What’s the air quality been like this winter?

Posted on March 5, 2013

This winter is a good example of how calmer, colder weather can lead to more incidents of high risk air quality ratings on the provincial Air Quality Health Index scale.

In the last four months (November – February), Edmonton and surrounding areas saw three high risk air quality episodes that together totalled about 21 hours. On the most recent occasion, Alberta Health Services issued a precautionary air quality advisory on February 7 that stayed in effect until February 13. By comparison, Fort Saskatchewan did not have a single hour last winter that rated as a high risk to health.

In the same November to February period, the Air Quality Health Index also recorded a greater number of moderate risk ratings across the region. The Fort Saskatchewan monitoring station, for example, recorded a total of 544 hours in the moderate risk to health category, compared to 115 hours last winter. Even with the higher rate of high and moderate risk hours this winter, it is important to note these ratings make up less than 5 per cent of the time.

As we explain in How cold weather affects air quality, populated areas generate a lot more vehicle idling and chimney smoke that adds to the levels of pollution in winter. On top of this, cold temperatures and stagnant air have a way of creating a build-up of substances near the ground during a weather phenomenon called a temperature inversion. In other seasons or weather conditions, warm air sits near the ground but it can rise easily and carry away pollutants. In a temperature inversion, cold air is trapped near the ground by a layer of warm air. The warm air acts like a lid, holding down pollutant substances like smoke and carbon monoxide.

From an air quality perspective, storms are a welcome weather event. Wind, rain and snow storms are sometimes called scrubbers because they help clear out and disperse substances of concern. But the winter of 2012-2013 has so far been one of calmer, but colder conditions – the “perfect” mix for the higher and moderate risk ratings that have occurred.