The Seasonal, Weekly, and Daily Cycles of Atmospheric Smoke Content in Central Montreal

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Abstract
Time variations of soiling index measurements obtained from three AISI smoke samplers located in Central Montreal during the period January I960-April 1963 are analyzed. A marked seasonal cycle is found, with midwinter smokiness two to three times midsummer values. The mean value at an elevation of 600 ft on the summit of ML Royal is only 21% of that in the city below. A 46% reduction in smoke is also observed at the location adjacent to the large Mt. Royal Park. The. average weekend reduction in smoke is approximately 20% with a significant change in the diurnal pattern on Sunday. There are two basic types of weekday daily cycle. A winter type with small amplitude, and morning and evening maxima of similar magnitude; a secondary late evening peak is also noted. A summer type with large amplitude and a marked morning maximum. The time of morning peak at the upper station lags behind the lower stations by 2-3 hr in the winter, but in the summer the peaks occur almost simultaneously. These two types are related to the interaction of the daily cycles in both smoke production and ventilation of the city’s atmosphere.

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