Sample date: May 22, 2015

Clear. Wind north 20 km/h gusting to 40 becoming light early this evening. Low zero with frost.


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Outdoor Air Quality

This page was reviewed or revised on Thursday, April 23, 2015 2:07 PM

Poor air quality is largely a product of burning fossil fuels. We use them to power our vehicles, to produce energy and to manufacture consumer products. The increasing consumption of carbon based fuels has a direct impact on air quality – it harms the earth’s ecosystems and negatively affects our health.

This section defines smog – its sources and health effects. It also describes how you can minimize your risk to harmful air pollutants and provides tips about what you can do to reduce your own emissions."

What is the Air Quality Index?

The Ministry of Environment measures the air quality in Ontario using a rating scale called the Air Quality Index (AQI). The scale ranges from 0 to over 100 - the lower the AQI number, the better the air quality.

The AQI is based on six key air pollutants including:

  • Sulphur dioxide
  • Ozone
  • Nitrogen dioxide
  • Total reduced sulphur compounds
  • Carbon monoxide
  • Fine particulate matter

Each hour, the concentration of the six pollutants is measured at particular stations across Ontario. Two of those stations are located in Lambton County - one in Sarnia and one in Grand Bend (summer station only).

The Ministry of Environment Air Quality Index Categories are as follows:

Check the Air Quality Index for Sarnia-Lambton at or call 1-800-387-7768.

What is a smog alert?

A Smog Alert is issued when air quality is expected to be poor over a period of time. The Ministry of the Environment may issue two types of Smog Alerts:

  • A Smog Watch is issued when there is a 50% probability that elevated smog levels will occur within the next three days.
  • A Smog Advisory is issued when there is a strong likelihood of elevated smog levels occurring within the next 24 hours or if smog conditions happened without warning.

A Smog Advisory Termination Notice is issued by the Ministry of the Environment after the weather changes, the air clears and a Smog Advisory is no longer required.

For more information about smog alerts or to subscribe to the Smog Alert Network, visit the Ministry of the Environment.

Components of smog

The components that form smog include ground-level ozone, fine particulate matter, nitrogen oxides, volatile organic compounds, sulphur dioxide, and carbon monoxide.

The two components of smog that have the most impact on our health and the environment are ground-level ozone and fine particulate matter.

Ground-level ozone (O3)

Ground-level ozone is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight and high temperatures. These pollutants come from the burning of coal, gas, and oil in motor vehicles, homes, industries, and power plants. Ground level ozone is a harmful pollutant and should not be confused with the protective ozone in the upper atmosphere which shields the earth from the sun’s ultraviolet (UV) rays.

Fine particulate matter (PM2.5)

Fine particulate matter is a mixture of microscopic particles of soot, ash, dirt, dust and metals in the air measuring less than 2.5 micrometers (about 1/30th the diameter of a human hair). PM2.5 is primarily formed from chemical reactions in the atmosphere and through all types of combustion, including vehicle exhaust, power plants, wood burning, construction activity, and agriculture. It poses a health concern because it can pass through the nose and throat and get deep into the lungs.