The Ministry of the Environment and Climate Change (MOECC) has adopted by reference into law the use of two updated air dispersion models under section 6 of its Local Air Quality Regulation (O. Reg. 419/05). These models are used to determine whether a facility meets the MOECC's local air quality standards and guidelines. An information notice (EBR Registry #012-5177) announcing the change was posted to the Environmental Registry on November 2, 2015. Adoption of the updated models took effect on that date.

The MOECC has replaced the previously approved versions with the following updated models:

  • The US Environmental Protection Agency's AERMOD dispersion model version 07026 is replaced with version 14134, dated May 14, 2014.
  • The AERMOD model is to be used in conjunction with the AERMET meteorological pre-processor version 14134, dated May 14, 2014, which replaces the earlier version 06341.
  • The ASHRAE method of calculating same structure contamination, described in Chapter 45, "Building Air Intake and Exhaust Design," of the 2011 ASHRAE Handbook – HVAC Applications, replaces the method set out in the 2007 edition.

The mathematical models are used to assess the concentration of air contaminants at the "point of impingement" where they contact the ground or a neighbouring building. The calculated results are then compared to the MOECC's general air standards, site-specific standards, technical standards or guidelines, as applicable.

The approved dispersion models, as well as the Ontario Regional Meteorological data sets (that have been reprocessed with the updated AERMET 14134 version), are all available through the MOECC's Rules on Air Quality website at www.ontario.ca/page/rules-air-quality-and-pollution. Additional information is available from MOECC's Air Quality Monitoring and Transboundary Air Sciences Section by e-mail at MetDataENE@ontario.ca or by telephone at 416-235-6171.

As dispersion models continue to evolve, stakeholders will receive advance notification six months in advance of the formal adoption of any future updated versions. They will also be notified, on an annual basis, if there will be no updates that year. MOECC says this will give facilities time to contact their local District Office for any assistance that may be needed "in developing a path forward." Notice will also be posted on the Environmental Registry six months following pre-notification to formally adopt the updated model versions.

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