r use U.S. Census receptors Use alternate receptors
Name Run Group (optional):
*3 1 Please select a Facilities List Options file
*3 2 Please select a HAP Emissions file:
-Q 3 Please select an Emissions Location file:
-J Please select an alternate receptor CSV file:
ANALYZE OUTPUTS
LOG
H
m
~
REVISE CENSUS DATA
HEM4 USER GUIDE
AERMOD USER GUIDE
Figure 5. Run HEM4 with Alternate Receptors
For either type of run, you can (optionally) enter a run group name in the Name Run Group box
provided. This is recommended because the name will be used to identify the subfolder
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containing the results of your run, located within HEM4's main "output" folder, and will be helpful
in identifying which outputs HEM4's post-modeling tools should summarize, view graphically
and analyze (discussed in Sections 4.5 and 4.7), as well as which outputs HEM4's
Demographic Assessment module should break down demographically (discussed in Section
4.6). The name you enter in the "Name Run Group" box will also be prepended to the output
files containing the results for the run as a whole. (Note: Do not enter a name of a subfolder that
already exists in the output folder from a previous run.) If you do not enter a run group name,
the model will name the run group output folder with a date and timestamp.
After you have indicated what type of receptors should be used for the modeling run and
entered the three required input files on this initial screen, click Next at the bottom right corner
of the screen to continue. If no additional input files are needed beyond the Facility List Options,
Emissions Location and HAP Emissions files already entered, then a pop-up box will appear
asking you to confirm the start of the HEM4 run, as shown below in Figure 6.
KW Confirm HEM4 Run X
©Clicking OK will start HEM4. Check the log tab for updates
on your modeling run.
OK Cancel
Figure 6. Confirm HEM4 Run Pop-Up Start Box
Clicking 'OK' in this box will initiate the modeling, and a log of the modeling progress will appear
as shown and described in Section 4.4. Click Cancel if you need to change any input files
already entered. If additional input files are required, one or two additional screens will appear
after you click Next, which are discussed in Sections 4.2 and 4.3
4.2 Provide Additional Input Files
If additional inputs are required, one of two screens will appear next, depending on the nature of
your sources in the Emissions Location file and the modeling options you indicated in your
Facility List Options file. One screen that may appear is shown below in Figure 7. The other
input screen which may appear is shown and discussed in Section 4.3.
This screen will prompt you for one or more of the following additional input files: a user
receptors file; an emissions variation file; a buoyant line parameters file; a polygon vertex file;
and/or a building dimensions file. For example, if you indicated in your Facility List Options file
that you'd like to include emissions variations for one or more facilities to be modeled, then a
button will appear on this screen asking for the location of your Emissions Variation file.
Likewise, if one of the sources in your Emissions Location file is a buoyant line source, then a
button will appear prompting you to browse your computer and select a buoyant line parameter
file. If other input files are needed based on your Facility List Options file and Emissions
Location file, additional buttons will appear and request that you browse for and select the
required file (as shown in Figure 7). When you hover over each of these input file buttons,
instructions will be displayed on the top of the screen describing each file type.
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e
e
9$
t
0
SUMMARIZE RISKS
DEMOGRAPHIC ASSESSMENT
ANALYZE OUTPUTS
REVISE CENSUS DATA
-fl Please select a User Receptors file:
-Q Please select an Emissions Vanahon file
-Q Please select associated Buoyant Line Parameters file
-Q Please select associated Polygon Vertex file
-Q Please select associated Building Dimensions file
HEM4 USER GUIDE
AERMOOUSER GUIDE
Q EXIT
| Back |
| Next |
Figure 7. Provide Additional Input Files
After you have entered these additional input files, click Next at the bottom right corner of the
screen to continue. If no other inputs are needed, HEM4 will display the pop-up box, shown
above in Figure 6, stating "Clicking 'OK' will start HEM4. Check the log tab for updates on your
modeling run." Click Cancel if you need to change any input files. If you are ready for HEM4 to
start your modeling run, click OK, and a log of the modeling progress will appear as shown and
described in Section 4.4. If additional inputs are needed for deposition and depletion modeling,
another input screen will open next, as shown and discussed in Section 4.3.
4.3 Provide Deposition and Depletion Input Files
When modeling deposition/depletion, HEM4 can direct AERMOD to (1) calculate a deposition
flux and (2) deplete the plume based on the calculated deposition. You can direct HEM4 to
provide the deposition flux in the outputs, or not (to save space). Generally, deposition modeled
with plume depletion will reduce the ambient impacts from the emission source by removing
pollutants from the plume. Air concentrations will be depleted as pollutants are deposited to the
ground. Deposition and plume depletion have more of an effect on ambient concentrations
farther from the facility than it does closer to the facility where the maximum impact generally
occurs. Alternatively, you may choose to calculate the deposition flux, but not deplete the plume
(to allow for higher, more conservative air concentrations). Either way, the modeled deposition
flux may be used as an input to a separate multipathway model such as the Total Risk
Integrated Methodology (TRIM) (EPA 2021b).
In most cases, if you chose to model deposition and/or depletion in the Facility List Option file,
HEM4 will require additional input files9. HEM4 uses AERMOD to calculate deposition and
9 Note: The one deposition and/or depletion modeling case, which requires no additional inputs and
therefore no deposition/depletion input screen, is if you are modeling only particle deposition and/or
depletion AND chose in your Emissions Location input file to use Method 2 for the Deposition Method. It
HEM4 User's Guide
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depletion effects for particulate matter, vapor (gaseous) pollutants, or both. The make-up of your
emissions - that is, the percentage particulate and gas - is dictated to HEM4 by your HAP
Emissions input file. Specifically, the fifth column in the HAP Emission input file ("Fraction
emitted as particulate matter") indicates to HEM4 whether your emissions are 100% particle (if
this column is populated with 100 for all pollutants), 100% vapor (if this column is left blank or
populated with 0 for all pollutants), or a mixture of particles and gas. You will need to browse
your computer and select the additional files needed for modeling of deposition and/or depletion
on the screen depicted in Figure 8. You will be prompted to provide between 1 and 3 deposition/
depletion related input files, depending on your modeling options and the nature of the
emissions to-be-modeled.
SUMMARIZE RISKS
DEMOGRAPHIC ASSESSMENT
\" ANALYZE OUTPUTS
-Q Please select Particle Size file:
-fl Please select Land Use file:
-Q Please select Month-to-Season Vegetation file:
REVISE CENSUS DATA
HEM4 USER GUIDE
AERMODUSER GUIDE
| Next |
Figure 8. Provide Deposition and Depletion Input Files
If your Facility List Options file indicates that you chose to model particle deposition and/or
particle depletion using AERMOD's Method 1 (as discussed in Section 3.4.2) AND your HAP
Emissions file indicates that some of the emissions are in particle form, then a particle data file
is required by HEM4/AERMOD. Upload the particle data input file containing the particle size
information, mass fraction and particle size density for each pollutant (HAP) by browsing your
computer for it at the first Browse button on this screen, as shown in Figure 8.
If your Facility List Options file indicates that you chose to model vapor (gaseous) deposition
and/or vapor depletion AND your HAP Emissions file indicates that some of the emissions are in
vapor form, then HEM4 will instruct AERMOD to model vapor deposition and/or depletion.
Depending on the type of vapor deposition/depletion you indicated in your Facilities List Option
file, two additional inputs may be required by HEM4/AERMOD: a land use input file and a
month-to-seasons input file. These additional input files are needed only to quantify dry (or "wet
and dry") deposition and/or depletion of vapor emissions, as discussed in Section 3.5.4. If you
wish to model "wet only" deposition and/or depletion of gaseous pollutants, these additional
should also be noted that AERMOD does not model deposition or depletion of emissions from buoyant
line sources. Therefore, if you indicate in your Facility List Options file that deposition or depletion should
be modeled for a facility with buoyant line sources in your Emissions Location file, AERMOD will not run
successfully. In this case, remove the buoyant line source IDs from your input files and model that source
separately, without deposition or depletion.
HEM4 User's Guide
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input files are not needed by HEM4. (These files are also not needed to model particle-only
deposition and/or depletion.) Upload these files by browsing your computer for them at the
second and third buttons on this screen shown in Figure 8.
As noted in Section 3.5.4, you should also check to ensure that the vapor (gaseous) pollutants
in your HAP Emissions file are included in the Gas Parameter reference file. If these pollutants
are not included - or if you wish to include different parameter values than the Gas Parameter
file currently lists - you should edit the Gas Parameter file located in HEM4's resources folder,
as discussed in Section 3.5.4. Otherwise, generic default gas parameter values will be used.
(The Gas Parameter file is located at "HEM4\resources\Gas_Param.xlsx".)
It should be noted that HEM4 requires significantly more time to run if you opt to model
deposition and/or depletion. The exact run time will depend on the particular source
configuration and modeling domain but can be over an hour or more per facility. You can utilize
the FASTALL option in the Facility List Options file to expedite the run. As noted in Section
3.2.10, FASTALL conserves model runtime by simplifying the AERMOD algorithms used to
represent the meander of the pollutant plume (EPA 2022a).
After you enter the required files on the deposition/depletion input screen, click Next on the
bottom right and HEM4 will display the pop-up box (shown above in Figure 6) stating "Clicking
'OK' will start HEM4. Check the log tab for updates on your modeling run." Click Cancel if you
need to change any file locations on this screen, and the Back button to change any input files
on the previous screen. If you are ready for HEM4 to start your modeling run, click OK and a log
of the modeling progress will appear as shown and described in Section 4.4.
4.4 Check HEM4 Log
After HEM4 starts modeling your facilities (or facility), the LOG screen will appear to show you
HEM4's progress in real-time including any errors in processing, if there are any. The Log
screen is shown below in Figure 9. (Note: The cursor is visually disabled on the log screen, but
it is recommended that you not place your cursor on the log tab screen itself, because doing so
may reset where the log displays the next line of progress and result in seemingly non-
sequential progress messages; rather use the scroll bar on the right to show more of the log
screen, as needed.) Once the modeling run is complete, HEM4 also produces a log text file as a
permanent record of the modeling.
The Log screen and text file will provide you with the following modeling run information:
• the meteorological period used, whether annual (the default) or a different period you
selected;
• the full list of input files uploaded for the modeling run;
• any mismatch between input files prior to you correcting the mismatched files (e.g.,
mismatched Source IDs between the HAP Emissions and Emissions Location files);
• the default values used for any parameters with out-of-range (unacceptable) values
specified in your input files;
• the run group name;
• the Facility IDs modeled and the location of each facility's center;
• the start and end time for the AERMOD portion of the modeling run;
• the full list of outputs produced; and
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• the number of minutes required for HEM4 to model each facility and produce the facility-
specific outputs.
HIM
-
~ X
•
ft
RUN HEM4
SUMMARIZE RISKS
Facility Fac1-NC Using period start = 2019 02 11 12
Facility Fac1-NC: Using penod end = 2019 06 301
Facility Fac2-IL Using annual met option
Uploaded facilities options list file for 2 facilities
Uploaded HAP emissions file for 101 source-HAP combinations
Uploaded emissions location file for 13 facility-source combinations
B£i
DEMOGRAPHIC ASSESSMENT
Uploaded user receptors for [Fac1 -NC]
Uploaded emissions vanatiorts for [Fac2-IL,CT000001 ,Fac2-IL,FU000001]
ANALYZE OUTPUTS
Uploaded buoyant line parameters for [Fac1-NC]
0
LOG
Uploaded polyvertex sources for |Fac1-NC, MS000001)
Uploaded building downwash parameters for [Fac1-NC]
Uploaded particle data for [Fac2-IL]
0
ABORT HEM RUN
Uploaded land use data for [Fac1-NC,Fac2-IL]
Uploaded seasonal variation data for [Fac1-NC,Fac2-ILl
IB
HEM4 USER GUIDE
HEM4 is starting
RUN GROUP test
-------
summaries based on the facilities modeled within your run group. Six of the summaries produce
results specific to each facility (i.e., individual facility IDs are connected to the results, which
account for impacts from each facility's emissions in isolation), and five of the summaries
combine results across the run group (i.e., individual facility IDs are not present in these
summaries, which account for multiple impacts on receptors from neighboring facilities).
The "Facility Summaries" available on this screen are:
• Cancer Drivers;
• Hazard Index Drivers;
• Acute Impacts;
• Multipathway;
• Max Concentration; and
• Max Risk and HI by Source and Pollutant.
The "Run Group Summaries" available on this screen are:
• Max Risk and Hazard Indices;
• Risk Histogram;
• Hazard Index Histogram;
• Incidence Drivers; and
• Source Type Risk Histogram.
The Summarize Risks screen is shown in Figure 10. Note: Before you choose to summarize
your risk results via these reports, you may wish to perform certain QA checks on the modeled
results, as described in Section 10.
Q
&
Ln
0
V
~
SUMMARIZE RISKS
DEMOGRAPHIC ASSESSMENT
ANALYZE OUTPUTS
REVISE CENSUS DATA
HEM4 USER GUIDE
AERMOD USER GUIDE
¦i Select output folder
Facility Summaries
0 Cancer Drivers
0 Hazard Index Drivers
[~I Acute Impacts
~ Multipathway
[~I Max Concentration
Enter a pollutant
name
Max Risk and HI by Source
and Pollutant
Enter the position in the source ID where the
source type begins The default is 1
Enter the number of characters
n the sourcetype ID
Run Group Summaries
PI Max Risk and Hazard Indices
~ Risk Histogram
PI Hazard Index Histogram
~ Incidence Drivers
PI Source Type Risk Histogram
~ Enter the position in the source ID where the
source type begins The default is 1
n—| Enter the number of characters
^—' in the sourcetype ID
|Run Reports|
Figure 10. Run the Risk Summary Programs
First, click on the Select output folder button to browse for the folder where the HEM4 outputs
you want summarized are located. Next, select which summaries you would like to run by
checking the box before each, and then click the "Run Reports" button to initiate the selected
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summaries. As noted above, the outputs produced by these summary programs are risk
summary reports for all facilities modeled in your run group and are described in Section 7.
There are a few summary programs on this screen that require additional information from you.
The Max Concentration summary requires you to enter a pollutant name. The pollutant name
you enter should be a name of a pollutant in your HAP Emissions input file, spelled exactly as it
appears in this file. Note: If you would like the maximum concentration for more than one
pollutant, you may come back to this Summarize Risks screen and enter another pollutant
name after you run the report for the first pollutant.
The Max Risk and HI by Source and Pollutant summary and the Source Type Risk Histogram
summary require you to indicate where in your Source IDs the source type begins and ends. As
discussed in Section 3.3.1, it is helpful to create your Source IDs so that the type of source is
identified always in the same location in the Source ID string. For example, if you are modeling
a series of storage tanks and wastewater vessels, you could identify them with IDs such as
ST01, ST02, ST03, WW01, WW02, and so on. In this example, the source type starts in location
1 of the Source ID string and is 2 characters long (i.e., ST and WW). Therefore, in this case,
after you check the Max Risk and HI by Source and Pollutant box and/or the Source Type Risk
Histogram box (shown above in Figure 10), you would enter a 1 next to "Enter the position in the
source ID where the source type begins." You would then enter a 2 next to "Enter the number of
characters in the sourcetype ID."
After you have selected the summaries you want to run, check the Log screen for progress. The
HEM4.log text file will also report any errors. When the Risk Summary Reports have finished, a
pop-up message will appear (shown below).
HEU1 Summary Reports Finished X
Risk summary reports for Facl-NC, Fac2-IL run.
OK
The Risk Summary Reports you choose to run will be placed in the same output folder where
you indicated the HEM4 results are located (which were summarized using these programs).
These summary reports are described in Section 7.
4.6 Assess Demographics of Modeled Population
If you used U.S. Census receptors for your modeling, the DEMOGRAPHIC ASSESSMENT
button on the menu bar on the left allows you to assess the demographics of the communities
surrounding your modeled facilities, including the potentially disproportionate cancer and
noncancer risks posed to certain demographics within these communities by the modeled
emissions. HEM4 links each U.S. census block receptor around your modeled facilities with
census-based demographic factors including racial, ethnic, age, economic, educational, and
linguistically isolated population categories. (Note: Alternate receptors do not have demographic
data associated with their populations and therefore cannot be used with the Demographic
Assessment module.) The Demographic Assessment screen is shown below in Figure 11.
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ft
9£i.
s
ANALYZE OUTPUTS
SUMMARIZE RISKS
DEMOGRAPHIC ASSESSMENT
Note The Demographic Assessment module may be used with HEM4 runs based on US Census
Block receptors only Demographic results are available out to the smallest radius modeled for any
facility in the run group
Select output folder
Enter a run group name and prefix
Name:
Prefix «7pCmH
Choose type of impact (cancer or noncancer) for basis of demographics analysis, the radius around each facility
to include, and the impact level at which population percentages will be calculated Note proximity statistics
will be included at your specified radius
REVISE CENSUS DATA
Combination Radius (km) |S0
f Cancer Risk Level (in a million) >= |l
Add combination
HEM4 USER GUIDE
AERMODUSER GUIDE
P? Run Reports
Q EXIT
Figure 11. Demographic Assessment Screen
Note that you must have an output folder with modeled results to run the Demographic
Assessment module. Do not add or remove files to that output folder, or change the filenames of
any output files, as the module's code requires certain files to be present in the output folder
(e.g., the Facility Max Risk and HI file), and to contain the same prefix as the output folder that
HEM4 placed them in. After you have run HEM4 and have modeled results, follow these steps
on the Demographic Assessment screen:
1. At the top of this screen, select the output folder containing the HEM4 modeling results
of the group of facilities for which you wish to assess the surrounding demographics.
Click on Select output folder to browse for the folder containing your HEM4 outputs.
2 Use the "Name" text box to enter the name you wish to appear in the outputs produced
by this Demographic Assessment run. The name you enter will be used for every
demographic table produced by this module. Use the "Prefix" text box to enter a prefix
that will be used at the beginning of the filenames for the outputs produced by this
Demographic Assessment run. The name and prefix you enter here need not be the
same name/prefix used in the HEM4 output folder you pointed to in step #1. The
demographic outputs are discussed in Section 8.2. (Keep the prefix brief; if the path
length plus file name length is > 260 characters, Windows® may not write the file.)
3. Choose whether you wish to assess cancer risk or noncancer HI level, the radius (in km)
at which you wish to assess the community demographics surrounding the facilities in
your run group, and the impact level - cancer risk level or noncancer HI level - at which
population percentages that exceed this level will be provided. You may enter a radius
up to the smallest radial distance modeled for any facility in your run group, as indicated
in the Max. Distance column of your Facility List Options file. You may enter cancer risk
levels of 1, 5, 10, 20, 30, 40, 50, 100, 200 or 300-in-1 million, and the module will output
population percentages with cancer risk greater than or equal to the level you choose.
You may enter noncancer HI levels of 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, and the module will
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output population percentages with noncancer HI greater than the level you choose.
Entering a radius greater than the smallest radial distance modeled for any facility or
entering impact levels other than these will cause an error message to pop-up.
The Add combination button, allows you to choose up to four such combinations for a
single Demographic Assessment run, all of which will be based on the HEM4 outputs
you selected in step #1. Proximity statistics, which are the total demographic populations
and percentages around your modeled facilities irrespective of risk or HI levels, will also
be provided at whatever radius you specify (up to the smallest radial distance modeled
for any facility in your run group, as noted above).
4. Click on Run Reports to initiate the Demographic Assessment run.
Figure 12 provides an example of a Demographic Assessment in which four combinations are
chosen for a run group that will be named "Primary Copper Smelting" in the demographic output
tables produced. In this example, all outputs will have filenames beginning with the prefix
"PrimCop" and the following outputs will be provided, based on the four combinations chosen.
• Demographic-specific population percentages for people with a cancer risk greater than
or equal to 1 in a million at a radius of 50 km;
• Demographic-specific population percentages for people with a cancer risk greater than
or equal to 10 in a million at a radius of 5 km;
• Demographic-specific population percentages for people with a noncancer HI level
greater than 1 at a radius of 50 km; and
• Demographic-specific population percentages for people with a noncancer HI level
greater than 2 at a radius of 5 km.
B£t
Q
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¥
E
¦
~
SUMMARIZE RISKS
DEMOGRAPHIC ASSESSMENT
ANALYZE OUTPUTS
REVISE CENSUS DATA
HEM4 USER GUIDE
AERMOD USER GUIDE
Note The Demographic Assessment module may be used with HEM4 runs based on U S Census
Block receptors only Demographic results are available out to the smallest radius modeled for any
facility in the run group.
|| Select output folder
Enter a run group name and prefix
Name: i Primary Copper Smtlting
Prefix jPrimCop
Choose type of impact (cancer or noncancer) for basis of demographics analysis, the radius around each facility
to include and the impact level at which population percentages will be calculated Note proximity statistics
will be included at your specified radius
Combination
Radius (km)
50
r
Cancer Risk Level (in a million) >=
1
Combination
Radius (km)
5
if
r
Cancer Risk Level (in a million) >=
10
[RbitosJ
Combination
Radius (km)
50
r
| Remove)
rf
Noncancer Hazard Index Level >
1
Combination
Radius (km)
5
r
PT
| Remove]
(t
Noncancer Hazard Index Level >
E' Run Reports
Figure 12. Sample Demographic Assessment Run Combinations
If you require more than four combinations for your Demographic Assessment, you may come
back to this screen after running the first four reports, to run more combinations. Based on the
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radii indicated in the above combinations shown in Figure 12, proximity demographics at 5 km
and 50 km will be provided (irrespective of cancer or HI level). Binned cancer risk and
noncancer HI levels for the full array of HEM4 results at each of these radii will also be provided,
as discussed further in Section 8.2. It should also be noted that, if the noncancer radio button is
selected, noncancer HI results will be provided for whatever TOSHI is the maximum plus any
other TOSHIs that are greater than 1. (As discussed in Section 2.2.1, there are a total of 14
TOSHIs modeled by HEM4.) Upon commencement of the Demographic Assessment run, HEM4
will create a new subfolder named "ej" in your run group output folder, and the demographic
results will be placed in this subfolder, each with a date and time stamp. The Demographic
Assessment methodology and results are discussed in more detail in Section 8.
4.7 Analyze Outputs
The ANALYZE OUTPUTS button on the menu bar on the left allows you to view and analyze
(1) the HEM4 Outputs, including facility-specific modeling results and the run group-wide Risk
Summary outputs, as well as (2) the Demographic Assessment Outputs. The View and Analyze
Outputs screen is show below in Figure 13.
SUMMARIZE RISKS
2$. DEMOGRAPHIC ASSESSMENT
ANALYZE OUTPUTS ~3 °^>en a facility or summary output table
q L0G (£ Open a chronic of acute risk map
^ Vi ew summary graphi cal outputs i n web browser
REVISE CENSUS DATA
Vi ew demographic assessment outputs i n web browser
QQ HEM4 USER GUIDE
WR AERMOD USER GUIDE
Q EXIT
Figure 13. View and Analyze Outputs
4.7.1 HEM4 Outputs
The top portion of the "View and Analyze Outputs" screen consists of three buttons that allow
you to (1) open a facility or summary output table via a spreadsheet app for further analysis and
graphing; (2) open a chronic or acute risk map; and (3) view summary graphical outputs in your
web browser. After you click on these buttons, HEM4 will prompt you to identify the location of
the output files you wish to view and analyze further.
If you choose to open a facility or summary Excel or CSV output table using the first button
(shown in Figure 13), HEM4 will open the file within a spreadsheet app with numerous widgets
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available for further analysis and graphing. This widget is provided by a pandastable library as
an interactive way to review and analyze HEM4's tabular output data (see
https://pandastable.readthedocs.io/en/latest/description.html.) An example of a Hazard Index
Drivers output (spreadsheet) opened via this first button is shown in Figure 14. The spreadsheet
and graphing widgets along the right-hand side include: Load table; Save; Import CSV; Load
Excel file; Copy table to clipboard; Paste table; Select data to plot; Transpose; Aggregate; Pivot;
Melt; Merge, concatenate or join; Prepare a sub-table; Filter table; Calculate; Model fitting; Clear
table; Contract columns; Expand columns; Zoom out; and Zoom in.
$ C:/Git_l-IEM4/HEM4/output/test4-20/test4-20_hazardJndex_drivers.xlsx — ~ X
isflaiiuw
HI_Type
Pollutant
I ^
tm
Fac1-NC
Developmental HI
9.479141
SR000001
arsenic compounds
9.431920
199.500000 |
HI"
2
Fac1-NC
Kidney HI
1.570466
SR000001
cadmium compounds 1.506065
95.900000
\m_
S
3
Fac1-NC
Respiratory HI
0.47091
RW000001
acrolein
0.29061
61.710000
4
Fac1-NC
Respiratory HI
0.47091
FU000001
bis(2-ethylhexyl)phthalate
0.132177
28.070000
5
Fac1-NC
Respiratory HI
0.47091
RW000001
acrolein
0.0321697
6.830000
g
6
Fac1-NC
Liver HI
0.190013
FU000001
bis(2-ethylhexyl)phthalate
0.144408
76.000000
Fac1 NC
Liver HI
0.190013
RW000001
trichloroethylene
0.0312142
16.430000
8
Fac1-NC
Reproductive HI
0.090131
RV000001
1,3-butadiene
0.0887254
98.440000
9
Fac1-NC
Neurological HI
0.065151
RW000001
trichloroethylene
0.0348731
53.530000
10
Fac1-NC
Neurological HI
0.065151
FU000001
mercury (elemental)
0.0229932
35.290000
11
Fac1-IMC
Neurological HI
0.065151
RW000001
trichloroethylene
0.00386036
5930000
12
Fac1-NC
Immunological HI
0.039509
RW000001
trichloroethylene
0.0348731
88.260000
r—
13
Fac1-NC
Immunological HI
0.039509
RW000001
trichloroethylene
0.00386036
9.770000
«$
14
Fac2-IL
Liver HI
0.024612
FU000001
bis(2-ethylhexyl)phthalate
0.0225351
91.560000
\*
15
Fac2-IL
Respiratory HI
0.024087
FU000001
bis(2-ethylhexyl)phthalate
0.0225351
93550000
16
Fae2-IL
Neurological HI
0.016217
FU000001
mercury (elemental)
0.0141467
87.230000
lit.
17
Fac2-IL
Neurological HI
0.016217
FU000001
mercury (elemental)
0.00155341
9.580000
18
Fac1-NC
Hematological HI
0.000931
FU000001
selenium compounds
0.00090521
97.180000
19
Fac2-IL
Hematological HI
0.000522
FU000001
selenium compounds
0.000517802
99.180000
u5_
20
Fac1-NC
Skeletal HI
0.000461
RW000001
hydrofluoric acid
0.000415156
90.030000
fs"
21
Fac1-NC
Endocrine HI
7.09803e
RV000001
cumene
5.67842e-06
80.000000
l»
22
Fac1-NC
Endocrine HI
7.09803e
RV000001
cumene
1.41961 e-06
20.000000
23
Fac2-IL
Reproductive HI
1.28789e
FU000001
benzo[a]pyrene
9.69533e-07
75.280000
nj
24
Fac2-IL
Developmental HI
1 28789e
FU000001
benzo[a]pyrene
9.69533e-07
75.280000
25
Fac2-IL
Reproductive HI
1.28789e
FU000001
benzo[a]pyrene
3.18352e-07
24.720000
26
Fac2-IL
Developmental HI
1.28789e
FU000001
benzo[a]pyrene
3.18352e-07
24.720000
26 rows
x 7 columns
\m\m\e l°'
Figure 14. Hazard Index Drivers File Opened via Spreadsheet App
As a further example of this tool, if you click on the "SeIect-data-to-pIot" widget on the right-hand
side of the spreadsheet, a data plot automatically pops-up with numerous formatting options for
graphing. A depiction of one plot is shown in Figure 15.
0 Plot Viewer — ~ X
5-a4 Plot ^ Apply Options ^ X ill ® dpi 80 | P grid layout I 3D plot
Base Options Annotation Grid Layout Other Options 3D Options Animate
global labels
extto add
textbox
textbox format
add objects
title
box style
font size
add object
square (~
12
textbox ~
x label
facecolor
coord qrstem
HI Type
white |r
font
data ~
ylabel
linecolor
monospace ~
Create
black |-r
fontw eight
HI Total value
rotate
0
normal [¦»
Clear
ticklabel angle
align
l°
I ~~
center !~
Figure 15. Select Data to Plot Widget
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If you choose to open a chronic or acute risk map with the second button (shown in Figure 13),
you wiii be asked to select a chronic kmz file from your modeled outputs, which HEM4 will
launch in Google Earth™. Or you can select an acute map html file to view on a satellite street
map. An example of a chronic kmz file is shown below in Figure 16 displayed via Google
Earth™, with the cancer and noncancer chronic results overlaid on the map. These results are
discussed further in Section 6. Note: The first time you run HEM4, your computer may take
several minutes to open Google Earth™; but the application will open quickly after subsequent
runs.
ft Weather
& Galtey
Figure 16. Chronic Risk Map shown in Google Earth™
To open an acute map, you must first run the Acute Impacts summary from the Summarize
Risks ("Create Risk Summary Reports") screen, shown in Figure 10. After you run the Acute
Impacts summary program, if there is an acute HQ greater than or equal to 1.5 based on any
benchmark, then HEM4 will produce an output subfolder called "Acute Maps". This subfolder will
be located in the same place where the other facility-specific and summary outputs from your
run are located. (Note: No Acute Maps folder is produced if all acute HQ are less than 1.5.)
Click on the "Open a chronic or acute map" button under "HEM4 Outputs" on the "View and
Analyze Outputs" screen (shown in Figure 13). HEM4 will ask you to select the html file you
wish to view. Choose an html file from any of the html files located in the "Acute Maps" subfolder
and HEM4 will display your map in your default browser window. An example html acute map is
shown in Figure 17, for one of the acute benchmarks (REL) based on modeled acrolein results.
The acute output files underlying these mapped results are explained in Sections 6 and 7.
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Acrolein (AEGL-1 1-hr) Acrolein (REL) Arsenic Compounds (REL) Mercury (Elemental) (REL)
Fac1-NC Acrolein Acute HQ (REL)
Figure 17. Acute Map View of HTML File
Finally, you can choose to view summary graphical outputs in your default web browser by
clicking on the third button, under "HEM4 Outputs" (shown in Figure 13). To use these
statistical and graphical visualization tools, you must choose a folder containing Risk
Summary reports run from the Summarize Risk screen (shown in Figure 10). Note that all risk
summary reports must be present in your selected folder to use these statistical and graphing
tools, except the Max Risk report, Multipathway report and Acute Impact report: these three
reports may be present in your selected folder but are not required. After you select your
desired output folder, the graphical visualizations of your results that appear in your default web
browser are constructed via the Dash app, which is a Python framework for building interactive
web applications. The graphical displays of your results offered by this application include:
• a map of your modeled facilities;
• pie charts based on the cancer incidence percentages by pollutant and source type:
• bar charts showing the number of people at increasing levels of cancer risk (e.g., less
than 1 -in-1 million risk, greater than or equal to 1 -in-1 million risk, greater than or equal
to 10-in-1 million risk, greater than or equal to 100-in-1 million risk);
• bar charts showing the number of people at increasing noncancer hazard index levels
for each of the 14 modeled target organ specific hazard indices (e.g., less than or equal
to 1, greater than 1, greater than 10, greater than 100, greater than 1000);
• bar charts showing the source and pollutant risk drivers of your modeling run for both
cancer and noncancer;
• bar charts showing the acute screening hazard quotients by benchmark and pollutant for
each facility with modeled acute impacts; and
• an interactive and exportable spreadsheet displaying the maximum cancer risk and
noncancer hazard index values for each modeled facility.
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An example of one of the several graphical visualizations of your results offered by this
application is shown in Figure 18, which displays pie charts based on the cancer incidence
percentages by pollutant and source type, for a modeling run based on 5 different pollutants and
8 different source types.
Cancer Incidence by Pollutant and Source Type
(Total Incidence is 4.80E-02)
¦ SR
¦ RV
¦ FU
¦ RW
¦ MS
¦ HV
¦ CV
Figure 18. Example Graphical Visualization of Incidence by Pollutant and Source Type
The output files underlying these results are explained in Sections 6 and 7.
4.7.2 Demographic Assessment Outputs
The bottom portion of the "View and Analyze Outputs" screen consists of a single button that
allows you to view Demographic Assessment outputs in your web browser. When you click this
button, HEM4 will prompt you to identify the location of the output files you wish to view and
analyze further. To use these statistical and graphical visualization tools, you must
choose a folder containing Demographic Assessment reports run from the Demographic
Assessment screen (shown in Figure 11). After you select your desired output folder, the
graphical visualizations of your results that appear in your default web browser are constructed
via the Dash app, which is a Python framework for building interactive web applications. The
graphical displays of your results offered by this application's dashboard include:
Cancer Incidence by Pollutant for test_8-l-2020
(for pollutants that contribute at least 1%)
Cancer Incidence by Source Type for test_8-l-2020
Arsenic Compounds
1,3-Butadiene
Cadmium Compounds
Naphthalene
Benzene
• a bar chart displaying the risk at each facility according to parameters determined by six
dropdown menus, namely
o risk metric (cancer or noncancer HI);
o distance (in km, the radius around each modeled facility for which you requested
the demographic breakdown via the Demographic Assessment interface);
o risk/Hi level (determined by the risk/Hi level you requested on the interface);
o demographic group (discussed more below);
o bar heights (percentage or population); and
o sorting method (percentage or population);
• a map of your modeled facilities that can be customized according to five dropdown
menus, namely
o metric to display (cancer or noncancer HI);
o linear or log scale (how risk metric will be displayed);
o basemap style (light, dark, satellite, streets);
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o color ramp (color used for facility information displays); and
o dot size (indicating facility locations);
• an interactive and exportable spreadsheet displaying the number or percentage of
facilities exceeding the nationwide, state, and county geographic average for varying
metrics, distances, and risk levels by a selected percentage amount.
The dashboard also includes a "Learn More" tab with additional information about each display.
The bar chart, map and table display provided in each of the three tabs that will appear in your
web browser are described below.
The Bar Graph tab displays the results of HEM4's Demographic Assessment module, which as
noted in Section 4.6, provides demographic estimates for scenarios that are based on distance
and risk level. The demographic groups included are People of Color (previously called
Minority), African American (or Black), Native Americans, Other races and multiracial, Hispanic
or Latino, Children 17 years of age and under, Adults 18 to 64 years of age, Adults 65 years of
age and over, Adults without a high school diploma, People living below the poverty level, and
Linguistically isolated people. As discussed more in Section 8, statistics on total population,
race, ethnicity, age, education level, low household income, poverty status and linguistic
isolation are obtained from the Census' American Community Survey (ACS) five-year averages
for 2016-2020 (Census 2022b). Figure 19 is from the "Learn More" tab, and provides helpful
information about the contents of the bar graph.
A scenario consists of a risk metric and level, and a distance. If you are only interested in proximity,
then choose a distance and "Proximity Only.* These dropdown* are populated based on the
scenarios run in HEM4's Demographic Assessment module.
Risk Metric
Concur fbak
Distance (km)
Demographic Group
People of color
Bar Heights: % or Pop
Demographics for Cancer Risk for Radius 20 km (Proximity Onl<
2.
5
3
The number at the top of each bar is the
estimated number of people in the
demographic group for the chosen scenano (if
the y-axis is percent), or the percent of people
in the demographic group (if the y-axis is
population).
Each bar represents a facility
Sort by % or Pop
You can sort by % (default) or by
population. It may be informative
to sort by population because
there could be high percentages
but low associated populations.
The plum-colored horizontal band
is the range of the nationwide,
state, and county averages of the
demographic group percentages.
These geographic averages are
based on proximity, not risk level.
For example, the county average
includes all counties with census
blocks within the scenario
distance, not just the ones above
the scenario risk level. These are
included to allow a comparison
with the facility estimates.
Figure 19. The Demographic Assessment Bar Graph under "Analyze Outputs"
The bar graph is interactive, and you can change several properties of it. If you mouse over the
graph, a widget bar appears in the upper right. There are several widgets, including zoom and
pan, and a widget that allows you to download the graph as an image file.
Next to the Bar Graph tab is a tab entitled "Map of Facilities". This map tab shows the locations
of all the facilities included in your HEM4 run group, and is based on the Facility Max Risk and
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HI file generated by HEM4 (and described more in Section 6.2.1). The map is linked to the bar
graph; when you select a facility bar in the graph, the map zooms to that facility. Figure 20 is
also from the "Learn More" tab, and provides helpful information about the contents of the map
graphic. Like the bar graph, the map is interactive, and if you mouse over the map, a widget bar
appears in the upper right of the map, which allows you to zoom, pan, and download the map as
an image file.
The metric can be cancer risk (in a
million)(default), or one of the
noncancer target-organ-specific
hazard indices.
The scale can be linear (default) or
log. Risk estimates are sometimes
skewed, and the log scale may display
the distribution better.
There are four basemap choices: light
(default), dark, satellite, and
streetmap.
There are six color ramp choices. The
default ramp is purple (low) to yellow
(high).
You can change the dot size to make
it easier to see for a given map scale.
Figure 20. The Demographic Assessment Map of Facilities under "Analyze Outputs"
Finally, next to the map tab is a "Summary Table" tab, which provides the number (or percent)
of facilities that exceed the geographic averages for each of the demographic groups listed
above. Similar to the bar and map graphs, the table is interactive with changeable properties.
There is a radio button below the table that allows you to show either the number of facilities
(default) or the percent of facilities that exceed the geographic averages. Because you may be
interested in how many facilities exceed the geographic averages by a certain amount, there is
a slider widget below the table that allows you to select any percentage above the geographic
averages, from 0 to 100%, in increments of 5%. For example, if you wanted to know how many
facilities were twice the geographic averages, you would select 100% from the slider. There is
also a button at the top of the table that allows you to export the table to a spreadsheet.
As discussed more in Section 8, it should be noted that the nationwide, state, and county
geographic averages are population statistics not based on cancer or noncancer risk levels. For
example, the county average includes all counties with census blocks within the scenario
distance, not just the ones above the scenario risk level. These are included to allow a
comparison with the facility estimates.
The output files underlying these results are explained in Section 8.
Metric to Display
MIR (in a million)
Linear or Log Scale
Log
Basemap
Light
Color Ramp
Map of Facilities
Facility Map - MIR (in a million)
Dot Size
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4.8 Revise Census Data Option
The REVISE CENSUS DATA button on the menu bar on the left allows you to change your U.S.
Census file using the census update file described in Section 3.5.9. On this screen, shown in
Figure 21, click on the "Please select a census update file" button to select an update file from
your computer. Once your census update file is selected, click on the "Revise" button on this
screen, which will change the census files that HEM4 uses to model any facilities after the
change. (Note: this revision is permanent to your census files unless you change your census
files back to their original. For this reason, it is recommended that you save your original census
files to a separate location before clicking on "Revise" using this screen.)
You can use the census update file described in Section 3.5.9 to (1) zero-out the population of a
specific U.S. Census block, (2) move a block to a new latitude and longitude location, and/or (3)
delete or remove a census block. The reasons for making such revisions to your census dataset
are also discussed in Section 3.5.9.
IW -OX
RUN HEM4
ft summarize R.SKS ¦ Please select a census update file:
DEMOGRAPHIC ASSESSMENT Revise
IT! ANALYZE OUTPUTS
0 log
0 REVISE CENSUS DATA
^ HEM4 USER GUIDE
^ AERMOD USER GUIDE
Q EXIT
Figure 21. Revise Census Data Screen
4.9 Error Messages and Failed Runs
When initiating a model run, HEM4 will perform a series of checks on your inputs to identify
obvious errors that would cause the model (including AERMOD) to fail. Identifying these input
errors prior to HEM4 attempting to model the erroneous values avoids most unsuccessful model
runs and provides you with instructions to rectify the problem. Reviewing the AERMOD
documentation is also important and helpful if you receive an error from HEM4 or from
AERMOD (in the aermod.out file, described in Section 6.1.13) when running your inputs and the
resolution of the error is not clear (EPA 2022a, EPA 2022b).
For example, on the user interfaces that instruct you to select input files (discussed above in
Sections 4.1 through 4.3), if you attempt to upload an input file with the wrong number of
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columns (a.k.a. fields), then an error message will pop-up indicating that the file you uploaded
had "x" columns, but should have "y" columns. HEM4 will also compare the Source IDs in your
input files to ensure they match. If the Source IDs in your Emissions Location file do not match
the Source IDs in your HAP Emissions file, then an error message will pop-up indicating that
"Your Emissions Location and HAP Emissions files have mismatched Source IDs. Please
correct one or both files with matching sources and upload again." A sample of the kinds of pop-
up error messages and their meanings are listed in Table 32.
Additionally, if you entered a value for an input parameter that is out-of-range of the acceptable
values for that parameter, then HEM4 will replace your problematic value with the default value,
and indicate the replacement in the log file, as noted above in Section 4.4. The values HEM4
defaults to are listed for applicable parameters within each standard input file starting in Section
3.2.
Table 32. Sample List of Error Messages and Causes in HEM4
Pop-Up Error Message
Meaning / Cause
"One or more facility IDs are missing in the List."
The uploaded file contains records without a
valid Facility ID.
"One or more met stations referenced in the Facility
List are invalid."
The uploaded Facility List Options file
contains facilities with met station references
that are not present in the master list of met
stations.
"One or more source IDs are missing in the List."
The uploaded file contains records without a
valid Source ID.
"One or more pollutants are missing in the List."
The uploaded file contains records without a
valid pollutant (HAP).
"One or more locations are missing a coordinate
system in the List."
The uploaded file contains records without
valid coordinate system values.
"One or more source types are missing a valid value in
the Emissions Locations List."
The uploaded Emissions Location file
contains records without a valid source type
value for one or more fields.
"The following pollutants were not found in HEM4's
Dose Response Library: [list of HAP names not found].
Would you like to amend your HAP Emissions file?
(They will be removed otherwise.)"
One or more HAP listed in the HAP
Emissions file is not included in the Dose
Response Library. Note: If you do not revise
your HAP Emissions file to include only HAP
listed in your Dose Response library, then
HEM4 will drop those HAP for the current
run. Alternatively, you may exit the run and
amend the Dose Response Library before
starting a new run.
"Facility : [lat/lon] value out of range in the
Emissions Locations List."
The uploaded Emissions Location file
contains an out-of-range latitude or longitude
value for one or more sources.
"Facility : UTM zone value malformed or invalid in
the Emissions Locations List."
The uploaded Emissions Location file
contains an invalid UTM zone value.
"Error: Some non-numeric values were found in
numeric columns in this data set."
The uploaded file contains non-numeric
values in a field that should have only
numbers.
"Length Mismatch: Input file has x columns but should
have y columns."
The uploaded file contains the wrong number
of columns.
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Pop-Up Error Message
Meaning / Cause
" parameters are specified in the Facilities List
Options file. Please upload a File."
The Facility List Options file specifies
modeling options requiring additional input
files that have not been uploaded.
"AERMOD models building downwash from point
sources only (i.e., vertical P, horizontal H, or capped C
point sources). Your building dimensions file includes
non-point sources. Please edit your building
dimensions file to remove all non-point sources."
AERMOD models building downwash of
emissions from vertical point (P), capped
point (C), and horizontal point (H) source
types only. The uploaded Facility List
Options file indicates building downwash for
one or more facilities and the Source IDs for
those facilities in the uploaded building
dimensions input file include sources other
than P, C, or H types.
"AERMOD cannot currently model deposition or
depletion of emissions from buoyant line sources, and
the Emissions Location file includes a buoyant line
source for one or more facilities. Please disable
deposition and depletion for each of these facilities or
remove the buoyant line source(s)."
The current AERMOD version can model
deposition and/or depletion from all source
types except buoyant lines. The uploaded
Facility List Options file indicates deposition
and/or depletion for one or more facilities
and one or more Source IDs for those
facilities in the uploaded Emissions Location
file are buoyant lines.
"AERMOD's FASTALL option cannot be used with
buoyant line sources, and the Emission Location file
includes a buoyant line source for one or more
facilities. Please disable FASTALL for each of these
facilities or remove the buoyant line source(s)."
The current AERMOD version does not allow
the FASTALL option with buoyant line
sources. The uploaded Facility List Options
file indicates FASTALL for one or more
facilities and one or more Source IDs for
those facilities in the uploaded Emissions
Location file are buoyant lines.
"AERMOD ran unsuccessfully. Please check the error
Section of the aermod.out file in the output
folder."
AERMOD didn't run successfully, for a
reason specified in the aermod.out file.
"At least one buoyant line group ID in the Buoyant Line
Parameter file is longer than 8 characters."
The Buoyant Line Parameter input file
contains at least one buoyant line group ID
that is longer than 8 characters, which is the
maximum length.
"There is at least one buoyant line group in the
Buoyant Line Parameter file with source IDs that do not
have the same parameters."
All Source IDs within one buoyant line group
must use the same parameters. The Buoyant
Line Parameter input file contains at least
one buoyant line group where this is not the
case.
"The Buoyant Line Parameter file contains one or more
facilities with non-unique source IDs."
The Source IDs of each buoyant line group
must be unique. This Buoyant Line
Parameter input file contains at least one
facility with non-unique Source IDs.
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Pop-Up Error Message
Meaning / Cause
"For at least one facility, there are mismatched buoyant
line Source IDs in the Emission Location file and the
Buoyant Line Parameter file."
All Source IDs identified as buoyant line
sources in the Emission Location file and
part of a buoyant line group must also
appear in the Buoyant Line Parameter file.
Either a Source ID is in the Buoyant Line
Parameter file and is not identified as a
buoyant line source in the Emissions
Location file, or the Source ID is identified as
a buoyant line source in the Emissions
Location file but is missing in the Buoyant
Line Parameter file.
"Buoyant line parameters for have not
been assigned. Please edit the 'source type' column in
the Emissions Location file."
The Buoyant Line Parameter input file
contains at least one facility that does not
have any Source IDs identified as buoyant
line sources in the Emissions Location input
file. The Emissions Location file should be
edited to correct this.
At least one buoyant line group ID in the Buoyant Line
Parameter file is blank. Please add an ID.
The Buoyant Line Parameter file cannot
contain a blank Group ID. At least one Group
ID is blank in this file.
"Cannot generate summaries because there is no
Facility_Max_Risk_and_HI Excel file in the folder you
selected."
The Risk Summary reports could not be run
because the Facility_Max_Risk_and_HI
output file is needed, but is missing.
"You must have at least one configuration."
At least one combination (configuration),
including radius and risk/Hi level, must be
entered on the Demographic Assessment
interface to initiate a run.
"Please ensure all run combinations contain a value for
radius and the selected risk threshold."
For one or more combinations requested, the
needed parameters (radius and/or risk/Hi
level) were not entered on the Demographic
Assessment interface.
"Please ensure all radius values are numbers."
One or more radius values were input with
non-numeric characters on the Demographic
Assessment interface.
"Please ensure all radius values satisfy 1 <= radius <=
50."
A radius value less than 1 km or greater than
50 km was entered on the Demographic
Assessment interface, which are outside the
allowable range of radius values.
"The selected HEM4 output folder included a facility
run at maxdist = [X] km. Please ensure all radii are <=
this value."
A radius requested on the Demographic
Assessment interface was larger than that
used for the modeling domain of at least one
facility (i.e., the max distance in the Facility
List Options file).
"Please ensure all cancer risk values are one of the
following: [1,5, 10, 20, 30, 40, 50, 100, 200, 300]"
For the current HEM4 version, the value
entered for the risk level on the Demographic
Assessment interface must be one of the
values shown.
"Please ensure all HI values are one of the following:
[1,2, 3, 4, 5, 6, 7, 8, 9, 10]"
For the current HEM4 version, the value
entered for the HI level on the Demographic
Assessment interface must be one of the
values shown.
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Pop-Up Error Message
Meaning / Cause
"The folder selected for a Demographic Assessment
contains HEM4 outputs that use Alternate Receptors.
These cannot be used with the Demographic
Assessment Tool."
HEM4's Demographic Assessment module
can only run a demographic analysis on
outputs of a modeling run that used U.S.
Census receptors.
"The folder selected for a Demographic Assessment is
deeply nested or contains long names. Consider using
a different path to avoid unexpected behavior that
arises from exceeding the Windows path length limit of
260 characters."
HEM4's Demographic Assessment output
file names tend to be long to cover the run
parameters (especially the facility-specific
output file names). If the path length plus file
name length is longer than 260 characters,
the file may not be written.
"Unable to find required ACS data. Please check your
HEM4 resources folder and try again."
HEM4 could not find required American
Community Survey data necessary for a
Demographic Assessment run.
"Please check the output folder for a properly named
Facility Max Risk and HI file."
HEM4 could not find a facility max risk and
HI file with the expected name. For a
Demographic Assessment run, the prefix
used for this file must be the same as the run
group folder name:
'[rungroup]_facility_max_risk_and_hi.xlsx'.
"The directory chosen does not contain an ej sub-
directory. Please ensure that the Demographic
Assessment tool has been run on this directory."
The directory chosen for the "View
Demographic Assessment outputs in web
browser" selection on the Analyze Outputs
interface does not contain a sub-directory
named "ej". This viewing tool can only be run
on a directory where a Demographic
Assessment has been performed [and has
produced an environmental justice/ej folderl.
If HEM4 is unable to model a facility or facilities due to errors in the inputs, HEM4 will not only
note the errors in the log file but will also produce an Excel file entitled "Skipped Facilities" in the
run group's output subfolder. You can use the list of skipped facilities in column A of this output
file to create a new Facility List Options file, after you fix the errors, to model these facilities.
This is discussed further in Section 10.
Finally, in the event of a failed modeling run, you should close down HEM4 and then re-
start before your next modeling run. A full shutdown and re-start of HEM4 ensures the
memory has been cleared, which will reset values in the underlying model code and avoid a
variety of potential issues in the next run.
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5. HEM4 Modeling Calculations for Each Facility
Section 3 describes the HEM4 input files and Section 4 describes the step-by-step instructions
for the user to initiate a HEM4 modeling run. This section describes the internal modeling
algorithms and simplifying assumptions employed by HEM4, once initiated, during a modeling
run. We list the AERMOD options used to model emission dispersion from each facility and
describe the method HEM4 implements to transform AERMOD's single pollutant concentration
modeling into multiple pollutant concentration estimations. This section also discusses HEM4's
post-dispersion computation of health impacts at modeled receptors, including cancer risk and
noncancer health hazards, as well as HEM4's calculations to estimate the contributions of
individual pollutants and emission sources to the estimated concentrations and health impacts
at the modeled receptors.
5.1 Dispersion Modeling
As noted previously in this guide, HEM4 carries out dispersion modeling by running the
AERMOD dispersion model. Section 3 describes a number of input options you can specify for
running AERMOD—for example, incorporating deposition and depletion, emissions variations,
and using urban or rural dispersion parameters. This section discusses the options that HEM4
implements by default. In addition, this section describes the dilution factor methodology used in
HEM4 for modeling multiple pollutants based on AERMOD's unit-emission rate modeling.
5.1.1 Regulatory Default, ALPHA and BETA Options
HEM4 uses primarily the regulatory default options when running AERMOD. These options
include the following:
• Uses stack-tip downwash (except for Schulman-Scire downwash);
• Uses buoyancy-induced dispersion (except for Schulman-Scire downwash);
• Does not use gradual plume rise (except for building downwash);
• Uses the "calms processing" routines;
• Uses upper-bound concentration estimates for sources influenced by building
downwash; from super-squat buildings;
• Uses default wind profile exponents;
• Uses low wind speed threshold;
• Uses default vertical potential temperature gradients; and
• Uses missing-data processing routines.
However, it should also be noted that AERMOD includes model option keywords ALPHA and
BETA for certain modeling options. The ALPHA keyword indicates one or more options are
being used that are scientific/formulation updates considered to be in the research phase and
have not been fully evaluated and peer reviewed by the scientific community; and/or non-
scientific model options in development that still need rigorous testing and for which EPA is
seeking feedback from the user community. The BETA keyword indicates one or more options
are being used that have been fully vetted through the scientific community with appropriate
evaluation and peer review. BETA options are planned for future promulgation as regulatory
options in AERMOD. See the AERMOD Model Formulation document (Appendix B) for more
information (EPA 2022e).
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For the current version of HEM4, the only ALPHA options available are Method 2 particle
deposition and gaseous (vapor) deposition. The only current BETA options in AERMOD version
22112, RLINE (a source type intended mainly for roadway modeling) and GRSM (Generic
Reaction Set Method for NO-to-N02 conversion via ozone), are not currently available options
in HEM4. To keep HEM4 general, the ALPHA and BETA keywords will always be included in
the AERMOD runstream file prepared by HEM4, even when no ALPHA or BETA options are
being used.
5.1.2 Dilution Factors
HEM4 uses AERMOD to compute a series of dilution factors, in units of (|jg/m3) per (g/sec),
specific to each emission source and receptor. This approach more quickly analyzes the
impacts of multiple pollutants than if separately modeling each pollutant. The dilution factor for a
particular emission source and receptor is defined as the predicted ambient impact from the
given source and at the given receptor, divided by the emission rate from the given source.
If you choose not to analyze deposition or depletion, then the dilution factor does not vary from
pollutant to pollutant. If you do select deposition or depletion, HEM4 will compute separate
dilution factors for gaseous and particulate pollutants. In addition, you can specify different
particle sizes and densities for each particulate matter emission source. To use pollutant-
specific parameters for particulates and/or gases, requires a separate Source ID for each
pollutant at a given source. As noted in Section 3.4, you can create multiple Source IDs using
the same locations and source parameters to accommodate different pollutants when modeling
deposition or depletion.
5.2 Estimating Risks and Hazard Indices
HEM4 estimates the total cancer risk, noncancer hazard indices (His) and optionally acute
hazard quotients (HQs) for all U.S. Census block locations or alternate receptor locations in the
modeling domain, all user receptors, and all receptors in the polar network. Receptors in the
HEM4 domain fall into two categories: those with impacts explicitly modeled by HEM4/
AERMOD, and those with impacts estimated via interpolation rather than explicit modeling.
Section 5.2.1 describes methods used to calculate cancer risks and noncancer health hazards
for receptors that HEM4/AERMOD explicitly models. Section 5.2.2 describes the interpolation
approach used to estimate cancer risks and noncancer health hazards at receptors not explicitly
modeled.
Based on the results for U.S. Census blocks or alternate receptors, and other receptors, HEM4
estimates the maximum individual risk (MIR), maximum HI, and optionally high acute value for
populated receptors (Section 5.2.3); as well as the maximum impacts for all offsite receptors,
including unpopulated locations (Section 5.2.4). For these locations, the model calculates the
contributions of individual pollutants and emission sources to cancer risks, chronic HI, and
optionally acute HQ (Section 5.2.5).
5.2.1 Explicit Modeling of Inner Receptors, User Receptors and Polar Receptors
HEM4 calculates cancer risks, target-organ-specific HI, and optionally acute HQ for three types
of discrete receptors that are explicitly modeled by AERMOD. These are (1) U.S. Census blocks
or alternate receptors within the user-defined modeling "cutoff" distance for explicit modeling of
individual receptors, (2) all user receptors, and (3) the user-defined polar receptor network.
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As noted above in Section 5.1.2, Dilution Factors, HEM4 combines pollutants into two
categories — particulates and gases (vapor) — for the purposes of dispersion modeling. The
model retains these categories to calculate cancer risks, noncancer HI and optionally acute HQ.
HEM4 uses the following algorithms:
For cancer risk:
CRt = Eij CRi, j
CRi.j = DFU xCFxXk [Ei,k x UREk]
For noncancer hazard indices:
HIt = Si.j HQi.j
HQi, j = DFi, j x CF x Sk [Ei, k / (RfC k x 1000 |a,g/mg)]
where:
CRt = total cancer risk at a given receptor (probability for one person)
j = the sum over all sources i and pollutant types j (particulate or gas)
CRi.j = cancer risk at the given receptor for source i and pollutant type j
DFi.j = dilution factor [(|a,g/m3) / (1000 g/sec)] at the given receptor for source i and
pollutant type j
CF = conversion factor, 0.02877 [(g/sec) / (tons/year)]
2k = sum over a" pollutants k within pollutant group j (particulate or gas)
Ei, k = emissions (tons/year) of pollutant k from source i
UREk = cancer unit risk estimate [1/(|a,g/m3)] for pollutant k
(cancer risk for an individual exposed to 1 |a,g/m3 over a lifetime)
HIt = TOSHI at a given receptor and for a given organ
HQi, j = organ-specific hazard quotient at the given receptor for source i and
pollutant type j
RfC k = noncancer health effect reference concentration (mg/m3) for pollutant k
(concentration at and below which no adverse health effect is expected)
The above equations are equivalent to the following simpler equations:
CRt = Si, k ACi, k x UREk
HIt= Si, k ACi, k / (RfC k x 1000 |J.g/mg)
where:
ACi, k = ambient concentration (|j.g/m3) for pollutant k at the given receptor. This is the
same as [Ei, k x DFij x CF]
However, use of these simpler equations would require modeling all pollutants individually in
AERMOD, and performing separate risk calculations for each pollutant.
If the cancer unit risk estimate (URE) is not available for a given pollutant, then that pollutant is
not included in the calculation of cancer risk. Likewise, if the noncancer reference concentration
(RfC) is not available for a given pollutant, that pollutant is not included in the calculation of HI.
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Note that separate reference concentrations are used for acute HQ and chronic HQ. As
discussed in Section 2.2.1, for acute impacts, instead of the chronic RfC, the short-term
concentration is compared with various threshold or benchmark levels for acute health effects
(e.g., the California EPA reference exposure level [REL] for no adverse effects).
5.2.2 Interpolated Modeling of Outer Receptors using the Polar Receptor Network
For U.S. Census blocks and alternate receptors outside of the user-defined modeling "cutoff"
distance for individual block modeling, HEM4 estimates cancer risks, noncancer HI and
optionally acute HQ by interpolation from the polar receptor network. HEM4 estimates impacts
at the polar grid receptors using AERMOD modeling results and the algorithms described in
Section 5.2.1. If you choose to model terrain effects with the elevation option in your Facility List
Options file, then HEM4 estimates an elevation for each polar receptor. HEM4 estimates
elevations and controlling hill heights for the polar grid receptors based on values from the U.S.
Census library for modeling runs using the U.S. Census, or from the alternate receptor file for
runs not based on the U.S. Census. HEM4 divides the modeling domain into sectors based on
the polar grid receptor network, with each census block assigned to the sector corresponding to
the closest polar grid receptor.
HEM4 then assigns each polar grid receptor an elevation based on the highest elevation for
any U.S. Census block receptor, user receptor, or alternate receptor in its sector. The controlling
hill height is also set to the maximum hill height within the sector. If a sector does not contain
any census blocks or alternate receptors, the model defaults to the elevation and controlling hill
height of the nearest block or nearest alternate receptor outside the sector, or defaults to the
elevation of the nearest source (if the polar grid receptor is closer to a source than to a block or
alternate receptor outside its sector).
HEM4 interpolates the impacts at each outer U.S. Census block receptor or alternate receptor
from the four nearest polar grid receptors. The interpolation is linear in the angular direction, and
logarithmic in the radial direction, as summarized in the following equations:
la, r = IA1, r + (IA2, r — IA1, r) x (a — A1) / (A2 — A1)
IA1, r = exp{ln(lAi,Ri) + [ln(lAi,R2) - ln(lAi,Ri)] x [(In r) - ln(R1)] / [ln(R2) - ln(R1)]}
IA2, r = exp{ln(lA2,Ri) + [ln(lA2,R2) - ln(lA2,Ri)] X [(In r) - ln(R1)] / [ln(R2) - ln(R1)]}
the impact (cancer risk, chronic HI or acute HQ) at an angle, a, from north, and
radius, r, from the center of the modeling domain
the angle of the target receptor, from north
the radius of the target receptor, from the center of the modeling domain
the angle of the polar network receptors immediately counterclockwise from the
target receptor
the angle of the polar network receptors immediately clockwise from the target
receptor
the radius of the polar network receptors immediately inside the target receptor
the radius of the polar network receptors immediately outside the target receptor
where:
a =
r =
A1 =
A2 =
R1 =
R2 =
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5.2.3 Maximum Individual Risks, Hazard Indices, and Hazard Quotients
HEM4 evaluates the predicted chronic impacts for all populated receptors to identify the
locations of the MIR and the highest HI for various target organs (maximum TOSHIs). For these
calculations, populated receptors include all U.S. Census block locations or alternate receptors
and any user receptors you included in the run designated as type P (for populated). In general,
type P receptors should include houses near the facility, as well as other residences not
represented well by the location of the U.S. Census blocks or alternate receptors.
The maximum cancer risk may occur at a location other than the maximum HI for a given organ,
orTOSHI. Likewise, TOSHI locations may differ: the location of the maximum HI for one organ
will not necessarily be the same as the location for a different organ. HEM4 performs a separate
evaluation of the maximum impact location for each health impact.
The model also tests for instances where U.S. Census blocks, alternate receptors or type P
user receptors appear to be located on facility property. To do so, HEM4 calculates the distance
between each receptor and each emission source. These distances are compared with the
overlap distance that you specified in the Facility List Options file. If a populated-type receptor is
located within the overlap distance, then HEM4 does not use these calculated results for this
receptor to estimate the maximum individual cancer risk or maximum HI for populated areas.
Instead, the model assumes the impacts at the overlapping receptor to be equal to the
maximum impacts for any receptors that do not overlap facility property. This could include both
populated and unpopulated receptors (e.g., polar receptors), as long as they do not overlap
facility property.
If you chose to model acute (short-term) impacts in the Facility List Options file, HEM4 will also
evaluate predicted acute impacts for all receptors to identify the locations of the highest acute
HQs. For the acute calculations, all receptors are evaluated - both populated and unpopulated
receptors - including U.S. Census blocks or alternate receptors, all user receptors you may
have specified and all polar receptors. As described in the preceding paragraph, HEM4 also
checks to ensure that the maximum populated acute receptor is not overlapped. In the case of
an overlapped populated receptor, then the next highest non-overlapped populated receptor is
chosen.
5.2.4 Maximum Offsite Impacts
In addition to evaluating the maximum cancer risks, chronic HI, and acute HQ (if modeled) for
populated receptors (including census blocks, alternate receptors, and populated P type user
receptors), HEM4 evaluates maximum offsite impacts for all receptors, including unpopulated
receptors. All U.S. Census blocks or alternate receptors, all user receptors (populated and
unpopulated types), and all points (unpopulated receptors) on the polar receptor network are
included in the evaluation of maximum offsite impacts, except for those receptors that are found
to be overlapping emission sources.
5.2.5 Contributions of Different Pollutants and Emission Sources
HEM4 calculates the contributions of different pollutants and emission sources to cancer risks,
chronic HI, and acute HQ (if modeled) at the receptors where impacts are highest, both for
populated receptors and for all offsite receptors. As noted in Section 5.2.1, HEM4 groups
pollutants together when calculating total risks, HI, and HQ (if modeled) for the large number of
receptors that are typically included in an overall modeling domain. Thus, the model does not
compute the contributions of individual pollutants and emission sources for all receptors.
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However, HEM4 retains the information needed to determine the contributions of individual
pollutants and emission sources at the receptors where impacts are highest. HEM4 calculates
these contributions using the following equations:
ACi, k, m = Ei, k x DFi.j, m x CF
CRi, k, m = ACi, k, m x UREk
HQi, k, m = ACi, k, m / (RfC k x 1000 |j,g/mg)
where:
ACi, k, m = the predicted ambient concentration (|j.g/m3) for pollutant k, from source i, at
receptor m (as shown in sample calculation below10)
Ei, k = emissions (tons/year) of pollutant k from source i
DFi, j, m = the dilution factor [(|a,g/m3) / (1000 g/sec)] for source i, receptor m, and pollutant
group j, which includes pollutant k
CF = conversion factor, 0.02877 [(g/sec) / (ton/year)]
CRi, k, m = the estimated cancer risk from source i, and pollutant k, at receptor m
UREk = cancer unit risk estimate [1/(|a,g/m3)] for pollutant k
(cancer risk for an individual exposed to 1 |a,g/m3 over a lifetime)
HQi, k, m = the organ-specific hazard quotient as a result of emissions of pollutant k, from
source i, at receptor m
RfC k = noncancer health effect reference concentration (mg/m3) for pollutant k
(concentration at and below which no adverse health effect is expected)
Note that the methodology outlined above for cancer and chronic noncancer impacts is similar
for acute impacts, although acute emissions are used (including any acute factor/multiplier you
may have indicated in your Facility List Options files) as well as acute benchmarks discussed in
Section 2.2.1.
5.3 Population Exposures and Incidence
Using the predicted impacts for U.S. Census blocks or alternate receptors, HEM4 estimates the
populations exposed to various cancer risk levels and noncancer HI levels. To do so, the model
adds up the populations for receptors that have predicted cancer risks or noncancer HI above a
given threshold. For cancer risk, around each facility HEM4 predicts the number of people
exposed to a risk greater than or equal to the following thresholds:
• 1 in 1,000 (or 1,000-in-1 million) risk;
• 1 in 10,000 (or 100-in-1 million) risk;
• 1 in 20,000 risk;
10 Sample calculation: If at a particular receptor location, AERMOD (in the AERMOD outputs discussed
in Section 6.1.13) calculates a unit concentration of 3,853.5 |jg/m3 caused by a specific source, to derive
the concentration of a specific pollutant (e.g., arsenic) at that receptor location caused by that source,
HEM4 uses the tons per year (tpy) emission rate of arsenic from that source in your HAP Emissions input
file (e.g., 0.01164 tpy) as follows:
0.01164 tpy arsenic * (3,853.48 /jg/m3) /(1,000 g/sec) * 0.02877 (g/sec)/tpy = 0.00129 pg/m3
arsenic at that location caused by that source
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• 1 in 100,000 (or 10-in-1 million) risk;
• 1 in 1,000,000 (or 1 -in-1 million) risk; and
• 1 in 10,000,000 (or0.1-in-1 million) risk.
For noncancer HI, around each facility HEM predicts the number of people exposed to each of
the 14 TOSHIs above the following thresholds:
• Greater than 100;
• Greater than 50;
• Greater than 10;
• Greater than 1.0;
• Greater than 0.5; and
• Greater than 0.2.
If you opt to model acute impacts, HEM4 will provide the acute concentration for every pollutant
at every receptor, including every populated receptor, and will also include the population of
those receptors (whether U.S. Census blocks or alternate receptors). Because of the transitory
nature of acute exposures, acute health impacts are modeled not only where people reside but
at all receptors in the modeling domain. Therefore, the highest acute health impacts often occur
at unpopulated polar receptor locations close to the modeled facility. It is important to note that
the maximum acute impacts will occur at different times for different spatial locations (receptors)
and are therefore not additive. For this reason, population exposures are not tallied by HEM4 for
acute health impacts, only for cancer and chronic noncancer TOSHI.
HEM4 also estimates the contributions of different pollutants and emission sources to total
annual cancer incidence for the overall modeling domain using the following equations:
Cli, k, m = CRi, k, m x Pm / LT
where:
Clm - Si, k [cii, k, m]
TCI = Xm [Clm]
Cli, k, m = the estimated annual cancer incidence (excess cancer cases/year) for populated
receptor m due to emissions from pollutant k and emission source i
CRi, k, m = the estimated cancer risk from source i, and pollutant k, at populated receptor m
Pm = the population of populated receptor m
LT = the average lifetime used to develop the cancer unit risk estimate, 70 years
Si, k = the sum over all modeled pollutants k and emission sources i
Clm = the estimated total cancer incidence for populated receptor m due to emissions
from all modeled pollutants and emission sources
Sm= the sum over all populated receptors m in the modeling domain
TCI = the estimated total annual cancer incidence (excess cancer cases/year) for the
population living within the modeling domain from all modeled pollutants and
emission sources
It should be noted that the above incidence calculations are made for the pollutant types "j"
being modeled (whether particulate, gas, or combined).
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For each facility, HEM4 provides the estimated total annual cancer incidence (excess cancer
cases/year) predicted to be caused by all modeled pollutants emitted from all modeled sources
Increasing in specificity, HEM4 also provides the annual cancer incidence predicted to be
caused by each emission source at a facility for all pollutants emitted from that source, as well
as by each pollutant from all sources emitting that pollutant at a facility. At the greatest level of
specificity, HEM4 provides the estimated cancer incidence broken down by both pollutant and
emission source - that is, for every pollutant individually from each source separately.
5.4 Summarizing Human Health Impacts
Section 5.1 above discusses how HEM4 uses AERMOD for dispersion modeling of your inputs
to produce multi-pollutant concentration predictions at the receptors in your modeling domain,
around a given facility. Sections 5.2 and 5.3 above discuss the methodology and algorithms
used by HEM4 to transform predicted concentrations into human health impacts around each
modeled facility. The following sections describe the outputs produced by HEM4 for each facility
and for your run group as a whole, which allow you to summarize the risk and health impacts
per facility and across all facilities you choose to group together in a modeling run.
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6. HEM4 Output Files
After running the AERMOD dispersion model to determine receptor-specific concentrations,
HEM4 completes the post-AERMOD risk and exposure calculations (explained in Section 5) and
then produces a variety of facility-specific concentration, cancer risk, noncancer hazard
quotients (HQ) and hazard indices (HI), incidence and population exposure output files. These
facility-specific outputs are discussed in Section 6.1. HEM4 also produces three summary
output files, based on the results for the entire run group (e.g., source category/sector) of
modeled facilities. These multi-facility outputs are updated after the output files for the individual
facilities have been created and essentially concatenate the individual facility results into group-
wide summary files. These run group summary files are discussed in Section 6.2. The Risk
Summary Reports are discussed in Section 7.
6.1 Facility-Specific Outputs
A standard HEM4 run produces the following facility-specific output files:
• 6 risk and HI files (maximum individual risk [MIR], maximum offsite impacts, risk
breakdown, block summary chronic, ring summary chronic, and source risk KMZ),
• 3 incidence and population exposure files (incidence, cancer risk exposure, noncancer
risk exposure),
• 3 concentration files (all inner receptors, all outer receptors, all polar receptors),
• dispersion model output file(s) from AERMOD (the number depends on the type run),
• 1 file cataloging modeling options used (input selection options).
In addition, depending on the modeling options chosen, a HEM4 run may produce 3 other non-
standard/optional files, including the following 3 acute files:
• acute breakdown,
• acute chem populated, and
• acute chem max.
These facility-specific standard and optional files are described below in this section.
6.1.1 Maximum Individual Risk
The Maximum Individual Risk output file provides the MIR value for cancer and the max TOSHI
value for noncancer chronic health effects predicted for any populated receptor that does not
overlap facility property, such as census blocks, alternate receptors, and user-defined receptors
that are designated as "populated". (Note: user-defined "P" receptors are considered populated
receptors but are assigned a population of zero.) This file also indicates the population and
exact location of the receptors where these maxima occur. Note that the MIR and max TOSHIs
may or may not occur at the same receptors/locations, depending on what pollutants are being
emitted from one source versus another source (indicated in the HAP Emissions input file) and
the locations and parameters of the sources (indicated in the Emissions Location input file).
Table 33 below describes the fields of information provided in the Maximum Individual Risk file.
A sample Maximum Individual Risk output file is provided in Appendix A.
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Table 33.
Field
Fields Included in the Maximum Individual Risk & Maximum Offsite Impacts
Files
Description
Parameter
Value of MIR
orTOSHI
Population
Distance
Angle
Elevation
Hill Height
FIPS code
Block ID
UTM east
coordinate
UTM north
coordinate
Latitude
Longitude
Receptor type
Maximum individual cancer risk (MIR) or maximum TOSHI including maximum respiratory
HI, maximum liver HI, maximum neurological HI, etc. for 14 TOSHIs
MIR value or maximum TOSHI value, including a rounded value and a value in scientific
notation
Population at the location of the MIR or maximum HI, if it is a census block or alternate
receptor
Distance from the center of the modeling domain, in meters
Angle from north
Elevation in meters above sea level
Controlling hill height of receptor, in meters above sea level, as described in Section 2.3.1.
Notes
Five-digit Federal Information Processing Standard (FIPS) code which uniquely identifies
the county of the receptor, if the receptor is a census block. (Note: For alternate receptor
run, there is a field called "Receptor ID")
10-digit census block ID for linking to census demographic data, if the receptor is a
census block. (Note: For alternate receptor run, there is a field called "Receptor ID")
In meters
In meters
Decimal
Decimal
C, P, B, M, S, PG: Census block receptors (C), P-type populated user receptors, and
alternate receptors (P) can be sites of MIR and max TOSHI in the MIR file. The Maximum
Offsite Impacts file includes this list of populated receptors plus unpopulated receptors
including polar grid receptors (PG), B-type boundary user receptors, monitors (M), and
schools (S).
This field indicates whether the receptor was modeled discretely or interpolated and also
indicates if the original maximum receptor was overlapped (and therefore not used). In the
case of interpolation or an overlap, you may wish to re-model the facility.
Relevant to the Maximum Individual Risk file, it should be noted that if any populated receptor is
located within the minimum overlap distance, then it is assumed that either the source location
or the receptor location is inappropriate. (A block centroid may be inappropriate as a receptor
location if the block partially encompasses an emission source, such as at a corner of the
facility.) When an overlap condition occurs, this is indicated in the Notes field/column and the
calculated results for the overlapping receptor are not used. Instead, the maximum cancer risk
and TOSHIs are assumed equal to the maximum (next highest) impacts for any receptor that
does not overlap facility property. This could include both populated (census, alternate, and
populated user-defined) receptors and unpopulated (polar and user-defined boundary)
receptors, as long as they do not overlap facility property. In this situation, check the source
coordinates in the emissions location input file, and define a set of facility boundary receptors in
the user-defined receptors file.
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6.1.2 Maximum Offsite Impacts
The Maximum Offsite Impacts output file provides similar information to the Maximum Individual
Risk output file, but the receptors of maximum impact in this file include any receptors, not only
populated receptors. This file lists the highest cancer risks and TOSH I predicted at any receptor
that does not overlap with the emission sources, whether the receptor is populated or
unpopulated. The receptors included in this file include all discretely modeled census blocks
(a.k.a. "inner receptors"), all user-defined receptors (including populated-type P receptors,
boundary receptors, monitors, and schools), and all points in the polar receptor network, except
for those receptors overlapping emission sources. Table 33 above describes the fields of
information provided in the Maximum Offsite Impacts file. A sample Maximum Offsite Impacts
output file is provided in Appendix A.
6.1.3 Risk Breakdown
The Risk Breakdown output file provides the breakdown of risk and TOSH I by pollutant and
source, including a listing of pollutant concentrations and unit risk estimates (URE) and
reference concentration (RfC) values. This file includes information about the MIR and HI (for
populated census block receptors, P type user receptors, and alternate receptors), as well as
the maximum offsite impacts (for any receptor, including unpopulated receptors such as polar
grid receptors, boundary receptors, monitors, and schools), as discussed in Section 5.2.
This file also shows the contributions of gaseous and particulate emissions for any pollutants
that are emitted in both forms, if you opted to model deposition/depletion or if you merely
elected to show the particulate/gaseous breakdown, as explained in Section 3.2.6. Table 34
below describes the fields of information provided in the Risk Breakdown file. A sample Risk
Breakdown output file is provided in Appendix A.
As previously noted, HEM4 computes cancer risks using the EPA's recommended UREs for
HAP and other toxic air pollutants. The resulting estimates reflect the risk of developing cancer
for an individual breathing the ambient air at a given receptor site over a 70-year lifetime.
Noncancer health effects are quantified using HQ and HI for various target organs. The HQ for a
given pollutant and receptor site is the ratio of the ambient concentration of the pollutant to the
RfC level at which no adverse effects are expected. The HI for a given organ is the sum of HQs
for substances that affect that organ.
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Table 34. Fields Included in the Risk Breakdown File
Field
Description
Site type
MIR (for max populated receptor) or maximum offsite impact (for max of
any receptor, populated or not)
Parameter
Cancer risk, all 14 TOSHIs (e.g., respiratory HI, liver HI, neurological HI)
Source ID
Individual source identification code, "Total by pollutant all sources", or
"Total" for all pollutants and all sources combined
Pollutant
Pollutant name, "all modeled pollutants" for all pollutants combined for
each source, or "all pollutants all sources" for all pollutants and all
sources combined
Emission
P = particulate, V = vapor (gas), C = combined, NA = not applicable
(Pollutant) type
(e.g., NA is used for rows for "all modeled pollutants")
Value
Cancer risk or noncancer HQ
Value_rnd
Cancer risk or noncancer HQ rounded to one significant figure
Conc_ugm3
Pollutant concentration (|j.g/m3)
Conc_rnd
Pollutant concentration (|j.g/m3) rounded to two significant figures
Emissions_tpy
Modeled tons per year (tpy) emitted of pollutant
URE
Unit risk estimate used to compute cancer risks for the pollutant
[1 / (^g/m3)]
RfC
Reference concentration used to compute HQs for the pollutant (mg/m3);
Note that HEM4 converts this to |ag/m3 to compute TOSHIs
6.1.4 Block Summary Chronic
The Block Summary Chronic file provides the total cancer risk and all 14 TOSHIs for every
populated census block receptor, populated alternate receptor, and all user-defined receptors
(including types P, B, M, and S receptors), and also indicates whether the receptor is an overlap
location. As noted above, if any populated receptor is located within the minimum overlap
distance, then it is assumed that either the source location or the receptor location is
inappropriate. (For example, a block centroid may be inappropriate as a receptor location if the
block partially encompasses an emission source, such as at a corner of the facility.) When an
overlap condition occurs, the calculated results for the overlapping receptor are not used.
Instead, the maximum cancer risk and HI are assumed equal to the maximum impacts for any
receptor that does not overlap facility property. This could include both populated (census block,
populated user-defined, or alternate) receptors and unpopulated (polar and boundary)
receptors, as long as they do not overlap facility property. In the case of an overlap, you may
wish to check the coordinates in your Emissions Location input file, and define a set of facility
boundary receptors in the user-defined receptors file.
To facilitate detailed geographic information system (GIS) analyses of HEM4 results, the file
gives the latitude and longitude, and the UTM coordinates of each receptor, in addition to
cancer risk estimates and HI. This output file also gives the county FIPS code and block
identification number for U.S. Census-based runs or alternate Receptor ID for non-census runs,
as well as the population of each receptor. This information is intended to facilitate studies
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linking HEM4 results with census information, such as demographic or economic data. Table 35
below describes the fields of information provided in the Block Summary Chronic file. A sample
Block Summary Chronic output file is provided in Appendix A.
6.1.5 Ring Summary Chronic
The Ring Summary Chronic file provides the same information provided by the Block Summary
Chronic File, but for points in the polar receptor network. However, because these are polar
receptors, the FIPS, Block, and population fields are not included in the Ring Summary Chronic
File, while three additional fields are provided: distance from center of polar network, angle from
north, and sector number. Table 35 describes the fields of information in the Ring Summary
Chronic file, and a sample file is provided in Appendix A.
Note: For both the Block Summary Chronic and Ring Summary Chronic files, in the case of an
overlapped receptor, the risk and TOSHI values for that receptor displayed in these files will not
be the originally modeled values. Instead, the maximum cancer risk and TOSHIs are assumed
equal to the maximum (next highest) impacts for any receptor that does not overlap facility
property. This could include both populated (census, alternate, populated P-type user-defined)
receptors and unpopulated (polar and boundary) receptors, as long as they do not overlap
facility property. The originally modeled values that occurred in the location of the overlap are
available in the All Inner Receptor, All Outer Receptor, and/or All Polar Receptor files described
in Sections 6.1.10,6.1.11, and 6.1.12, respectively.
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Table 35. Fields Included in the Block Summary and Ring Summary Chronic Files
Field Description
Latitude
Longitude
Overlap
Elevation
FIPS code
Block ID
X
Y
Hill Height
Population
Parameter
Discrete/
Interpolated
Receptor Type
Distance
Angle
(from north)
Sector
Decimal
Decimal
N for No, Y for Yes. If Yes, the values shown for the receptor in that row
are the next highest receptor (whether populated or unpopulated), not
overlapped. See also the Overlapping Source Receptors file.
Elevation in meters above sea level
Five-digit Federal Information Processing Standard (FIPS) code which
uniquely identifies the county of the receptor, if the receptor is a census
block. (Not part of Ring Summary Chronic File) Note: For alternate
receptor run, there is a field called "Receptor ID".
10-digit census block ID for linking to census demographic data, if the
receptor is a census block. (Not part of Ring Summary Chronic File)
Note: For an alternate receptor run, there is a field called "Receptor ID".
UTM Easting Coordinate
UTM Northing Coordinate
Controlling hill height of receptor, in meters above sea level, as
described in Section 2.3.1
Population at the location of the MIR or maximum HI, if it is a census
block, or has user-provided population in the case of an alternate
receptor. (Not part of Ring Summary Chronic File)
Cancer risk, all 14 TOSHIs (e.g., respiratory HI, liver HI, neurological HI)
D for Discretely modeled receptor (within the modeling distance, aka
"inner receptors"), I for Interpolated receptor (outside the modeling
distance, aka "outer receptors") (Not part of Ring Summary Chronic File)
C for census block; P for populated user or alternate receptor; B for
boundary user receptor; M for monitor; S for school. (Not part of Ring
Summary Chronic File)
Distance in meters from the center of the polar network of the polar
receptor's location on polar ring (Not part of Block Summary Chronic
File)
Angle from north of the polar radial on which the polar receptor is
located (0 to 360 degrees) (Not part of Block Summary Chronic File)
Sector number within the polar network (the number depends on number
of radials indicated in your Facility List Options file; default is 1-16) (Not
part of Block Summary Chronic File)
6.1.6 Source Risk KMZ Image
The Source Risk KMZ file is a Google Earth™ map centered on the facility, as shown in Figure
22. The map displays the emission sources in the center as red circles for point/stack sources,
red rectangles for area sources, red polygons for polygon-shaped sources, and red lines for line
and buoyant line sources. The map also displays all receptors within the modeled area including
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populated census block centroid receptors or alternate receptors (displayed as squares),
polar grid receptors (displayed as circles), unpopulated monitors and schools (displayed
as squares with a "U"), and all user-defined receptors (also displayed as squares with a
"U"). The MIR receptor is marked with a red "X".
Figure 22. Sample Google Earth™ Map of Results
You can click on the square census block, alternate, and user receptors to see the total cancer
risk and maximum TOSH I for that receptor, the FIRS and block ID of the receptor (for census
blocks) or receptor ID (for alternate and user receptors), as well as a listing of the top pollutants
contributing to that receptor's total cancer risk and maximum TOSHI, You can click on the
circular polar receptors to view similar information for each polar receptor. The cancer and
noncancer risk at the receptors are color coded on the Google Earth™ map. For cancer risk, red
indicates a receptor with a modeled total cancer risk greater than 100 in a million. Yellow
indicates a risk level between 20 and 100 in a million. Green indicates a risk less than 20 in 1
million. Figure 22 shows an example in which only two unpopulated polar grid receptors have a
cancer risk greater than 100 in a million (shown as dark red circles). All populated census block
receptors shown have modeled risks between 20 and 100 in a million (shown as yellow
squares) or less than 20 in a million (shown as green squares). No unpopulated census block or
user receptors are shown in this example.
6.1.7 Incidence
The facility-specific Incidence file provides the overall total incidence for all modeled pollutants
from all sources in the given facility, the pollutant-specific total incidence for all sources
combined, and the individual incidence per source for each pollutant. As explained in Section
5.3, the incidence is calculated as the cancer risk of each populated receptor (e.g., census block
or alternate receptor) times the receptor population, divided by a 70-year average lifespan. This
individual populated receptor incidence is then summed over all populated receptors in the
modeling domain of the facility. Table 36 below describes the fields of information provided in
the facility-specific Incidence file. A sample Incidence output file is provided in Appendix A.
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Table 36. Fields Included in the Incidence File
Field
Description
Source ID
Pollutant
Emission (Pollutant) type
Incidence
Incidence, rounded
Individual source identification code, or "Total" for all sources
combined
Pollutant name, or "All modeled pollutants" for all pollutants
combined for each source and for the Total
P = particulate, V = vapor (gas), C = combined
Incidence calculated as (cancer risk) X (population) / 70-year
lifespan, summed overall populated receptors
Incidence, rounded
6.1.8 Cancer Risk Exposure
The Cancer Risk Exposure file is a simple two column (two field) file that provides the
population numbers exposed to various cancer risk levels in the modeling domain surrounding
the facility. Population numbers are provided for the following cancer risk levels:
Greater than or equal to 1 in 1,000 (>1,000-in-a-million risk);
Greater than or equal to 1 in 10,000 (>100-in-a-million risk);
Greater than or equal to 1 in 20,000 (>50-in-a-million risk);
Greater than or equal to 1 in 100,000 (> 10-in-a-million risk);
Greater than or equal to 1 in 1,000,000 (>1-in-a-million risk); and
Greater than or equal to 1 in 10,000,000 (>0.1-in-a-million risk).
A sample Cancer Risk Exposure output file is provided in Appendix A.
6.1.9 Noncancer Risk Exposure
The Noncancer Risk Exposure file, like the Cancer Risk Exposure file described above, is a
simple file that provides the population numbers exposed to various HI levels for all 14 TOSHIs,
in the modeling domain surrounding the facility. Population numbers are provided for the
following noncancer HI levels:
• Greater than 100;
• Greater than 50;
• Greater than 10;
• Greater than 1.0;
• Greater than 0.5; and
• Greater than 0.2.
Population numbers at each of the above noncancer HI levels are provided for the following
TOSHIs:
• Respiratory HI;
• Liver HI;
• Neurological HI;
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• Developmental HI;
• Reproductive HI;
• Kidney HI;
• Ocular HI;
• Endocrine HI;
• Hematological HI;
• Immunological HI;
• Skeletal HI;
• Spleen HI;
• Thyroid HI; and
• Whole Body HI.
A sample Noncancer Risk Exposure output file is provided in Appendix A.
6.1.10 All Inner Receptors
The All Inner Receptors file provides the chronic concentration (in jjg/m3) and (if optionally
modeled) the acute concentration of every populated (census block or alternate) receptor inside
the modeling distance, as well as every user-defined receptor, both populated and unpopulated.
Note: All concentrations in this file are discretely (explicitly) modeled, not interpolated. If you
opted to calculate deposition with or without depletion, this file will also contain the deposition
flux (in g/m2/y if modeled using annual averages, or in g/m2 if modeled using period averages).
Columns for both dry and wet deposition flux results are provided and will be populated with
non-zero results depending on the type of deposition modeling (wet, dry or both) you selected in
the Facility List Option fields. Table 37 below describes the fields of information provided in the
All Inner Receptors file. A sample All Inner Receptors file output file is provided in Appendix A.
6.1.11 All Outer Receptors
The All Outer Receptors file includes nearly the same information provided in the All Inner
Receptor file (described above) for every receptor located between the modeling distance (often
specified as 3 km) and the outer edge of the modeling domain (the "maximum distance" often
specified as 50 km). The dry and wet deposition fluxes provided in the All Inner Receptors file,
however, are not provided in this file, for the outer receptors. Note: All concentrations in this file
are interpolated using the polar grid receptors, not discretely (explicitly) modeled. Table 37
below describes the fields of information provided in the All Outer Receptors file. A sample All
Outer Receptors file output file is provided in Appendix A.
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Table 37. Fields Included in the All Inner and All Outer Receptor Files
Field
Description
FIPS code
Block ID
Latitude
Longitude
Source ID
Emission
(Pollutant) type
Pollutant
Cone
Acute Cone
Elevation
Dry deposition
Wet deposition
Population
Overlap
Receptor Type
Five-digit Federal Information Processing Standard (FIPS) code which
uniquely identifies the county of the receptor if the receptor is a census
block. (Note: For alternate receptor run, there is a field called "Receptor
ID")
10-digit census block ID for linking to census demographic data, if the
receptor is a census block. (Note: For alternate receptor run, there is a
field called "Receptor ID")
Decimal
Decimal
Individual source identification code affiliated with given concentrations
P = particulate, V = vapor (gas), C = combined
Pollutant name affiliated with given concentrations
Chronic air concentration in |jg/m3
Acute (short-term) air concentration in |jg/m3, if modeled
Elevation in meters above sea level
Dry deposition flux in g/m2/year if modeled using annual averages, or in
g/m2 if using period option (not included in All Outer Receptor file)
Wet deposition flux in g/m2/year if modeled using annual averages, or in
g/m2 if using period option (not included in All Outer Receptor file)
Population of receptor
N for No, Y for Yes. Note: the value shown is the originally modeled
value, even if overlapped (and therefore not used in other files such as
the Maximum Individual Risk, Risk Breakdown, and Block Summary
Chronic files)
C for census block; P for populated user receptor or alternate receptor;
B for boundary receptor; M for monitor; S for school
6.1.12 All Polar Receptors
The All Polar Receptors file provides similar information to the All Inner Receptors and All Outer
Receptors for the nodes of the polar receptor grid, including the chronic concentration (in |jg/m3)
and (if optionally modeled) the acute concentration of every polar receptor. Note: Like the All
Inner Receptors file, all concentrations in the All Polar Receptors file are discretely (explicitly)
modeled, not interpolated. If you opted to calculate deposition with or without depletion, this file
will also contain the deposition flux (in g/m2/y if modeled using annual averages, or in g/m2 if
modeled using period averages). Columns for both dry and wet deposition flux results are
provided and will be populated with non-zero results depending on the type of deposition
modeling (wet, dry or both) you selected in the Facility List Option fields. In addition, this file will
contain the distance from the center of the polar network, the angle, sector, and ring number
that describes the location of each polar receptor. Table 38 below describes the fields of
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information provided in the All Polar Receptors file. A sample All Polar Receptors file output file
is provided in Appendix A.
Table 38. Fields included in the All Polar Receptors File
Field
Description
Source ID
Individual source identification code
Emission
P = particulate, V = vapor (gas), C = combined
(Pollutant) type
Pollutant
Pollutant name affiliated with given concentrations
Cone
Chronic air concentration in |jg/m3
Acute Cone
Acute air concentration in |jg/m3
Distance
Distance in meters from the center of the polar network of the polar
receptor's location on polar rina
Angle
Anale from north of the polar radial on which the polar receptor is
(from north)
located (0 to 360 degrees)
Sector
Sector number within the polar network ("the number depends on number
of radials indicated in vour Facility List Options file: default is 1-16)
Ring number
The number of the rina ("circle") in the polar network on which the
receptor is located, beginning with number 1 closest to facility center
Elevation
Elevation in meters above sea level
Latitude
Decimal
Longitude
Decimal
Overlap
N for No, Y for Yes. Note: the value shown is the originally modeled
value, even if overlapped (and therefore not used in other files such as
the Maximum Individual Risk, Risk Breakdown, and Ring Summary
Chronic files).
Wet deposition
Wet deposition flux in g/m2/year if modeled using annual averages, or in
a/m2 if usina period option
Dry deposition
Dry deposition flux in g/m2/year if modeled using annual averages, or in
a/m2 if usina period option
6.1.13 AERMOD Outputs
With each run, HEM4 automatically provides a set of AERMOD text files that track the inputs
and keywords (modeling commands) passed to AERMOD, including the receptor network and
meteorological files, as well as the AERMOD outputs. The outputs produced by AERMOD are
then passed back to HEM4 and used to produce the other outputs described in this guide. You
should review these AERMOD text files (especially the aermod.out file described below) to
confirm that AERMOD completed its modeling without error. These text files are described
below:
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• aermod.inp - a text file for combined particle and vapor phase emissions listing the
inputs passed to AERMOD for modeling, including modeling control options (see
AERMOD User's Guide), rural or urban dispersion environment, averaging time, specific
input file parameters (e.g., from the Emissions Location file), the network of discrete
receptor coordinates (block or alternate receptors in UTM), elevations and hill heights,
meteorological data, and designated text formatted output files. Note: If particle and
vapor phase emissions are modeled separately, then the above information will be
provided for particle phase emissions in an aermod_P.inp file and for vapor phase
emissions in an aermod_V.inp file.
• aermod.out - a text file for combined particle and vapor phase emissions listing the
inputs received by AERMOD in the aermod.inp file (noted above), any fatal error
messages, warning messages, informational messages, indication of successful
AERMOD set-up or not, AERMOD version number used for modeling, type of deposition
and depletion modeled if any, modeling options employed, whether short-term (acute)
concentrations were modeled along with their period, number and type of sources,
number of receptors, vintage of meteorological data used, emission rates modeled for
each source (in grams per second), elevations and hill heights of every discrete (census
block or alternate) receptor and every polar grid receptor, UTM coordinates and unit
HAP chronic concentration at every receptor for each source, UTM coordinates and unit
HAP short-term/acute concentration (if modeled) based on the acute high value
selected, the number of hours processed, the number of calm (very low wind) hours
identified, the number of missing hours in the meteorological data used for modeling,
and an indication whether AERMOD finished the modeling run successfully or not. Note:
If particle and vapor phase emissions are modeled separately, then the above
information will be provided based on particle phase emissions in an aermod_P.out file
and for vapor phase emissions in an aermod_V.out file. Deposition fluxes (wet/dry) will
be provided with depletion applied to concentrations, if modeled.
• plotfile.plt - a text file for combined particle and vapor phase emissions listing the
average modeled chronic concentration at every UTM receptor location and each
modeled source. Note: If particle and vapor phase emissions are modeled separately,
then these concentrations will be provided based on particle phase emissions in a
plotfile_p.plt file and in a plotfile_v.plt file for vapor phase emissions. Deposition fluxes
(wet/dry) will be provided with depletion applied to concentrations, if modeled.
• maxhour.plt - a text file for combined particle and vapor phase emissions listing the
modeled short-term/acute concentration (based on the acute high value indicated in your
Facility List Options file) at every UTM receptor location and each modeled source. Note:
If particle and vapor phase emissions are modeled separately, then these acute
concentrations will be provided based on particle phase emissions in a maxhour_p.plt
file and for vapor phase emissions in an maxhour_v.plt file.
Note: Concentration results provided by AERMOD in the above files should not be interpreted
as predicted concentrations of any pollutant listed in the HEM4 input files. Rather, these
AERMOD results reflect concentrations attributable to a unit-emission rate (1 kg/s), which HEM4
converts to specific modeled pollutant emissions, as explained in Section 5 above. To fully
understand the AERMOD processing and output files, refer to the AERMOD documentation for
further guidance (EPA 2022a, EPA 2022b).
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6.1.14 Input Selection Options
The Input Selection Options output file is a useful QA file to refer to because it provides a record
of the modeling options you chose for the run, as well as the names and location of the input
files you indicated. The following information is provided in this file:
• Facility ID;
• AERMOD control options used;
• Phase of emissions;
• Dispersion environment (rural or urban or blank for default);
• Whether deposition was modeled;
• Whether depletion was modeled;
• Type of deposition modeled for particle and vapor;
• Type of depletion modeled for particle and vapor;
• Whether elevations were modeled (or flat terrain used);
• Acute averaging period (e.g., 1 hour);
• Acute multiplier (factor applied to annual average emissions, if any);
• Whether building downwash was modeled;
• Whether user receptors were modeled;
• Maximum domain distance used (in meters);
• Modeling distance used (in meters);
• Overlap distance used (in meters);
• Number of polar rings used;
• Number of polar radials used;
• Whether acute was modeled;
• Distance to first ring (meter);
• Whether FASTALL was used;
• Run group name;
• Facility List Options file - name/location;
• Emissions Location file - name/location;
• HAP Emissions file - name/location;
• User Receptor file - name/location (if used);
• Particle Size file - name/location (if used);
• Building downwash file - name/location (if used);
• Buoyant line file - name/location (if used);
• Landuse file - name/location (if used);
• Month-to-Seasons file - name/location (if used);
• Polygon vertex file - name/location (if used);
• Whether Alternate Receptors were used; and
• Whether any of the Alternate Receptors were missing population values. Note: To
compute incidence, population values are needed at every populated alternate receptor.
Even if only one Alternate Receptor is missing a value in its population field, incidence is
not computed by HEM4.
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6.1.15 Acute Maximum Concentrations (Optional)
If you optionally chose to model acute impacts for a given facility, HEM4 will produce an Acute
Chem Max output file. The Acute Chem Max output provides the maximum acute (short-term)
pollutant concentration at any receptor for all sources combined. The "maximum" reported in
this file refers to the acute high value you identified (e.g., the absolute maximum, the 99th
percentile, the 98th percentile) and is based on the acute multiplier you provided (e.g., 10 times
the average annual emission rate), as well as the acute averaging period (e.g.,1-hour) you
indicated in the respective acute fields of your Facility List Options file. The maxima provided in
the Acute Chem Max output may occur at any receptor—populated or unpopulated—including
census blocks, alternate receptors, polar grid receptors, and user-defined receptors. This file
also provides the specific location of the receptor with highest modeled concentration for each
pollutant - including UTM and latitude/longitude coordinates, FIPS, Block, distance from facility
center, and angle from north - as well as the elevation and hill height of the receptor. It should
be noted that each pollutant may cause a different receptor to be the maximum (based on
emissions of that specific pollutant). Finally, this output file also lists the acute reference
concentrations for 11 different acute benchmarks, above which adverse short-term health
impacts can be expected. For example, the file provides:
• the California Acute Reference Exposure Level (REL) benchmark;
• the Acute Exposure Guideline Level (AEGL1) for transient, reversible effects and AEGL2
for long-lasting, irreversible effects, based on one and eight hours of exposure;
• the Emergency Response Planning Guideline (ERPG-1) for mild or transient effects and
the ERPG-2 for irreversible or serious effects, based on one hour of exposure; and
• several other acute benchmark concentrations, as described in Table 39.
The EPA's Air Toxics Risk Assessment Library (EPA 2020) provides a more detailed description
of these acute benchmarks (available for download at http://www.epa.gov/fera/air-toxics-risk-
assessment-reference-library-volumes-1-3). Table 39 below describes the fields of information
provided in the Acute Chem Max file, and a sample file output file is provided in Appendix A.
Note: the concentrations reported in Table 39 are in |a,g/m3, while the acute benchmark values
(reference concentrations) are in mg/m3, and should therefore be multiplied by 1,000 for
comparison to the modeled concentrations.
6.1.16 Acute Populated Concentrations (Optional)
If you optionally chose to model acute impacts for a given facility, HEM4 will also produce an
Acute Chem Pop output file. The Acute Chem Pop file provides the same information described
above in the Acute Chem Max file, but for only populated receptors (census blocks, alternate
receptors and user-defined receptors), not unpopulated receptors. Therefore, the concentrations
shown in this file may or may not be the acute maxima/high values for all receptors; but they are
the acute high values for the populated receptors. See discussion above in Section 6.1.15.
Table 39 below describes the fields of information provided in the Acute Chem Pop file, and a
sample file output file is provided in Appendix A. Note: the concentrations reported in Table 39
are in |a,g/m3, while the acute benchmark values (reference concentrations) are in mg/m3, and
should therefore be multiplied by 1,000 for comparison to the modeled concentrations.
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Table 39. Fields included in the Acute Chem Max and Acute Chem Pop Files
Field Description
Pollutant
Cone
Cone sci
AEGL-1, 1-hour
AEGL-1, 8-hour
AEGL-2, 1-hour
AEGL-2, 8-hour
ERPG-1
ERPG-2
IDLH/10
MRL
REL
TEEL_0
TEEL_1
Population
Distance
Angle
Elevation
Hill
County FIPS
Census block ID
UTM east coordinate
UTM north coordinate
Latitude
Longitude
Receptor type
Notes
Pollutant name
High value maximum Acute Concentration in |ig/m3
High value maximum Acute Concentration, scientific notation, in |ig/m3
Acute Exposure Guideline Level 1 (AEGL-1) for a 1-hour exposure: the concentration
above which it is predicted that the general population, including susceptible individuals,
could experience notable discomfort, irritation, or certain asymptomatic, non-sensory
effects (mg/m3)
See AEGL-1 above, but for an 8-hour exposure
Concentration above which it is predicted that the general population, including
susceptible individuals, could experience irreversible or other serious, long-lasting
adverse health effects or an impaired ability to escape for a 1-hour exposure (mg/m3)
See AEGL-2 above, but for an 8-hour exposure
Emergency Response Planning Guideline 1 (ERPG-1): concentration below which it is
believed nearly all individuals could be exposed for up to 1 hour without experiencing
other than mild transient adverse health effects or perceiving a clearly defined
objectionable odor (mg/m3)
Concentration below which it is believed nearly all individuals could be exposed for up to
1 hour without experiencing or developing irreversible or other serious health effects or
symptoms that could impair an individual's ability to take protective action (mg/m3)
Immediately Dangerous to Life or Health: concentration believed likely to cause death or
immediate or delayed permanent adverse health effects or prevent escape from such an
environment, divided by a factor of 10 (mg/m3)
Acute Minimal Risk Level: daily human exposure that is likely to be without appreciable
risk of adverse noncancer health effects over a specified duration of exposure (mg/m3)
Reference Exposure Level: concentration below which no adverse health effects are
anticipated, based on the most sensitive adverse health effect reported (mg/m3)
Temporary Emergency Exposure Limit 0 (TEEL) defined by the U.S. Department of
Energy: the threshold concentration below which most people will experience no adverse
health effects
Maximum airborne concentration below which it is believed nearly all individuals could
be exposed for up to 1 hour without experiencing more than mild, transient adverse
health effects or perceiving a clearly defined objectionable odor
If the receptor is a census block or alternate receptor
From the center of the modeling domain (in meters)
From north
In meters above sea level
Controlling hill height in meters above sea level, as described in Section 2.3.1
If the receptor is a census block. (Note: For alternate receptor run, there is a field called
"Receptor ID")
For linking to demographic data (if the receptor is a census block). (Note: For an
alternate receptor run, there is a field called "Receptor ID")
In meters
In meters
Decimal
Decimal
C = census block, P = populated user receptor or alternate receptor,
PG = polar grid receptor, B = boundary receptor, M = monitor, S = school
Indicates whether the receptor was discretely (explicitly) modeled or interpolated
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6.1.17 Acute Breakdown (Optional)
If you chose to optionally model acute impacts for a given facility, HEM4 also produces a third
acute output file entitled Acute Bkdn, which provides the contribution ("breakdown") of each
emission source to the receptor of maximum acute impact for each pollutant (i.e., the acute
concentration of pollutant at the maximum receptor for that pollutant, caused by each source).
This information is provided for both the maximum/high value receptor (whether populated or
unpopulated) and for the highest populated receptor.
The acute breakdown file includes the following fields:
• pollutant;
• Source ID;
• emission type (P for particle, V for vapor, C for combined);
• the maximum pollutant concentration (|jg/m3) at a populated receptor;
• the maximum pollutant concentration (|jg/m3) at all receptors (both populated and
unpopulated); and
• columns indicating whether the pollutant's concentration at each receptor was
interpolated or not.
Note: Concentration values are interpolated outside the modeling distance (e.g., between 3 km
and 50 km).
6.2 Run Group Outputs
In addition to the facility-specific outputs listed in Section 6.1, HEM4 produces three summary
output files, based on the results for the entire run group of modeled facilities. These multi-
facility outputs are updated after the output files for the individual facilities have been created
and essentially concatenate the individual facility results into group-wide summary files. In each
of these three Excel™ (.xlsx) files, HEM4 writes one row of information for each facility upon
completion of that facility's individual modeling run. The three group-wide output files created by
HEM4 in the following sections and sample files are provided in Appendix A. Note: These files
will be produced even if you are modeling only one facility.
6.2.1 Facility Max Risk and HI
The Facility Max Risk and HI output file provides the maximum modeled risk and hazard index
results for every facility as well as additional facility-specific modeling results, including:
• a listing of all Facility IDs modeled;
• the cancer risk at the receptor that experiences the highest risk in the modeled
radius around each facility (i.e., facility-specific MIR);
• whether or not the MIR (max cancer risk) is interpolated from nearby receptors11;
• the type of receptor where the MIR (max cancer risk) occurs (e.g., census block,
alternate receptor, polar grid, user-defined P-type receptor);
• the latitude and longitude of the MIR (cancer) receptor;
11 An interpolated MIR generally suggests that the modeling distance should be increased and the facility
remodeled.
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• the census block ID, alternate receptor ID or user receptor ID of the MIR receptor;
• the 14 TOSHIs at the receptors that experience the maximum TOSHI for each facility
including: whether or not the TOSHI value is interpolated, the receptor type(s) where
the max TOSHIs occur, the latitude and longitude for certain max TOSHI receptors
(e.g., respiratory, neurological), and the census block ID, alternate receptor ID or
user receptor ID of each max TOSHI receptor;
• the population, if any, excluded from the modeling run because of any census block
centroid(s) located within the overlap distance around each emission source (and
therefore considered on facility property)12;
• the cancer incidence (predicted excess cancers per year due to modeled emissions)
at each facility;
• the file name of the meteorological station used in the modeling of each facility;
• the distance (in kilometers) from the facility center to the meteorological station used
in the modeling run;
• the latitude and longitude location of the facility center; and
• the dispersion environment used by HEM4 for modeling each facility - rural or urban.
The TOSHIs modeled by HEM4 can impact the following organs and organ systems:
respiratory; liver; neurological; developmental; reproductive; kidney; ocular; endocrine;
hematological; immunological; skeletal; spleen; thyroid; and whole body. In the sample
abbreviated Facility Max Risk and HI provided in Appendix A, only respiratory HI is shown,
which is commonly the highest TOSHI level based on the dispersion and inhalation modeling
performed by AERMOD and HEM4.
6.2.2 Facility Cancer Risk Exposure
The Facility Cancer Risk Exposure output file lists the facilities by ID, their corresponding
latitudes and longitudes (of the calculated facility centers), and the population exposed to
different cancer risk levels surrounding each facility, including:
• the number of people from each facility exposed to a cancer risk level greater than
or equal to 1 in 1,000 (or 1,000 in a million);
• the number of people from each facility exposed to a cancer risk level greater than
or equal to 1 in 10,000 (or 100 in a million);
• the number of people from each facility exposed to a cancer risk level greater than
or equal to 1 in 100,000 (or 10 in a million);
• the number of people from each facility exposed to a cancer risk level greater than
or equal to 1 in 1,000,000 (or 1 in a million); and
• the number of people from each facility exposed to a cancer risk level greater than
or equal to 1 in 10,000,000 (or 0.1 in a million).
Note that each row of this output file is facility-specific and does not reflect the impacts of
multiple facilities with overlapping modeling domains (which may impact the same receptor and
12 A value in the population overlap field generally indicates that the facility should be remodeled (e.g.,
with a smaller overlap distance specified) to ensure that the population associated with the census block
centroid(s) is accounted for.
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increase population numbers at various risk levels beyond what each single facility causes). A
sample Cancer Risk Exposure file is provided in Appendix A.
6.2.3 Facility TOSHI Exposure
The Facility TOSHI Exposure output file lists the facilities by ID and the number of people with a
TOSHI greater than 1 for each facility and for each of the 14 TOSHIs currently modeled by
HEM4. Note: Because the convention of one significant figure is employed, an HI greater than 1
equates mathematically to an HI greater than or equal to 1.5. A Facility TOSHI Exposure file is
provided in Appendix A.
6.2.4 Additional Run Group Outputs
HEM4 will also produce several other group output files with each run, including:
• An Inputs folder containing every input file used by HEM4 (that you provided) for
your modeling run - a useful QA feature to ensure the inputs you intended to be
modeled were indeed the ones modeled
• A Google Earth™ map showing the source locations at every facility in your
modeling run - named AIIFacility_source_locations.kmz
• A hem4.log text file, as described in Section 4.4, which provides a permanent
record of your model run - includes the files uploaded, the output files produced,
whether the run was successful and/or any errors that occurred
• If HEM4 could not model all facilities listed in your inputs, a Skipped Facilities file
(Skipped_Facilities.xlsx) will be produced which simply lists the IDs of those skipped
facilities. You may use this to remodel those facilities, after correcting or amending
the issues that caused the facilities to be skipped. This is discussed further in
Section 10.
Note: Do not change the names of the facility-level or HEM4 output files (discussed above),
as several of these files are referenced by their specific names in the code of the Risk Summary
Report programs, described next in Section 7.
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7. Risk Summary Reports
You may choose to run 11 different Risk Summary Reports, as described in the step-by-step
HEM4 instructions in Section 4.5. These reports, like the run group outputs described in Section
6.2, are based on risk results from all facilities modeled in your run group. However, certain Risk
Summary Reports have the added benefit of taking into account multiple impacts on the same
receptor from neighboring facilities. The 11 Risk Summary Reports are described in this section.
7.1 Facility-Specific Summaries
As noted in Section 4.5, six of the 11 summaries produce results specific to each facility. These
summaries include individual facility IDs connected to the results, for all facilities in your run
group, which account for impacts from each facility's emissions in isolation (i.e., not considering
impacts from other facilities, including even neighboring facilities). The six facility-specific
summaries discussed in this section include: cancer drivers, hazard index drivers, acute
impacts, multipathway, max concentration, and max risk and HI by source and pollutant.
7.1.1 Cancer Drivers Summary
The Cancer Drivers output (cancer_drivers.xlsx) provides the pollutants and sources that are
driving the maximum risk at each modeled facility (i.e., those pollutant-source combinations
driving the risk at the receptor with the highest risk, for each facility). This file lists the facilities
by ID; the MIR modeled at each facility from all pollutants and emission sources acting on the
receptor; the predominant pollutant(s) and emission source(s) contributing to at least 90% of
that facility's MIR; the cancer risk associated with each of those pollutant-source combinations;
and the percentage risk contribution to the MIR for each. Figure 23 shows a sample output.
Note: The Risk Contribution column for each facility will not sum to 100%, because only the
pollutant-source combinations that sum to at least 90% are displayed.
A\ A
B
C
D
E
F
1 Facility ID
MIR
Pollutant
Cancer Risk
Risk Contribution
Source ID
2 *270536222111
1.13E-06
Arsenic compounds
8.90885E-07
78.84
CEPM0005
3 *270536222111
1.13E-06
Nickel compounds
2.35101E-07
20.81
CEPM0005
4 *3 605517127011
1.02585E-06
Arsenic compounds
9.7294E-07
94.84
CEPM0002
S 484535678711
3.45674E-07
Arsenic compounds
4.61526E-08
13.35
CEPM0006
6 484535678711
3.45674E-07
Arsenic compounds
4.25802E-08
12.32
CEPM0026
7 "484535678711
3.45674E-07
Arsenic compounds
3.81743E-08
11.04
CEPM0024
8 ^84535678711
3.45674E-07
Arsenic compounds
3.30016E-08
9.55
CEPM0007
9 "484535678711
3.45674E-07
Arsenic compounds
3.27424E-08
9.47
CEPM0001
10 *484535678711
3.45674E-07
Arsenic compounds
3.24023E-08
9.37
CEPM0004
11 *484535678711
3.45674E-07
Arsenic compounds
2.62015E-08
7.58
CEPM0029
12 "484535678711
3.45674E-07
Arsenic compounds
2.52855E-08
7.31
CEPM0005
13 *484535678711
3.45674E-07
Arsenic compounds
2.46037E-08
7.12
CEPM0003
14 *484535678711
3.45674E-07
Arsenic compounds
2.29875E-08
6.65
CEPM0002
Figure 23. Sample Cancer Drivers Summary Output
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7.1.2 Hazard Index Drivers Summary
The Hazard Index Drivers output (hazard_index_drivers.xlsx) provides the sources arid
pollutants that are driving the maximum TOSHI at each modeled facility (i.e., those source-
pollutant combinations driving the HI at each receptor with the highest TOSHI, for each facility).
This file lists the facilities by ID; the "HI type" (respiratory, neurological, liver, etc., for all non-
zero TOSHI values); the maximum TOSHI ("HI Total") modeled at each facility from all
pollutants and emission sources acting on the receptor, the predominant sources and pollutants
contributing to at least 90% of each maximum TOSHI; the TOSHI ("Hazard Index") value
associated with each of these source-pollutant combinations; and the percentage each source-
pollutant combination contributes to each maximum TOSHI (for all nonzero TOSHIs at each
facility). Figure 24 shows a sample output. Note: The Percentage column for each facility will
not sum to 100%, because only the source-pollutant combinations that add to at least 90% are
displayed.
A
B
C
0
E
F
G
|
1
Facility ID
HI Type
HI Total
Source ID
Pollutant
Hazard Index
Percentage
2
Facl-NC
Developmental HI
8.9969812
SR000001
arsenic compounds
8.964020301
99.63
3
Facl-NC
Kidney HI
1.4796741
SR000001
cadmium compounds
1.445809726
97.71
4
Facl-NC
Respiratory HI
0.6770494
RW000001
acrolein
0.557883699
82.4
5
Facl-NC
Respiratory HI
0.6770494
FU000001
bis(2-ethylhexyl)phthalate
0.113999602
16.84
6
Facl-NC
Liver HI
0.1816668
FU000001
bis(2-ethylhexyl)phthalate
0.113999602
62.75
7
Facl-NC
Liver HI
0.1816668
RW000001
trichloroethylene
0.066946044
36.85
S
Facl-NC
Neurological HI
0.0882496
RW000001
trichloroethylene
0.066946044
75.86
9
Facl-NC
Neurological HI
0.0882496
FU000001
mercury (elemental)
0.020602338
23.35
10
Facl-NC
Reproductive HI
0.0746997
RW000001
trichloroethylene
0.066946044
89.62
11
Facl-NC
Reproductive HI
0.0746997
RV000001
1,3-butadiene
0.007751977
10.38
12
Facl-NC
Immunological HI
0.0671872
RW000001
trichloroethylene
0.066946044
99.64
13
Fac2-IL
Liver HI
0.0405107
FU000001
bis(2-ethylhexyl)phthalate
0.037081163
91.53
14
Fac2-ll
Respiratory HI
0.039644
FU000001
bis(2-ethylhexyl)phthalate
0.037081163
93.54
15
Fac2-IL
Neurological HI
0.0266972
FU000001
mercury (elemental)
0.023278107
87.19
16
Fac2-ll
Neurological HI
0.0266972
FU000001
mercury (elemental)
0.00256432
9.61
Figure 24. Sample Hazard Index Drivers Summary Output
7.1.3 Acute Impacts Summary
The Acute Impacts output (acute_impacts.xlsx) provides the maximum acute concentration for
every modeled pollutant, six acute benchmark values (REL, AEGL1, AEGL2, ERPG1, ERPG2
and IDLH, as defined above in Table 39), and the hazard quotient (HQ) based on the ratio of the
pollutant's max acute concentration to those six benchmark values. It should be noted that the
max acute concentration is based on the acute high value you chose in your Facility List
Options file. The file also provides the receptor ID at which this max acute concentration occurs,
including the FIPS and block ID for a census block receptor, the alternate receptor ID, the user
receptor ID, or the distance and angle for a polar receptor.
The Acute Impacts Summary is available only if you entered Y in the acute column of the
Facility List Options input file prior to modeling, for one or more facilities in your run group. Note:
The pollutant concentration is provided in mg/m3 in this output (not pg/m3 as provided by
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HEM4 at receptor locations in other output files) because the benchmark values are based on
mg not |jg). Figure 25 shows an abbreviated sample screenshot of the Acute Impacts Summary
file.
7.1.4 Multipathway Summary
The Multipathway Summary output (multi_pathway.xlsx) provides arsenic, polycyclic aromatic
hydrocarbon (PAH) and dioxin/furan (D/F) concentrations and risk at MIR receptors and within
directional octants around each facility, which are useful for a post-HEM4 multipathway
analysis.
This file lists the following information:
• the run group's label;
• the Facility ID;
• whether the facility was modeled using an urban or rural dispersion environment;
• whether the receptor in a given output row is an MIR or the closest receptor to the
facility center in a specific octant direction (E, N, NE, NW, S, SE, SW, W);
• the pollutants the MIR is attributable to (All HAP, As for Arsenic, PAH, or D/F for
Dioxins/Furans);
• whether the closest octant receptor is at a census block centroid, alternate receptor,
or a discrete user receptor;
• the FIPS plus Block ID of the census receptor, or the ID of alternate and user
receptor;
• the latitude and longitude location of the receptor;
• the population of the receptor;
• the total inhalation risk of that receptor (for all HAP);
• the total inhalation risk of that receptor attributable to Arsenic compounds;
• the total inhalation risk of that receptor attributable to PAHs; and
• the total inhalation risk of that receptor attributable to Dioxins/Furans.
Figure 26 shows a screenshot of a sample Multipathway Summary file. Note that blank cells
indicate that emissions from this sample facility do not include arsenic, PAH, or D/F.
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Facility ID
Pollutant
CONC_MG/M J
REL
AEGlllH
[4 other
benchmark
columns]
HQ_REL
HQ_AEGL1
(4 other HQ
columns based
on 4 other
benchmarks]
[4 columns
indicating Receptor
ID or distance and
angle for polar
receptor]
Facl-NC
acetaldehyde
0.014339116
0.47
81
0.03050876
0.00017703
Facl-NC
acrolein
0.100373815
0.0025
0.069
40.149526
1.45469297
Facl-NC
arsenic compounds
0.069242032
0.0002
0
346.210161
0
Facl-NC
benz[a]anthracene
1.61754E-06
0
0
0
0
Facl-NC
benzene
0.029947323
0
170
0
0.00017616
Figure 25. Sample Acute Impacts Summary Output (abbreviated)
Run Group
Facility
ID
Rural/
Urban
Octant or
MIR
Chem,
Centroid,
or Discrete
Fips + Block
Lat
Lon
Population
Total Inhalation
Cancer Risk
Total Inhalation
As Cancer Risk
Total Inhalation
PAH Cancer Risk
Total Inhalation
D/F Cancer Risk
test_8-8-2020
Facl-NC
U
MIR
All HAP
370639801001074
35.89908
-78.888
3
0.000610761
0
0
0
test_8-8-2020
Facl-NC
U
MIR
As
0
0
0
test_8-8-2020
Facl-NC
U
MIR
PAH
0
0
0
test_8-8-2020
Facl-NC
U
MIR
DF
0
0
0
test_8-8-2020
Facl-NC
11
E
Centroid
"370630020283011
35.89548
-78.8494
1
1.28285E-05
0
0
0
test_8-8-2020
Facl-NC
U
N
Centroid
^70630020271050
35.91643
-78.8859
55
7.45249E-05
0
0
0
test_8-S-2020
Facl-NC
U
NE
Centroid
"370630020281025
35.92024
-78.8455
3
2.99575E-05
0
0
0
test_8-8-2020
Facl-NC
U
NW
Centroid
*370630020272047
35.90438
-78.8882
7
0.000248176
0
0
0
test_8-8-2020
Facl-NC
U
S
Centroid
r370630020272057
35.89265
-78.8873
219
0.00017255
0
0
0
test_8-8-2020
Facl-NC
u
SE
Centroid
*370630020283042
35.88258
-78.864
41
1.48092E-05
0
0
0
test_8-8-2020
Facl-NC
u
SW
Discrete
UOOOOOOOOURCPTl
35.90016
-78.8888
0
0.000518777
0
0
0
test_8-8-2020
Facl-NC
u
W
Discrete
UOOOOOOOOURCPT2
35.90434
-78.8909
0
0.00018499
0
0
0
Figure 26. Sample Muitipathway Summary Output
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7.1.5 Max Concentration Summary
The Max Concentration Summary (max_conc_locations.xlsx) provides the maximum
concentration and the location of that maximum, for each facility, of the pollutant you identify on
the Summarize Risks interface, as noted in Section 4.5. The summary lists the maximum
concentration of this pollutant (in jjg/m3) for every facility that emits that pollutant, the latitude
and longitude of the location where this maximum concentration occurs, the receptor type (e.g.,
polar grid receptor, census block receptor, user receptor), and the FIPS and Block ID for the
receptor, if it is a census block. Figure 27 shows a screenshot of a sample Max Concentration
Summary, in which the user entered "arsenic compounds" on the Summarize Risks interface,
under the Max Concentration check box. The "PG" listed under Receptor Type in this example
indicates that the maximum occurs at a polar grid receptor; hence the FIPS and Block ID
columns are blank.
Facility ID
Pollutant
Max
Concentration
(jig/m3)
Lat
Lon
FIPS
Block
Receptor
Type
Facl-NC
arsenic compounds
0.004157229
33.01296
-110.784
PG
Fac2-SC
arsenic compounds
0.03816163
33.00462
-110.778
PG
Fac3-IL
arsenic compounds
0.17524S2S9
33.41242
-110.856
PG
Figure 27. Sample Max Concentration Summary
Note: Only facilities containing the pollutant will appear in this summary; if you ask for the max
concentration of a pollutant not contained in certain facilities, those facilities will not appear in
this output. Likewise, if you ask for a pollutant not in your HAP Emissions input file at all, no max
concentrations will be provided.
7.1.6 Max Risk and HI by Source and Pollutant Summary
The Max Risk and HI by Source and Pollutant Summary (faciiity_risk_hi_bysrchap.xisx)
provides the maximum risk for each facility, the facility-wide incidence, the maximum noncancer
hazard index (HI) for each facility, and the target organ type for that facility-specific maximum HI
from the 14 modeled TOSHIs (e.g., respiratory, neurological, developmental). In addition, this
summary provides the risk, incidence, and noncancer hazard quotient (HQ) by source type and
by pollutant, within each modeled facility. Figure 28 shows a screenshot of a portion of a
sample Max Risk and HI by Source and Pollutant Summary. In this sample, results are shown
for one modeled facility and the facility's ID/name, MIR, incidence, noncancer max TOSHI
value, and TOSHI type (for all pollutants and sources combined) are listed in each row of this
output in the first five columns. In addition, each row provides a different risk, noncancer
(pollutant-specific) HQ, and incidence caused by each modeled source type and pollutant
("HAP") combination. For example, the risk caused by trichloroethylene from source type "RW'
is 6.43E-07 (or 0.6 in a million), as shown in row 2 of Figure 28. The noncancer HQ caused by
trichloroethylene from source type RW is 0.0669, and the incidence caused by trichloroethylene
from source type RW is 4.17E-06.
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Facility
Facility
MIR
Facility
Incidence
Facility
Max HI
Max HI Type
Source
Type
Pollutant
Risk by
Source
and HAP
HQ by
Source
and HAP
Incidence
by Source
and HAP
Facl-NC
0.000611
0.0480683
8.998161
developmental
RV
xylenes (mixed)
0
0.000111
0
Facl-NC
0.000611
0.0480683
8.998161
developmental
RW
trichloroethylene
6.43 E-07
0.066946
4.171E-06
Facl-NC
0.000611
0.0480683
8.998161
developmental
FU
selenium compounds
0
0.00091
0
Facl-NC
0.000611
0.0480683
8.998161
developmental
RV
naphthalene
4.49E-07
0.004401
4.268E-05
Facl-NC
0.000611
0.0480683
8.998161
developmental
FU
mercury (elemental)
0
0.027301
0
Facl-NC
0.000611
0.0480683
8.998161
developmental
CT
indeno[l,2,3-c,d]pyrene
3.13E-14
0
3.071E-12
Facl-NC
0.000611
0.0480683
8.998161
developmental
CV
indeno[l,2,3-c,d]pyrene
1.51E-13
0
1.201E-11
Facl-NC
0.000611
0.0480683
8.998161
developmental
HV
indeno[l,2,3-c,d]pyrene
1.59E-13
0
1.651E-11
Facl-NC
0.000611
0.0480683
8.998161
developmental
RW
hydrofluoric acid
0
0.000797
0
Figure 28. Sample Max Risk and HI by Source and Pollutant Summary
As suggested by the above example, this summary output provides a detailed breakdown of
cancer risk, noncancer HQ, and incidence for every modeled pollutant and source type.
7.2 Run Group Summaries
As noted in Section 4.5, five of the 11 summaries produce results for the entire run group, which
are not specific to each facility in isolation. These summaries account for impacts on receptors
from multiple, neighboring facilities (if their modeling domains intersect), and therefore individual
facility IDs are not connected to the results. The five run group-wide summaries discussed in
this section include: the max risk and hazard indices summary, the risk histogram summary, the
hazard index histogram summary, the incidence drivers summary, and the source type risk
histogram summary.
7.2.1 Max Risk and Hazard Indices Summary
The Max Risk Summary output (max_risk.xlsx) provides the maximum cancer risk and
maximum noncancer risk (HI) for all 14 TOSHI's at any populated receptor in the run group,
accounting for multiple impacts on receptors from neighboring facilities. This summary also
provides the FIPS and block ID for census blocks, the alternate receptor ID, or the user receptor
ID of each of the maxima, as well as the receptor's population. The Max Risk Summary also
lists the Facility ID(s) of the facility or facilities that impact these max receptors (i.e., contribute
to the max risk and max TOSHIs at these receptors). Note: The maxima reported in this
summary will equal the highest facility-specific risk and HI listed in the Facility Max Risk and HI
output (discussed in Section 6.2.1), except when multiple facilities' impacts on the same
receptor cause the max risk and HI to be greater than the highest individual facility-specific risk
and HI. A sample Max Risk Summary file is shown in Figure 29.
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A
B
C
D
E
F
G
H
1 J
K
L
M
N
0
1
RISK_TYPE
FIPS
BLOCK
POPULATION
RISK
2
mir
36045
>613001004
126
4.8218E-07
3
respiratory
36045
>613001004
126
0.003784775
4
liver
36045
>613001004
126
0.00016653
5
neurological
37165
>104001092
16
0.115473556
6
developmental
36045
>613001004
126
2.37305E-05
7
reproductive
0
0
8
kidney
0
0
9
ocular
0
0
10
endocrine
0
0
11
hematological
0
0
12
immunological
0
0
13
skeletal
0
0
14
spleen
0
0
15
thyroid
0
0
16
whole body
0
0
17_
Facilities
Impacting mir
Block
Facilities
Impacting
respiratory
Block
Facilities
Impacting
liver Block
Facilities
Impacting
neurological
Block
Facilities
Impacting
developmental
Block
Facilities
Impacting
reproductive
Block
Facilities
Impacting
kidney Block
Facilities
Impacting
ocular Block
Facilities
Impacting
endocrine
Block
Facilities
Impacting
hematological
Block
Facilities
Impacting
immunological
Block
Facilities
Impacting
skeletal
Block
Facilities
Impacting
spleen
Block
Facilities
Impacting
thyroid
Block
Facilities
Impacting
whole body
Block
18
3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
*3604511259
19
Figure 29. Sample Max Risk Summary Output
7.2.2 Risk Histogram Summary
The Risk Histogram output (histogram_risk.xlsx) provides the population and facility counts at
various risk levels. This file lists the number of people and facilities in the modeled run group in
the following risk bins:
• less than 1 in 1 million risk (displayed as "<1e-6");
• greater than or equal to 1 in 1 million risk (displayed as ">= 1e-6");
• greater than or equal to 10 in 1 million risk (displayed as ">=1e-5");
• greater than or equal to 100 in 1 million risk (displayed as ">=1e-4"); and
• greater than or equal to 1,000 in 1 million risk (displayed as ">=1e-3").
Note: This program assigns populations and facilities to cancer risk bins based on their risk
level after rounding to one significant figure, per EPA convention. Also, note that the Risk
Histogram Summary takes into account multiple impacts on the same receptor (from facilities
located close to one another). This may cause the population numbers from this file to differ
slightly from the population numbers provided by the Facility Cancer Risk Exposure file. Figure
30 shows a sample output. Finally, it should also be noted that the total population modeled in
the run group can be determined by summing cells B2 and B3; and the total number of facilities
modeled can be determined by summing cells C2 and C3.
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A
B
C
1
Risk level
Population
Facility count
2
=le-6
835305
2
4
>=le-5
45866
1
5
>=le-4
435
1
6
>=le-3
0
0
Figure 30. Sample Risk Histogram Summary Output
7.2.3 Hazard Index Histogram Summary
The Hazard Index Histogram output (hi_histogram.xlsx) provides the population and facility
counts at various noncancer HI levels, for all 14 TOSHIs. This file lists the number of people and
facilities in the modeled run group in the following noncancer HI bins:
• > 1,000;
• > 100;
• > 10;
• >1; and
• <=1.
Note: This program assigns populations and facilities to noncancer HI bins based on their HI
level after rounding to one significant figure, per EPA convention. Also, note that the Hazard
Index Histogram Summary takes into account multiple impacts on the same receptor (from
facilities located close to one another). This may cause the population numbers from this file to
differ slightly from the population numbers provided by the Facility TOSHI Exposure file. Figure
31 shows an abbreviated sample output for 3 TOSHIs; the actual file shows results for all 14
TOSHIs.
A
e
C
D
E
F
G
Respiratory
Respiratory
Liver
Neurological
Neurological
1 J
HI Level
Pop
Facilities
Liver Pop
Facilities
Pop
Facilities
2
>1000
0
0
0
0
0
0
3
>100
0
0
0
0
0
0
4
>10
0
0
0
0
0
0
5
>1
167
1
0
0
22
1
6
<=1
3924289
1
3924289
2
3924434
1
Figure 31. Sample Hazard Index Histogram Summary Output (Partial)
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7.2.4 Incidence Drivers Summary
The Incidence Drivers output (incidence_drivers.xlsx) provides the pollutants driving the
incidence across the entire run group of modeled facilities. (As noted in previous sections, the
incidence is equal to the cancer risk of each block times the population of that block, divided by
a 70-year lifetime, and summed over all blocks in the modeling domain.) In this file, the total
incidence and individual incidence attributable to each pollutant are provided, as well as the
percentage that each pollutant-specific incidence is of total incidence. The pollutants are listed
in descending order of contribution to the total incidence. Figure 32 shows a sample output.
A
B
C
1
Pollutant
Incidence
% of Total Incidence
2
arsenic compounds
0.039060199
81.83%
3
1,3-butadiene
0.003666767
*7.68%
4
cadmium compounds
0.003205572
r6.72%
5
naphthalene
0.00105277
*2.21%
6
benzene
0.000444901
*0.93%
7
bis(2-ethylhexyl)phthalate
0.000219206
*0.46%
8
chromium (vi) compounds
5.6644E-05
0.12%
9
trichloroethylene
1.01883E-05
*0.02%
10
Total incidence
0.04773414
rioo%
Figure 32. Sample Incidence Drivers Summary Output
7.2.5 Source Type Risk Histogram Summary
The Source Type Risk Histogram Summary (source_type_risk.xlsx) output provides a table
showing the maximum cancer risk overall for the run group, as well as individually by emission
source type. For the maximum overall risk and for the source type-specific risk, the file also
provides the number of people estimated at three risk levels: >= 1 in 1 million, >= 10 in 1 million,
and >= 100 in 1 million. The overall incidence and the incidence attributable to each emission
source type is also provided. Figure 33 shows a screenshot of a sample Source Type Risk
Histogram Summary file. Note that in this example, the source types included in the input files
for the run on which this summary file is based are SR, RV, FU, MS, RW, CV, HV, and CT. As
shown in Figure 33, the SR source type contributes almost all of the risk to the overall cancer
risk.
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Maximum
Overall
SR
RV
FU
MS
RW
CV
HV
CT
Cancer Risk
Maximum (in 1 million)
600
600
5
4
0.5
0.4
0.009
0.007
0.002
Number of people
>= 100 in 1 million
435
435
0
0
0
0
0
0
0
>=10 in 1 million
48,998
37,478
0
0
0
0
0
0
0
>= 1 in 1 million
800,229
528,652
214,494
239
0
0
0
0
0
Incidence
0.047
0.035
0.012
0.00022
5.9E-06
0.000011
3.3E-06
3.8E-06
2.1E-06
Run Group MIR (in a million) = 600.0
Figure 33. Sample Sourcetype_Histogram_Sorted RTR Summary Output
Note: The Maximum Overall column lists the population at various risk levels attributable to all
source types/emission process groups combined, while the other columns list the population at
various risk levels attributable to each individual source type in isolation. The sum of the
population tallies across the individual source types may not necessarily equal the
corresponding value in the maximum overall column, at a given risk level, because: (a) two or
more source types' impact in combination may be required to cause a census block population
to exceed a given risk level; or conversely (b) an individual source type's impact in isolation may
be enough to cause a census block population to exceed a given risk level, while other source
types may similarly impact the same census block population and also (in isolation) cause that
population to exceed the given risk level.
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8. Demographic Assessment Methodology & Results
This section discusses the data sources and methodology behind HEM4's Demographic
Assessment results, and also describes the outputs produced using sample results for
explanation. Appendix B contains a more detailed description of the methodology.
8.1 U.S. Census Source Data and Demographic Methodology
HEM4's Demographic Assessment module can be used only when modeling with U.S. Census
receptors because the Census provides demographic estimates for its population counts. When
modeling with U.S. Census receptors, HEM4 estimates population exposures to air pollution at
the census block level, which is the finest level of spatial resolution reported in the U.S.
Decennial Census (Census 2022a). HEM4's Demographic Assessment module links your
modeled population (including cancer and noncancer estimates for each census block receptor)
to demographic information at the block group level from the Census' 2016-2020 American
Community Survey (ACS) on race and ethnicity, age, poverty status, educational attainment,
and linguistic isolation (Census 2022b). The ACS data is included in HEM4's "resources" folder
when you download the model.
The ACS (Census 2022b) is a population survey continuously carried out by the Census
Bureau, in parallel with the Decennial Census (Census 2022a) and independent of the
decennial schedule. The ACS dataset is a five-year rolling average updated annually, with a lag
time of about two years from the last year of the rolling average. The five-year average ACS
product provides the finest level of spatial resolution available for demographic information, with
demographic statistics computed at a mixture of block group and tract levels. Most data in the
five-year ACS are computed at the block group level; but in some geographic areas, some
statistics are only computed at the tract level. The ACS also produces 1 year and 3-year
surveys for states and counties, although HEM4's Demographic Assessment module uses the
five-year (2016-2020) averages from the ACS at the block group level for the nationwide, state,
county, and modeling domain demographic statistics, for greater spatial resolution. (Note: Within
the Census, blocks are aggregated into block groups, and block groups are aggregated into
tracts. Tracts do not cross county boundaries, so each tract is contained entirely within a county.
On average, there are about 30 populated blocks per block group, three block groups per tract,
and 20 tracts on average in a county.)
Using data from the ACS, HEM4 computes demographic statistics within the radius/proximity
you chose on the Demographic Assessment interface, for each individual facility's modeling
domain and for your run group as a whole, as well as demographic-specific cancer and
noncancer risk for your modeled population. As noted above, HEM4 uses demographic data
extracted from the 2016-2020 five-year ACS, which includes data for the 50 States, the District
of Columbia, and Puerto Rico. Once extracted, HEM4 computes population subgroup
percentages within the five following subject categories:
• Race and ethnicity
o Percent People of Color, which is the Total population minus the White
population and includes African American, American Indian or Alaska Native,
Other or Multiracial, and Hispanic or Latino ethnicity of any race
o Percent White, not Hispanic or Latino
o Percent African American, not Hispanic or Latino
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o Percent American Indian or Alaska Native, not Hispanic or Latino
o Percent Other races or Multiracial, not Hispanic or Latino
o Percent Hispanic or Latino, any race
• Age
o Percent under age 18
o Percent aged 18 to under 65
o Percent aged 65 and older
• Poverty status
o Percent living in households with total household income under the poverty line
o Percent living in households with total household income under twice the poverty
line
• Educational attainment
o Percent of people over age 25 without a High School Diploma
• Linguistic isolation
o Percent of households in which no one over age 14 is proficient in English
As noted earlier, the above demographic data is used by HEM4 at the census block group level,
because this is the finest spatial resolution available in the ACS (Census 2022b). Table 40
summarizes the census data used by HEM4, showing the source of each dataset and the level
of geographic resolution. The statistics for People of Color, age groups, educational attainment,
poverty, and linguistic isolation are consistent with the demographic statistics used in
EJSCREEN, EPA's Environmental Justice Screening and Mapping Tool (EPA2022f). HEM4
derives its demographic statistics from the ACS, which is the source of data for EJSCREEN's
statistics, although HEM4 provides the impact on different racial and ethnic groups in more
detail than EJSCREEN provides, as Table 40 illustrates.
HEM4's Demographic Assessment module uses the modeled census block and census block
group identification codes to link the HEM4 modeling results for each census block to the
appropriate ACS census block group demographic statistics. This allows HEM4 to estimate the
number of people in different demographic categories for each census block modeled by HEM4.
For the demographic analysis, the total nationwide population is determined by summing the
total population of all census block groups in the Census' ACS five-year average for 2016-2020.
The demographic characteristics of the population potentially impacted by emissions from
facilities in your run group is determined by applying the characteristics of a census block group
to the HEM4 modeled census block populations located within that block group. The
demographic characteristics of a given block group - that is, the percentage of people in
different races/ethnicities, the percentage in different age groups, the percentage without a high
school diploma, the percentage at certain low-income levels, and the percentage that are
linguistically isolated - are presumed to also describe each block located within that block group
(since block level demographic data is not available).
Appendix B describes the calculation methods used to estimate the total population exposed to
different risk levels, as well as the calculation methods used to compute risks for racial, ethnic,
age, education status, low household income, poverty status, and linguistically isolated
demographic categories. Appendix B also describes the gap-filling approach used by HEM4
when block group statistics are not available for a given block, based on computing default
averages for the missing demographic(s) at the tract level or from the nearest block group.
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Table 40. Summary of Census Data used for Demographic Groups
Type of population category
Source of data
Level of
geographic
resolution
Total population (HEM4 risk analysis)
2020 P.L. 94-171 Tables*
Census block
Total population (Demographic analysis)
ACS** Table B03002 (e1)***
Block group
Race/ethnicity categories (percentages):
• White (non-hispanic):
• People of Color (non-white + hispanic)
• African American (non-hispanic):
• Native American (non-hispanic):
• Other & Mixed race (non-hispanic):
• Hispanic (all races):
ACS Table B03002, Hispanic or
Latino Origin by Race (Tiger
table X03):
• e3/e1
• (e1-e3)/e1
• e4/e1
• e5/e1
• (e6+e7+e8+e9)/e1
• e12/e1
Block group
Age groups
ACS Table B01001, Sex by
Age (Tiger table X01)
Block group
Level of education - percentage of adults 25
years and older without a high school
diploma
ACS Table B15002, Sex by
Educational Attainment (Tiger
table X15)
Block group
Individuals living in households earning below
the poverty level (percentage of
individuals)
ACS Table C17002, Ratio of
Income to Poverty Level (Tiger
table X17): (e2+e3)/e1
Block group
Individuals living in households earning below
twice the poverty level (percentage of
individuals)
ACS Table C17002, Ratio of
Income to Poverty Level (Tiger
table X17): (e1-e8)/e1
Block group
Individuals living in linguistically isolated
households (percentage of households)
ACS Table C16002, Household
Language by Household (Tiger
table X16):
(e4+e7+e10+e13)/e1
Block group
Notes:
* U.S. Decennial Census (Census 2022a')
** U.S. Census' 2016-2020 American Community Survey (Census 202213)
*** The "e" designations refer to data elements (columns/fields) specific to the different ACS tables listed.
8.2 Discussion of Sample Demographic Results
When you initiate a Demographic Assessment run, the module will access the ACS data
described above and will also access every facility's Block Summary Chronic output from the
run group to create a large file called MIR_HI_allreceptors.csv. The MIR_HI_allreceptors file
contains the FIPS, Block ID, latitude/longitude, population, MIR, and all 14 TOSHI values for
every modeled block in your run group. It also contains the number of facilities that impact each
block (to account for multiple impacts from neighboring facilities) and the distance of the block
from the facility center (used to determine if the block is within your specified radius). Depending
on the size of your run group, this file may be quite large and once complete, will be placed by
HEM4 in the output directory you pointed to on the Demographic Assessment interface (i.e., the
same folder in which the Facility_Max_Risk_and_Hl.xlsx file is located). The Demographic
Assessment module will select blocks from the MIR_HI_allreceptors file that fall within the
radius you specified on the interface, and determine their demographics from the ACS data.
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Note: The MIR_HI_allreceptors file will not be overwritten during a subsequent
Demographic Assessment run in which you have pointed to the same HEM output folder.
This saves time when additional Demographic Assessment scenarios are desired (beyond the
four allowed per run), but be careful to move or delete the existing MIR_HI_allreceptors file if
you do wish for a new one to be created.
For each combination of radius and risk/Hi level you select on the Demographic Assessment
interface. HEM4 produces four types of output files.
1. Run group wide Excel™ workbook of binned results covering all risk/Hi levels for each
demographic category (listed in Table 40) are produced, which also include:
o the total population in the run group's modeled domain exceeding your chosen
risk/Hi level, broken out into demographic percentages (exceeding your chosen
risk/Hi level),
o the max risk/Hi for your entire run group of modeled facilities as a whole,
o run group wide proximity results showing the total population (at your chosen
radius) broken out into demographic percentages (irrespective of risk/Hi), and
o nationwide, state, and county total populations, broken out into demographic
percentages for comparison.
2. Facility-specific Excel™ workbook of binned results covering all risk/Hi levels for each
demographic category (listed in Table 40) are produced, which also include:
o the total population in the facility's modeled domain exceeding your chosen
risk/Hi level, broken out into demographic percentages (exceeding your chosen
risk/Hi level),
o the max risk/Hi at that facility,
o facility-specific proximity results showing the total population (at your chosen
radius) broken out into demographic percentages (irrespective of risk/Hi), and
o nationwide, state, and county total populations, broken out into demographic
percentages for comparison.
3. Environmental justice (EJ) Summary Excel™ worksheets are produced, that display the
results contained in #1 and #2 above in rows collected into one summary table,
including:
o run group wide proximity results showing the total population (at your chosen
radius) broken out into demographic percentages (irrespective of risk/Hi),
o the total "At Risk" or "Above HI" population in the run group's modeled domain
exceeding your chosen risk/Hi level, broken out into demographic percentages
(exceeding your chosen risk/Hi level),
o facility-specific "Proximity" results showing the total population surrounding each
facility (at your chosen radius) broken out into demographic percentages and
irrespective of risk/Hi,
o the total population "At Risk" or "Above HI" in each modeled facility's modeled
domain exceeding your chosen risk/Hi level, broken out into demographic
percentages (exceeding your chosen risk/Hi level), and
o the nationwide, state, and county total populations, broken out into demographic
percentages for comparison.
4. Defaulted block groups text files at each radius you selected are produced, at both the
facility-specific and run group wide levels, listing the populated (non-zero) Census blocks
that could not be matched to block groups. These listed blocks therefore required the
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use of tract or nearest block group defaults to estimate their demographic compositions.
(See Appendix B, Section B.6 for a discussion regarding demographic defaulting by
HEM4's Demographic Assessment module.) These text files do not contain any
demographic results, but are useful for QA reviews because they indicate the degree to
which spatially resolved demographic statistics are available.
In addition to the above four file types, the Demographic Assessment module also produces a
hem4.log file that chronicles the Demographic Assessment run. This is similar to the hem4.log
file produced for your modeling run and discussed in Sections 4.4 and 6.2.4, although this
hem4.log tracks the activity performed by the Demographic Assessment module. Finally, at the
completion of certain runs, the Demographic Assessment module also produces another type of
QA output named Skipped EJ Facilities.xlsx. This file is produced if one or more of the facility-
specific folders are empty to alert you to the fact that not all facilities are included in the
demographic assessment outputs. (Empty facility folders may occur when AERMOD fails to run
during HEM modeling due to inconsistent inputs or errors in the input files, as discussed in
Section 4.9 and Section 6.2.4.)
As noted in Section 4.6, when you initiate a Demographic Assessment run, HEM4 will
automatically create a new subfolder named "ej" in your run group output folder, and the results
described above (including the hem4.log specific to the Demographic Assessment run) will be
placed in this subfolder. The outputs containing the demographic results will contain both the
date and time stamp in their file names, indicating when they were produced. Samples of
several Demographic Assessment output files are provided in figures below, along with a short
discussion to explain the demographic data shown.
Figure 34 below is a sample of one of the tables provided in the workbook described in #1 on
the previous page, based on run-group wide results for cancer at 50 km and demographics by
race/ethnicity. A similar table and workbook are produced for each facility (described in #2
above). Columns A and B and rows 6 through 16 in Figure 34 show the array of binned cancer
risk results that the Demographic Assessment module provides, while row 17 shows the
population modeled at all risk levels combined. Columns D through H show the population of
each race/ethnicity category in each of the cancer risk bins, while column C shows all
races/ethnicities combined. For example, for this run group, there are a total of 43,807 people
(shown in cell C17) in the 50 km modeling domain, and out of those 43,807 people, there are
18,559 people at a cancer risk less than 1-in-1 million (cell C6), 10,915 people at a risk at least
1 -in-1 million but less than 5-in-1 million (cell C7) and so on, with 163 people at a risk at least
50-in-1 million but less than 100-in-1 million (cell C13). Of the 43,807 people modeled, 18,812
are white (cell D17), 269 are African American (cell E17), 7,650 are Native American (cell F17),
1,714 classify as "Other and Multiracial" (cell G17), and 15,362 are Hispanic or Latino (cell
G17). Of the 163 people in the highest cancer risk bin - which for this run group is 50-in-1
million to less than 100-in-1 million - 67 are white (cell D13), 12 are African American (cell E13),
none are Native American (cell F13), 17 are Other and Multiracial (cell G13), and 66 are
Hispanic or Latino (cell H13).
Finally, row 18 in Figure 34 provides the average cancer risk (chance in one million) for the total
population and for each racial/ethnic demographic category in the modeled population in this
run group as a whole. Note that the average risk is less than the maximum risk (MIR) because
the average risk takes into account risk levels at all populated block receptors for the entire
modeled domain of the source category, whereas the maximum risk occurs at an individual
populated receptor (that receptor with the highest modeled risk level). The average risk statistic
encompasses higher risk levels (generally) closer into facility emissions as well as lower risk
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locations (generally) farther away in the domain. Similar tables to the one shown in Figure 34
are produced by the Demographic Assessment module for the other socio-economic categories
listed in Table 40 (i.e., by age, education level, poverty status, and linguistic isolation), at both
the run group level and the individual facility level. At the run group level, cumulative risk is
accounted for from neighboring facilities with overlapping domains of impact, while at
the facility level only risk from that individual facility is accounted for, regardless of how
close a neighboring facility may be. This allows for consideration of the demographic impacts
from each individual facility in isolation, as well as from the group of facilities modeled as a
whole. Finally, as noted above, these tables are produced for every radius you selected on the
Demographic Assessment interface.
ABCDEFGH
Table A-l. Distribution of Cancer Risk for Racial and Ethnic Groups - SO km Study Area Radius
1
2 | Number of People within 50 km of any Facility in Different Ranges for Ufetime Cancer
Risk b
3
Range of Lifetime
4
Individual Cancer Risk from
the Primary Copper Source
Category (Chance in One
Total
Population
White
African
American
Native
American
Other and
Multiracial
Hispanic or
Latino'
5
Million) *
6
0to=300
0
0
0
0
0
0
17 |
Total Number
43,807
18,812
269
7,650
1,714
15,362
Average Risk (Chance in
18
One Million)®
4
4
10
2
5
5
Notes:
19
' Modeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not adjusted for
20 |exposure factors. Risks from Primary Copper emissions are modeled at the census block level.
b Distributions by race are based on demographic information at the census block group level.
2 c In order to avoid double counting, the "Hispanic or Latino" category is treated as a distinct demographic
category for these analyses. A person is identified as one of five racial/ethnic categories above: White,
African American, Native American, Other and Multiracial, or Hispanic/Latino.
-igure 34. Sample Demographic Assessment Output: Distribution of Cancer Risk for
Racial and Ethnic Categories
Figure 35 shows another sample table in the workbook described in #1 on page 135, labeled
the "Proximity & Ave. Risk Summary" on its worksheet tab. The results depicted in this
sample table are based on run-group wide results for cancer risk at 50 km, for all demographic
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categories provided by the Demographic Assessment module. A similar table is produced for
each facility (described in #2 above). This table provides proximity statistics at the radius you
selected on the Demographic Assessment interface as both number of people (in row 13 of
Figure 35) and percentage of total (in row 14). The average risk (in one million) for every
demographic category provided by the Demographic Assessment module is also listed (in row
15). In addition, the table shown in Figure 35 provides nationwide, state and county
demographic breakdowns (in rows 3 through 11). The nationwide population counts and
percentages are based on the five-year U.S. national averages provided in the 2016-2020 ACS
(Census 2022b) and include Puerto Rico. Note that average(s) based on fewer years will differ
slightly and will be impacted more by the value in any one year. The state and county
demographic breakdowns are tabulated by HEM4's Demographic Assessment module based
on the average statistics of every state and county within which any facility's receptor is located,
at the radius you chose for your run group. Therefore, it should be noted that even if only one
receptor is located in a given state or county, that state or county is included in the demographic
breakdowns shown. It should also be noted that the nationwide, state, and county demographic
breakdowns are not based on risk or HI levels, but are merely total population counts and
percentages, or "proximity statistics".
Another table in the same workbook that provides the tables shown in Figures 34 and 35 is
shown in Figure 36. This table, labeled the "Pop. at Risk Summary" on its worksheet tab, is
also provided at the run group level and individual facility level. The table shown in Figure 36
provides the same nationwide, state and county percentages as provided in the previous table
shown in Figure 35. However, this table also provides the maximum risk (or HI) for the run
group (or for the individual facility for the facility-specific outputs) as well as the total population
above the risk or HI level you selected on the Demographic Assessment interface, with the
demographic breakdown of that same population exceeding the risk/Hi threshold you selected.
The Demographic Assessment module also produces a tab labeled "Preamble Summary" (not
depicted herein) that produces similar results as the "Pop. at Risk Summary" but organized
differently and grouped into the following categories: Race and Ethnicity by Percent, Income by
Percent, Education by Percent, and Linguistically Isolated by Percent.
Finally, the table shown in Figure 37 is a sample of the "EJ Summary" output file, noted in #3
above (on page 135). This summary provides the nationwide, state, and county demographic
breakdowns as well as the "At Risk" (or "Above HI") demographic percentages above the risk/Hi
level and at the radius you selected, for the run group and for each individual facility. The EJ
Summary output provides the comprehensive results of your Demographic Assessment run in
one file and is used by Python's Dash app to produce the interactive browser-based graphs of
the demographic results, described in Section 4.7.2. The Demographic Assessment module
produces a separate EJ Summary output file for cancer risk and for noncancer HI, at each
radius you selected. Within each radius-specific EJ Summary file (for cancer/noncancer),
separate Excel™ workbook tabs are produced for each risk/Hi level you selected on the
interface. For example, if you choose to run a Demographic Assessment for cancer risk at 50
km with a risk level greater than or equal to 1-in-1 million, and also at 50 km with a risk level
greater than or equal to 10-in-1 million, then one EJ Summary output file will be produced that
will contain "50_km_Cancer" in the filename (with the date), and within that file will be a two-
tabbed workbook. One worksheet tab will be labeled "Risk >= 1 -in-1 million" and the other
worksheet tab will be labeled "Risk >= 10-in-1 million". The same is true for different noncancer
HI levels you choose at a given radius on the Demographic Assessment interface.
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A B
C
D
E
F
G
H
1
J
K
L
M
N
O
P
Q
1
C-6. Distribution of Cancer Risk for Racial and Ethnic Groups, Age Groups, Adults without
a High School Diploma, People Living in Low Income Households, and People Living in Linguistic Isolation - SO km Study Area Radius
2
Total
Population
White
People of
Color*
African
American
Native
American
Other and
Multiracial
Hispanic or
Latin od
Age (Years)
0-17
Age (Years)
18-64
Age (Years)
>=65
People Living
Below the
Poverty Level
People Living
Below Twice
the Poverty
Level
Total
Number >=
25 Years Old
Number >=
25 Years Old
without a
High School
Diploma
People Living
in Linguistic
Isolation
3
Nationwide Demographic Breakdown
4
Total population3
329,824,950
196,283,090
133,541,860
39,997,867
2,076,003
28,894,345
62,573,645
73,907,898
202,887,029
53,030,023
42,311,284
99,653,072
225,188,926
26,087,112
17,242,818
5
Percentage of total
59.5%
40.5%
12.1%
0.6%
8.8%
19.0%
22.4%
61.5%
16.1%
12.8%
30.2%
68.3%
11.6%
5.2%
6
State Demographic Breakdown
7
Total population®
7,174,064
3,883,722
3,290,342
305,973
272,294
451,385
2,260,690
1,639,645
4,272,215
1,262,204
990,528
2,364,111
4,846,407
587,920
295,524
8
Percentage of total
54.1%
45.9%
4.3%
3.8%
6.3%
31.5%
22.9%
59.6%
17.6%
13.8%
33.0%
67.6%
12.1%
4.1%
9
County Demographic Breakdown
10
Total population3
4,952,488
2,711,903
2,240,585
256,951
100,072
349,934
1,533,628
1,173,145
2,995,546
783,797
622,650
1,507,562
3,327,659
391,817
178,723
11
Percentage of total
54.8%
45.2%
5.2%
2.0%
7.1%
31.0%
23.7%
60.5%
15.8%
12.6%
30.4%
67.2%
11.8%
3.6%
12
Proximity Results plus Modeled Risk b from the Primary Copper Source Category
Total population within 50
13
km of any facility
43,807
18,812
24,995
269
7,650
1,714
15,362
9,589
23,243
10,974
8,977
19,100
31,349
4,910
1,329
14
Percentage of total
42.9%
57.1%
0.6%
17.5%
3.9%
35.1%
21.9%
53.1%
25.1%
20.5%
43.6%
71.6%
15.7%
3.0%
15
Average risk (in one million]
4
4
4
10
2
5
5
4
5
4
4
4
4
5
5
Figure 35. Sample Demographic Assessment Output: Proximity and Average Risk Summary
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A
B
C
D
E
F
G
H
]
J
K
L
M
N
O
1
Table 2. Summary of Community Assessment of Risk Results for the Primary Copper Source Category - 50 km Study Area Radius
zl
Demographic Group
Age
(Years)
0-17
Age
(Years)
18-64
Age
(Years)
>=65
Below
Below
Over 25
3
Population Basis
Total
People
of Color
African
American
Native
American
Other and
Multiracial
Hispanic
or Latino
the
Poverty
Level
Twice the
Poverty
Level
Without a
High School
Diploma
Linguistically
Isolated
4
Nationwide
329,824,950
40.5%
12.1%
0.6%
8.8%
19.0%
22.4%
61.5%
16.1%
12.8%
30.2%
11.6%
5.2%
5
State
7,174,064
45.9%
4.3%
3.8%
6.3%
31.5%
22.9%
59.6%
17.6%
13.8%
33.0%
12.1%
4.1%
6
County
4,952,488
45.2%
5.2%
2.0%
7.1%
31.0%
23.7%
60.5%
15.8%
12.6%
30.4%
11.8%
3.6%
7
8
Maximum Risk
(in 1 million)
Population With Risk Greater Than or Equal to 1 in 1 million
9
Source Category
SO
25,248
65.9%
0.9%
29.2%
3.4%
32.4%
25.9%
56.4%
17.7%
25.4%
44.2%
18.0%
2.8%
10
11 | Notes:
12 | ] | I
The People of Color population is the total population minus the White population.
3 Source Category population figures are for the population residing within 50 km from the center of the
modeled facilities with cancer risk greater than or equal to 1 in 1 million.
14
Figure 36. Sample Demographic Assessment Output: Population at Risk Summary
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A B C D E F G H I J K L M N O
Summary of Community Assessment of Risk Results for Facilities in the Primary Copper run group -
1 Population With Risk Greater Than or Equal to 1 in 1 million within a 50 km Study Area Radius around each facility.
2
Demographic Group
3
Population
Basis
Total
People of
Color
African
American
Native
American
Other and
Multiracial
Hispanic or
Latino
Age (Years)
0-17
Age (Years)
18-64
Age (Years)
>=65
Below the
Poverty Level
Below Twice
the Poverty
Level
Over 25
Without a
High School
Diploma
Linguistically
Isolated
4
Nationwide
329,824,950
40.5%
12.1%
0.6%
8.8%
19.0%
22.4%
61.5%
16.1%
12.8%
30.2%
11.6%
5.2%
5
State
7,174,064
45.9%
4.3%
3.8%
6.3%
31.5%
22.9%
59.6%
17.6%
13.8%
33.0%
12.1%
4.1%
6
County
4,952,488
45.2%
5.2%
2.0%
7.1%
31.0%
23.7%
60.5%
15.8%
12.6%
30.4%
11.8%
3.6%
7
3.6%
8
Primary
Proximity
43,807
57.1%
0.6%
17.5%
3.9%
35.1%
21.9%
53.1%
25.1%
20.5%
43.6%
15.7%
3.0%
9
Copper
At Risk
25,248
65.9%
0.9%
29.2%
3.4%
32.4%
25.9%
56.4%
17.7%
25.4%
44.2%
18.0%
2.8%
10
11
Facility 1
Proximity
39,232
57.9%
0.7%
15.6%
3.9%
37.8%
22.2%
53.7%
24.1%
20.2%
43.1%
15.6%
3.3%
12
At Risk
803
75.8%
0.0%
0.5%
1.9%
73.4%
20.5%
59.3%
20.2%
23.9%
57.5%
22.5%
3.5%
13
Facility 2
Proximity
39,248
57.9%
0.7%
15.6%
3.9%
37.8%
22.2%
53.7%
24.1%
20.2%
43.1%
15.6%
3.3%
14
At Risk
550
71.1%
0.0%
0.4%
1.6%
69.1%
20.6%
58.4%
21.0%
20.6%
56.6%
22.5%
2.9%
15
Facility 3
Proximity
32,283
61.6%
0.7%
23.5%
4.0%
33.4%
23.3%
54.8%
21.9%
23.0%
42.7%
16.9%
3.2%
16
At Risk
23,674
65.5%
1.0%
29.9%
3.4%
31.2%
25.9%
56.5%
17.6%
25.5%
43.5%
17.9%
2.8%
Figure 37. Sample Demographic Assessment Output: EJ Summary
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9. Understanding the Risk Results
This section contains an overview on using the HEM4 outputs, Risk Summary Reports, and
Demographic Assessment tables to ascertain the cancer risks, noncancer hazards and acute
impacts posed by your group of modeled facilities to the population in your modeling domain.
Step 1: Open the Max_Risk.xlsx summary report output to obtain the highest cancer
risk and noncancer TOSHIs for all the modeled facilities in your run group, as well as the
max receptor IDs and population at each max receptor. You can also view the number of
facilities impacting each maximum receptor (in the case of nearby facilities impacting the
same receptor).
Step 2: Open the Facility_max_risk_and_Hl.xlsx output to obtain the facility-specific
MIR in column B (mx_can_rsk), as well as the facility-specific maximum TOSHI values in
each of their respective columns. Note: Multi-facility impacts on the same receptor (from
facilities located close to one another) are not accounted for in the Facility_max_risk_
and_Hl.xlsx output file, because each row of this output file is specific to each individual
facility. Therefore, the run group maximum reported in the Max_Risk.xlsx summary
report (which, as mentioned in Step 1, accounts for multiple impacts on the same
receptor from more than one facility) will either be equal to or greater than the highest
facility-specific MIR in the Facility max risk and Hl.xisx output.
Step 3: Open the Cancer_drivers.xlsx output to obtain the pollutant and emission
source type driving the modeled risk. To report the top cancer drivers for a run group,
use the Pollutant from column C and the Source ID from column F for all rows
associated with the facility showing the highest risk. The MIR value from this highest
facility will equal that listed in the Facilty_max_risk_and_Hl.xlsxf\\e from Step 2. Note:
This output does not account for 100% of the modeled risk, but rather provides those
pollutant-emission source combinations that contribute at least 90% to each facility's
MIR (from one or more pollutant-emission source combinations, depending on how
many combinations are needed to describe 90% of the modeled risk at each facility).
Step 4: Open the Histogram_risk.xisx output to obtain the number of people and
facilities at various risk levels. The total population within the modeling domain (by
default a 50-kilometer radius around each facility or your user-specified radius) equals
the sum of cells B2 + B3. This histogram output counts facilities based on modeled risk
at populated census blocks, alternate receptors, and user receptors. Consequently, this
file's facility count numbers will be in accord with the manual counting of facilities at each
risk level from the Facility_max_risk_and_Hl.xlsx file. Note: What risk bin a facility falls
into in this output is based on the one significant figure rounding convention adopted by
the EPA.
Step 5: Open the Hazard_lndex_Drivers.xlsx output to obtain the pollutant and
emission source driving all (non-zero) TOSHIs at each modeled facility. To report the top
HI drivers for a run group, use the Pollutant from column E and the Source ID from
column D for all rows associated with the facility showing the highest total TOSHI in
column C ("HI Total"). The TOSHI value from this highest facility should equal the TOSHI
value listed in the Facilty_max_risk_and_Hl.xlsx file from Step 2. Note: This output
does not account for 100% of the modeled TOSHI, but rather provides those pollutant-
emission source combinations that contribute at least 90% to the facility's total TOSHI.
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Step 6: Open the Hi_histogram.xlsx output to obtain the number of people and
facilities at various HI levels for each of the 14 TOSHIs. These numbers are based on
the one significant figure rounding convention (e.g., an HI of 1.4 rounds to 1 and so is
considered <= 1).
Step 7: Open the lncidence_drivers.xlsx output to obtain the run group-wide incidence
attributable to each pollutant. This file is sorted in descending order of incidence and
column C provides the percentage each pollutant drives the total incidence for all of
your modeled facilities.
Step 8: Open the Source_type_risk.xlsx output to obtain the number of people at
various risk levels caused by each emission source type, and the incidence attributable
to each source type. This output also shows the run group max risk and the number of
people at various risk levels attributable to all source types combined ("Maximum
Overall" which accounts for impacts on the same receptor by different source types), as
well as the overall incidence.
Step 9: Open the Acutejmpacts.xlsx output, if you modeled acute impacts, to obtain
the hazard quotients (HQs) based on various benchmarks for each pollutant of interest,
as well as the highest acute concentration for each HAP. You can perform a manual
count using this output file to determine the number of facilities with an HQ >= 1.5 for
any benchmark. (Note: An HQ >=1.5 is the mathematical definition of "greater than 1"
when using EPA's one significant figure rounding convention.) This output file also
provides (in the far-right columns) the receptors experiencing the maximum acute
concentration for each pollutant at every modeled facility.
Step 10: Open the AIIFacility_source_locations.kmz output to see all modeled
sources at each facility in your run group on a Google Earth™ map. This map provides a
ready view of the distance between your modeled facilities, and it allows you to perform
QA to determine whether the modeled locations of your sources are reasonable.
For additional details regarding the modeling results for each of the facilities in the run group,
open the individual facility subfolders in the output folder. Section 6 discusses these facility-
specific output files. Each facility folder also contains a source_risk.kmz output file which
displays the detailed modeled risk results for that facility on a Google Earth™ map.
The tables produced by the Demographic Assessment module (described in Section 8.2)
provide the demographic breakdown of the population in your modeling domain, and include risk
and HI results consistent with the outputs discussed above, at the same radii. For example, the
maximum risk/Hi for your run group that is reported in one of the Demographic Assessment
tables (shown in Figure 36) is the same maximum risk/Hi that is reported by the Max_Risk.xlsx
summary noted in Step 1 above. The facility-specific risk/Hi maxima provided in similar
Demographic Assessment tables at the facility level are the same risk/Hi maxima listed for each
facility in the Facilty_max_risk_ and_Hl.xlsx in Step 2 above. The number of people in various
risk/Hi bins in the run group wide Demographic Assessment table (exemplified in Figure 34) is
consistent with the number of people listed in the cancer risk histogram (Histogram_risk.xlsx)
and HI histogram (Hi_histogram.xlsx) noted in Steps 4 and 6 above, respectively, although
grouped into fewer bins than provided by the Demographic Assessment module.
Finally, HEM4 provides numerous graphical ways to review and analyze your (cancer and
noncancer) risk and Demographic Assessment outputs, as discussed in Section 4.7 regarding
the Analyze Outputs interface of HEM4.
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10. Quality Assurance Remodeling
There are several quality assurance (QA) checks that you should perform after HEM4 has
completed modeling each of your facilities. Ideally, these QA checks should be made before you
run the Risk Summary Reports (described in Section 4.5), to determine if any of the facilities
need to be revised and remodeled.
Ensuring the Maximum Individual Risk (MIR) and Max Target Organ-Specific Hazard Index
(TOSHIs) are Located at Populated Receptors
First, open and review the Facility_max_risk_and_Hl.xlsx f\\e to ensure that:
• the number of facilities modeled in column A equals the number of facilities in the input
files (e.g., Facility_List_Options.xisx),
• the maximum cancer risk values in column B occur at census blocks, alternate
receptors, or populated user-defined receptors rather than at unpopulated polar grid (or
boundary or monitor) receptors, as noted in column D; and
• the TOSH I values in the various HI columns occur at census blocks, alternate receptors,
or populated user-defined receptors rather than at unpopulated polar grid (or boundary
or monitor) receptors.
The cancer risk and noncancer TOSHI QA checks described above are especially important for
facilities of interest, such as those facilities with relatively high cancer risk or TOSHI values in
the modeled set. Remodel those facilities (as described below) that failed one or more of the QA
checks before running the Risk Summary Reports. Rerunning HEM4 for such facilities will
ensure that all facilities in the run group are modeled and that the modeled maximum risk and
TOSHI values occur at populated receptors.
Follow these steps to rerun a facility when the MIR or the maximum TOSHIs occur at an
unpopulated receptor (such as a polar grid receptor)13. First, review the Source_risk.kmz file
located in the individual facility subfolder. Opening this file will start Google Earth™ if it is
installed on your computer. Figure 38 shows a sample Google Earth™ kmz output file.
Zoom in on the facility center and turn on the polar grid (by checking the box next to "Polar
receptor cancer risk" in the Places key) to make visible the polar grid receptor at which the MIR
or TOSHI value occurs. Next, find the census block centroid closest to the MIR polar receptor.
Use the 'ruler' tool to measure the distance (in meters) from the census block centroid to the
approximate facility center. Increase this distance enough to ensure that a census block
centroid near the current polar MIR receptor will be closer to the facility center than this revised
first polar ring when the facility is rerun, as explained further below. Follow these steps for all
facilities of interest requiring remodeling due to an overlapped populated receptor.
13 The MIR or maximum TOSHIs can occur at a polar grid receptor if there is a census block or alternate
receptor located within the overlap distance of the facility boundary. In this case, HEM4 will select the
closest receptor to the facility boundary (i.e., census block, alternate, user-defined, or polar) to estimate
the MIR at a location nearest to the population inside the overlap distance that has been excluded.
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Figure 38. Sample Source_risk.kmz HEM4 Output
To rerun the facility or facilities, create a copy of the input file Facility_List_Options.xlsx. Be
careful to name the new file so that it is obvious it is not the original Facility_List_Options.xlsx
file (e.g., QA 1_Facility_list_options.xlsx to indicate it is the first QA run). Delete the rows for
the facilities that do NOT have to be rerun.
Next, under the column heading ring 1', enter the value determined from the above instructions
(i.e., the distance in meters between the approximate facility center and the census block
centroid closest to the MIR polar receptor, rounded up). Save these changes and close the file.
Re-start HEM4 using the new QA1_Facility_list_ options.xlsx file as an input. (Note: There
may be extra facilities in the HAP Emissions and Emissions Location files from your original run,
because HEM4 will only use data for the facilities listed in the Facility List Options file you
specify for the QA run.) HEM4 will then remodel the facilities with revised first ring distances.
This "bumping out" of the first polar ring will allow HEM4 to choose a populated census block or
alternate receptor as the MIR or TOSH I receptor, because the first polar ring of polar receptors
will be more distant from the facility center than the closest populated receptor. When re-running
HEM4, it is advisable to name the 'output' folder using "QA1" in case additional QA runs are
necessary.
Once you have rerun the facility or facilities, check the outputs to determine if the relevant MIR
or TOSHI is now at a populated receptor by opening the QA1_Facility_max_risk_and_Hl.xlsx
file. If the MIR or TOSHI is still at a polar grid receptor, repeat the above steps (starting with
opening the Source_risk.kmz file) using the identifier QA2 for the naming convention. Make the
first ring of the polar grid more distant from the facility center than in the first adjustment.
After you have successfully adjusted the distance so that the MIR and maximum TOSHIs occur
at populated receptors, copy the most recent facility rows from all QA_Facility_max_risk_
andJHI.xIsx files (e.g., QA1, QA2, QA3) into the original Facility_max_risk_and_Hl.xlsx file.
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Perform this row replacement for each remodeled facility, using the most recent QA run
applicable to that facility. In addition, replace the original subfolder for each remodeled facility by
copying the most recent facility output subfolder (including all its revised contents) from the QA
run to the location of the original facility output. Move or delete the original subfolder.
Ensuring Maxima are Discretely Modeled, not Interpolated:
A facility may require remodeling (using the steps described above) if the MIR and/or max
TOSHI values of that facility are interpolated, rather than explicitly modeled. The Facility_
max_risk_and_Hl.xlsx output indicates interpolated maximum risk values in column C and
maximum TOSHI values in the columns to the right of each TOSHI value (e.g., column I for the
respiratory HI). If these fields contain an N, then the values are not interpolated. Generally, a
value is interpolated if the maximum receptor is located outside the modeling distance within
which receptors are explicitly modeled (e.g., at a default value of 3,000 m or 3 km). This can
occur if a modeled facility is located in a sparsely populated area, where there are no census
block centroids or alternate receptors within the modeling distance (e.g., 3 km) of the facility
center.
Open the Source_risk.kmz file located in the individual facility subfolder to determine if a facility
with an interpolated MIR and/or TOSHI should be remodeled with an increased modeling
distance. This Google Earth™ kmz file will show where the closest populated receptors are
located. The modeling distance should be increased to include the populated receptor(s). Use
Google Earth's™ ruler tool to determine the new modeling distance. Remember to increase this
distance slightly before remodeling the facility in a QA run, as discussed above. Note: If the risk
and all TOSHIs are considered low—and if the reason for the low values is that the facility is
located in a sparsely populated area—you may decide that revising the modeling distance and
remodeling is not necessary.
An interpolated MIR or TOSHI value may also occur if one or more of the emission sources is
mislocated - for example, with an incorrect latitude or longitude that places a source too far
from the actual facility location and other modeled sources. This interpolated situation requires
remodeling to correct the location inaccuracy. If one or more source is mislocated (as
determined by reviewing the facility specific Source_risk.kmz or the run group-wide
AIIFacilityjsourceJocations.kmz file), perform a QA rerun for that facility using a corrected
Emissions Location file (and a corrected polygon vertex file and/or buoyant line parameters file,
if the misplaced source is configured as a polygon or buoyant line source).
In general, the image of each facility's emission sources and receptors on a Google Earth™
satellite map (i.e., the Source_risk.kmz file) is a powerful tool for QA checks of the inputs and
modeling parameters that HEM4 uses (see Figure 38 above as an example). It is best practice
to review each Source_risk.kmz file, even if all MIR and TOSHI values listed in the
Facility_max_risk_and_Hl.xlsx output occur at populated receptors and no values are
interpolated. Reviewing these map images allows you to determine if sources are mislocated
and require remodeling and if the surrounding populations are represented well enough by the
populated receptors. (If surrounding populations are not represented sufficiently by the
receptors, you can remodel with the addition of user-defined receptors placed near residences.)
This QA check of each Source_risk.kmz image is highly recommended. Even a QA check of a
kmz image that shows nothing amiss may prove useful. For example, if nothing looks amiss in
the Source_risk.kmz image, but the MIR and/or TOSHI values seem too high to be reasonable,
this may indicate an error in the emission amounts or pollutant names provided in the HAP
Emissions input file.
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Once you have performed all QA checks and remodeled any facilities, you are ready to run the
Risk Summary Reports, as described in Section 4.5. The Risk Summary Report programs need
as inputs the final Facility_max_risk_and_Hi.xisx and several facility-specific outputs (depending
on the HEM4 options you selected and which Risk Summary Reports you run). Therefore, do
not rename the HEM4 output files.
Modeling Skipped Facilities:
As noted in Section 4.9, if HEM4 is unable to model a facility or facilities due to errors in the
inputs, HEM4 will produce an Excel file entitled "Skipped Facilities" (SkippedJacilities.xslx) in
the run group's output subfolder. After you fix the errors in the inputs, you can use the list of
skipped facilities in column A of this output file to create a new Facility List Options file. Use the
new Facility List Options file to model the facilities as a group. Then copy the resulting skipped
facility output folders back into the directory/folder containing the original group's modeled
outputs. Next, append the resulting Facility Mask Risk and HI rows into the original Facility Max
Risk and HI file (described in Section 6.2.1). Do the same appending for the Facility Cancer
Risk Exposure file (described in Section 6.2.2) and the Facility TOSH I Exposure file (described
in Section 6.2.3). Finally, run the Risk Summary Reports on the full set of HEM4 outputs (as
described in Section 4.5 and Section 7).
Note that if you have remodeled any facilities, you should rerun the Demographic Assessment
module, discussed in Section 4.6, to ensure the demographic results are based on the
remodeled cancer risks, noncancer risks, and proximity statistics of the current domain.
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11. References
Census, 2022a. USA Census 2020 Redistricting Blocks. ArcGIS feature layer from Esri
containing block level 2020 Decennial Census data as reported by the U.S. Census Bureau with
attributes from the 2020 Public Law 94-171 (P.L. 94-171) tables. Available at
https://www.arcgis.com/home/item.htmI?id=b3642e91 b49548f5af772394b0537681. Updated
January 25, 2022. See also https://www.census.gov/programs-surveys/decennial-
census/about/rdo/summarv-files.html#P2 (Websites last accessed November 2022.)
Census, 2022b. 2020 American Community Survey. 2016-2020 ACS 5-year Estimates: Tract
and Block Group Files by State: https://www2.census.gov/programs-
survevs/acs/summarv file/2020/data/5 year entire sf/Tracts Block Groups Only.zip
prepared by the U.S. Census Bureau, Washington, DC, April 5, 2022. See also
https://www.census.gov/programs-survevs/acs/about.html. (Websites last accessed November
2022.)
EPA, 1986. User's Manual for the Human Exposure Model (HEM). EPA-450/5-86-001, U.S.
Environmental Protection Agency, Research Triangle Park, NC.
EPA, 1995. User's Guide for the Industrial Source Complex (ISC3) Dispersion Models (revised)
Volume II - Description of Model Algorithms. EPA-454/B-95-003b, U.S. Environmental
Protection Agency, Research Triangle Park, NC. https://www.epa.gov/scram/air-gualitv-
dispersion-modeling-alternative-models#isc3 (Website last accessed November 2022.)
EPA, 2005. Revision to the Guideline on Air Quality Models: Adoption of a Preferred General
Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions. Amendment to
Appendix W of 40 CFR Part 51. https://www.federalregister.goV/documents/2005/11/09/05-
21627/revision-to-the-guideline-on-air-gualitv-models-adoption-of-a-preferred-general-purpose-
flat-and (Website last accessed November 2022.)
EPA, 2018a. User's Guide for the AERMOD Terrain Preprocessor (AERMAP). EPA-454/B-18-
004, U.S. Environmental Protection Agency, Research Triangle Park, NC. April 2018.
https://www.epa.gov/scram/air-guality-dispersion-modeling-related-model-support-
prog ram s#aermap (Website last accessed November 2022.)
EPA, 2018b. AMTIC - Air Toxics Data Ambient Monitoring Archive, Version 2018. U.S.
Environmental Protection Agency. Research Triangle Park, NC.
https://www.epa.gov/amtic/amtic-air-toxics-data-ambient-monitoring-archive. See also Technical
Memorandum dated June 12, 2018, at
https://www3.epa.gov/ttn/amtic/files/toxdata/techmemo2018.pdf. (Website last accessed
November 2022.)
EPA, 2020. Risk Assessment and Modeling - Air Toxics Risk Assessment Reference Library,
U.S. Environmental Protection Agency, Research Triangle Park, NC.
http://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-
library. Website updated January 2, 2020. (Website last accessed November 2022.)
EPA, 2021a. Dose-Response Assessment for Assessing Health Risks Associated With
Exposure to Hazardous Air Pollutants. U.S. Environmental Protection Agency, Research
Triangle Park, NC. http://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-
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associated-exposure-hazardous-air-pollutants. See also "Toxicity Value Files" available for
download on the HEM Download webpage at https://www.epa.gov/fera/download-human-
exposure-model-hem. (Websites last accessed November 2022.)
EPA, 2021b. Total Risk Integrated Methodology (TRIM) - General. EPA's FERA (Fate,
Exposure, and Risk Analysis) webpage. U.S. Environmental Protection Agency.
http://www.epa.qov/fera/total-risk-inteqrated-methodoloqy-trim-qeneral. Website updated
January 26, 2021. (Website last accessed November 2022.)
EPA, 2022a User's Guide for the AMS/EPA Regulatory Model (AERMOD). EPA-454/B-22-007,
U.S. Environmental Protection Agency, Research Triangle Park, NC. June 2022.
https://qaftp.epa.qov/Air/aqmq/SCRAM/models/preferred/aermod/aermod userquide.pdf. See
also Model Change Bulletin 16 available at https://www.epa.gov/scram/air-quality-dispersion-
modelinq-preferred-and-recommended-models#aermod under "Model Documentation".
(Websites last accessed November 2022.)
EPA, 2022b. AERMOD Implementation Guide. EPA-454/B-22-008, U.S. Environmental
Protection Agency, Research Triangle Park, NC. June 2022.
https://gaftp.epa.gov/Air/agmg/SCRAM/models/preferred/aermod/aermod implementation guid
e.pdf. Or see https://www.epa.gov/scram/air-guality-dispersion-modeling-preferred-and-
recommended-models#aermod under "AERMOD Implementation Guide". (Websites last
accessed November 2022.)
EPA, 2022c. AirToxScreen Glossary of Terms. 2018 Air Toxics Screening Assessment. U.S.
Environmental Protection Agency. https://www.epa.gov/AirToxScreen/airtoxscreen-glossarv-
terms. Website updated October 3, 2022. (Website last accessed November 2022.)
EPA, 2022d. User's Guide for the AERMOD Meteorological Preprocessor (AERMET). EPA-
454/B-22-006, U.S. Environmental Protection Agency, Research Triangle Park, NC. June 2022.
https://www.epa.goV/scram/meteorological-processors-and-accessorv-programs#aermet.
(Website last accessed November 2022.)
EPA, 2022e. AERMOD Model Formulation, EPA-454/B-22-009
(https://gaftp.epa.gov/Air/agmg/SCRAM/models/preferred/aermod/aermod mfd.pdf).
AERMOD Model Evaluation, EPA-454/B-22-010
(https://gaftp.epa.gov/Air/agmg/SCRAM/models/preferred/aermod/aermod med.pdf). U.S.
Environmental Protection Agency, Research Triangle Park, NC. June 2022. See also
https://www.epa.gov/scram/air-gualitv-dispersion-modeling-preferred-and-recommended-
models#aermod under "Model Documentation". (Websites last accessed November 2022.)
EPA, 2022f. EJSCREEN: EPA's Environmental Justice Screening and Mapping Tool (Version
2.0). U.S. Environmental Protection Agency, https://www.epa.gov/eiscreen. Website updated
April 1, 2022. (Website last accessed November 2022.)
ERT, 1980. Buoyant line and point source (BLP) dispersion model user's guide. Prepared by
Environmental Research & Technology (ERT) for The Aluminum Association, Inc. Document P-
7304B, July 1980.
Federal Register, 2022. Urban Area Criteria for the 2020 Census-Final Criteria. 87 FR 16706
(24 March 2022). p. 16706. https://www.federalregister.gov/documents/2022/03/24/2Q22-
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06180/urban-area-criteria-for-the-2020-census-final-criteria. (Website last accessed November
2022.)
ICF International, 2015. The HAPEM User's Guide, Hazardous Air Pollutant Exposure Model,
Version 7. Prepared for the Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC. July 2015.
http://www.epa.gov/sites/production/files/2015-12/documents/hapem7usersquide.pdf.
Additional HAPEM documentation available at http://www.epa.gov/fera/human-exposure-
modeling-hazardous-air-pollutant-exposure-model-hapem (Websites last accessed November
2022.)
Jindal, M. and D. Heinold, 1991. Development of particulate scavenging coefficients to model
wet deposition from industrial combustion sources. Paper 91-59.7, 84th Annual Meeting -
Exhibition of AWMA, Vancouver, BC, June 16-21, 1991.
NCES, 2022a. CCD Public School data 2021-2022 school year, Institute of Education Sciences,
National Center for Education Statistics (NCES) of the U.S. Department of Education,
Alexandria, VA. http://nces.ed.gov/ccd/schoolsearch/ (Website last accessed November 2022.)
NCES, 2022b. PSS Private School Universe Survey data for the 2019-2020 school year,
Institute of Education Sciences, National Center for Education Statistics (NCES) of the U.S.
Department of Education, Alexandria, VA. http://nces.ed.gov/survevs/pss/privateschoolsearch/
(Website last accessed November 2022.)
Sander, R., 2015: Compilation of Henry's law constants (version 4.0) for water as solvent,
Atmos. Chem. Phys., 15, 4399-4981, doi:10.5194/acp-15-4399-2015, 2015. http://www.atmos-
chem-phys.net/15/4399/2015/ (Website last accessed November 2022.)
Schulman, L.L., D.G. Strimaitis, and J.S. Scire, 2000. Development and Evaluation of the
PRIME Plume Rise and Building Downwash Model. Journal of the Air & Waste
Management Association, Vol. 50, pp. 378-390.
Scire, J.S., D.G. Strimaitis and R.J. Yamartino, 1990. Model formulation and user's guide for the
CALPUFF dispersion model. Sigma Research Corp., Concord, MA.
USGS, 2022. USGS Seamless Data Warehouse. U.S. Department of the Interior - U.S.
Geological Survey, Washington, DC. https://apps.nationalmap.gov/viewer/ (Website last
accessed November 2022.)
Wesely, M.L, P.V. Doskey, and J.D. Shannon, 2002. Deposition Parameterizations for the
Industrial Source Complex (ISC3) Model. ANL/ER/TR-01/003, Argonne National Laboratory,
June 2002. Work sponsored by the U.S. Department of Energy, Office of Science, Office of
Biological and Environmental Research, Environmental Sciences Division and partially by the
U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards.
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12. Appendix A: Sample HEM4 Output Files
This appendix contains examples (some abbreviated to fit) of the facility-specific and run group HEM4 output files. Sample risk summary reports are
provided in Section 7. Sample results for Demographic Assessments are provided in Section 8.
A
B
C
D
E
F
G
H
1 ! J
K
L
M
N
0
P
Q
Parameter
Value
Value
rounded
Value
scientific
notation
Population
Distance
(m)
Angle
(from
north)
Elevation
(m)
Hill
height
(m)
FIPs
Block
UTM
easting
UTM
northing
Latitude
Longitude
Receptor type
Notes
Cancer risk
0.00061
0.0006 6.1e-04
3
491.8557
217.7
89.7
89.7
*37063
*9801001074
690605
3974816
35.89908
-78.888
Census block
Discrete
Respiratory HI
0.67705
0.7^>.8e-01
0
459.4366
233.9
90.5
90.5
UOOOO
OOOOURCPT1
690535
3974934
35.90016
-78.88875
User receptor
Discrete
Liver HI
0.18167
0.2rl.8e-01
0
459.4366
233.9
90.5
90.5
UOOOO
OOOOURCPT1
690535
3974934
35.90016
-78.88875
User receptor
Discrete
Neurological HI
0.08825
0.09 "8.8e-02
0
459.4366
233.9
90.5
90.5
UOOOO
OOOOURCPT1
690535
3974934
35.90016
-78.88875
User receptor
Discrete
Developmental HI
8.99698
sVoe+OO
3
491.8557
217.7
89.7
89.7
*37063
'9801001074
690605
3974816
35.89908
-78.888
Census block
Discrete
Reproductive HI
0.0747
0.07"7.5e-02
0
459.4366
233.9
90.5
90.5
UOOOO
OOOOURCPT1
690535
3974934
35.90016
-78.88875
User receptor
Discrete
Kidney HI
1.47967
1 l.Se+OO
3
491.8557
217.7
89.7
89.7
*37063
*9801001074
690605
3974816
35.89908
-78.888
Census block
Discrete
Ocular HI
0
0
0
0
0
0
0
0
0
0
0
0
Endocrine HI
2.3E-06
2E-06
r2.3e-06
219
1124.139
191.4
85.8
85.8
*37063
*0020272057
690684
3974103
35.89265
-78.8873
Census block
Discrete
Hematological HI
0.00092
0.0009 9.2e-04
3
491.8557
217.7
89.7
89.7
*37063
*9801001074
690605
3974816
35.89908
-78.888
Census block
Discrete
Immunological HI
0.06719
0.07^.7e-02
0
459.4366
233.9
90.5
90.5
UOOOO
OOOOURCPT1
690535
3974934
35.90016
-78.88875
User receptor
Discrete
Skeletal HI
0.0008
0.0008 ^.0e-04
0
459.4366
233.9
90.5
90.5
UOOOO
OOOOURCPT1
690535
3974934
35.90016
-78.88875
User receptor
Discrete
Spleen HI
0
0
0
0
0
0
0
0
0
0
0
0
Thyroid HI
0
0
0
0
0
0
0
0
0
0
0
0
Whole body HI
0
0
0
0
0
0
0
0
0
0
0
0
Figure 39. Sample Maximum Individual Risk HEM4 Output (facility-specific)
A
B
C D
E
F
G
H
1
J
K
L
M
N
0
P
Parameter
Value
Value_ Value_
rnd sci
Population
Distance
(in meters)
Angle
(from
north)
Elevation
(in
meters)
Hill Height
(in meters)
Fips
Block
Utm_east
Utmnorth
Latitude
Longitude
Rec_type
Cancer risk
0.000783
0.0008 "7.8e-04
0
565
67.5
92
92
691428
3975421
35.90438
-78.878745
Polar grid
Respiratory HI
0.677049
0.7 ^>.8e-01
0
459.436612
233.85
90.5
90.5
UOOOO
0000URCPT1
690535
3974934
35.90016
-78.88875
User receptor
Liver HI
0.277505
0.3 ^.8e-01
0
565
90
92
92
691471
3975205
35.90242
-78.878321
Polar grid
Neurological HI
0.08825
0.09l8.8e-02
0
459.436612
233.85
90.5
90,5
UOOOO
0000URCPT1
690535
3974934
35.90016
-78.88875
User receptor
Developmental HI
11.47101
10rl.le+01
0
565
67.5
92
92
691428
3975421
35.90438
-78.878745
Polar grid
Reproductive HI
0.0747
0.07*7.5e-02
0
459.436612
233.85
90.5
90.5
UOOOO
0000URCPT1
690535
3974934
35.90016
-78.88875
User receptor
Kidney HI
1.974576
2*2.06+00
0
565
67.5
92
92
691428
3975421
35.90438
-78.878745
Polar grid
Ocular HI
0
0 0
0
0
0
0
0
0
0
0
0
Endorcrine HI
4.2E-06
4E-06l4.2e-06
0
565
90
92
92
691471
3975205
35.90242
-78.878321
Polar grid
Hematological HI
0.001641
0.002 r1.6e-03
0
565
90
92
92
691471
3975205
35.90242
-78.878321
Polar grid
Immunological HI
0.067187
0.07r6.7e-02
0
459.436612
233.85
90.5
90.5
UOOOO
0000URCPT1
690535
3974934
35.90016
-78.88875
User receptor
Skeletal HI
0.000797
0.0008l8.0e-04
0
459.436612
233.85
90.5
90.5
UOOOO
0000URCPT1
690535
3974934
35.90016
-78.88875
User receptor
Spleen HI
0
0 0
0
0
0
0
0
0
0
0
0
Thyroid HI
0
0 0
0
0
0
0
0
0
0
0
0
Whole body HI
0
0 0
0
0
0
0
0
0
0
0
0
Figure 40. Sample Maximum Offsite Risk HEM4 Output (facility-specific)
HEM4 User's Guide
Page 149
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A
B
c
D
E
F
G
H
1
K
L
Site type
Parameter
Source ID
Pollutant
Emission
type
Value
Value
rounded
Cone
(ug/m3)
Cone
rounded
(ug/mJ)
Emissions
(tpy)
URE
l/(ug/ml)
RFc
(mg/m3)
Max indiv risk
Cancer risk
CTOOOOOl
All modeled pollutants
NA
1.8SE-09
2E-09
6.95E-10
7E-10
2.456E-07
0
0
Max indiv risk
Cancer risk
CTOOOOOl
2,3,4,7,8-pentachlorodibenzofuran
C
1.04E-09
1E-09
1.05E-10
1E-10
3.7E-08
9.9
1.3E-07
Max indiv risk
Cancer risk
CTOOOOOl
1,2,3,7,8-pentachlorodibenzo-p-dioxin
C
2.25E-10
2E-10
6.82E-12
7E-12
2.41E-09
33
4E-08
Max indiv risk
Cancer risk
Total
All pollutants all sources
NA
0.000611
0.0006
1.964495
2
39.355593
0
0
Max indiv risk
Cancer risk
Total by pollutant all sources
arsenic compounds
NA
0.000579
0.0006
0.134549
0.1
1.06
0
0
Max indiv risk
Cancer risk
Total by pollutant all sources
cadmium compounds
NA
2.61E-05
0.00003
0.014526
0.01
0.2
0
0
Max offsite impact
Cancer risk
CTOOOOOl
All modeled pollutants
NA
6.26E-09
6E-09
2.31E-09
2E-09
2.456E-07
0
0
Max offsite impact
Cancer risk
CTOOOOOl
2,3,4,7,8-pentachlorodibenzofuran
C
3.44E-09
3E-09
3.48E-10
3E-10
3.7E-08
9.9
1.3E-07
Max offsite impact
Cancer risk
Total
All pollutants all sources
NA
0.000783
0.0008
2.157177
2
39.355593
0
0
Max offsite impact
Cancer risk
Total by pollutant all sources
arsenic compounds
NA
0.000739
0.0007
0.171925
0.2
1.06
0
0
Max offsite impact
Cancer risk
Total by pollutant all sources
cadmium compounds
NA
3.54E-05
0.00004
0.019652
0.02
0.2
0
0
Max indiv risk
Developmental HI
CTOOOOOl
2,3,4,7,8-pentachlorodibenzofuran
C
0
0
1.05E-10
1E-10
3.7E-08
9.9
1.3E-07
Max indiv risk
Developmental HI
CTOOOOOl
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
C
0
0
5.15E-12
5E-12
1.82E-09
3.3
4E-07
Max indiv risk
Developmental HI
CTOOOOOl
All modeled pollutants
NA
0
0
6.95E-10
7E-10
2.456E-07
0
0
Max indiv risk
Developmental HI
Total
All pollutants all sources
NA
8.995981
9
1.964495
2
39.355593
0
0
Max indiv risk
Developmental HI
Total by pollutant all sources
arsenic compounds
NA
8.969901
9
0.134549
0.1
1.06
0
0
Max indiv risk
Developmental HI
Total by pollutant all sources
trichloroethylene
NA
0.027078
0.03
0.054157
0.05
0.24
0
0
Max offsite impact
Developmental HI
CTOOOOOl
2,3,4,7,8-pentachlorodibenzofuran
C
0
0
3.48E-10
3E-10
3.7E-08
9.9
1.3E-07
Max offsite impact
Developmental HI
CTOOOOOl
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
C
0
0
1.71E-11
2E-11
1.82E-09
3.3
4E-07
Max offsite impact
Developmental HI
CTOOOOOl
All modeled pollutants
NA
0
0
2.31E-09
2E-09
2.456E-07
0
0
Max offsite impact
Developmental HI
Total
All pollutants all sources
NA
11.47101
10
2.157177
2
39.355593
0
0
Max offsite impact
Developmental HI
Total by pollutant all sources
arsenic compounds
NA
11.46165
10
0.171925
0.2
1.06
0
0
Max offsite impact
Developmental HI
Total by pollutant all sources
trichloroethylene
NA
0.009358
0.009
0.018716
0.02
0.24
0
0
Figure 41. Sample Risk Breakdown HEM4 Output (facility-specific, abbreviated)
Note: To capture the full extent of the kind of information provided in this output, the above sample Risk Breakdown file includes missing rows as
indicated by the ellipses (...) for risk by individual source and pollutant, for risk by individual source and all pollutants combined, and for risk by
individual pollutant and all sources combined. The above sample file also depicts only one of the 14 TOSHIs (Developmental HI) included in the
actual file. The file includes the above breakdown for cancer risk and for all 14 (noncancer) TOSHIs, for both populated receptors ("Max indiv risk")
and for any receptor whether populated or unpopulated ("Max offsite impact").
HEM4 User's Guide
Page 150
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A
B
C
D
E
F
G
H |
i
J !
K
L
M
N
O
Latitude
Longitude
Overlap
Elevation
FIPs
Block
X
Y
Hill
Population
MIR
Respiratory HI
Liver HI
Neurological HI
36.09438
-79.38606
N
181.3
37001
203004018
645293
3995623
181.3
66
3.86E-07
0.000246666
3.85E-05
1.43 E-05
...
36.09624
-79.37883
N
173.5
37001
203005002
645941
3995840
173.5
3
3.89E-07
0.000248244
3.87E-05
1.43 E-05
...
36.09475
-79.38259
N
178.3
37001
203005005
645605
3995669
178.3
3
3.88E-07
0.000247772
3.86E-05
1.43E-05
...
36.09726
-79.38345
N
173.7
37001
203005007
645523
3995946
173.7
55
3.85E-07
0.000245794
3.83E-05
1.42E-05
...
36.09843
-79.3833
N
171.2
37001
203005008
645534
3996075
171.2
35
3.84E-07
0.00024509
3.82E-05
1.42E-05
36.08863
-79.3819
N
174.5
37001
203005010
645678
3994991
174.5
57
3.94E-07
0.0002521
3.93E-05
1.46E-05
...
36.092
-79.38435
N
185.3
37001
203005011
645452
3995361
185.3
2
3.B9E-07
0.000248895
3.88E-05
1.44E-05
...
36.09427
-79.38459
N
179.3
37001
203005012
645426
3995613
179.3
13
3.87E-07
0.000247309
3.86E-05
1.43E-05
...
36.09397
-79.38536
N
183.4
37001
203005013
645357
3995577
183.4
2
3.87E-07
0.000247214
3.86E-05
1.43 E-05
...
36.09193
-79.38555
N
185.4
37001
203005014
645343
3995351
185.4
13
3.88E-07
0.000248466
3.88E-05
1.44E-05
36.09238
-79.38517
N
184.4
37001
203005015
645377
3995402
184.4
10
3.88E-07
0.000248321
3.87E-05
1.44E-05
...
36.09002
-79.38582
N
181
37001
203005017
645323
3995140
181
14
3.90E-07
0.000249604
3.90E-05
1.44E-05
...
36.08975
-79.38621
N
178
37001
203005018
645288
3995109
178
11
3.90E-07
0.000249626
3.90E-05
1.44E-05
...
36.08996
-79.3878
N
183.5
37001
203005019
645144
3995129
183.5
19
3.89E-07
0.000248859
3.89E-05
1.44E-05
...
36.0873
-79.38689
N
183.1
37001
203005039
645232
3994836
183.1
36
3.91E-07
0.000250958
3.92E-05
1.45E-05
...
36.08769
-79.3852
N
181.4
37001
203005040
645383
3994881
181.4
37
3.92E-07
0.00025139
3.93E-05
1.46E-05
...
36.08671
-79.3833
N
174.7
37001
203005042
645556
3994776
174.7
24
3.94E-07
0.000252807
3.95E-05
1.46E-05
...
36.08729
-79.38956
N
189.6
37001
203005046
644991
3994831
189.6
82
3.90E-07
0.000249883
3.90E-05
1.45E-05
...
36.08615
-79.38586
N
181.1
37001
203005048
645326
3994709
181.1
26
3.93E-07
0.000252133
3.94E-05
1.46E-05
...
36.08476
-79.38295
N
171.2
37001
203005050
645591
3994560
171.2
12
3.96E-07
0.000254249
3.97E-05
1.47E-05
...
36.08756
-79.37782
N
169.4
37001
203005052
646047
3994878
169.4
24
3.97E-07
0.000254489
3.97E-05
1.47E-05
...
36.0909
-79.37605
N
166.8
37001
203005053
646200
3995251
166.8
99
3.95E-07
0.000252943
3.94E-05
1.46E-05
...
36.0907
-79.37304
N
156.3
37001
203005054
646472
3995234
156.3
19
3.98E-07
0.000254301
3.96E-05
1.47E-05
...
36.09164
-79.37145
N
157.3
37001
203005056
646614
3995340
157.3
8
3.98E-07
0.000254305
3.96E-05
1.47E-05
...
36.09327
-79.37612
N
166
37001
203005057
646190
3995514
166
24
3.93E-07
0.000251308
3.92E-05
1.45 E-05
...
36.0889
-79.37362
N
154.5
37001
203005061
646424
3995033
154.5
46
3.99E-07
0.00025531
3.98E-05
1.48E-05
...
36.08887
-79.371
N
157
37001
203005062
646659
3995034
157
16
4.01E-07
0.000256407
4.00E-05
1.48E-05
...
36.08803
-79.37061
N
159.1
37001
203005063
646696
3994941
159.1
17
4.02E-07
0.000257159
4.01E-05
1.49E-05
...
Figure 42. Sample Block Summary i
Chronic HEM4 Output (facility-specific, abbreviated)
Note: The Block Summary Chronic file is large because it includes the cancer risk ("MIR") and all 14 TOSIHIs for every modeled block or alternate
receptor. The above sample file includes ellipses (...) as it shows only a partial list of rows and only 3 of the 14 TOSHI's (Respiratory HI, Liver Hi
and Neurological HI). In addition, the actual file includes a column indicating whether the concentration at each receptor was discretely modeled or
interpolated, as well as a final Receptor Type column (not shown above), which indicates C for census block, P for populated user-defined or
alternate receptor, B for boundary receptor, M for monitor, or S for school.
HEM4 User's Guide
Page 151
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Latitude
Longitude
Overlap
Elevation
(m)
X
Y
Hill
MIR
Respiratory
HI
Liver HI
Neurological
HI
Developmental
HI
Distance
(m)
Angle
(from
north)
Sector
35.90762
-78,88444
N
92
690906
3975770
92
0.000276
0.16267133
0.06719334
0.022959781
4.061680358
565
0
1
35.91028
-78.88437
N
85
690906
3976065
85
0.000163
0.08834714
0.03991907
0.012732447
2.405209191
860
0
1
35.91433
-78.88426
N
86
690906
3976515
86
9.86E-05
0.05006334
0.02351642
0.007284751
1.449323028
1310
0
1
35.92046
-78.8841
N
86
690906
3977195
86
5.67E-05
0.02748919
0.01321489
0.004022705
0.830353561
1990
0
1
35.92956
-78.88386
N
98
690906
3978205
98
3.29E-05
0.01497071
0.00728229
0.002192643
0.476986257
3000
0
1
35.94127
-78.88355
N
108
690906
3979505
108
1.98E-05
0.00851103
0.00414235
0.001235919
0.283698446
4300
0
1
35.95749
-78.88311
N
128
690906
3981305
128
1.19E-05
0.00487219
0.00221982
0.000669144
0.164677271
6100
0
1
35.93092
-78.88249
N
128
690906
3983905
128
7.18E-06
0.00297086
0.00127924
0.000389865
0.098200187
8700
0
1
36.01425
-78.88159
N
126
690906
3987605
126
4.30E-06
0.00182397
0.00072968
0.000225519
0.057813435
12400
0
1
36.0611
-78.88034
N
134
690906
3992805
134
2.61E-06
0.0011715
0.00040331
0.000128775
0.03383493
17600
0
1
36.12777
-78.87855
N
174
690906
4000205
174
1.60E-06
0.00087183
0.00020231
7.08E-05
0.018804954
25000
0
1
36.22237
-78.87599
N
234
690906
4010705
234
9.40E-07
0.00061899
9.59 E-05
3.64E-05
0.00985544
35500
0
1
36.35301
-78.87245
N
207
690906
4025205
207
6.14E-07
0.00039616
6.43E-05
2.42E-05
0.00651898
50000
0
1
35.90719
-78.88206
N
92
691122
3975727
92
0.000317
0.20423035
0.08411586
0.028758088
4.672317905
565
22.5
2
35.90963
-78.88074
N
92
691235
3976000
92
0.000192
0.10610333
0.04725769
0.015216162
2.82876806
860
22.5
2
35.91334
-78.87874
N
86
691407
3976415
86
0.000106
0.05416447
0.02491204
0.007832226
1.5593033
1310
22.5
2
35.91895
-78.8757
N
86
691668
3977044
86
5.91E-05
0.02814812
0.01306979
0.004078483
0.86713832
1990
22.5
2
35.92728
-78.8712
N
98
692054
3977977
98
3.20E-05
0.01471825
0.00679289
0.002115014
0.466186678
3000
22.5
2
35.938
-78.86539
N
115
692552
3979178
115
1.81E-05
0.00825512
0.00360303
0.001123976
0.256202648
4300
22.5
2
35.95285
-78.85736
N
126
693240
3980841
126
1.10E-05
0.00516917
0.00198365
0.000625377
0.149211565
6100
22.5
2
35.9743
-78.84575
N
126
694235
3983243
126
6.79E-06
0.00327005
0.00114822
0.000363808
0.089533991
8700
22.5
2
36.00481
-78.82921
N
122
695651
3986661
122
4.11E-06
0.00201365
0.00066383
0.000211097
0.053338866
12400
22.5
2
36.04769
-78.80594
N
119
697641
3991465
119
2.48E-06
0.00123679
0.00037985
0.000121813
0.031601403
17600
22.5
2
36.1087
-78.77279
N
128
700473
3998302
128
1.51E-06
0.00079302
0.00020903
6.91E-05
0.0185 3 6631
25000
22.5
2
36.19526
-78.72566
N
185
704491
4008003
185
9.14E-07
0.00055697
0.00010008
3.60E-05
0.010134297
35500
22.5
2
36.31474
-78.66039
N
161
710040
4021399
161
5.74E-07
0.0003369
6.18E-05
2.22E-05
0.006426578
50000
22.5
2
35.90606
-78.88005
N
92
691306
3975605
92
0.000421
0.26615504
0.10388434
0.036941868
6.177728359
565
45
3
35.90789
-78.8777
N
92
691514
3975813
92
0.000272
0.16583271
0.06683816
0.023219576
3.998420365
860
45
3
...
Figure 43. Sample Ring Summary Chronic HEM4 Output (facility-specific, abbreviated)
Note: The Ring Summary Chronic file includes the cancer risk ("MIR") and all 14 TOSHIs for every modeled polar receptor. The above sample file
includes ellipses (...) as it shows only a partial list of rows and only 4 of the 14 TOSHI's (Respiratory HI, Liver HI, Neurological HI, and
Developmental HI). The final 3 columns shown (above) cycle through polar receptor ring distances over each angle from north (or sector) for a total
of 16 angles/sectors by default, unless you indicate a different number of radials in your Facility List Options file.
HEM4 User's Guide
Page 152
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^ Google Earth Pro
File Edit View Jools Add Help
~ Search
Get Directions
T Places
~ Lavers
^ Primary Database
Q Announcements
* ' V Borders and Labels
; ® Q Places
* 9 Photos
' IS Roads
~ B 3D Buildings
~ 0 Weather
~ # Gallery
* D More
' "terrain
~ ¦ My Places
* ^ "Si Temporary Places
~ ' -vi srcmao
~ * Q Emission sources
~ ' ED Domain center
~ ' ED MIR
~ ' ED User receptor cancer risk
~ ' ED User receptor TOSHI
~ ' CD Census block cancer risk
~ ' ED Census block TOSHI
~ J O Polar receptor cancer risk
~ ' ED Polar TOSHI
Figure 44. Sample Source Risk KMZ Google Earth™ Image (facility-specific)
HEM4 User's Guide
Page 153
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A
B
C
D
E
Source ID
Pollutant
Emission
type
Incidence
Incidence
rounded
Total
All modeled pollutants
C
0.047682
0.048
CT000001
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
C
1.513E-09
1.5E-09
CTOOOOOl
1,2,3,4,6,7,8-heptachlorodibenzofuran
C
6.008E-09
6E-09
CT000001
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
C
1.23SE-08
1.2E-08
CTOOOOOl
1,2,3,4,7,8-hexachlorodibenzofuran
C
1.44E-07
1.4E-07
CTOOOOOl
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
C
1.317E-0S
1.3E-08
CTOOOOOl
1,2,3,6,7,8-hexachlorodibenzofuran
C
1.296E-07
1.3E-07
CTOOOOOl
1,2,3,7,8,9-hexachlorodibenzofuran
C
2.316E-08
2.3E-08
CTOOOOOl
1,2,3,7,8-pentachlorodibenzo-p-dioxin
C
1.744E-07
1.7E-07
Total
1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin
C
5.041E-1.0
5E-10
Total
1,2,3,4,6,7,8,9-octachlorodibenzofuran
C
5.209E-11
5.2E-11
Total
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
C
8.953E-09
9E-09
Total
1,2,3,4,6,7,8-heptachlorodibenzofuran
C
3.556E-0S
3.6E-08
CTOOOOOl
All modeled pollutants
c
1.462E-06
0.0000015
CV000001
All modeled pollutants
C
3.309E-06
0.0000033
FU000001
All modeled pollutants
C
0.0001703
0.00017
|hvoooooi
All modeled pollutants
C
3.8SE-06
0.0000039
MSOOOOOl
All modeled pollutants
C
5.983E-06
0.000006
RVOOOOOl
All modeled pollutants
C
0,0051644
0.0052
RV000002
All modeled pollutants
C
3.079E-06
0.0000031
RV000003
All modeled pollutants
C
1.772E-06
0.0000018
RV000004
All modeled pollutants
C
0.0069082
0.0069
RWOOOOOl
All modeled pollutants
C
1.116E-05
0.000011
SROOOOOl
All modeled pollutants
C
0.0354084
0,035
Figure 45. Sample Incidence HEM4 Output (facility-specific, abbreviated)
Note: The sample Incidence file above includes ellipses (...) for some rows because the file is too long to depict fully. The above rows indicate the
kinds of information provided in this file.
HEM4 User's Guide
Page 154
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A
B
1
Level
Population
2
Greater than or equal to 1 in 1,000
0
3
Greater than or equal to 1 in 10,000
435
4
Greater than or equal to 1 in 20,000
2119
5
Greater than or equal to 1 in 100,000
48998
6
Greater than or equal to 1 in 1,000,000
800221
7 |
Greater than or equal to 1 in 10,000,000
1545731
Figure 46. Sample Cancer Risk Exposure HEM4 Output (facility-specific)
A
B
C
D
E
F
G
1
J
K
L
M
N
0
Level
Respiratory
HI
Liver
HI
Neurological
HI
Developmental
HI
Reproductive
HI
Kidney
HI
Ocular
HI
Endocrine
HI
Hematological
HI
Immunological
HI
Skeletal
HI
Spleen
HI
Thyroid
HI
Whole
body HI
Greater than 100
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Greater than 50
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Greaterthan 10
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Greaterthan 1.0
0
0
0
435
0
0
0
0
0
0
0
0
0
0
Greaterthan 0.5
0
0
0
3065
0
12
0
0
0
0
0
0
0
0
Greaterthan 0.2
12
0
0
19289
0
432
0
0
0
0
0
0
0
0
F
igure 47.
Sample Noncancer Risk Exposure HEM4 Output (facility-specific)
HEM4 User's Guide
Page 155
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A
B
C
D
E
F
G
H
1
J
K
L
M
FIPs
Block
Latitude
Longitude
Source ID
Emission
type
Pollutant
Cone
(ug/m3)
Elevation
(m)
Dry
deposition
(g/m2/yr)
Wet
deposition
(g/m2/yr)
Population
Overlap
17063
1022007
41.459428
-88.264967
CT000001
P
2,3,4,7,8-pentachlorodibeniofuran
l.OOE-11
189.2
2.15 E-12
2.46E-12
11
N
17063
1022007
41.459428
-88.264967
CT000001
P
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
6.50E-13
189.2
1.40E-13
1.60E-13
11
N
17063
1022007
41.459428
-88.264967
CT000001
P
1,2,3,7,8-pentachlorodibenzo-p-dioxin
6.93E-13
189.2
1.49 E-13
1.70E-13
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzofuran
6.25E-12
189.2
1.34E-12
1.53E-12
11
N
17063
1022007
41.459428
-88.264967
CT000001
P
1,2,3,4,7,8-hexachlorodibenzofuran
6.97E-12
189.2
1.49E-12
1.71E-12
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
1,2,3,7,8,9-hexachlorodibenzofuran
1.11E-12
189.2
2.38E-13
2.72E-13
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
2,3,4,6,7,8-hexachlorodibenzofuran
4.56E-12
189.2
9.78E-13
1.12E-12
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzofuran
2.95 E-12
189.2
6.32E-13
7.24E-13
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
5.92E-13
189.2
1.27E-13
1.45E-13
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzofuran
6.37E-12
189.2
1.37E-12
1.56E-12
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
indeno[l,2,3-c,d]pyrene
4.06E-11
189.2
8.70E-12
9.96E-12
11
N
17063
1022007
41.459428
-88.264967
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
7.57E-13
189.2
1.62E-13
1.86E-13
11
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
2,3,4,7,8-pentachlorodibenzofuran
9.21E-12
189.1
2.00E-12
2.27E-12
16
N
17063
102200S
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
5.97E-13
189.1
1.29E-13
1.47E-13
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzo-p-dioxin
6.36E-13
189.1
1.38E-13
1.57E-13
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzofuran
5.73E-12
189.1
1.24E-12
1.41E-12
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzofuran
6.39E-12
189.1
1.39E-12
1.58E-12
16
W
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,7,8,9-hexachlorodibenzofuran
1.02E-12
189.1
2.21E-13
2.51E-13
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
2,3,4,6,7,8-hexachlorodibenzofuran
4.18E-12
189.1
9.07E-13
1.03E-12
16
M
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzofuran
2.71E-12
189.1
5.87E-13
6.68E-13
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
5.43E-13
189.1
1.18E-13
1.34E-13
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzofuran
5.84E-12
189.1
1.27E-12
1.44E-12
16
N
17063
1022008
41.4587614
-88.2642443
CTOOOOOl
P
indeno[lr2,3-c,d]pyrene
3.72E-11
189.1
8.08E-12
9.19E-12
16
N
F
igure 48.
Sample All Inner Receptors HEM4 Output (facility-specific, abbreviated)
Notes:
• The Dry deposition and Wet deposition flux units will be in g/m2/yr if you modeled with annual averages, or in g/m2 if you modeled with
period averages. These columns will be blank if you did not choose to model deposition in your Facility List Options file.
• Receptor Type (not shown above) is also provided in this output: C for census block, P for populated user-defined or alternate receptor, B for
boundary receptor, M for monitor, S for school
HEM4 User's Guide
Page 156
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A
E
c
D
E
F
G
H
1
K
Emission
Cone
Elevation
FIPs
Block
Latitude
Longitude
Source ID
type
Pollutant
(Hg/m3)
(m)
Population
Overlap
17093
S907002213
41.5097585
-88.271948
CT000001
P
2,3,4,7,8-pentachlorodibenzofuran
8.50E-12
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
5.51E-13
177.7
5
N
17093
8907002213
41.5097585
-SS. 271948
CT000001
P
1,2,3,7,8-pentachlorodibenzo-p-dioxin
5.87E-13
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzofuran
5.29E-12
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzofuran
5.90E-12
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,7,8,9-hexachlorodibenzofuran
9.40E-13
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
2,3,4,6,7,8-hexachlorodibenzofuran
3.86E-12
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzofuran
2.50E-12
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
5.01E-13
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzofuran
5.39E-12
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
indeno[l,2,3-c,d]pyrene
3.44E-11
177.7
5
N
17093
8907002213
41.5097585
-88.271948
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
6.41E-13
177.7
5
N
17093
8907002186
41.4973643
-88,294909
CTOOOOOl
P
2,3,4,7,8-pentachlorodibenzofuran
5.56E-12
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
3.61E-13
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzo-p-dioxin
3.84E-13
173.3
11
N
17093
8907002186
41.4973643
-88,294909
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzofuran
3.46E-12
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzofuran
3.86E-12
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,7,8,9-hexachlorodibenzofuran
6.15E-13
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
2,3,4,6,7,8-hexachlorodibenzofuran
2.53E-12
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzofuran
1.63E-12
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
3.28E-13
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzofuran
3.53E-12
173.3
11
N
17093
8907002186
41.4973643
-88.294909
CTOOOOOl
P
indeno[l,2,3-c,d]pyrene
2.25E-11
173.3
11
N
F
:igure 49. Sample All Outer
Receptors HEM4 Output file (facility-specific, abbreviated)
Notes:
• The All Outer Receptor file tends to be a very large file, especially if you chose to model with the default maximum distance for your
modeling domain of 50 kilometers and a default (discrete / inner) modeling distance of 3 kilometers. Deposition flux is not calculated for the
outer modeling domain represented by the All Outer Receptor file, so these columns will not appear in this file even if you chose to model
deposition.
• Receptor Type (not shown above) is also provided in this output: C for census block, P for populated user-defined or alternate receptor, B for
boundary receptor, M for monitor, S for school
HEM4 User's Guide
Page 157
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A
8
C
D
E
F
G
H
1
J
K
L
M
N
Source ID
Emission
type
Pollutant
Cone
(ug/mJ)
Distance
(m)
Angle
(from
north)
Sector
Ring
number
Elevation
(m)
Latitude
Longitude
Overlap
Wet
deposition
(g/m2/yr)
Dry
deposition
(g/m2/yr)
|CT000001
P
2,3,4,7,8-p e nta ch I o rod i b e nzof u ra n
1.61E-11
100
0
196
41.49089612
-88.27001629
N
2.21E-12
3.69E-12
j CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
1.04E-12
100
0
196
41.49089612
-88.27001629
N
1.43E-13
2.39 E-13
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzo-p-dioxin
1.11E-12
100
0
196
41.49089612
-88.27001629
N
1.52E-13
2.55E-13
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzofu ran
l.OOE-11
100
0
196
41.49089612
-88.27001629
N
1.37E-12
2.30E-12
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzofurari
1.12E-11
100
0
196
41.49089612
-88.27001629
N
1.53E-12
2.56E-12
CTOOOOOl
P
1,2,3,7,8,9-hexachlorodibenzofuran
1.78E-12
100
0
196
41.49089612
-88.27001629
N
2.44E-13
4.08E-13
CTOOOOOl
P
2,3,4,6,7,8-hexachlorodibenzofuran
7.31E-12
100
0
196
41.49089612
-88.27001629
N
"1.00E-12
1.68E-12
]CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzofuran
4.73E-12
100
0
196
41.49089612
-88.27001629
N
6.48E-13
1.08E-12
CTOOOOOl
P
1,2,3,4,7, S-hexachlorodibertzo-p-dioxin
9.49 E-13
100
0
196
41.49089612
-88.27001629
N
1.30E-13
2.18E-13
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzofuran
1.02E-11
100
0
196
41.49089612
-88.27001629
N
1.40E-12
2.34E-12
CTOOOOOl
P
indeno[l,2,3-c,d]pyrene
6.51E-11
100
0
196
41.49089612
-88.27001629
N
8.9 IE-12
1.49E-11
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxiri
1.21E-12
100
0
196
41.49089612
-88.27001629
N
1.66E-13
2.79E-13
CTOOOOOl
P
2,3,4,7,8-pentachlorodibenzofuran
1.41E-11
500
0
2
196
41.49449822
-88.27008666
N
4.31E-12
3.08E-12
CTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
9.17E-13
500
0
2
196
41.49449822
-88.27008666
N
2.79E-13
2.00E-13
]CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzo-p-dioxin
9.76E-13
500
0
2
196
41.49449822
-88.27008666
N
2.97E-13
2.13E-13
jCTOOOOOl
P
1,2,3,6,7,8-hexachlorodibenzofuran
8.80E-12
500
0
2
196
41.49449822
-88.27008666
N
2.68E-12
1.92E-12
|CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzofu ran
9.81E-12
500
0
2
196
41.49449822
-88.27008666
N
2.99E-12
2.14E-12
CTOOOOOl
P
1,2,3,7,8,9-hexachlorodibenzofuran
1.56E-12
500
0
2
196
41.49449822
-88.27008666
N
4.76E-13
3.41E-13
CTOOOOOl
P
2,3,4,6,7,8-hexachlorodibenzofu ran
6.42E-12
500
0
2
196
41.49449822
-88.27008666
N
1.96E-12
1.40E-12
CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzofuran
4.15E-12
500
0
2
196
41.49449822
-88.27008666
N
1.27E-12
9.06E-13
CTOOOOOl
P
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
8.34E-13
500
0
2
196
41.49449822
-88.27008666
N
2.54E-13
1.82E-13
CTOOOOOl
P
1,2,3,7,8-pentachlorodibenzofuran
8.97E-12
500
0
2
196
41.49449822
-88.27008666
N
2.73E-12
1.96E-12
CTOOOOOl
P
indeno[l,2,3-c,d]pyrene
5.72E-11
500
0
2
196
41.49449822
-88.27008666
N
1.74E-11
1.25E-11
|CTOOOOOl
P
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
1.07E-12
500
0
2
196
41.49449822
-88.27008666
N
3.25E-13
2.33E-13
Figure 50. Sample All Polar Receptors HEM4 Output file (facility-specific, abbreviated)
Note:
• The Dry deposition and Wet deposition flux units will be in g/m2/yr if you modeled with annual averages, or in g/m2 if you modeled with
period averages. These columns will be blank if you did not choose to model deposition in your Facility List Options file
HEM4 User's Guide
Page 158
-------
aermod.inp - Notepad
File Edit Format View Help
CO STARTING
~ X
CO TITLEONE Facl-NC
CO TITLETWO Combined particle and vapor-phase emissions
CO MODELOPT CONC ALPHA BETA ELEV
CO URBANOPT 347602.0
CO AVERTIME 1 PERIOD
CO POLLUTID UNITHAP
CO RUNORNOT RUN
CO FINISHED
SO STARTING
SO ELEVUNIT METERS
SO LOCATION CT000001 POINT 690956 3974986 92
SO SRCPARAM CT000001 1000 50.292 322.04 21.06275 2.819
SO URBANSRC CT000001
SO BUILDHGT CT000001 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 :
SO BUILDWID CT000001 111.07 107.16 100.0 115.85 128.17 136.6 140.88 140.88 136.6 128.17 115.85 100.0 107.16 111.07 111.6 108.74 108
SO BUILDLEN CT000001 128.17 115.85 100.0 107.16 111.07 111.6 108.74 108.74 111.6 111.07 107.16 100.0 115.85 128.17 136.6 140.88 140
SO XBAD] CT000001 -93.97 -98.48 -100.0 -107.16 -111.07 -111.6 -108.74 -108.74 -111.6 -111.07 -107.16 -100.0 -98.48 -93.97 -86.6
SO YBAD] CT000001 55.54 53.58 50.0 40.56 29.88 18.3 6.16 -6.16 -18.3 -29.88 -40.56 -50.0 -53.58 -55.54 -55.8 -54.37 -54.37 -55.8
SO LOCATION CV000001 POINTCAP 690817 3975122 92
SO SRCPARAM CV000001 1000 60.0 350.0 0.005 1.8
SO URBANSRC CV000001
SO LOCATION HV000001 POINTHOR 690561 3975207 92
SO SRCPARAM HV000001 1000 45.0 300.0 0.006 3.0
SO URBANSRC HV000001
SO LOCATION FU000001 AREA 690957 3974943 92
SO SRCPARAM FU000001 0.1 2.0 100.0 100.0 45.0 0.0
SO URBANSRC FU000001
SO LOCATION SR000001 VOLUME 690991 3974996 92
SO SRCPARAM SR000001 1000 10.0 10.0 10.0
SO URBANSRC SR000001
SO LOCATION RW000001 LINE 690560 3975117 690751 3975163 92
SO SRCPARAM RW000001 0.0678675172 3.0 75.0 3.0
SO URBANSRC RW000001
< >
Note:
• If particle and vapor phase emissions are modeled separately (e.g., when modeling deposition/depletion), then two aermod.inp files will be
provided in the facility folder: an aermod_P.inp file for particle phase emissions and an aermod_V.inp file for vapor phase emissions.
Ln 1, Col 1
100% Windows (CRLF) UTF-8
Figure 51. Sample AERMOD.inp file (facility-specific, abbreviated)
HEM4 User's Guide
Page 159
-------
aermod.out - Notepad
File Edit Format View Help
CO STARTING
~ X
A
CO TITLEONE Facl-NC
CO TITLETWO Combined particle and vapor-phase emissions
CO MODELOPT CONC ALPHA BETA ELEV
CO URBAMOPT 347602.0
CO AVERTIME 1 PERIOD
CO POLLUTID UNITHAP
CO RUNORNOT RUN
CO FINISHED
SO STARTING
SO ELEVUNIT METERS
SO LOCATION CT000001 POINT 690956 3974986 92
SO SRCPARAM CT000001 1000 50.292 322.04 21.06275 2.819
SO URBANSRC CT000001
SO BUILDHGT CT000001 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 26.0 :
SO BUILDWID CT000001 111.07 107.16 100.0 115.85 128.17 136.6 140.88 140.88 136.6 128.17 115.85 100.0 107.16 111.07 111.6 108.74 108
SO BUILDLEN CT000001 128.17 115.85 100.0 107.16 111.07 111.6 108.74 108.74 111.6 111.07 107.16 100.0 115.85 128.17 136.6 140.88 140
SO XBAD] CT000001 -93.97 -98.48 -100.0 -107.16 -111.07 -111.6 -108.74 -108.74 -111.6 -111.07 -107.16 -100.0 -98.48 -93.97 -86.6
SO YBADJ CT000001 55.54 53.58 50.0 40.56 29.88 18.3 6.16 -6.16 -18.3 -29.88 -40.56 -50.0 -53.58 -55.54 -55.8 -54.37 -54.37 -55.8
SO LOCATION CV000001 POINTCAP 690817 3975122 92
SO SRCPARAM CV000001 1000 60.0 350.0 0.005 1.8
SO URBANSRC CV000001
SO LOCATION HV000001 POINTHOR 690561 3975207 92
SO SRCPARAM HV000001 1000 45.0 300.0 0.006 3.0
SO URBANSRC HV000001
SO LOCATION FU000001 AREA 690957 3974943 92
SO SRCPARAM FU000001 0.1 2.0 100.0 100.0 45.0 0.0
SO URBANSRC FU000001
SO LOCATION SR000001 VOLUME 690991 3^74996 92
SO SRCPARAM SR000001 1000 10.0 10.0 10.0
SO URBANSRC SR000001
SO LOCATION RW000001 LINE 690560 3975117 690751 3975163 92
SO SRCPARAM RW000001 0.0678675172 3.0 75.0 3.0
SO URBANSRC RW000001
< >
Note:
• If particle and vapor phase emissions are modeled separately (e.g., when modeling deposition/depletion), then two aermod.out files will be
provided in the facility folder: an aermod_P.out file for particle phase emissions and an aermod_V.out file for vapor phase emissions.
Deposition fluxes (Dry Depo and Wet Depo) will be provided with depletion applied to concentrations, if modeled.
Ln 30, Col 37
100% Windows (CRLF) UTF-8
Figure 52. Sample AERMOD.out file (facility-specific, abbreviated)
HEM4 User's Guide
Page 160
-------
_| plotfile.plt- Notepad
File Edit Format View Help
|* AERMOD ( 19191): Facl-NC 08/25/20
* AERMET ( 19191): 12:00:45
* MODELING OPTIONS USED: NonDFAULT CONC ELEV ALPHA URBAN AD3_U* BUOYLINE
* PLOT FILE OF PERIOD VALUES AVERAGED ACROSS 0 YEARS FOR SOURCE GROUP: CT000001
* FOR A TOTAL OF 329 RECEPTORS.
* FORMAT: (2(1X,F13.5),IX,E13.6,3(1X,F8.2),2X,A6,2X,A8,2X,18.8,2X,A8)
X
Y
AVERAGE CONC
ZELEV
ZHILL
ZFLAG
AVE
GRP
NUM HRS NET ID
688085.00000
3975161.00000
0.253092E+02
100.00
100.00
0
00
PERIOD
CT000001
00003326
688431.00000
3974590.00000
0.297584E+02
89.00
89.00
0
00
PERIOD
CT000001
00003326
688074.00000
3974564.00000
0.275790E+02
96.00
96.00
0
00
PERIOD
CT000001
00003326
688329.00000
3973976.00000
0.301464E+02
87.00
87.00
0
00
PERIOD
CT000001
00003326
688603.00000
3974075.00000
0.311166E+02
81.00
81.00
0
00
PERIOD
CT000001
00003326
689200.00000
3973740.00000
0.356151E+02
84.00
84.00
0
00
PERIOD
CT000001
00003326
688986.00000
3973544.00000
0.331389E+02
86.00
86.00
0
00
PERIOD
CT000001
00003326
688843.00000
3975073.00000
0.302065E+02
87.00
87.00
0
00
PERIOD
CT000001
00003326
688627.00000
3975147.00000
0.292191E+02
94.00
94.00
0
00
PERIOD
CT000001
00003326
688703.00000
3974777.00000
0.307262E+02
87.00
87.00
0
00
PERIOD
CT000001
00003326
688794.00000
3974637.00000
0.319091E+02
86.00
86.00
0
00
PERIOD
CT000001
00003326
688857.00000
3974368.00000
0.336242E+02
88.00
88.00
0
00
PERIOD
CT000001
00003326
688897.00000
3974590.00000
0.336846E+02
89.00
89.00
0
00
PERIOD
CT000001
00003326
688987.00000
3974348.00000
0.358162E+02
91.00
91.00
0
00
PERIOD
CT000001
00003326
688771.00000
3973458.00000
0.318658E+02
87.00
87.00
0
00
PERIOD
CT000001
00003326
688844.00000
3973490.00000
0.327004E+02
89.00
89.00
0
00
PERIOD
CT000001
00003326
688649.00000
3973298.00000
0.299506E+02
85.00
85.00
0
00
PERIOD
CT000001
00003326
688548.00000
3973225.00000
0.288798E+02
83.00
83.00
0
00
PERIOD
CT000001
00003326
688950.00000
3972883.00000
0.298544E+02
79.00
79.00
0
00
PERIOD
CT000001
00003326
689303.00000
3973138.00000
0.338950E+02
81.00
81.00
0
00
PERIOD
CT000001
00003326
689577.00000
3972790.00000
0.358756E+02
74.00
74.00
0
00
PERIOD
CT000001
00003326
689172.00000
3972686.00000
0.330014E+02
84.00
84.00
0
00
PERIOD
CT000001
00003326
689054.00000
3972778.00000
0.316748E+02
84.00
84.00
0
00
PERIOD
CT000001
00003326
689351.00000
3972699.00000
0.339758E+02
77.00
77.00
0
00
PERIOD
CT000001
00003326
688985.00000
3973950.00000
0.367440E+02
92.00
92.00
0
00
PERIOD
CT000001
00003326
690232.00000
3977482.00000
0.245790E+02
82.00
82.00
0
00
PERIOD
CT000001
00003326
689973.00000
3977269.00000
0.233639E+02
88.00
88.00
0
00
PERIOD
CT000001
00003326
<
Ln1 Coll 100% Window
Figure 53. Sample plotfile.plt output file (facility-specific, abbreviated)
Note:
• If particle and vapor phase emissions are modeled separately (e.g., when modeling deposition/depletion), then these concentrations will be
provided based on particle phase emissions in a plotfile_p.plt file and in a plotfile_v.plt file for vapor phase emissions. Deposition fluxes (Dry
Depo and Wet Depo) will be provided with depletion applied to concentrations, if modeled.
HEM4 User's Guide
Page 161
-------
_j[| maxhour.plt - Notepad
~ X
File Edit Format View Help
|* AERMOD ( 19191): Facl-NC
* AERMET ( 19191): Combined particle and vapor-phase emissions
* MODELING OPTIONS USED: NonDFAULT CONC ELEV ALPHA URBAN
* PLOT FILE OF HIGH 87TH HIGH 1-HR VALUES FOR SOURCE
* FOR A TOTAL OF 329 RECEPTORS.
* FORMAT: (2(1X,F13.5),1X,E13.6,3(1X^8.2)^3X^5,2X^8,
AVERAGE CONC
ZELEV
ZHILL
ADJJJ* BUOYLINE
GROUP: CT000001
2X, A5, 5X, A8, 2X, 18 )
ZFLAG AVE GRP
08/25/20
12:00:45
RANK
NET ID DATE(CONC)
688085.00000
3975161.00000
0.284562E+03
100
00
100.00
0
00
1-HR
CT000001
87TH
19032801
688431.00000
3974590.00000
0.316115E+03
89
00
89.00
0
00
1-HR
CT000001
87TH
19030220
688074.00000
3974564.00000
0.301197E+03
96
00
96.00
0
00
1-HR
CT000001
87TH
19021915
688329.00000
3973976.00000
0.329636E+03
87
00
87.00
0
00
1-HR
CT000001
87TH
19022215
688603.00000
3974075.00000
0.329503E+03
81
00
81.00
0
00
1-HR
CT000001
87TH
19060919
689200.00000
3973740.00000
0.406146E+03
84
00
84.00
0
00
1-HR
CT000001
87TH
19030908
688986.00000
3973544.00000
0.375320E+03
86
00
86.00
0
00
1-HR
CT000001
87TH
19060911
688843.00000
3975073.00000
0.336322E+03
87
00
87.00
0
00
1-HR
CT000001
87TH
19052105
688627.00000
3975147.00000
0.325032E+03
94
00
94.00
0
00
1-HR
CT000001
87TH
19060814
688703.00000
3974777.00000
0.314162E+03
87
00
87.00
0
00
1-HR
CT000001
87TH
19040119
688794.00000
3974637.00000
0.335495E+03
86
00
86.00
0
00
1-HR
CT000001
87TH
19021214
688857.00000
3974368.00000
0.370621E+03
88
00
88.00
0
00
1-HR
CT000001
87TH
19041011
688897.00000
3974590.00000
0.364171E+03
89
00
89.00
0
00
1-HR
CT000001
87TH
19021710
688987.00000
3974348.00000
0.385640E+03
91
00
91.00
0
00
1-HR
CT000001
87TH
19052724
688771.00000
3973458.00000
0.361640E+03
87
00
87.00
0
00
1-HR
CT000001
87TH
19022311
688844.00000
3973490.00000
0.364316E+03
89
00
89.00
0
00
1-HR
CT000001
87TH
19051506
688649.00000
3973298.00000
0.326036E+03
85
00
85.00
0
00
1-HR
CT000001
87TH
19042910
688548.00000
3973225.00000
0.315116E+03
83
00
83.00
0
00
1-HR
CT000001
87TH
19021121
688950.00000
3972883.00000
0.301050E+03
79
00
79.00
0
00
1-HR
CT000001
87TH
19052120
689303.00000
3973138.00000
0.344125E+03
81
00
81.00
0
00
1-HR
CT000001
87TH
19021622
689577.00000
3972790.00000
0.379355E+03
74
00
74.00
0
00
1-HR
CT000001
87TH
19021609
689172.00000
3972686.00000
0.330885E+03
84
00
84.00
0
00
1-HR
CT000001
87TH
19032014
689054.00000
3972778.00000
0.307257E+03
84
00
84.00
0
00
1-HR
CT000001
87TH
19051805
689351.00000
3972699.00000
0.353838E+03
77
00
77.00
0
00
1-HR
CT000001
87TH
19021619
688985.00000
3973950.00000
0.415687E+03
92
00
92.00
0
00
1-HR
CT000001
87TH
19032002
690232.00000
3977482.00000
0.241090E+03
82
00
82.00
0
00
1-HR
CT000001
87TH
19062313
689973.00000
3977269.00000
0.229380E+03
88
00
88.00
0
00
1-HR
CT000001
87TH
19040417
Ln 1, Co! 1 100% Windows (CRLF)
Figure 54. Sample maxhour.plt output file (optional facility-specific, abbreviated)
UTF-8
Note:
• The Maxhour plot file will be produced if you opted to model acute concentrations in your Facility List Options file. If particle and vapor phase
emissions are modeled separately (e.g., when modeling deposition/depletion), then these acute concentrations will be provided based on
particle phase emissions in a maxhour_p.plt file and for vapor phase emissions in an maxhour_v.plt file.
HEM4 User's Guide
Page 162
-------
A
B
C
D
E
F
G
H
'
j
K
L
M
N
°
p
Q
R
S
T
U
Facility
ID
Aermod Title2
Emissions
Phase
Rural/
Urban
Deposition
(YN)
Depletion
(YN)
Deposition
Type
(particle/
vapor)
Depletion
Type
(particle/
vapor)
Elevation
(YN)
Acute
Hours
Acute
Multiplier
Building
Downwash
(YN)
User
Receptors
(YN)
Max
Modeling
Distance
Discrete
Modeling
Distance
Overlap
Distance
Number
of Polar
Rings
Number
of Polar
Radials
Acute
(YN)
First Ring
Distance
Facl-NC
CO TITLETWO
Combined
particle and vapor-
phase emissions
N
N
NO/NO
NO/NO
Y
1
50
Y
Y
50000
3000
30
13
16
Y
565
Figure 55. Sample Input Selection Options HEM4 Output file (facility-specific, abbreviated)
Note:
• The above Input Selection Options files does not show all information provided; the actual file contains 34 fields / columns providing chosen
modeling run options.
A
e c
E
G
H
1
J
<
L
M
N
0
p
Q
R
S
T
Pollutant
Cone sci
Conc(ug/m3) (ug/m3)
Aegll
lhr
(mg/mi)
Rel
(mg/m3)
Population
Distance
(in
meters)
Angle
(from
north)
Elevation
(in
meters)
Hill
Height
(in
meters)
Fips
Block
Utm
easting
Utm
northing
Latitude
Longitud
e
Receptor
type
Notes
1,3-butadiene
64.17283562 ^j.4e+01
1500
0
0
565
90
92
92
na
na
691471
3975205
35.90242
-78.87832
PG
Polar
acetaldehyde
14.33911644 1.4e+01
81
0.47
0
459
233
90
90
UOOOO
OOOOURCPT1
35
3974934
35.90016
-78.88875
P
Discrete
acrolein
100,37381511.06+02
0.069
0.0025
0
459
233
90
90
UOOOO
0000URCPT1
35
3974934
35.90016
-78.88875
P
Discrete
arsenic compounds
69.24203227 *6.9e+01
0
0.0002
0
565
180
92
92
na
na
690906
3974640
35.89744
-78.88471
PG
Polar
benzene
29.94732329 r3.0e+01
170
0
0
565
90
92
92
na
na
691471
3975205
35.90242
-78.87832
PG
Polar
bis(2-ethylhexyl)phthalate
1839.115705rl.8e-M)3
0
0
0
565
180
92
92
na
na
690906
3974640
35.89744
-78.88471
PG
Polar
cadmium compounds
7.45282988 ^.5e-KM)
0.1
0
0
565
180
92
92
na
fta
690906
3974640
35.89744
-78.88471
PG
Polar
chloroform
0.409275616'i.le-Ol
0
0.15
0
565
67
92
92
na
na
691428
3975421
35.90438
-78.87874
PG
Polar
chromium (iii) compounds
39.58179966'i.Oe+Ol
0
0
0
565
180
92
92
na
na
690906
3974640
35.89744
-78.88471
PG
Polar
chromium (vi) compounds
0.0395818 ^.0e-02
0
0
0
565
180
92
92
na
na
690906
3974640
35.89744
-78.88471
PG
Polar
cumene
1.026765371.0e+00
250
0
0
565
90
92
92
na
na
691471
3975205
35.90242
-78.87832
PG
Polar
Figure 56. Sample Acute Maximum Concentrations HEM4 Output file (optional facility specific, abbreviated)
Note:
• The Acute Maximum Concentrations (acute_chem_max) file will be produced if you opted to model acute concentrations in your Facility List
Options file. The above sample file is abbreviated; the actual file contains 11 acute benchmark columns, not only the AegMhr and Rel
columns shown.
HEM4 User's Guide
Page 163
-------
A
B j C
D
E
F
G
H
1
J
K
L
M
N
0
P
Q
R
S
T L
Pollutant
Cone Cone sci
(ug/m3) (ug/m3)
Aegl_l
lhr
(mg/m3)
Rel
(mg/m3)
Population
Distance
(in
meters)
Angle
(from
north)
Elevation
(in
meters)
Hill
Height (in
meters)
Fips
Block
Utm
easting
Utm
northing
Latitude
Longitude
Receptor
type
Notes
1,3-butadiene
10.2245116 ^.Oe+Ol
1500
0
219
1124
191
85
85
37063
K)20272057
690684
3974103
35.89265
-78.8873
C
Discrete
acetaldehyde
9.9961.0e-K>l
81
0.47
7
383
301
97
97
37063
>020272047
690578
3975403
35.90438
-78.88816
C
Discrete
jacrolein
69.972 r7.0e-H)l
0.069
0.0025
7
383
301
97
97
37063
>020272047
690578
3975403
35.90438
-78.88816
C
Discrete
arsenic compounds
60.7940659 "fi.le+Ol
0
0.0002
2
492
220
90
90
37063
1020272056
690588
3974829
35.89921
-78.88819
C
Discrete
jbenzene
4.77143877 ^.Se+00
170
0
219
1124
191
85
85
37063
>020272057
690684
3974103
35.89265
-78.8873
C
Discrete
!bis(2-ethylhexyl)phthalate
942.976132 l9.4e+02
0
0
2
492
220
90
90
37063
>020272056
690588
3974829
35.89921
-78.88819
C
Discrete
cadmium compounds
6.54636892 "6.5e+00
0.1
0
2
492
220
90
90
37063
>020272056
690588
3974829
35.89921
-78.88819
C
Discrete
j chloroform
0.05841962^.8e-02
0
0.15
2
4329
48
117
117
37063
>018091060
694160
3978061
35.92762
-78.84785
c
Interpolated
chromium (iii) compounds
35.B686185 *3.6e+01
0
0
2
492
220
90
90
37063
>020272056
690588
3974829
35.89921
-78.88819
c
Discrete
1 chromium (vi) compounds
0.03586862 "3.6e-02
0
0
2
492
220
90
90
37063
>020272056
690588
3974829
35.89921
-78.88819
c
Discrete
|cumene
0.16359219 ^..6e-01
250
0
219
1124
191
85
85
37063
0020272057
690684
3974103
35.89265
-78.8873
c
Discrete
J-
Note
Figure 57. Sample Acute Populated Concentrations HEM4 Output file (optional facility-specific, abbreviated)
The Acute Populated Concentrations (acute_chem_pop) file will be produced if you opted to model acute concentrations in your Facility List
Options file. The above sample file is abbreviated; the actual file contains 11 acute benchmark columns, not only the AegMhr and Rel
columns shown.
A
b
D
E
F
G
Pollutant
Source ID
Emission
type
Max cone at
populated
receptor
(ug/m3)
Is max
populated
receptor
interpolated?
(Y/N)
Max cone at
any
receptor
(ug/m3)
Is max cone at
any receptor
interpolated?
(Y/N)
1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin
FU000001
C
6.81669E-07
N
1.3295E-06
N
1,2,3,4,6,7,8,9-octachlorodibenzofuran
FU000001
C
7.04392E-08
N
1.3738E-07
N
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
CT000001
C
3.11291E-09
N
2.0383E-09
N
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
CV000001
C
1.87004E-08
N
1.1675E-08
N
1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin
HV000001
C
8.13071E-09
N
2.569E-08
N
1,2,3,4,6,7,8-heptachlorodibenzofuran
CT000001
C
1.23623E-08
N
8.0945E-09
N
1,2,3,4,6,7,8-h e ptach 1 orod i be n zof u ran
CV000001
C
7.42649E-08
N
4.6364E-08
N
1,2,3,4,6,7,8-heptachlorodibenzofuran
HV000001
C
3.22894E-08
N
1.0202E-07
N
1,2,3,4,7,8,9-heptachlorodibenzofuran
FUQ00001
C
9.42976E-08
N
1.8391E-07
N
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
CT000001
C
2.54693E-09
N
1.6677E-09
N
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
CV000001
C
1.53004E-08
N
9.552E-09
N
1,2,3,4,7,8-hexachlorodibenzo-p-dioxin
HV000001
C
6.6524E-09
N
2.1019E-08
N
1,2,3,4,7,8-hexachlorodibenzofuran
CT000001
C
2.96397E-08
N
1.9407E-08
N
1,2,3,4,7,8-hexachlorodibenzofuran
CV000001
C
1.78057E-07
N
1.1116E-07
N
1,2,3,4,7,8-hexachlorodibenzofuran
HV000001
c
7.74168E-08
N
2.446E-07
N
1,2,3,4,7,8-hexachlorodibenzofuran
RV000003
c
3.94583E-09
N
1.2858E-09
N
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
CT000001
c
2.71077E-09
N
1.7749E-09
N
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
CV000001
c
1.62846E-08
N
1.0166E-08
N
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
HV000001
c
7.08033E-09
N
2.2371E-08
N
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin
RV000002
c
5.67075E-10
N
5.9953E-11
N
1,2,3,6,7,8-hexachlorodibenzofuran
CT000001
c
2.66608E-08 N
1.7457E-08
N
1,2,3,6,7,8-hexachlorodibenzofuran
CV000001
c
1.60162E-07 N
9.9989E-08
N
1,2,3,6,7,8-hexachlorodibenzofuran
HV000001
c
6.96362E-08 N
2.2002E-07
N
1,2,3,6,7,8-hexachlorodibenzofuran
RV000003
c
3.54927E-09 N
1.1565E-09
N
Sample Acute Breakdown HEM4 Output file
optional faci
Note:
The Acute Breakdown file will be produced if you opted to model acute concentrations in your Facility List Options file.
HEM4 User's Guide Page 164
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A
Facilid
E
mxcanrsk
C
can_rsk_
interpltd
D
E
| ^ 1
F
( 1
G
H
1
J
K
L
M
N
O
P
canrcpttype
canlatitude
canlongitude
canblk
respiratory
hi
[59 TOSHI
columns]
popoverlp
incidence
metname
km_to_
metstation
fac_center_
latitude
fac_center_
longitude
rural_
urban
Facl-NC
0.000610761
N
Census block
35,8990843
-78.8880045
*9801001074
0.6770494
0
0.047682
NC13722 2019.SFC
9.2712
35.9025311
-78.884577
U
Fac2-IL
9.00146E-07
N
Census block
41.4797356
-88.2618629
'8907002218
0.03653
0
4.581E-06
I104808_2019.SFC
35.6838
41.49
-88.27
R
Figure 59. Sample Facility Max Risk arid HI HEM4 Output file (for run group, abbreviated)
Note:
• The Facility Max Risk and HI file covers the entire run group with one row of output per facility. The above sample file is abbreviated; there
are 59 additional columns not shown pertaining to all 14 TOSHI values and locations.
A
B
C
D
E
F
G
H
Number people
Number people
Number people
Number people
Number people
exposed to >= 1 in
exposed to >= 1 in
exposed to >= 1 in
exposed to >= 1 in
exposed to >= 1 in
Facilid
latitude
longitude
1,000 risk
10,000 risk
100,000 risk
1,000,000 risk
10,000,000 risk
Facl-NC
35.90253
-78.884577
0
435
48998
800221
1545731
| Fac2-IL
41.49
-88.27
0
0
0
0
296
Figure 60. Sample Facility Cancer Risk Exposure HEM4 Output file (for run group)
A
B
I C j
D
E
F
G
H 1
J
K
L
M
N
O
Facility
ID
Number people
exposed to > 1
Respiratory HI
Number people
exposed to > 1
Liver HI
Number people
exposed to > 1
Neurological HI
Number people
exposed to > 1
Developmental HI
Number people
exposed to > 1
Reproductive HI
Number people
exposed to > 1
Kidney HI
Number people Number people
exposed to > 1 exposed to > 1
Ocular HI Endocrinological HI
Number people
exposed to > 1
Hematological HI
Number people
exposed to > 1
Immunological HI
Number people
exposed to > 1
Skeletal HI
Number people
exposed to > 1
Spleen HI
Number people
exposed to > 1
Thyroid HI
Number people
exposed to > 1
Whole Body HI
Facl-NC
0
0
0
435
0
0
0 0
0
0
0
0
0
0
Fac2-IL
0
0
0
0
0
0
0 0
0
0
0
0
0
0
Figure 61. Sample Facility TOSHI Exposure HEM4 Output file (for run group)
HEM4 User's Guide
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•v Google Earth Pro
File Edit View Tools Add Help
~ Search
Get Directions History
* > My Places
' €3 Temporary Places
~ * ^ srcmap
' Q Facility Fac1-NC Emission sources
' t—I Facility Fac2-IL Emission sources
~ Layers
w' ° $ Primary Database
0 Announcements
~ ' f Borders and Labels
< ~ Places
~ J 9 Photos
: ' S Roads
* B [QS 3D Buildings
~ 0 Weather
~ # Gallery
~ D More
' Terrain
Figure 62. Sample All Facility Source Locations Google Earth™ Image (for run group)
Note:
• The All Facility Source Locations Google Earth™ image depicts the two sample facilities modeled in this run group - located in Illinois and
North Carolina - on a map. On the actual map image, you can zoom In to see the individual sources at each facility in more detail.
HEM4 User's Guide
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3 *hem4,log - Notepad
File Edit Format View
2020-08-25 11:58:10.
2020-08-25 11:58:53.
2020-08-25 11:58:53.
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2020-08-25 11:59:54.
2020-08-25 12:00:02.
2020-08-25 12:00:08.
2020-08-25 12:00:15.
~
X
2020-08-25 12:00
HEM4 is starting
2020-08-25 12:00
2020-08-25 12:00
2020-08-25 12:00
2020-
2020-
2020-
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2020-
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08-25
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12:00
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Help
713299:
831761
832758
840773
846757
256229:
760734:
611239:
574244:
214533:
848230:
047909:
154159:
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496536:
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736947
HEM4 Logging Initialized. See output subfolder for the log of your HEM4 run.
Facility Facl-NC
Facility Facl-NC
Facility Fac2-IL
Using period start = 2019 02 11 12
Using period end = 2019 06 30 1
Using annual met option.
Uploaded facilities options list file for 2 facilities.
Uploaded HAP emissions file for 101 source-HAP combinations.
Uploaded emissions location file for 13 facility-source combinations.
Uploaded user receptors for [Facl-NC]
Uploaded buoyant line parameters for [Facl-NC]
Uploaded polyvertex sources for [Facl-NC, MS000001]
Uploaded building downwash parameters for [Facl-NC]
Uploaded particle data for [Fac2-IL]
Uploaded land use data for [Fac2-IL,Facl-NC]
Uploaded seasonal variation data for [Fac2-IL,Facl-NC]
RUN GROUP: test2_8-25-2020
KMZ for all sources completed
Preparing Inputs for 2 facilities
The facility ids being modeled: Facl-NC, Fac2-IL
Running facility 1 of 2
Building runstream for Facl-NC
Using facility center [x, y, lat, Ion] = [690906, 3975205, 35.90253110232091, -78.88457746645928]
Running Aermod for Facl-NC. Started at time 12:00:44
Aermod ran successfully. Ended at time 12:01:33
Processing Outputs for Facl-NC
Completed InputSelectionOptions output
Completed AllPolarReceptors output
Completed AllInnerReceptors output
Completed AllOuterReceptors output
Figure 63. Sample HEM4 Log Output file (for run group, abbreviated)
HEM4 User's Guide
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13. Appendix B: Demographic Assessment Calculations
The overall methodology and Census data used by the Demographic Assessment module of HEM4 are
discussed in Section 8.1 of this guide. This Appendix provides additional detail on the calculation methods
HEM4 uses to produce the Demographic Assessment results discussed in Section 8.2 of this guide.
When a user chooses to model with U.S. Census receptors, HEM4 models the cancer risk and noncancer
"risk" (hazard index, HI) at a point near the geographic center of each census block called the block centroid.
HEM4's risk estimates are assumed to apply to all individuals residing in the census block. The Demographic
Assessment module uses the modeled census block and census block group identification codes to link the
HEM4 modeling results for each census block to the appropriate American Community Survey (ACS) census
block group demographic statistics (Census 2022b). This linkage allows HEM4 to estimate the number of
people in different demographic categories for each modeled census block. (The ACS data is included in
HEM4's "resources" folder when you download the model.)
Within the Census, blocks are aggregated into block groups, and block groups are aggregated into tracts.
Tracts also do not cross county boundaries, so each tract is completely contained within a county. Each
Census block is designated by a 15-digit code which includes identifiers for the block group, tract and county in
which the block is located. The first five digits designate the county, followed by six digits to designate the tract,
one digit to designate the block group, and three digits to designate the block. On average, there are about 30
populated blocks per block group, three block groups per tract, and 20 tracts on average in a county.
For the demographic analysis, the total nationwide population is determined by summing the total population of
all census block groups in the Census' ACS five-year average for 2016-2020. The demographic characteristics
of the population potentially impacted by emissions from facilities in the run group are determined by applying
the characteristics of a census block group to the HEM4 modeled census block populations located within that
block group. For the Demographic Assessment, the characteristics of a given block group - that is, the
percentage of people in different races/ethnicities, the percentage in different age groups, the percentage
without a high school diploma, the percentage at certain low-income levels, and the percentage that are
linguistically isolated - are presumed to also describe each block located within that block group.
Section B.1 describes the calculation method used to estimate the total population exposed to different risk
levels. Sections B.2 through B.5 describe calculation methods used to compute risks for racial, ethnic, age,
education status, low household income, poverty status, and linguistic isolation demographic categories.
Section B.6 describes the gap-filling approach used by HEM4's Demographic Assessment module when block
group statistics are not available for a given block, based on computing default averages for the missing
demographic(s) at the tract level or from the nearest (non-zero population) block group.
B.1 Total Population Risks
HEM4 calculates the (cancer and noncancer) risk distributions for the total population using a block-by-block
accumulation of people at various risk levels. The Demographic Assessment module identifies a set of bins
reflecting the level of risk and then assigns the population of each block to the appropriate risk bin based on
HEM4's modeled risk level in the block. The numbers of people in each risk bin are then added together for all
modeled census blocks in the run group.
where:
H(Rab) =
Ri =
^.(Ra
-------
The average risk for the total population was then calculated using the following equation:
A(s) = li [N(i) x Ri]/Ii [N(i)] (2)
where:
A(s) = the average risk for the population in the modeling domain (cancer or noncancer), population
weighted
Y.\ refers to the summation over all blocks T modeled for the run group
N(i) and Ri were defined above
These risk bins, populations within each risk bin and population-weighted average risk results are shown in the
outputs produced by HEM4's Demographic Assessment module. Note that the average risk (cancer risk or
noncancer HI) is less than the maximum risk because the average risk takes into account risk levels at all
populated block receptors for the entire modeled domain of the run group, whereas the maximum risk occurs
at an individual populated receptor (that receptor with the highest modeled risk level). The average risk statistic
encompasses higher risk levels (generally closer into facility emissions) as well as lower risk locations
(generally farther away in the domain). HEM4's Demographic Assessment module reports the average risk for
the total population as well as separately for each demographic group described below.
B.2 Race, Ethnicity and Age Categories
Table B03002 (Hispanic or Latino origin by race) of the ACS data (Census 2022b) provides race/ethnicity
statistics for each census block group nationwide. Table B01001 provides age statistics for the population by
ranges (in years) for each census block group nationwide. For each modeled census block, HEM4's
Demographic Assessment module estimates the race/ethnicity (White, African American, Native American,
Multiracial/Other, and Hispanic or Latino) and age range (0-17, 18-64 and >65 years) for that block based on
the demographic information provided at the block group level, as follows:
N(s,b/bg) = N(t,b/bg) x P(s,bg)/100
where:
N(s,b/bg) = number of people in racial/ethnic or age subgroup "s", in block "b" of block group "bg"
N(t,b/bg) = total number of people in block "b" of block group "bg"
P(s,bg) = percentage of people in racial/ethnic or age subgroup "s", in a block group "bg"
Equation (1) on page 169 was then used to generate cancer and noncancer risk distributions based on the
block-level results, and Equation (2) on page 170 was used to compute the average cancer and noncancer risk
for people in each racial/ethnic or age subgroup.
B.3 Level of Education
Table B15002 (educational attainment) of the ACS (Census 2022b) provides education attainment statistics for
each census block group nationwide. For each modeled census block, HEM4's Demographic Assessment
module estimates the number of people 25-years and older without a high school diploma based on the
demographic information provided at the block group level, as follows:
N(nhs,b/bg) = N(t,b/bg) x P(nhs,bg)/100
where:
N(nhs,b/bg) = number of people 25-years and older without a high school diploma "nhs", in block "b" of block
group "bg"
N(t,b/bg) = number of people 25-years and older in block "b" of block group "bg"
P(nhs,bg) = percentage of people 25-years and older without a high school diploma "nhs", in a block group
"bg"
HEM4 User's Guide
Page 169
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Equation (1) on page 169 was then used to generate cancer and noncancer risk distributions based on the
block-level results, and Equation (2) on page 170 was used to compute the average cancer and noncancer risk
for adults without a high school diploma.
B.4 Poverty Level
Table C17002 (poverty) of the ACS (Census 2022b) estimates the numbers of individuals within a census
block group who live in households where the household income is below the poverty line, and below various
multiples of the poverty line. HEM4's Demographic Assessment module calculates two poverty statistics based
on the fractions of (1) individuals living in households earning incomes below the poverty level and (2)
individuals living in households earning incomes below two times the poverty level, respectively. For each
modeled census block, HEM4's Demographic Assessment module estimates the block's household income
level based on the demographic information provided at the block group level, as follows:
N(hi,b/bg) = N(t,b/bg) x P(hi,bg)/100
where "hi" indicates household income, whether below the poverty level or below two times the poverty level,
depending on the statistic, and:
N(hi,b/bg) = number of people living in low-income households "hi" relative to the poverty level, in block "b"
of block group "bg"
N(t,b/bg) = total number of people in block "b" of block group "bg"
P(hi,bg) = percentage of people living in low-income households "hi" relative to the poverty level, among
the population for which poverty status is known, in block group "bg"
Equation (1) on page 169 was then used to generate cancer and noncancer risk distributions based on the
block-level results, and Equation (2) on page 170 was used to compute the average cancer and noncancer risk
for people living in low-income households.
B.5 Linguistic Isolation
Linguistic Isolation has been re-defined in the ACS as "Limited English-speaking households" in which all
members age 14 years and over speak a non-English language and also speak English less than "very well"
(i.e., have difficulty with English).14 Table C16002 (Tiger table X16_language_spoken_at_home) of the ACS
(Census 2022b) provides the number of households in linguistic isolation in each block group. For each
modeled census block, HEM4's Demographic Assessment module estimates the number of people living in
linguistic isolation based on the demographic information provided at the block group level, as follows:
N(li,b/bg) = N(t,b/bg) x P(li,bg)/100
where:
N(li,b/bg) = number of people living in linguistic isolation "li", in block "b" of block group "bg"
N(t,b/bg) = total number of people in block "b" of block group "bg"
P(li,bg) = percentage of linguistically isolated households "li", in block group "bg"
Equation (1) on page 169 was then used to generate cancer and noncancer risk distributions based on the
block-level results, and Equation (2) on page 170 was used to compute the average cancer and noncancer risk
for people living in linguistically isolated households.
14 U.S. Census Bureau, 2021. American Community Survey and Puerto Rico Community Survey 2020 Subject Definitions,
p. 50. https://www2.census.gov/proqrams-survevs/acs/tech docs/subiect definitions/2020 ACSSubiectDefinitions.pdf
HEM4 User's Guide
Page 170
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B.6 Demographic Defaults
Block and block group designations used in the Census may be modified to accommodate population growth in
some U.S. regions. As a result, certain blocks modeled in HEM4, which are based on the last Decennial
Census, may not map to the block group designations used in the latest five-year ACS survey. In addition,
some statistics may not be reported in the ACS for every block group. Race, ethnicity, and age statistics are
generally reported for all block groups. However, poverty, linguistic isolation, and educational attainment
statistics are not available for some block groups.
In these cases, HEM4's Demographic Assessment module computes default estimates for the missing
demographic statistics based on the average statistics for the tract in which the block is located. If no tract-level
data are available, demographic statistics are estimated based on the statistics of the nearest (non-zero
population) block group neighbor to the unmatched block location. This gap-filling exercise is performed
separately for each type of demographic data. That is, in the case where some categories of data are available
(for instance, race, age and ethnicity) and others are not available (educational attainment, poverty, or
linguistic isolation), HEM4's Demographic Assessment module only computes defaults for the categories of
data that are missing.
The tract level defaults are computed using weighted averages based on all the other block groups in the tract
for which data are available. Defaults are calculated as follows for race, ethnicity, and age subgroups:
P(s,T) = {I P(s,bg/T) x N(t,bg) }/¦£ N(t,bg)}
where:
P(s,T) = percentage of people in race, ethnicity, or age subgroup "s", in tract "T"
Y. refers to the summation over all block groups in tract "T" for which data are available
P(s,bg/T) = percentage of people in race, ethnicity, or age subgroup "s", in a block group "bg" of tract "T"
N(t,bg) = total number of people in block group "bg"
Defaults for educational attainment, poverty, and linguistic isolation are calculated in a similar fashion, except
that the population weighting term N is replaced by the population over age 25, the population for which
poverty status is known, and the number of households, respectively.
As noted earlier, the demographic results produced by HEM4's Demographic Assessment module using the
above calculation methods are described in Section 8.2 of this guide, and include sample result tables.
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