Outdoor Air Quality Sulphur Dioxide (SO2)

HealthLinkBC File Number: 
Last Updated: 
April 2019
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How is air quality determined?

Air quality is determined by the concentrations of pollutants in the air. Air quality can vary greatly from one area or community to the next and from one hour to the next. This is because air quality is influenced by several things. The types and amounts of pollutants released into the air and weather conditions such as wind and temperature affect air quality. It is also influenced by natural geographical features such as mountains or bodies of water. For example, valleys can prevent mixing of air, which can then cause pollutants to be trapped close to the ground where people can inhale them.

Concentrations of common air pollutants, including sulphur dioxide, are continually monitored at fixed locations in many communities in British Columbia (B.C.). They are reported on-line as hourly average concentrations.

Air quality is also reported in the form of an Air Quality Health Index (AQHI). The AQHI provides information about current air quality. It also provides a forecast of air quality for the next 36 hours. The level of health risk is provided on a scale of 1 to 10 or higher, as well as with a health risk label of “low”, “moderate”, “high” or “very high”. It also provides advice on how to minimize health risks. To check the current and forecast AQHI, visit BC Air Quality www.env.gov.bc.ca/epd/bcairquality/data/aqhi-table.html.

Please note that the AQHI is derived from measurements of fine particulate matter, ozone and nitrogen dioxide so it does not provide information on sulphur dioxide levels.

What is sulphur dioxide?

Sulphur dioxide is a highly reactive, colourless gas. It has an odour like the smell of a struck match. When released, sulphur dioxide can react with other pollutants in the air to form fine particulate matter, which are small solid or liquid particles suspended in air. For more information on particulate matter, see HealthLinkBC File #65e Particulate Matter and Outdoor Air Pollution.

What are the sources of sulphur dioxide in outside air?

In B.C., several industrial sources contribute to sulphur dioxide emissions in the air. The main emission sources are:

  • Oil and gas industry
  • Pipeline operations
  • Marine operations
  • Metal smelting
  • Pulp and paper production

Other emission sources of sulphur dioxide include large ships and off-road equipment that burn high sulphur-containing fuels. Natural sources such as volcanic eruptions may also release sulphur dioxide. In low quantities, forest fires may release it as well.

Who is at the highest risk of sulphur dioxide exposure?

The people most often exposed to sulphur dioxide are workers in industrial facilities where sulphur dioxide is used or is a by-product of industrial processes. People who live near these industries and other point sources can also be exposed to high levels of sulphur dioxide.

What are the health concerns of sulphur dioxide?

If you breathe air that contains sulphur dioxide, you may absorb it into your body through your nose and lungs. Sulphur dioxide can be life-threatening if you are exposed to very high levels. These life-threatening levels rarely occur in community settings and are mainly seen in work settings where sulphur dioxide is used or directly generated.

Short-term exposure to high concentrations of sulphur dioxide can cause health concerns. This is especially true for people with asthma or chronic obstructive pulmonary disease (COPD). Young children and the elderly are also at risk. Symptoms may include constriction or tightening of the airways in the lungs, coughing, wheezing and shortness of breath. It may also cause irritation of the respiratory system and eyes. For these sensitive individuals, sulphur dioxide exposure may increase emergency room visits and hospital admissions for respiratory illnesses.

Long-term exposure to sulphur dioxide can also affect your health. It can reduce your ability to breathe deeply or take in as much air for each breath. The particles produced by the reaction of sulphur dioxide with other compounds in the air can penetrate deeply into the lungs. These particles can then damage the lining of the lungs as well as cause other effects in the body. Particles can worsen existing heart and respiratory disease, including emphysema and bronchitis.

Children who have been chronically exposed to sulphur dioxide may also develop more breathing problems as they get older.

How can you reduce the risk of exposure to sulphur dioxide?

You should limit your exposure during times of high concentrations of air pollution. Rescheduling exercise times, avoiding outdoor sources of sulphur dioxide and remaining indoors with windows closed can help. Also reduce indoor sources of sulphur dioxide, including tobacco smoke, matches and unvented gas stoves.

People with medical conditions, such as asthma, chronic respiratory disease or heart disease, should continue to follow a management plan developed with their health care provider. If you have symptoms such as coughing, wheezing or shortness of breath, seek medical attention.

For More Information

For more information about sulphur dioxide in your area, contact your local Ministry of Environment & Climate Change Strategy office www2.gov.bc.ca/gov/content/environment/air-land-water/land/regional-environment-contacts or visit:

Is it an emergency?

If you or someone in your care has chest pains, difficulty breathing, or severe bleeding, it could be a life-threatening emergency. Call 9-1-1 or the local emergency number immediately.
If you are concerned about a possible poisoning or exposure to a toxic substance, call Poison Control now at 1-800-567-8911.

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