Pollution & air quality
Outdoor air quality
Smog can cause health problems in everyone, even in people who don’t have lung disease. It can damage your lungs and heart. Certain people are more sensitive to smog. If you have a lung or heart disease, you should take extra steps to protect your breathing on smog days – learn about strategies to protect your breathing on smog days.
What is smog?
The word smog was first used to describe a mixture of smoke and fog. Today when we talk about smog, we’re talking about a harmful mixture of gases and particles. Smog is a form of air pollution.
Smog can be made up of several kinds of pollutants. Sometimes smog is invisible, because some pollutants in smog are gases or tiny particles that are too small to see. Other times smog is clearly visible as a haze in the air. It depends on the mix of pollutants and other factors such as humidity.
What are the main pollutants in smog, and what are their health effects?
Smog is a mixture of pollutants. Different pollutants in smog can have different health effects. Read more about the main pollutants in smog and their health effects.
How does smog affect our health?
Health effects of smog may include:
- eye, nose and throat irritation
- coughing and wheezing
- worsening of symptoms for people who have lung diseases like asthma and COPD
- difficulty breathing
- reduced lung capacity
- lowered resistance to infections
- increased heart and lung conditions
- increases in visits to emergency room and hospital admissions
- premature death1
Is it true that smog can kill?
Yes. Studies show that smog can make people die before their time. Researchers looking at the health of people in eight large Canadian cities found that smog causes 5 900 early deaths every year.2
Who is most sensitive to smog?
Smog can damage everyone’s health. Some people are especially sensitive:
- people with lung diseases, such as asthma and COPD (emphysema and chronic bronchitis)
- people with other long-term health problems, like heart disease
- children and teenagers. Their lungs are still developing and they tend to be more active outdoors. Also, because of their smaller size, children breathe more air per pound of body weight, so their bodies absorb more pollutants per breath.
- people who do vigorous exercise outdoors, such as athletes, farmers and construction workers.
What should at-risk people do to protect their breathing on smoggy days?
Everyone should pay attention to smog levels and watch how smog affects their health. If you have a lung disease (or you're sensitive to smog for another reason), you should be especially careful. Learn how to protect your breathing on smoggy days- find out how to be Smog Smart.
On hot smoggy days, you suggest people cool off in an air conditioned room. How does air conditioning affect my breathing?
When outdoor air quality is bad and the temperature is warm, spend time inside in air-conditioned rooms. If your home does not have central air conditioning, you may want to buy a one-room air conditioner for at least one room in your house, likely your bedroom. One-room air conditioning units can cost as little as $150. Remember to keep your air conditioner clean and change the filter regularly.
Generally, air conditioning set at a moderate temperature can help people breathe more comfortably in the summer. Air conditioners remove humidity from the air and lower the temperature. Opening windows to cool your home can let in smog and pollen, a trigger for some people with asthma and allergies. Rooms that are cooled with air conditioners usually have lower pollen counts than rooms that rely on open windows to keep cool.
Sometimes, if air conditioners are badly maintained, they can make air less clean and cause breathing problems. If air conditioners filters are dirty, or if collected moisture is sitting stagnant somewhere in the unit, it is possible that mould or bacteria can develop and be spread by the air conditioner. You can avoid problems by keeping air conditioners clean and well maintained.
Only use your air conditioning if it helps you breathe easier. When using your air conditioner, try to reduce your electricity use in other ways. For example, don’t use your stove or clothes dryer while the air conditioner is working.
The Lung Association does not endorse any particular air conditioner. For recommendations on air conditioning units, check out the ratings in Consumer Reports, published by an independent non-profit evaluation organization. You can get the magazine in your local library or visit the Consumer Reports website.
What time of year do we get smog?
Although “smog season” is usually April to September, smog can happen at any time in the year.
During warmer months, smog usually contains higher amounts of ground-level ozone. Ground-level ozone is a gas created when certain pollutants from vehicle exhaust and factory smoke react under strong sunlight.
In colder months, smog is usually made up of fine particulate matter, tiny liquid and solid particles that are suspended in the air. Winter smog is usually caused by wood burning and vehicle exhaust.
What parts of the country are affected by smog?
Smog affects many parts of the country. Air pollution can be released in one place and get blown by the wind over long distances to other places. For example, smog from Canada can travel to the United States. Smog from the U.S. often travels to certain parts of Canada, because of the prevailing wind direction. Smog can also be a problem in the suburbs, in the countryside, in small towns, and in cottage country.
Where does smog come from?
Smog comes from many sources, including:
- factories (industrial emissions and byproducts, energy use)
- transportation (vehicle exhaust, road dust)
- electricity generation
- petroleum production
- mining and smelting metals
- pulp and paper operations
- farming (pesticides, vehicle emissions)
- smoke from burning stubble, brush and wood
- forest fires
- oil-based paints, cleaners and solvents
- exhaust from gas lawnmowers, leaf blowers, snow blowers,
The federal government monitors smog and greenhouse gas emissions from factories and other point sources.
How is smog measured?
Provinces monitor and report on smog levels. They also issue forecasts that predict what the smog levels will be for the coming days. The Air Quality Index is a scale from 0 -100; the lower the number, the cleaner the air. The Air Quality Health Index is a new and different scale. It goes from 1 to 10 or more. A lower number means healthier air. Read more about the Air Quality Index (AQI) and the Air Quality Health Index (AQHI).
What is a smog watch?
A smog watch is issued when it’s likely that the Air Quality Index (AQI) will reach or exceed 50 in the next three days.
What is a smog advisory?
A smog advisory is issued when it is highly likely that the Air Quality Index (AQI) will reach or exceed 50 in the next 24 hours.
Why do smog levels rise and fall?
Smog levels depend on many things:
- how much pollution is being created
- the temperature outside
- the weather and the wind
- the landscape (topography) – certain landscapes can trap pollutants in the air
- sunlight and ultraviolet (UV) intensity
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1. Canadian Medical Association, No Breathing Room: National Illness Costs of Air Pollution, 2008. http://www.cma.ca/multimedia/cma/content_Images/Inside_cma/Office_Public_Health/ICAP/CMA_ICAP_sum_e.pdf
2. Health Canada study finds 5900 excess deaths per year linked to air pollution in eight Canadian cities. Available from : http://www.hc-sc.gc.ca/ahc-asc/media/nr-cp/2005/2005_32_e.html