Note: Measurement of aerosol optical depth is conducted by the Canadian sunphotometer network. In a study to investigate spatial and temporal commonalities between the network member stations, data for the 1987-1992 period were statistically analyzed. Four stations, all located in rural areas and free of local pollution, were chosen to provide a spatially representative sampling of atmospheric optical conditions across Canada (i.e. east coast, eastern continental, western continental, and west coast). One of the four was Sable Island. The results showed significant differences between eastern and western Canadian stations. The effect of the volcanic eruption of Mount Pinatubo (Philippines) in June 1991 was clearly seen in the measurements acquired at Sable