HARP2 is the standard.
We rebuilt it on the cloud, parity-validated to five significant figures.

AB2588 is the California Air Toxics "Hot Spots" Information and Assessment Act, passed in 1987. It requires facilities that emit toxic air contaminants to inventory their emissions, and for prioritized facilities, to prepare a Health Risk Assessment (HRA) characterizing cancer risk and non-cancer health hazards to nearby populations. CARB and the local air districts (BAAQMD, SCAQMD, SJVAPCD, and others) administer the program, and the official tool for the HRA calculations is HARP2, which implements the OEHHA 2015 risk assessment methodology.

The Air Toxics Hot Spots Information and Assessment Act, also known as AB2588, is the California statute that established the Hot Spots program in 1987. It directs facilities emitting listed toxic air contaminants to report their emissions, and for higher-priority facilities, to perform an HRA and notify the affected public if risk thresholds are exceeded. The science underlying the HRAs is the OEHHA 2015 risk assessment guidance, and the CARB-maintained software for running those calculations is HARP2.

HARP2 is the Hotspots Analysis and Reporting Program version 2, the official software the California Air Resources Board (CARB) maintains for AB2588 Air Toxics Hot Spots health risk assessments. It is a Microsoft Windows desktop application that runs on .NET Framework 4.7.2. HARP2 takes ground-level concentrations of toxic air contaminants predicted by EPA dispersion models such as AERSCREEN and AERMOD, then computes the Maximum Individual Cancer Risk (MICR), chronic Hazard Index (HIC), and acute Hazard Index (HIA) using the OEHHA 2015 risk assessment methodology.

HARP2 is the CARB-maintained tool for AB2588 Hot Spots reporting and California air districts (BAAQMD, SCAQMD, SJVAPCD, SBCAPCD, and others) review submissions against the OEHHA 2015 methodology HARP2 implements. It is not the only allowable path. Districts will accept results from any tool that correctly implements the OEHHA 2015 risk assessment guidance, provided the calculations are reproducible. That is the bar LSARS-HRA was built to clear.

No. LSARS-HRA does not replace HARP2 and does not replace OEHHA. It implements the same OEHHA 2015 methodology HARP2 implements, and is parity-validated against the official CARB HARP2 software to five significant figures. CARB still owns the science and the regulatory tool. LSARS rebuilds the production layer on the cloud, with audit trails, SDOH overlays, and a workflow that air districts and consultants can collaborate inside.

The responsible facility or consultant is always the entity of record on a regulatory submission, and the district is the reviewer. LSARS produces the same MICR, HIC, and HIA metrics HARP2 produces, against the same OEHHA 2015 methodology, with a full audit trail showing every input, factor, and calculation step. Reviewers who want to verify against HARP2 can reproduce the result on either system because the numbers match to five significant figures.

AERMOD is the EPA-recommended air dispersion model. It predicts ground-level concentrations of pollutants from a stack or fugitive source given meteorology, terrain, and emission rates. HARP2 is not a dispersion model. HARP2 takes the concentrations AERMOD or AERSCREEN produces and runs the OEHHA 2015 health risk assessment math on top, computing cancer risk and hazard indices for nearby receptors. They are sequential tools in the same workflow: AERMOD models how pollution moves, HARP2 models what that pollution does to people.

It means LSARS-HRA was tested against the official CARB HARP2 software across a battery of scenarios, and the cancer risk and hazard index outputs match HARP2 in the first five significant digits (10 to the negative 4 precision). When a consultant runs the same source, the same receptor grid, and the same emission rates through both tools, the MICR, HIC, and HIA values reproduce. This is the highest fidelity claim LSARS makes about any regulatory engine, and it is the reason agency reviewers can verify LSARS results against HARP2 directly.

HARP2 is a Windows desktop application on .NET Framework 4.7.2, distributed as an installer from CARB. That is fine for a one-off filing on a Windows workstation. It is harder for a multi-person consulting team that needs to share working files, track who changed what, run scenarios in parallel, layer SDOH context onto the risk numbers, or hit the calculation engine programmatically. LSARS gives the same OEHHA math a cloud workflow, an audit trail, and an API, without changing the underlying methodology.

Yes. LSARS-HRA implements the EPA AirToxScreen 2020 methodology and the CA-OEHHA 2015 methodology with Age Sensitivity Factors in the same engine. EPA methods are appropriate for federal AirToxScreen-style screening and most non-California work. OEHHA 2015 with Age Sensitivity Factors is what CARB and California air districts expect for AB2588 and CEQA HRAs. The same source data and the same dispersion inputs can be run through either methodology, with the calculation trail preserved for reviewers.