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Annual poor air quality statistics

Poor air quality days

A poor air quality day is defined as a day during which the air quality index is deemed “poor” at one station for at least one hour. An hourly index is deemed “poor” when the average three-hour concentration of PM2.5 is greater than 35 micrograms per cubic meter (µg/m3), or when the hourly ozone concentration is greater than 82 parts per billion (ppb). This indicator takes into account extreme smog days occurring both on a regional scale, and days when poor air quality is observed locally, over a short period of time.

Average number of poor air quality days by administrative region*, 2004–2016

*Based on the occurrence of either a three-hour PM2.5 concentration greater than 35 µg/m3 or an hourly concentration of ozone greater than 82 ppb at a minimum of one station in the region

Weather conditions influence the dispersion of contaminants, which explains the variation in the number of poor air quality days from one year to the next. However, the downward trending observed since 2004 suggests that anthropic factors such as legislation, high-performance antipollution systems and closure of polluting plants are also involved.

In 2016, the number of poor air quality days by administrative region continued its downward trend. Over a five-year period, the number of poor air quality days dropped by 57% overall. The only administrative regions in which results were above the 19.7 day average were Capitale-Nationale, Mauricie, Montréal and Abitibi-Témiscamingue.

Ozone contributed to the formation of only one poor air quality day in 2016.

Number of poor quality air days in 2016 per station*, grouped by administrative region

*Based on the occurrence of either a three-hour PM2.5 concentration greater than 35 µg/m3 or an hourly concentration of ozone greater than 82 ppb at a minimum of one station in the region

The number of poor air quality days per monitoring station makes it possible to determine which stations have the greatest impact on this statistic. The highest results are observed at urban monitoring stations in the Capitale-Nationale, Mauricie, Montréal, Abitibi-Témiscamingue, and Laval regions, which can be explained by a higher density of emissions sources in these areas (transportation, residential wood heating and industries). Some stations, like the one in Témiscamingue, stand out for very specific reasons; this particular station is under the influence of emissions from a nearby plant, hence the high number of poor air quality days. Generally speaking, poor air quality days in rural areas are rather rare, sincemonitoring stations are not under the influence of known sources of pollutants.

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