AbstractsGeography &GIS

Time variations of soiling index at three locations in central Montreal are analysed. The average week end reduction in smoke is about 20 percent. Readings adjacent to Mount Royal Park are reduced by nearly one half, but no attempt is made to separate out the effects of the Park acting as a smokeless zone, and the mountain acting as an obstacle to the wind flow. Data from the elevated location, together with visual observations, suggests that at night the smoke over the city is usually confined to a layer several hundred feet deep. A simple model is developed to consider the modification of stable air as it moves across a city acting as a heat and smoke source. An adiabatic mixing layer of increasing depth builds up due to the accumulation of heat. Applying this model indicates that half of the smoke in mid-winter is due to heating of buildings.