EPA AirToxScreen tells you the national picture.
It does not tell you what your facility contributes.

AirToxScreen (the Air Toxics Screening Assessment) is the U.S. Environmental Protection Agency’s national-scale assessment of outdoor air toxics. It estimates ambient concentrations and the resulting cancer and non-cancer health risks at the census-tract level for more than 180 Hazardous Air Pollutants. EPA built it as a screening tool to help identify which pollutants and which places may warrant further study, not to make regulatory decisions about individual facilities.

AirToxScreen replaced the National Air Toxics Assessment (NATA) in 2021. NATA had been EPA’s flagship national air toxics screening product since 1996, but it was published only every few years and lagged behind the underlying emissions inventory. AirToxScreen uses the same general methodology and is now updated annually, with each release tied to a specific National Emissions Inventory year. The most recent release at the time of writing is AirToxScreen 2020, published in 2024.

AirToxScreen pulls emissions from EPA’s National Emissions Inventory, runs them through the Human Exposure Model (HEM) using EPA’s preferred dispersion modeling approach, and combines the resulting ambient concentrations with toxicity values to produce cancer risk and hazard index estimates by census tract. The methodology is documented in the AirToxScreen Technical Support Document. It is a national-scale screening calculation, not a site-specific dispersion model run with refined meteorology and stack parameters.

AirToxScreen estimates are most reliable when used to compare relative burdens across many tracts and regions, which is what EPA designed them for. At the level of any individual census tract, the estimates carry meaningful uncertainty from emissions inventory gaps, model resolution, and assumptions about background concentrations. EPA states explicitly that the results are screening-level and should not be treated as facility-specific exposure estimates. For permit and enforcement work, refined facility-level dispersion modeling is the appropriate next step.

No, not on its own. EPA states directly that AirToxScreen "is a screening-level analysis. It is not appropriate for use in regulatory decisions about specific facilities." Permit applications, AB2588 Hot Spots filings, and CEQA Health Risk Assessments need facility-level dispersion modeling (typically AERMOD or AERSCREEN) and OEHHA-aligned or EPA-aligned risk math. AirToxScreen is a useful starting point and a reasonable sanity check, but the regulatory submission has to be built on a refined HRA on top.

AirToxScreen is EPA’s national screening dataset and the screening model that produced it. HARP2 is the California Air Resources Board’s Hot Spots Analysis and Reporting Program software, used for AB2588 facility-level Health Risk Assessments under California law. AirToxScreen tells you the regional, screening-level picture for any tract in the country. HARP2 produces facility-level cancer risk, chronic hazard index, and acute hazard index numbers that an air district reviewer expects to see on a Hot Spots filing. The two answer different questions.

EPA now updates AirToxScreen on a roughly annual cadence, with each release tied to a National Emissions Inventory year. AirToxScreen 2017 and AirToxScreen 2018 were released in 2022 and 2023 respectively. AirToxScreen 2019 and AirToxScreen 2020 followed. There is typically a three to four year lag between the inventory year and the public release, because the underlying emissions inventory has to be assembled, quality-checked, and modeled.

AirToxScreen 2020 was the first release built on the 2020 National Emissions Inventory, which itself reflected the unusual emissions patterns of the early COVID period. Some affected communities and industry groups felt the published cancer risk estimates were either too high or too low compared to what their own data and prior NATA releases suggested, and EPA addressed several methodology updates in the technical documentation. The controversy reinforced the underlying lesson EPA has stated since the NATA days: AirToxScreen is a screening tool, and any specific concern about a specific facility needs facility-level modeling on top.