Ontario’s air pollution regulation, 419/05, uses an American computer model to estimate how much air pollution from a stationary source reaches a point of impingement, usually the property boundary. This model, AERMOD, is used to determine whether organizations are complying with air emission limits in the regulation, and in their Environmental Compliance Approvals.
Like all computer models, AERMOD is imperfect, and it has been designed to be very conservative, that is to overestimate the emissions of individual facilities. In December, the US Environmental Protection Agency released an update to the model so that it more accurately reflects weather conditions as night turns to day and vice versa. The result is a dramatic reduction in the predicted air impacts of many facilities: 40 to 50% or more. This may have a significant impact on what organizations have to spend to reduce their emissions. Many Ontario businesses are facing significant new air limits under regulation 419/05 on February 1, 2013; some may now be able to make significant changes to their air pollution control plans.
Under section 6 of the regulation, made under the Environment Protection Act, the US EPA version of AERMOD, as amended from time to time, is automatically an approved dispersion model. Nevertheless, the Ministry of the Environment Technical Standards Branch is demanding that organizations apply for their permission to use the updated computer model. Otherwise, they must continue to use the old model, which may substantially over predict their emissions.