Annual regional air quality index statistics for 2005

In 2005, two new weather regions, Rivière-du-Loup and Témiscouata, were added to the list of regions for which an AQI was calculated. This therefore brought the number of regions to 20, since the Montréal Island is divided into 4 subregions.

The percentage of days for which the AQI was deemed “good” or “acceptable” varied between 82.5% in Montréal (approximately 300 days) and 98.2% in the Saguenay and Lac-Saint-Jean regions (332 days out of the 338 where AQI data was available).

Only the regions of Vallée-du-Richelieu, Rive-Sud de Montréal and Montréal Island experienced a percentage of days where the “poor*” air quality rose above 10%, to 12.6% (45 days out of 358), 13.2% (48 days out of 365) and 17.5% (64 days out of 365) respectively.

Except for the regions of Vallée-du-Richelieu and Montréal, where the percentage of days during which air quality was “poor” was similar to the previous year, the general air quality was “poor” more often in 2005 than in 2004. This situation is attributable in part to an unusually long episode in the winter of “poor air quality” in southern Québec that lasted 8 to 10 days; only the Saguenay and Lac-Saint-Jean regions were spared.

On the Montréal Island, the percentage of hours where the air quality was “poor” totalled 6.1% (538 hours out of 8759 valid hours). For the same reason as that indicated above, this represents 189 more hours than in 2004.

As in 2004, 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.