Updated air dispersion model versions under the local air quality regulation

Air dispersion models

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

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. This includes:

• The US EPA AERMOD dispersion model
• the ASHRAE method of calculation
• The US EPA SCREEN3 dispersion model

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 air dispersion models were:

• the US EPA 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) 
• the method of calculation for same structure contamination 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 (ASHRAE)
• the US EPA SCREEN3 dispersion model version (version date February 12, 2013)

Updated versions of the air dispersion models

We have replaced the previously approved versions of the AERMOD air dispersion models under O. Reg. 419/05 with these updated versions:

• AERMOD dispersion model version 22112 (version date April 22, 2022) used in conjunction with AERMET meteorological pre-processor version 22112 (version date April 22, 2022)

The approved dispersion model versions and Ontario Regional Meteorological data sets that have been reprocessed with AERMET 22112 (version date April 22, 2022) are available through the Ontario government website (MECP Website on Local Air Quality).

Implementation plan for model version updates

We developed an implementation plan for model version updates with input from stakeholders. Key elements of this annual process include:

• monitoring and assessing regulatory model update developments on an ongoing basis and discussing with stakeholders as required
• notifying stakeholders approximately six months in advance of formally adopting updated versions of the models to give facilities time to determine if they will be affected by model updates and to develop a path forward as needed
• posting a bulletin on the Environmental Registry approximately six months following prenotification to formally adopt the updated model versions
• updating regulatory data files/instruments and guidance materials to reflect the adoption of updated model versions as necessary

We will adopt updated model versions annually as necessary. Stakeholders will also be notified if there are no updates.