Peak Levels of Benzo(a)pyrene

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 concentration.

Overall, there has been a decreasing trend in 99th percentile benzo(a)pyrene concentrations from 1990 to 2007 (at all stations). The decreasing trends were statistically significant at Edmonton Central, Edmonton East, Edmonton Northwest and Calgary East. The majority of 99th percentile Benzo(a)pyrene concentrations in the cities monitored are above the proposed annual average objective of 0.3 ng/m³. Peak concentrations at the Edmonton East station, however, have dropped below the proposed objective in 2006 and 2007. There was a peak in 1994, which is likely due to a data-handling error or an error in sample analysis.