Air Quality Health Index classroom kit, grades 5 and 6, environment: chapter 7

B. Particulate Matter

Pile of blackened firewood burning

In winter, wood stoves can be running full blast in an entire community. The amount of particulate matter in the air can reach very high levels.

Particulate matter can be small or very, very small

Particulate matter (PM) is any speck of solid or drop of liquid so small it floats in the air. Sometimes, it is visible (smoke, soot or dust). Other times, it is so small is seems invisible. It can only be seen with a powerful microscope.

PM is so small that we breathe it into our nose or throat without even seeing it. Some PM travels deep into the lungs, causing illness.

Particulate matter comes from many places

PM is produced directly from renewable and non-renewablesources. The main sources from people are wood burning, such as wood stoves and forest fires (renewable), and diesel for offroad vehicles (non-renewable).

Road salt

Another source of PMduring winter is road salt.


A direct source of PM is burning fossil fuels (non-renewable) or biomass (renewable) to make electricity. Biomass power plants burn lumber, agricultural waste, building waste, or wood waste. Special equipment can be used to avoid putting PM out into the air.

Particulate Matter gets into the lungs

In some provinces and territories, PM is the most serious kind of local air pollution. It can be more dangerous to human health than ground-level ozone and other air pollutants.

A magnified  human hair is shown alongside two dots of different size where the bigger dots represent the PM10 and the smaller the PM2.,5

How Small Is Small?

  • PM is so small, it is measured in micrometres (µm). Look at a ruler and find the millimeters. Micrometres are so small you can fit 1000 of them in one millimetre!
  • PM that has a diameter of 10 µm or less is called PM10. It is seven times smaller than the width of a human hair.
  • PM2.5 has a diameter of 2.5 µm.

Did You Know?

No safe level has been identified for PM. People with respiratory problems may be affected by even a small decrease in air quality.

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