In April 2026, the Ministry of the Environment, Conservation and Parks (MECP) will adopt the updated AERMOD/AERMET air dispersion model version 24142 under Ontario Regulation 419/05, Air Pollution – Local Air Quality. The currently approved model version is 22112. This update reflects the latest advancements in atmospheric science and is intended to enhance the accuracy of air quality assessments in determining whether industrial facilities comply with Ontario’s stringent environmental standards.

The MECP will not be adopting a new version of the ASHRAE method of calculation at that time. The approved version will remain as Chapter 46 (Building Air Intake and Exhaust Design) from the 2019 ASHRAE Handbook – HVAC Applications. Facilities must continue to use this version for any assessments involving same-structure contamination under O. Reg. 419/05.

While the new model version is not expected to produce significantly different results, individual circumstances for a facility will determine impacts to predicted concentrations when using the new model. Beginning in April 2026, facilities conducting AERMOD modelling assessments for modifications will be required to use the updated modelling version. It is also recommended that facilities planning to submit an ECA application within six months of April 2026 consider using the new AERMOD version, as MECP review engineers may potentially request modelling using the new version if their technical review process falls close to that date.

It is important to note that MECP approval is required before using any alternative dispersion models. Facilities wishing to use AERMOD/AERMET version 24142 prior to its formal implementation in April 2026 may seek approval under section 7(1) of O. Reg. 419/05.

If you have any questions or require modelling updates, please call us at 437.291.2527 or email Sundar Sadashivam of Trinity’s Toronto office.