Annual regional air quality index statistics for 2009

In 2009, the AQI was calculated for 24 weather regions, since the Montréal Island is divided into 4 subregions.

The percentage of days for which the AQI was deemed “good” or “acceptable” varied between 81.4% on the Montréal Island (approximately 297 days out of 365) and 100% in 4 regions (La Tuque, Mont-Laurier, Lac-Saint-Jean and Saguenay).

Air quality was deemed “poor*” most often in Montréal (18.6% of the time, or 68 days out of 365, which was down slightly in 2008). In terms of hours, this was 5.3% (465 hours out of 8782 valid hours).Compared to the previous year, the percentage and number of days where air quality was “poor*” is similar for most regions, except for the Montréal Island where the percentage is higher.

As in 2008, there was a higher percentage and more days when the air quality was “poor” in Montréal, compared to previous years, because a new generation of devices to measure fine particles has been in use since 2008, the pollutant most responsible for high AQI values. These results cannot be interpreted as a deterioration of air quality compared to the previous years. The circumstances were similar in 2009 for the regions of Bois-Francs, Rive-Sud de Montréal, Lanaudière and Laval, when a new generation of devices to measure fine particles was introduced.

The further away a region is from Montréal, the better the air quality, regardless of direction

* Occurs where the concentration of fine particles is above at least 35 µg/m3 (over a three-hour period) or the hourly ozone concentration is above at least 82 ppb at at least one station in the region.