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Smog is made up of many air pollutants. The main ones are ground-level ozone and fine particulate matter. Smog can also contain sulphur dioxide, nitrogen dioxide, total reduced sulphur, and carbon monoxide.

Ground-level ozone (O3)

The ozone found high in the earth’s atmosphere is called “good ozone” because it helps protect us from the sun's rays. But ozone at the ground level is not good for human health. Ground-level ozone is not emitted directly into the air, but forms when nitrogen oxide and volatile organic compounds (VOCs) from vehicle exhaust, factory emissions and other sources react with sunlight.

It’s called the “bad ozone” because if you breathe it in, it can cause health problems. Ground-level ozone usually peaks between noon and 6 p.m. during the summer months.

Health effects of ground-level ozone:

  • worsening symptoms for people with asthma, COPD and other lung diseases, and for people with cardiovascular (heart) disease
  • swollen, irritated airways
  • irritation to your eyes, nose and throat
  • coughing, wheezing
  • headaches

Over time, ozone can cause permanent lung damage.

Sources of ground-level ozone

  • burning fossil fuels (gas, oil or coal) for industry and transportation consumer products (paints, wood laminates)
  • natural sources (plants, trees, lightning)

Fine particulate matter (PM)

Fine particulate matter is a broad name given to particles of liquids and solids that pollute the air. These particles come in different sizes and are made of different things.
PM 2.5 is particulate matter that is very small (2.5 microns or less – that’s about the width of human hair). PM 2.5 can be breathed deeply into your lungs and will stay there, causing health problems. PM 2.5 can stay in the air longer and travel farther than larger particles.

Health effects of fine particulate matter:

  • coughing or sneezing
  • irritation in your eyes, throat, and lungs
  • wheezing and breathing problems in people with asthma, COPD, and other lung diseases
  • cardiovascular health problems, including heart attacks in people with certain pre-existing heart diseases

Sources of fine particulate matter:

  • vehicle exhaust
  • road dust from paved and unpaved roads
  • construction
  • agriculture
  • wood stoves, fireplaces, and other kinds of wood burning
  • forest fires
  • industry

Sulphur dioxide (SO2)

Sulphur dioxide is a colourless gas that smells like burnt matches. It is one of the main ingredients in acid rain. Sulphur dioxide, combines with volatile organic chemicals (VOCs) and sunlight, creates ground-level ozone, the main ingredient in smog.

Health effects of SO2:

  • irritation in your nose and throat
  • breathing problems
  • new cases of lung disease
  • worsening symptoms in people with asthma, COPD, and other long-term lung diseases
  • worsening cardiovascular (heart) disease
  • changes in the lung's natural defences

Sources of SO2:

  • fossil fuels burned in petroleum refineries
  • pulp and paper mills
  • steel mills
  • electricity generating plants, including coal-fired power plants
  • non-iron ore smelters
  • diesel vehicles
  • volcanoes and hot springs

Nitrogen Oxides (NOx)

Nitrogen oxide is a reddish-brown gas that smells foul.

Health effects of NOx:

  • can lower your resistance to lung infections
  • can cause shortness of breath and irritate the upper airways, especially in people with lung disease, such as asthma and chronic obstructive pulmonary disorder (COPD)

Sources of NOx:

  • burning fossil fuels in motor vehicles, homes, and industries
  • oil, gas, and coal-fired power plants
  • metal production
  • incineration
  • forest fires, lightning and decaying vegetation

Carbon monoxide (CO)

Carbon monoxide is an odourless, tasteless, colourless gas. At high levels, carbon monoxide is poisonous.

Health effects of carbon monoxide:

  • headaches
  • dizziness
  • shortness of breath
  • slower reflexes and reduced perception
  • at high levels: seizures, unconsciousness, coma, respiratory failure and death.

Sources of carbon monoxide:

  • burning fossil fuels in vehicles
  • metal production
  • emissions from heating devices (gas heaters, etc.)