Peak Levels of Ozone

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 for 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 concentrations.

The 99th percentile concentrations for ozone in 2007 ranged between 0.046 - 0.061 parts per million (ppm). Trends in peak ozone concentrations have been variable across the province since 1990, with a statistically significant increase of 13% at Calgary Central, an increase of 17% at Fort McKay, and decreases of 12 and 15%, respectively, at the Fort McMurray and Fort Saskatchewan stations. At the other stations in the province, peak ozone concentrations have remained quite consistent.