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 MOECC 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 07026) used in conjunction with the AERMET meteorological preprocessor (version 06341).
- The method of calculation for same structure contamination described in Chapter 44 (Building Air Intake and Exhaust Design) of the 2007 ASHRAE Handbook — HVAC Applications, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
The MOECC has now replaced the previously approved versions of these models under O. Reg. 419/05 (listed above) with the following updated model versions:
- AERMOD dispersion model version 14134 (version date May 14, 2014) used in conjunction with AERMET meteorological pre-processor version 14134 (version date May 14, 2014), and
- ASHRAE method of calculation described in Chapter 45 (Building Air Intake and Exhaust Design) of the 2011 ASHRAE Handbook – HVAC Applications.
The approved dispersion models and Ontario Regional Meteorological data sets that have been reprocessed with AERMET 14134 (version date May 14, 2014) are available through the Ontario government website (MOECC Website on Local Air Quality).