In May 2025 the Michigan Department of Environment, Great Lakes, and Energy (EGLE) Air Quality Division (AQD) published two new guidance documents for air dispersion modeling: How to Model and Technical Modeling Considerations. These guidance documents are meant to provide direction on air dispersion modeling analyses performed in Michigan. It’s important to note that this guidance is truly only guidance, and it does not supersede any state or federal rules. The guidance follows United States Environmental Protection Agency (USEPA) guidelines published in 40 CFR 51, Appendix W.
The How to Model guidance details the different methodologies for performing an air dispersion modeling analysis as well as the different types of analyses that may be needed. For those unfamiliar with air dispersion modeling, the discussion on modeling analyses provides a great summary of when the different levels of analysis are required. The guidance also provides detail on completing air dispersion modeling under R 336.1227(1)(c) to satisfy the health-based screening level assessment under R 336.1225.
The Technical Modeling Considerations guidance provides technical details to assist in developing the air dispersion models. This includes details on setting up facility boundaries, adding receptor grids, finding meteorological data, and facility sources. New dispersion modelers will find this guidance helpful in understanding the basic inputs to an air dispersion model. Seasoned air dispersion modelers who may be unfamiliar with modeling in Michigan can benefit from the Michigan specific guidelines that may differ from approved methodologies in other jurisdictions.
When preparing an air dispersion modeling analysis for air permitting, Trinity highly recommends communicating with EGLE early and often during the modeling exercise. This will ensure the analysis satisfies EGLE’s requirements and will minimize additional review time during the application review process. For Prevention of Significant Deterioration (PSD) applications, EGLE requires a modeling protocol to be submitted through MiEnviro Portal prior to application submittal. The modeling protocol will be shared with USEPA so that all parties can come to agreement on the modeling analysis that will be completed. The modeling protocol can also form the basis for the air dispersion modeling report that will be required with the permit application.
Trinity Consultants was founded in 1974 and very quickly moved into the air dispersion modeling space. As a result, Trinity has extensive experience from small to complex air dispersion modeling projects. For more details on Trinity’s air dispersion modeling capabilities please visit Trinity’s website or contact our Ann Arbor office.
