Sample date: March 31, 2015

Partly cloudy. 30 percent chance of flurries overnight. Wind northeast 20 km/h becoming light early this evening. Low minus 3.


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Environment Canada
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Today's Air Quality

This page was reviewed or revised on Wednesday, October 20, 2010 2:09 PM

Check Today's Air Quality


What is the Air Quality Index?

What is a Smog Alert?

Components of Smog

Sarnia-Lambton Smog Advisories to Date

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:

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:

Air Quality Index (AQI) Categories



Health Effects


   Very Good

    Very Good

·         no known health effects




·         no known health effects for most people




·         some adverse health effects on very sensitive people




·         adverse health effects for sensitive people


 Very Poor

   Very Poor

·         may affect the health of a large number of people

Source: Ministry of the Environment

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.

More information about smog alerts or to subscribe to the Smog Alert Network, visit the Ministry of the Environment’s website.

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.

Health and Environmental Impacts

In 2005, The Ontario Ministry of the Environment released a report entitled Transboundary Air Pollution in Ontario. They found that based on 2003 demographics, Ontario is burdened with almost $9.6 billion in health and environmental damages each year due to the impact of ground-level ozone and fine particulate matter. Of this total, approximately 55% is attributable to U.S. emissions. Ontario cities and towns on the northern shore of Lake Erie, the eastern shore of Lake Huron and in the extreme southwest near the U.S. border are particularly affected by U.S. emissions. Click here to access this report and learn more about transboundary air pollution.

Furthermore, smog levels are affected by traffic congestion and the prevailing wind direction. Research has shown that truck line-ups caused by delays at the Bluewater Bridge may increase smog levels within 50 to 100 meters of highway 402. Diesel emissions from idling trucks could potentially raise the air quality index by one category (i.e. from moderate to poor). Click here to access the Ontario Ministry of the Environment's report entitled, Air Quality Assessment Related to Traffic Congestion at Sarnia’s Bluewater Bridge (2005). 

Sarnia-Lambton Smog Advisories to Date


Total # Smog Advisories

Total # Smog Days

2008 4 10
2007 13 29
2006 4 12
2005 13 46
2004 6 16
2003 5 14
2002 10 25
2001 7 23
2000 3 4
1999 5 9
1998 3 7
1997 3 5
1996 3 5
1995 6 12