Regional Air Quality Modelling in Canada — Applications for Policy and Real-Time Prediction

Acid rain and photochemical smog are two regional air-quality issues that have received considerable attention in the last two decades due to their harmful effects. Health impacts of particulate matter (PM) in the atmosphere is another issue of concern.Sulphur dioxide emission controls were introduced in both Canada and the U.S.A. to reduce acid-deposition-related damage. While these emission reductions have already resulted in reduced sulphate deposition, based on results from modelling studies much of southeastern Canada is still expected to experience damaging levels of acid deposition even after all currently legislated emission controls are fully implemented. Moreover, there has not been a corresponding reduction in the acidity of precipitation. This may be attributable to a concurrent reduction in base-cation concentration in precipitation.Models were also developed to understand the formation, transport and diffusion of tropospheric ozone. The models have been used to provide policy guidance for emission control options to reduce ground-level ozone to acceptable limits. In the summer of 1997 a Canadian pilot project was initiated to provide real-time forecasts of ground-level ozone in the southeastern part of the province of New Brunswick in eastern Canada.With the emergence of fine Particulate Matter (PM_2.5) as a health concern, efforts are underway in Canada to develop a “unified” regional air-quality model that will address the combined impacts of various pollutants in the atmosphere. In this effort the atmosphere is viewed as a single entity where the impacts of multiple pollutants are considered at the same time.