Peak Levels of Benzene

Maximum levels of a contaminant are important because of potential health or environmental effects of high concentrations. Scientists often find the "99th percentile" reading more helpful in tracking trends than a single, maximum reading. 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 concentrations observed during the year fall above the 99th percentile concentration.

Annual 99th percentile concentrations of benzene have generally declined from 1990 to 2007 (according to trend analysis). Statistically significant trends were found at Edmonton Central (a decrease of 86%) and at Calgary Central (a decrease of 91%). Benzene concentrations at Edmonton East have decreased overall since 1990 (not a statistically significant trend), however concentrations have increased from 2001 to 2007.