Atmospheric Disperson Models

What is a Dispersion Model?

A Dispersion Model is a tool used to predict the concentration of a contaminant at a receptor resulting from point, area or volume exhaust sources. Dispersion models use mathematical algorithms that simplify atmospheric dispersion and dilution phenomena. Typical model input variables include: contaminant emission rates; stack height; gas temperature; discharge velocity; flow rate; terrain topography; property dimensions; and building elevations.

When are Dispersion Models used?

Dispersion models are used to predict the impact of contaminant emissions at locations surrounding the source. Dispersion modelling is commonly used to demonstrate Regulation 346 compliance, when applying for a Certificate of Approval (Air) permit, or when developing or assessing abatement strategy.

Which Model Should I Use?

Regulation 346 dispersion equations have been used in Ontario for the past 30 years. However, in March 2001, the Ministry of the Environment issued a discussion paper on "Updating Ontario's Dispersion Models" that proposes the adoption of U.S. EPA model AERMOD. This model is considerably more stringent than the older models and the phase-in period and new compliance assessment protocols are as yet undetermined. In addition, the MOE recently lowered the allowable point of impingement concentration for 14 contaminants, and is progressively adding and evaluating others..

The following table identifies some of the common models used today.