As air dispersion models are constantly evolving as new science becomes available, MECP developed an implementation plan for model version updates to ensure we continue to use the best available science, and to provide clarity and consistency to the regulated community and stakeholders. This implementation plan was developed with input from stakeholders. Key elements of the plan include the following:

  • Monitoring and assessing regulatory model update developments on an ongoing basis and discussing with stakeholders, as required.
  • Notifying stakeholders, every year, approximately six months in advance of formally adopting updated versions of the models. This will give facilities time to determine if they will be affected by model updates and if so, to contact their local district office for assistance in developing a path forward, as needed.
  • Posting an Information Notice on the Environmental Registry approximately six months following pre-notification to formally adopt the updated model versions. We will adopt updated model versions annually as necessary.
  • Updating regulatory data files/instruments, and guidance materials to reflect the adoption of updated model versions, as necessary.

Ontario’s local air quality regulation (O. Reg. 419/05: Air Pollution – Local Air Quality) under the Environmental Protection Act is part of the province’s air management framework. It regulates air contaminants released into communities by various sources, including local industrial and commercial facilities.

The regulation includes three compliance approaches for industry to demonstrate environmental performance and make improvements when required. Industry can:

  • meet the air standard
  • request and meet a site-specific standard
  • register and meet the requirements under a sector-based technical standard (if available)

Most Ontario facilities are regulated by the air standards compliance approach (i.e., meet the air standard), although all three approaches are allowable under the regulation.

Models are part of the air standards and site-specific standards compliance approaches. Section 6 of O. Reg. 419/05 provides a list of approved dispersion models for use in assessing compliance with air standards or site-specific standards under the regulation. Currently, the approved dispersion models are:

  1. The AERMOD dispersion model (version 19191) available from the Ministry of the Environment, Conservation and Parks (MECP).
  2. The ASHRAE method of calculation. Section 1(1) of O. Reg. 419/05 defines the “ASHRAE method of calculation” to mean the method of calculation described in Chapter 46 (Building Air Intake and Exhaust Design) of the 2019 ASHRAE Handbook – HVAC Applications, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers.
  3. The SCREEN3 dispersion model on the USEPA's website, or available from the MECP.
  4. The method of calculation required by the Appendix to Regulation 346, if section 19 of O. Reg. 419/05 applies to the discharges. Note that these Regulation 346 models will be phased out on February 1, 2020.

In addition, section 13 of O. Reg. 419/05 provides a list of types of meteorological data, including regional surface and upper air meteorological data for use with AERMOD that must be processed using the AERMET model (meteorological preprocessor for the AERMOD model). The current regulatory model version for AERMET is AERMET meteorological preprocessor version 19191.

Under subsection 177 (6) of the Environmental Protection Act, the adoption of an amendment to a document that has been incorporated by reference (e.g. AERMOD/AERMET/ASHRAE), comes into effect once the MECP publishes a notice of the amendment in either The Ontario Gazette or the Environmental Registry under the Environmental Bill of Rights, 1993.

In keeping with the implementation plan, in April 2023 the MECP will be posting an Information Notice on the Environmental Registry to replace current regulatory models under O. Reg. 419/05 with the following updated model versions:

  1. AERMOD dispersion model
    • will be updated to AERMOD version 22112 (version date April 22, 2022)
  2. AERMET meteorological preprocessor
    • will be updated to AERMET version 22112 (version date April 22, 2022), and
  3. ASHRAE method of calculation
    • will be updated to Chapter 46 (Building Air Intake and Exhaust Design) of the 2019 ASHRAE Handbook – HVAC Applications

The ministry will make the approved dispersion models available through the Ontario government website.

Ontario Regional Meteorological data sets, reprocessed with AERMET 22112 (version date April 22, 2022), will be made available once the Information Notice is posted on the Environmental Registry. Until that time, proponents may request copies of the reprocessed meteorological datasets from the Environmental Monitoring and Reporting Branch at

Additional information may also be obtained from:

Ministry of the Environment, Conservation and Parks
Air Quality Monitoring and Transboundary Air Sciences Section
Environmental Monitoring and Reporting Branch
125 Resources Road, Toronto, ON M9P 3V6