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The Minnesota Pollution Control Agency (MPCA) hosted their annual air modeling open house on Thursday, July 18, 2019 in their St. Paul office. The event fostered conversation between industry, consultants, and regulators regarding the state's air dispersion modeling policies and methodologies moving forward.

The MPCA discussed proposed updates to the manual and concerns with EPA's resources for modeled emission rates for precursors (MERPs). Several significant takeaways from the seminar are as follows.

  • Ambient boundaries may now be defined by measures that deter general public such as clear signage or video surveillance. Applicants will need to provide maps and plans to denote these boundaries during modeling submittals to be reviewed by the MPCA. Facilities with approved deterrent measures will then maintain records of breeches to ensure effectiveness of the controlled ambient boundaries.
  • New versions of AERMET and AERSURFACE are coming soon which will be able to process more recent land cover data than previous versions which used 1992 data. This will allow the agency to provide updated meteorological data that will more accurately reflect current land usage.
  • EPA's hypothetical source spreadsheet contains three locations in Minnesota, one of which is located in the Twin Cities Metro and based on 2011 emissions data in the area. The MPCA has expressed concerns of overestimation in using the Twin City Metro source, because it is located near a large facility that has significantly reduced emissions since 2011. 

The MPCA is accepting comments on the proposed revisions until the close of business on July 31, 2019. If you have any questions on the MPCA's modeling open house, reach out to Alex Gelz at or (651) 275-9900 ext. 7.