Peak Levels of Sulphur Dioxide

Map of monitoring stations

Maximum levels of a contaminant are important because of potential health or environmental effects of high concentrations. Scientists often find the "99th percentile" concentration more useful in tracking trends than the maximum value. The annual 99th percentile concentration is the concentration that is higher than 99% of the concentrations recorded throughout the year. In other words, only 1% of the ambient concentrations observed during the year fall above the 99th percentile concentration.

The annual 99th percentile concentrations for sulphur dioxide have decreased at most Alberta stations since 1990 (by 5 to 74%), except those north of Fort McMurray in the oilsands region (increase of 6 to 128% since 1999). The highest 99th percentile concentrations are found at Redwater, Mannix and Mildred Lake. The Mannix station, north of Fort McMurray, also had the most significant increase in 99th percentile sulphur dioxide – a 128% increase since 1999.