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Annual poor air quality statistics

Poor air quality days

A poor air quality day occurs when air quality is poor for at least one hour at one of the stations in the network that measure fine particulates and ozone. The hourly index is deemed “poor” when the average concentration of fine particulates over a three-hour period exceeds 35 micrograms per cubic metre (µg/m3) or when the average concentration of ozone over a one-hour period exceeds 82 parts per billion (ppb). This indicator is calculated by station and takes account of both intense regional smog days and days when poor air quality is observed locally over a short period of time.

Average annual number of poor air quality days in Québec* (2004–2022)

*Based on daily occurrence of at least one hourly concentration of ozone or fine particulates (averaged over three hours) that respectively exceed 82 ppb and 35 µg/m3 at at least one station in the network in each station.

The average number of poor air quality days per station dropped to 8.7 in 2022. This downward result compared to 2021 can be principally explained by fewer summer poor air quality days. In 2021, 47% of poor air quality days occurred in summer, due to widespread forest fires in Northwest Ontario and Manitoba (Fichier PDFFrench, PDF, 33,5 MB). However, in 2022, only 15% of poor air quality days occurred during the summer season (May–October).

Weather conditions impact the dispersion of contaminants, which explains the variation in the number of poor air quality days between years. Nonetheless, the downward trend observed since 2004 suggests that anthropic factors such as legislation, more efficient antipollution systems and the closure of polluting industries (among others) also play a role.

Fine particulates are the main cause of poor air quality days. Ozone caused none in 2022, which is consistent with observations made in recent years.

Number of poor quality air days in 2022 per station*, grouped by administrative region

Number of poor quality air days in 2022 per station*, grouped by administrative region

*Based on at least one daily occurrence of an hourly concentration of ozone or fine particulates (averaged over three hours) that respectively exceed 82 ppb and 35 µg/m3.

The number of poor air quality days by station identifies which ones have the greatest statistical impact. The highest results are observed at urban Capitale-Nationale, Mauricie, Abitibi-Témiscamingue and Lanaudière stations, where levels of urban sources of pollution (transport, wood heating and industrial) are also highest. Most poor air quality days are seen in winter, when residential wood heating is a major source of emissions. This is confirmed by results at the Québec–École Les Primevères, Québec–Charlesbourg and Terrebonne–Parc Vaillant stations. In rural settings, poor air quality days are, generally speaking, rarer, due to the fact that measuring stations there are located far from sources of pollution.

Some stations, such as Trois-Rivières - Cap-de-la-Madeleine and Témiscaming, stand out for very specific reasons. Results from these stations are affected by emissions from nearby industries and explains their high number of poor air quality days.

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