Adopting updated air dispersion models under the Local Air Quality Regulation (O. Reg 419/05): Adopting AERMOD/AERMET 19191 and ASHRAE 2019

Air dispersion models are mathematical tools used to assess point of impingement concentrations that are then compared to ministry air standards and guidelines. A point of impingement is the point at which a contaminant contacts the ground or a building.

This notice is to inform the regulated community and the public that the MECP is adopting updated approved air dispersion models under O. Reg. 419/05. Adoption of the updated models will take effect upon publishing of this notice.

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, including the AERMOD dispersion model and the ASHRAE method of calculation. Section 13(1) of O. Reg. 419/05 approves the use of meteorological data processed by the AERMET computer program with the AERMOD dispersion model.

The previously adopted versions of these models were:

• The US EPA AERMOD dispersion model version 16216r (version date January 17, 2017) used in conjunction with AERMET meteorological pre-processor version 16216 (version date August 3, 2016).
• The method of calculation for same structure contamination described in Chapter 45 (Building Air Intake and Exhaust Design) of the 2015 ASHRAE Handbook — HVAC Applications, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

The MECP has now replaced the previously approved versions of these models under O. Reg. 419/05 (listed above) with the following updated model versions:

1. AERMOD dispersion model version 19191 (version date July 10, 2019) used in conjunction with AERMET meteorological pre-processor version 19191 (version date July 10, 2019)

2. ASHRAE method of calculation described in Chapter 46 (Building Air Intake and Exhaust Design) of the 2019 ASHRAE Handbook – HVAC Applications

The approved dispersion models and Ontario Regional Meteorological data sets that have been reprocessed with AERMET 19191 (version date July 10, 2019), are available through the Ontario government website (MECP Website on Local Air Quality).

The MECP has developed an implementation plan for model version updates, with input from stakeholders. Key elements of this annual process include the following:

• Monitoring and assessing regulatory model update developments on an ongoing basis and discussing with stakeholders, as required.
• Notifying stakeholders, every year, six months in advance of formally adopting updated versions of the models (stakeholders will also be notified if there are no updates). This will give facilities time to that 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 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.