An air emissions risk analysis (AERA) is a process that uses spreadsheets, computer models, and health benchmarks to estimate the potential human health risks from air pollution emitted by a facility. An AERA describes the potential risks posed to communities closest to the facility, which have the highest level of exposure to its emissions. When an AERA is conducted in a community that may be disproportionately affected by pollution, the MPCA may seek additional community engagement. Learn more:
In general, projects requiring an environmental review also require an AERA, but the MPCA may request a discretionary AERA when:
- The process might resolve substantive public comments received on the project
- Significant public interest indicates a need for further analysis
- The facility may contribute to cumulative air-pollution effects by adding to other nearby and background sources
- The facility's amount or types of emissions are of concern
An AERA may also help determine air permitting limits or monitoring requirements for facilities.
In Minnesota, potential health effects from air toxics (also known as hazardous air pollutants) are reviewed using the AERA process and accompanying risk screening tools, which are routinely updated. Learn more about air toxics:
The AERA's estimates of human-health risk are compared with facility risk guidelines that were developed with the Minnesota Department of Health and are consistent with U.S. EPA guidance. If the AERA risk estimates are below facility risk guidelines, a project may proceed without further refined modeling. If risk estimates are above facility risk guidelines, refinements may be made to better reflect a facility’s operating conditions. Learn more, including how to submit an AERA:
Minnesota’s surface waters are impaired by unacceptable levels of mercury, virtually all of which comes from the air. We strive to minimize mercury emissions from new or expanding facilities.
Processes of particular concern for mercury emissions include taconite production, secondary metal processing, fuel combustion in power generation and industrial boilers (except natural gas), and incinerating sewage sludge. Project proposers should identify mercury inputs, accurately quantify their mercury emissions, and outline their steps to minimizing emissions:
These project proposers may be asked to address potential adverse impacts to nearby bodies of water from their mercury emissions. Eating mercury-contaminated fish is a primary way people are exposed to mercury, but it's difficult to assess the risk posed by mercury from one facility to the fish in specific bodies of water. The MPCA has developed a model for risk estimation that eliminates much of the uncertainty.
Use the screening spreadsheet to estimate additional lifetime cancer risks and hazard indices, which is called quantitative analysis in the AERA process. Use Q/CHI spreadsheet to refine the risk estimate using different dispersion techniques. Contact the agency for a current copy of the spreadsheet.
- How is the information from AERAs used?
The AERA can be used as either a stand-alone analysis to be presented to the public or as an iterative screening process indicating if more refined analyses are appropriate. Information from an AERA is used to consider one of the following four possible courses of action:
- The need for further refined and focused analysis of the issues identified through the screening process.
- If no further analysis is needed and the project proposer can complete the environmental review and/or permitting process.
- Implementation of additional pollution prevention and/or mitigating measures to reduce or better disperse emissions.
- Recommendation that risk be evaluated within an Environmental Impact Statement.
- Do AERAs address cumulative exposures?
"Cumulative" can mean many things, including multiple pollutants, multiple endpoints, multiple sources, on-site and off-site, and multiple exposure routes.
The sources of emissions in AERAs are limited to on-site emissions, including on-site point, area and mobile sources. AERAs do however assess various exposure routes including inhalation and ingestion of home-grown vegetables, beef, chicken, eggs and the ingestion of local fish. An AERA is also cumulative in that it addresses exposures to multiple pollutants for multiple health endpoints.
A facility may be required to complete a cumulative AERA. Cumulative AERAs include both on-site and off-site sources as described in the two cumulative air emissions risk analysis guidance documents. The framework behind these documents and their development, accords with EPA guidance and the requirements within Minnesota State EQB rules concerning Environmental Assessment Worksheets. EQB rules concerning EAW completion require information concerning the assessment of cumulative potential impacts. The cumulative potential impacts inquiry requires a Responsible Governmental Unit “to inquire whether a proposed project, which may not individually have the potential to cause significant environmental effects, could have a significant effect when considered along with other projects that:
- are already in existence or planned for the future;
- are located in the surrounding area; and
- might reasonably be expected to affect the same natural resources.” This requirement was defined in the Minnesota Supreme Court decision between Citizens Advocating Responsible Development vs. Kandiyohi County Board of Commissioners. This court appeal is also known as the CARD decision.
- What air quality issues are not addressed in an AERA?
The AERA does not generally evaluate the following:
- Chemicals lacking approved inhalation health benchmarks
- Chemicals lacking emission estimates or emission factors
- Ecological risks from air emissions
- Dioxin/furan/polychlorinated biphenyls ingestion of breast milk by infants
- Traffic emissions not addressed by environmental review methods
- Emergency generator emissions
- Multimedia chemicals with oral toxicity values but no inhalation health benchmarks
- Visibility impacts from a facility
- Carbon dioxide emissions and Climate Change
- Emergency operations
- Airborne microorganisms
- What happens when the risk estimate for the facility exceeds inhalation health benchmarks?
The quantitative threshold of 1 for acute and chronic risk and 1/100,000 for cancer risks is not a regulatory “bright line.” Potential calculated risks under these guidelines suggest a very low probability of the health endpoint assessed, however estimated risks above these guidelines do not guarantee health effects. This is a guideline that allows risk assessors and risk managers to determine whether or not further analysis is necessary or if mitigation should be considered. If a facility's initial AERA assessment shows that a risk that is greater than a quantitative, or Risk Assessment Screening Spreadsheet, guideline the facility may consider refinements in the toxicity assessment, modeling or emission estimates. This may include fully refined dispersion modeling, limited hours of operation, or separation by health endpoint. If an AERA is submitted with refinements and risk estimates are still significantly above risk guidelines, the MPCA will meet with the project proposer to discuss appropriate courses of action. Possible actions may include re-evaluating emission factors used, focusing on qualitative elements of the analysis (e.g., location of nearest residences), prescribing engineering interventions such as increased stack heights for greater dispersion or installation of additional emission controls (e.g., low NOx burners), requiring pollution prevention efforts such as product substitutions or process improvements or risk reduction activities such as off-sets. If engineering interventions are adopted, they may become enforceable permit conditions. The AERA is an iterative process and will likely require supplemental information on the part of the proposer or revisions to the original submittals at the MPCA’s request. The MPCA also will consult with the Minnesota Department of Health for information to further evaluate exposures and potential health risks.