Air Emissions Risk Analysis (AERA) —
Emissions
One of the key elements in producing meaningful results in an Air Emission Risk Analysis (AERA) is providing a comprehensive list of pollutants and their emission rates. Without these data, the quantitative risk analysis will be inadequate and unreliable. The chemical list and the emission factors associated with that chemical list are the backbone on which the risk estimates are determined. As such, it is crucial that a facility make a good faith effort to provide emission rates and a complete list of chemicals of potential interest.
Emissions estimating guidance and an emissions estimating form are now available to facilitate the process of generating and documenting emission estimates.
What is an Emissions Factor?
"Emission factor" means the most accurate and representative emission data available from the sources contained in Minn. R. 7005.0100, Subp. 10a. The complete rule is available on the Minnesota Revisor's Office Web site. 
Emissions Data Resources
The following list provides some sources of emissions data have been used by project proposers in assembling air emission permit applications for the MPCA:
- Compilation of Air Pollution Emission Factors; AP 42
Introduction to AP-42 - California’s Best Available Control Technology
- California Air Toxics Emission Factors Search
- NCASI Technical Bulletins(forest products—mainly paper but some wood products also).
- North Carolina DENR Division of Air Quality
Emissions Estimating Guidance
The Emissions Estimating Guidance provides general guidance for preparing emission estimates for input into the risk analysis screening spreadsheet (RASS) AERA, and is to be viewed as a supplement to the MPCA’s AERA Guidance. It is the goal of the MPCA that emission estimates used in an AERA should be the most accurate estimate of emissions over the appropriate timeframe with a reasonable certainty that chemical emission rates are not underestimated, irrespective of the data source from which they are derived.
The MPCA regulates PM2.5 in air quality permits. Information on emissions of PM2.5 must now be included in all total facility permit applications. Additional information on PM2.5 and air permitting can be found on the PM2.5 and Air Quality Permits Web page.
The Estimating PM2.5 Emissions for AERAs guidance is reflected in the MPCA’s Air Emissions Risk Analysis (AERA) Guidance Version 1.1 dated September 2007 in section 2.6.1 “Criteria pollutants” and section 3.4.8 “PM2.5.”
- Estimating PM2.5 Emissions for AERAs (March 2006)
The emissions estimating form is now in an excel spreadsheet. The calculations and questions will be used to simplify and expedite the review of air emissions submitted to the Agency for Air Emission Risk Analyses.
- Engineer Form (February 2006)
Estimating Emissions from Natural Gas Combustion Sources
MPCA staff reviewed past practices of the onsite sources that should be included in the Risk Analysis Screening Spreadsheet (RASS) Q/CHI Spreadsheet and concluded that emissions from utilizing natural gas as a fuel should also be quantified. If your facility utilizes natural gas as a fuel in boilers or other devices and you are completing an AERA, the combustion products and their emissions from natural gas need to be included in the RASS and Q/CHI Spreadsheet.
Several developments prompted a review of the exclusion of emissions when utilizing natural gas. These developments include the availability of information, improved tools for assessing health impacts, and the need to address the health impacts of natural gas combustion in a facility’s evaluation.
Exempting Quantitative Review of Specific Pollutants
The following pollutants with E rated emission factors based on detection limits from AP-42 do not need to be included in quantitative emission estimates from natural gas fueled boilers because of the uncertainty associated with them. Instead, they should be discussed qualitatively. All other pollutants with AP-42 values should be included quantitatively.
- 56-49-5 3-Methylchloranthrene
- 57-97-6 7,12-Dimethylbenz(a)anthracene
- 83-32-9 Acenaphthene
- 203-96-8 Acenaphthylene
- 120-12-7 Anthracene
- 56-55-3 Benz(a)anthracene
- 50-32-8 Benzo(a)pyrene
- 205-99-2 Benzo(b)fluoranthene
- 191-24-2 Benzo(g,h,i)perylene
- 205-82-3 Benzo(k)fluoranthene
- 218-01-9 Chrysene
- 53-70-3 Dibenzo(a,h)anthracene
- 193-39-5 Indeno(1,2,3-cd)pyrene
- 7440-41-7 Beryllium
- 7782-49-2 Selenium
Operating Scenario
Potential to Emit or Estimated Future Actuals
The project proposer may choose to assess emissions at the facility’s Potential to Emit (PTE) as defined by state and federal rules. Alternatively, the project proposer may estimate another future operating scenario that is not the PTE but another business case. This alternative scenario is defined in the AERA as "estimated future actual emissions." If the facility chooses to assess this operating scenario, the project proposer must submit business information to support the future case, as well as three years of toxic release inventory (TRI) information for existing facilities to show current business conditions. The project proposer may need to propose production-based permit limits to restrict operating conditions that might lead to unassessed levels of risk.
Who to Contact
Construction and Operating Permits Supervisors
- Steven Pak, 651-757-2633
- Carolina Schutt, 651-757-2706
- Paula Connell, 651-757-2285
Policy
- Anne Jackson 651-757-2460
Risk Evaluation and Air Modeling Unit Supervisor
- Shelley Burman 651-757-2255
