Modeling Guidance Documents

AQD dispersion modelers created two guidance documents that explain how to perform and submit dispersion modeling for Permit to Install (PTI) applications. These documents outline current air quality modeling policies. The first document details methodologies on how to perform a modeling analysis and the second document provides some technical modeling considerations when setting up a dispersion model.  NOTE: the information within does not supersede any state or federal rules. 

• Air Dispersion Modeling Guidance Document- How to Model
• Air Dispersion Modeling Guidance Document- Technical Modeling Considerations

Meteorological Data Map for Air Permit Dispersion Modeling

Program Contact

Robert Irvine, Air Quality Division
IrvineR@Michigan.gov
517-648-7367

The Meteorology Data Map for Air Permit Dispersion Modeling displays AERMOD ready meteorological data for our 72 available meteorological (met) stations. After selecting a met station, download the stations ZIP files which includes a five-year dataset with both Surface Met Data and Profile Met Data. USEPA recommends the use of one-minute met data for input in dispersion modeling. Their reasoning is that hourly average winds calculated with the one-minute meteorological data are more reflective of actual conditions as opposed to the single two-minute observation used with the hourly met data. For more information on the data, see the About Map or the About Data section. 

AERMOD is the preferred USEPA regulatory dispersion model; therefore, only meteorological data to be used with AERMOD is available for download. 

When performing regulatory modeling for a stationary source, it is important to use data from the station most representative of conditions at the source location. The representativeness of a station is often measured by proximity. However, proximity alone does not guarantee that a particular station is the most representative station. The AQD can be consulted to help identify which station is the most representative for a specific modeling demonstration. 

The Meteorology Data Map for Air Permit Dispersion Modeling also displays Air Quality Control Regions (AQCR’s) across Michigan and the Major and Minor Source baseline dates for each region.  This information is displayed by clicking on any county within one of the AQCR’s. For more information on the data, see the About Map or the About Data section. 

Contact

Jim Haywood, Air Quality Division
HaywoodJ@Michigan.gov
517-648-6766

Ambient Backgrounds

Modeling for sources emitting criteria pollutants may be required to demonstrate compliance with National Ambient Air Quality Standards (NAAQS). If a demonstration is needed, guidelines specify that ambient backgrounds be added to predicted concentrations. Ambient backgrounds are calculated via data made available from various air monitoring stations located across the region. 

The appropriate selection of a particular air monitoring station depends on several factors including, but not limited to, the following: 

• proximity of the monitor to the modeled source, 
• demographics and geography of the modeled source, 
• location of the monitor with respect to the modeled source (e.g. upwind or downwind based on prevailing winds), 
• available years of data, 
• sighting objective of the monitor, completeness of data, and 
• availability of data from a potentially more representative monitor. 

When calculating a background, use data from the last three years. If data from the last three years is not available, consult with the AQD about alternatives that can be considered. 

Contact

Stephanie Hengesbach, Air Quality Division
HengesbachS1@Michigan.gov
517-648-7015