MICROBIOLOGICAL STUDIES OF AIR MASSES OVER MONTREAL DURING 1950 AND 1951

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Abstract
The numbers of bacteria and fungi in air masses over Montreal, Canada, were determined by sampling at the top of the Sun Life Building, 400 ft. above ground level, from September 1950 to December 1951. During 113 days of sampling, 978 exposures were made with agar plates in the General Electric Bacterial Air Sampler and the Bourdillon Slit Sampler. Eighty-seven exposures for fungus spores were made with silicone coated slides in the Slit Sampler. Most of the air encountered was continental polar either moving direct to Montreal, found on 38 days, or modified by moving over agricultural land, sampled on 51 days. Maritime polar air from the Atlantic was encountered on 21 days, and from the Pacific on one day. Maritime tropic air from the Gulf of Mexico was encountered twice. The seasonal variation of bacteria and fungi in all air masses showed low counts in January, February, and March. Higher bacterial counts were obtained from early April into July and from early September into November, covering a range from 3.0 to 55.0 per cu. ft. Lower counts were found during late July and August. The high fungus counts extended from May into November and covered a range from 5.0 to 56.3 per cu. ft. Both continental polar and maritime polar air that moved over considerable cultivated land showed generally higher counts than where these air masses moved directly to Montreal.