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Overview of Smog Pollutants




General Health Effects

Ground-level Ozone

Colourless, odourless, gas. Major component of smog.
High levels typically occur from May to September.

Results from photochemical reactions between nitrogen oxide and volatile organic compounds in the presence of sunlight.

Irritation of the lungs creating breathing difficulties. Eye irritation. Exposure to high concentrations can result in chest tightness, coughing and wheezing.

Fine Particulate Matter (PM 2.5)

A mixture of solid particles and fine liquid droplets in air. Includes aerosols, smoke, fumes, dust, ash and pollen.
Fine particulate matter (PM2.5) are respirable particles that penetrate deep into the lungs.

Primarily formed from chemical reactions in the atmosphere and through fuel combustion. Includes motor vehicles, power generation, industrial facilities, emissions from fire places and wood stoves, etc.

Particles 2.5 microns or less in diameter (PM 2.5) can aggravate bronchitis, asthma and other respiratory diseases.
Increased hospital admissions and premature death may also occur.
Children, the elderly and people with asthma, cardiovascular or lung disease are considered to be the most sensitive.

Total Reduced Sulphur

Offensive odours similar to rotten eggs or cabbage.

Industrial sources include the steel industry, pulp and paper mills, refineries and sewage treatment facilities

Not considered a health hazard.


Colourless gas. Smells like burnt matches.

Smelters and utilities are the main contributors. Other sources include iron and steel mills, petroleum refineries and pulp and paper mills.

High levels can cause breathing difficulty, respiratory illness, changes in lung defence mechanisms and worsening of respiratory and cardiovascular disease. People with asthma or chronic lung/heart disease are the most sensitive.

Nitrogen Dioxide

A reddish-brown gas with a pungent and irritating odour.

Automobiles, power plants, primary metal production and incineration.

Irritates the lungs and lowers resistance to respiratory infection. Sensitivity increases for people with asthma and bronchitis.

Carbon Monoxide

A colourless, odourless, tasteless but poisonous gas produced primarily by incomplete burning of fossil fuels.

Automobiles, primary metal producers and fuel combustion in space heating and industrial processes.

Carbon monoxide enters the blood stream and reduces oxygen delivery to the organs and tissues. Exposure to high levels can cause impairment of vision, work capacity, learning ability and performance of difficult tasks.