Daily air measurements at one midcontinental and two coastal sites on the Atlantic Ocean and Pacific Ocean in Canada during April 1992 to June 1993 are used to show the seasonality of methanesulfonate (MSA), non-sea-salt (nss) SO=4, and SO2. At the Atlantic site, Kejimkujik National Park, Nova Scotia (44¿22'N, 65¿12'W), the concentration ranges were <0.002--0.13, 0.2--26, and <0.2--10 μg m-3 for MSA, nss SO=4, and SO2, respectively, and the annual means were 0.02, 2.2, and 1.3 μg m-3. MSA had a monthly median peak of 0.036 μg m-3 in June, versus an SO2 peak of 2.7 μg m-3 in February, and no discernible nss SO=4 seasonal peak. The MSA/nss SO=4 ratios were low compared to ratios in other parts of the world but exhibited a seasonality dominated by that in MSA. At the midcontinental site, Experimental Lake Area, Ontario (49¿39'N, 93¿43'W), the concentrations were usually lower than at the coastal sites. The ranges were <0.002--0.066, 0.04--12.5, and <0.16--16.6 μg m-3 for MSA, nss SO=4, and SO2, respectively, and the annual means were 0.01, 1.6, and 0.93 μg m-3. The monthly median seasonal peaks at this site were 0.01 μg m-3 for MSA in September, 2.1 μg m-3 for nss SO=4 in March, and 2.8 μg m-3 for SO2 in January. The MSA/nss SO=4 ratio at this site was similar to that found at Kejimkujik. At Saturna Island, British Columbia (48¿47'N, 123¿08'W), the ranges were 0.002--0.2, 0.14--6.4, and 0.12--21 μg m-3 for MSA, nss SO=4, and SO2, respectively, and the annual means were 0.06, 1.1, and 3.0 μg m-3. The monthly median peaks were 0.12 μg m-3 for MSA in August, 5 μg m-3 for SO2 in February, and a nominal peak of 1.5 μg m-3 for nss SO=4 in August. The MSA/nss SO=4 ratio had a seasonal pattern dominated by that of MSA with a peak of 0.1 in August. These data should enhance the existing databases for testing global sulfur models. ¿ American Geophysical Union 1996