Air quality and weather

Improvements to the air quality model forecast maps are coming in June!

We are redesigning the FireWork webpage to improve usability and to provide access to upgraded air quality model forecast maps. The upgraded maps will provide forecasts of fine particulate matter (PM2.5) from wildfire smoke, along with the overall forecasts of total fine particulate matter (PM2.5), nitrogen dioxide, and ozone. These are the three pollutants used to calculate the Air Quality Health Index.

As a result of the redesign, the Air Quality model forecast webpage will be removed.

This redesign will be available at the end of July. Until then, smoke forecast maps on the FireWork webpage will continue to display the portion of PM2.5 emissions attributed to forest and wildland fires.

More information to follow.

How the weather affects air quality

Several weather conditions can come together resulting in a deterioration of air quality.

Wind can carry pollutants towards us or away from us.  Smoke from forest fires, as well as other less visible pollutants, can be carried over long distances to arrive on our doorstep.  When there is little or no wind, local pollutants build up in the air.  We see this in both summer and winter under temperature inversions that come with light or no wind.

Temperature Inversion. Hot air rises - this is how hot air balloons work.  We normally have warm air at ground level, and cooler air above.  In a temperature inversion, the temperatures are upside down - the cooler air is at ground level, and the warmer air higher up.  The cooler air cannot rise, and the warmer air above acts like a lid, trapping pollutants at the ground where we live and breath. Inversions can persist for hours or days.

Topography can create conditions that trap pollutants.  At night, cold air tends to drain downhill, settling into low-lying basins and valleys.  Unable to rise, the cool air settles and accumulates in these valleys, trapping air pollutants.

Long-range transport carries pollutants within the air hundreds and even thousands of kilometres from the source. Winds coming from the United States and industrialized areas of Ontario and Quebec can result in higher levels of air pollutants in neighbouring Canadian cities. 

Clear, cloudless skies allow more sunlight and UV to reach the Earth’s surface.  The intense summer sun causes chemical reactions among the pollutants that are already in the air, leading to the formation of ground-level ozone, a major component of smog.

How the weather affects wildfire smoke

Weather is a critical factor that affects whether a fire will start, how it will behave after it starts, and how the smoke will spread.

Dry conditions

Heat and Heat Waves


For more information

Air Quality and Weather Videos

Weather and Air Quality poster

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