Sulfate is a major constituent observed in Arctic haze. Sulfur sources include anthropogenic, biogenic, and other natural sources. Previous studies have examined the concentrations and temporal variability of the concentrations of methanesulfonic acid (MSA) and sulfate (SO=4) at Alert, Northwest Territories, Canada. A receptor modeling method called the potential source contribution function (PSCF) combines the concentration data for these species measured in 7-day samples continuously collected between 1980 and 1991 with meteorological information in the form of air parcel back trajectories into conditional probability maps indicating the possible source areas and/or the preferred pathways that give rise to the observed high-concentration samples. After examination of the time series for MSA and SO=4, the data were segregated into time periods representing the spring, summer, and winter months and the PSCF analyses performed based on criterion values of the annual average species concentration. The potential source contribution method has been found to be effective in identifying possible source locations and the preferred pathways of MSA and SO=4 in samples collected at Alert. Two concentration peaks are typically observed in the time series for MSA. The time series for SO=4 is quite different from the series for MSA. The SO=4 series only has peaks in the winter caused primarily by anthropogenic emissions. It was found that different regions of the North Atlantic Ocean contribute to the observed MSA concentrations during these different periods in agreement with prior hypotheses. Sources areas for sulfate during the summer and MSA during the winter can only be observed by changing the criterion value to the average during the period. ¿ American Geophysical Union 1995