The air we breathe
Each day, you breathe about 11 000 litres of air. Air pollution is harmful substances in that air. It can damage your lungs, heart and brain, harm plants and animals, and change the climate. The World Health Organization estimates that air pollution contributes to millions of early deaths around the world each year. In Canada, Health Canada estimates air pollution contributes to about 17 000 early deaths a year.
Sources of air pollution
| Source | Pollutants |
|---|---|
| Vehicles | Nitrogen oxides, carbon monoxide, particles, carbon dioxide |
| Power plants and factories | Sulfur dioxide, nitrogen oxides, particles, mercury |
| Wildfires | Smoke and fine particles |
| Wood stoves and fireplaces | Fine particles |
| Agriculture | Ammonia from fertilizer and manure; dust |
| Oil and gas production | Methane, volatile organic compounds |
| Natural sources | Volcanoes, dust storms, pollen |
Main air pollutants
| Pollutant | Source | Effects |
|---|---|---|
| Particulate matter (PM2.5 and PM10) | Burning fuel, wildfires, dust | Tiny particles (PM2.5 is 30 times thinner than a hair) reach deep into lungs and blood; cause asthma, heart and lung disease |
| Ground-level ozone | Forms when nitrogen oxides and volatile organic compounds react in sunlight | Irritates lungs; worse on hot, sunny days |
| Nitrogen dioxide (NO₂) | Vehicles, power plants | Irritates airways; forms smog and acid rain |
| Sulfur dioxide (SO₂) | Burning coal, smelting metals | Breathing problems; acid rain |
| Carbon monoxide (CO) | Car exhaust, faulty furnaces | Poisonous; colourless and odourless |
| Volatile organic compounds | Gasoline, paints, solvents | Help form ozone and smog; some cause cancer |
Good ozone vs. bad ozone
Ozone high in the stratosphere is good: it blocks harmful UV rays. Ozone near the ground is bad: it’s a pollutant that harms lungs. "Good up high, bad nearby."
Smog
Smog is a brownish haze of air pollution. The word combines "smoke" and "fog." Today’s smog is mostly ground-level ozone and fine particles, formed when sunlight cooks vehicle and industrial emissions.
In 1952, a deadly smog in London, England, caused by coal smoke killed thousands of people in days, leading to the first major clean-air laws.
Acid rain
When sulfur dioxide and nitrogen oxides mix with water in clouds, they form acids. Acid rain has damaged lakes, forests and buildings.
In the 1970s and 1980s, acid rain killed fish in thousands of lakes in Ontario and Quebec. Canada and the U.S. signed the Air Quality Agreement in 1991, and pollution controls on power plants and smelters have since cut sulfur dioxide emissions dramatically. Many lakes are slowly recovering. It’s a success story showing that pollution can be reduced.
Indoor air pollution
Air inside buildings can be polluted too:
- Radon: a radioactive gas from the ground; a leading cause of lung cancer after smoking. Canadians are encouraged to test their homes.
- Carbon monoxide from faulty furnaces or idling cars in garages. Every home needs a CO detector.
- Tobacco and vape smoke, mould, cleaning chemicals and cooking fumes.
Air pollution and climate
Many air pollutants come from burning fossil fuels, which also releases carbon dioxide, the main greenhouse gas. Cutting fossil fuel use improves air quality and fights climate change at the same time.
Checking the air: the AQHI
Canada uses the Air Quality Health Index (AQHI) to report air pollution risks.
| AQHI | Risk | Advice for at-risk people |
|---|---|---|
| 1–3 | Low | Enjoy outdoor activities |
| 4–6 | Moderate | Consider reducing strenuous outdoor activity if you have symptoms |
| 7–10 | High | Reduce or reschedule strenuous outdoor activities |
| 10+ | Very high | Avoid strenuous activity outdoors |
During the 2023 wildfire season, AQHI readings in many Canadian cities rose above 10.
What can we do?
| Action | Benefit |
|---|---|
| Walk, bike or take transit | Fewer vehicle emissions |
| Don’t idle the car | Less exhaust, especially near schools |
| Switch to electric vehicles and clean electricity | No tailpipe emissions |
| Plant trees | Filter some pollutants and provide shade |
| Use fewer chemical sprays | Fewer volatile organic compounds |
| Follow fire bans | Fewer wildfires |
Common mistakes
- Thinking all ozone is harmful.
- Thinking air pollution is only a big-city problem. Wildfire smoke and wood smoke affect rural areas too.
- Thinking indoor air is always cleaner.
Try it yourself
- Smear petroleum jelly on index cards and hang them in different places for a week. Compare the particles collected with a magnifying glass.
- Check today’s AQHI for your community.
- Track how your family travels for a week and suggest ways to reduce car trips.
Quick recap
- Air pollution harms health, ecosystems and the climate.
- Main pollutants include fine particles, ground-level ozone, nitrogen dioxide and sulfur dioxide.
- Smog forms when sunlight reacts with emissions.
- Acid rain was greatly reduced through international agreements.
- The AQHI tells Canadians how risky the air is each day.