Paul Makar
Air Quality Modelling and Integration Division
Comparisons of air-quality model results to observations
collected during a measurement intensive in August of 2001 showed
significant overpredictions of many chemicals in urban regions. An
analysis of the model processes suggests that the cause of these
overpredictions lies in the forecast atmospheric stability, with
insufficiently strong vertical diffusion relative to the ambient
atmosphere. A simple anthropogenic heat emissions parameterization,
incorporated into the operational regional GEM forecast model, suggests
that urban heat islands may account for the reduced stability over urban
regions. The results also suggest that incorporation of urban heating
effects may substantially improve forecasts of air quality and air
temperature in urban centres, particularly at night.