nickrye / hem4epa

HEM4

The Human Exposure Model 4 (HEM4) Open Source Version 1.0 is a streamlined, but rigorous tool you can use for estimating ambient concentrations, human exposures and health risks that may result from air pollution emissions from complex industrial facilities. HEM4 can be used to model impacts from a single facility or from multiple facilities located across the entire United States (U.S.) and its territories, as well as 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 entire source categories. In RTR assessments, HEM4 is used to model emissions and the resulting ambient concentrations from hundreds of facilities, located both near as well as 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. HEM4 incorporates risk summary reports that summarize the cancer risk and noncancer health impacts for your modeled group of facilities, and multiple output viewing and analysis tools. HEM4 also enables the user to model concentrations, risk and health impacts for their own receptors inside and outside the U.S. HEM4 is available for download at http://www.epa.gov/fera/download-human-exposure-model-hem.

The HEM4 model was thoroughly tested throughout its development. The quality assurance (QA) activities performed help to deliver consistent results through a set of standardized procedures. More specifically, quality control (QC) activities helped scrutinize the data quality of the end products (output files) to ensure that the data generated by the model faithfully reflects user-specific inputs and that the model produces reasonable and reliable predictions prior to public release. When assessing HEM-4 inputs and outputs the quality objective was to ensure that HEM4 maintains or exceeds the functionality of HEM-3, faithfully generates and transfers the inputs to AERMOD, and faithfully translates the AERMOD outputs into HEM4 concentration and risk predictions. Documentation of this testing can be found in the HEM4 QA/QC Report (download at https://github.com/USEPA/HEM4/raw/master/HEM4_QA-QC_Report_11-9-2020.pdf) and companion Testing Workbook (download at https://github.com/USEPA/HEM4/raw/master/HEM4_Master_QA_Testing_Workbook_11-9-2020.xlsx) that includes detailed information on all testing performed.