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Air quality dispersion modeling uses a computer model to estimate air pollution concentrations from regulated facilities and other sources of pollution. For pollutants emitted through a stack, modeling takes into account emission rates, stack heights, stack diameters, stack gas temperature and velocities, and the effect of nearby buildings and terrain. The models also factor in other emission sources, such as vehicle emissions or wind erosion from storage piles, and use meteorological data such as temperature, wind direction, and wind speed.

Modeling is particularly important to predict the impacts of new or changing sources of pollution. Results are compared with National Ambient Air Quality Standards (NAAQS)/Minnesota Ambient Air Quality Standards (MAAQS) to ensure that Minnesota air quality is protected from potential emissions. Modeling can also inform the placement of ambient air monitors and human health and ecological risk assessments.

Air modeling policy and practices

The MPCA developed the air quality modeling practices manual to provide current and acceptable modeling practices that conform to state and federal modeling requirements.

Air modeling protocols

Permit applicants who are required to conduct air quality dispersion modeling must first submit an air modeling protocol using MPCA e-Services (see information below). The MPCA reviews the protocols to ensure the modeling inputs and data are complete and follow acceptable practices. If the agency denies a protocol, it must be revised and resubmitted.

Air modeling reports

For air modeling conducted to support a permit amendment, include a copy of the air quality dispersion modeling report (AQDM-06) and all accompanying files with each required copy of the permit application. If you submit your air modeling report before the MPCA has notified you that your protocol was approved, the report won't be approved and your air-permit application will be deemed incomplete.

For air modeling not related to a permit application, send a PDF copy of the air quality dispersion modeling report and accompanying files on a USB drive (preferred) or compact disc to the Air Quality Permit Document Coordinator at the MPCA in St. Paul.

Using MPCA e-Services

Air modeling protocols and modeling information requests should be submitted using MPCA e-Services. If you are modeling for a new facility and can't find it in e-Services, email to request an "agency interest ID." Provide the facility name, its physical and mailing addresses (if available), city, and facility contacts in the email.

New users may also need to request access to MPCA e-Services for their facility:

Before sending in the form, request signatory access to the facility in e-Services using the “Add Facilities” option on the My Workspace page, under the My Facilities section. After hitting Continue on the Access Change screen, your online request will be listed as "pending" until the MPCA receives the form. The agency will email you when you have access to the facility in e-Services.

The tool below displays the point sources, fugitive sources, and corresponding source parameters that will pre-populate in e-Services for a particular facility. Users can also download the data:

Tools for modeling

Background concentrations

Background pollutant concentrations from other sources of pollution, particularly "nearby sources," are a critical component of cumulative modeling analyses. A nearby source is a regulated facility for which ambient air monitoring may not adequately represent its air-pollution impacts; emissions from nearby sources are explicitly modeled.

The nearby source tool uses ArcMap GIS software to map sources within a selected distance and screens for ones that should be included in a modeling analysis.

Use the MN lookup table for NAAQS/MAAQS analysis where nearby sources should be considered.

Ambient air monitoring, which represents the effects of regionally transported pollutants, natural sources, and smaller unidentified sources in the vicinity, provides background concentration data for modeling.

Ozone data

The MPCA has pre-processed hourly ozone data for use in Tier 3 NO2 modeling:

Make a note in the e-Service modeling protocol “Pollutant Based Considerations” section, under “NO2 Tier 3, Additional Information,” that pre-processed hourly data are being used. Learn more:

Urban vs. rural selection

This tool helps determine whether a project or facility location is considered urban or rural, per EPA’s guidance. It calculates the percentage of developed land use within a selected distance and creates a graphical map and numerical output spreadsheet. Greater than 50% developed area is considered urban.

Prevention of significant deterioration (PSD) increment modeling

A PSD increment reflects how much air pollution is allowed to increase in a geographic or baseline area. A PSD increment modeling analysis is created from the pollutant-specific ambient air quality baseline conditions in the project's area. Increment consumption and expansion are determined by emission changes relative to either the major source or minor source baseline date.

Increases in air pollution from major sources after the major source baseline date "consume" increment:

  • Particulate matter > 10 microns in diameter (PM10) and sulfur dioxide: January 6, 1975
  • Nitrogen oxide: February 8, 1988
  • Particulate matter > 2.5 microns in diameter (PM2.5): October 20, 2010

The major source baseline dates are the same for every county in Minnesota.

Increases in air pollution from all sources after the minor source baseline date “consume” increment. In Minnesota, the minor source baseline dates are county specific, based on the date the first complete PSD permit application for that county was submitted to the MPCA.

What's new

  • June 15, 2021: The MPCA expects that particulate emissions from paved roads will be included in ambient air quality modeling demonstrations. To facilitate this practice, we have developed interim modeling practices for paved roads.
  • Draft for comment: Outlines the internal review and approval practice for regulated parties that choose to develop and operate an ambient air quality network rather than conduct an ambient air quality modeling demonstration for compliance demonstration purposes. The practices provided should assist staff with planning, language, and developing ambient air quality monitoring requirements.