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News Article: Smog, smog alerts and human health

Wednesday, July 15th 2009 10:42:49am

To the Editor:

This is an article from a series of monthly columns by Environmental Law Specialist Dianne Saxe, one of the top 25 environmental lawyers in the world. These articles are available for publishing at no charge, provided Dr. Saxe is cited as the author. She can be contacted at (416) 962 5882 or For more information, visit

Smog, smog alerts and human health

Health effects of smog

How big a health issue is smog? Green Ontario claims that smog kills 1800 Ontarians each year.(1)  Health Canada analysed air pollution in relation to deaths in eight Canadian cities, and, (considering both short- and long-term effects), concluded that air pollution causes 5,900 deaths each year in these cities alone.(2)  On smoggy days, emergency room visits, hospital admissions and medication use all go up. As usual, the most vulnerable are children, the elderly, and those with underlying lung and heart problems. Pets, with their relatively fast respiration and small body size, suffer too.

What about asthma? It is controversial whether outdoor air pollution actually causes asthma.(3)  While asthma is often worse when air pollution is high, it is not clear whether this is due to the general increase in pollutant levels or to specific allergies to ozone, nitrogen oxides or particulate.(4)  

What is in it?

The dirty yellow smog that we see consists mainly of ground-level ozone and fine particulate matter (PM). It is most common when sunlight and hot stagnant air trap pollutants in the lower atmosphere.(5)  Smog levels usually peak mid-afternoon, when the sun is at maximum intensity.

Most smog is due to human activity; though some is also caused by forest fires, volcano dust, etc.(6)  Despite Ontario's Anti-Smog Action Plan, it's likely to get worse with time. Climate change is expected to bring hotter temperatures, more forest fires, worse air pollution, and more smog, in future years.

Keeping track of it

Ontario's Ministry of the Environment (MOE) has an extensive website that shows "air quality indices".(7)  The MOE issues smog advisories when they expect smog levels to be elevated over a relatively large area, and to persist. In 2005, there were 15 smog advisories (for a total of 53 days); in 2007, 13 such advisories (for a total of 39 days). In last year's wet summer, there were only 8 advisories (for a total of 17 days) and in 2009 (to the end of June) only two advisories (for 2 days total) had been issued.(8)  

The MOE reports air quality indices (AQI) every hour, every day of the year.(9)  The AQI is based on six air pollutants that adversely effect human health: ozone, PM, nitrogen dioxide, sulfur dioxide, total reduced sulfur compounds and carbon monoxide. Forecasts on the site are pretty generic, but easy to understand - air quality is categorized as "good", "moderate" and "poor".

If you want more detail, MOE provides hourly air concentrations for five pollutants at various "stations" (i.e., cities and towns) around the province.(10)  There are also useful links that explain the nature, source and effects of each pollutant.

What is being done about it

Ontario has an anti-smog action plan: details at

Most of the plan involves using less energy (especially for transportation), burning it cleanly, and promoting renewables. Closing Ontario's coal-fired power plants should help a lot, although more than half of our smog blows in from the US.

The best way to tackle smog is to design our cities, transportation systems, and energy use in such a way that it reduces air pollution. Smog is not an isolated problem; it is an indicator of poor urban and economic development.(11)

In addition, the MOE is encouraging municipalities to take a stronger role in fighting smog, and publishes a municipal guide for smog alert response.(12)

Individual and community action on smog issues looks about the same as action on climate change and energy conservation. Small wonder. Coal and petroleum are the biggest contributors to smog, and energy use is one of the easiest targets for individual action. Trees and other green plants also help clean the air, so if you have a street tree nearby, look after it!

Six suggestions if you or a loved one is vulnerable

• Pay attention to smog alerts.
• Chemicals: don't use aerosol sprays or oil-based paints and volatile chemicals that add to poor air quality both indoors and outdoors; don't smoke.
• Exercise: During smog alerts, vulnerable people should avoid strenuous outdoor exercise, especially in late afternoon when ground-level ozone peaks. (Glad I'm a morning person).
• Stay inside: when there is a smog alert, as susceptible individuals may suffer difficulty breathing as well as irritation of the eyes and/or throat.
• If you have asthma, increase monitoring lung capacity during smog alerts and adjust medication doses accordingly.
• Complain to your politicians. Make them take smog seriously.

2 Environment Canada. Health issues - air pollution is linked to varying degress to a number of health concerns…
3 The Global Initiative for Asthma - Global strategy for asthma management and prevention (2008 update):1-92 at 6. GINA guidelines Available at
4 GINA at 56
5 Environment Canada. Smog. Winter smog, due mainly to PM, can occur when stagnant air results in a buildup of air pollutants, e.g., through increased wood burning and use of vehicles
6 Environment Canada. Revised mortality estimates due to air pollution in Canada.
7 Ontario Ministry of the Environment - Smog alert site -
8 MOE - How many smog advisories were issued in previous years?
10 Ontario MOE - Pollutant Concentrations -
12 Smog Alert Response - A municipal guide to action. 2005:1-101. Available at
13 Ontario Ministry of the Environment - Spare the air actions.; Abelsohn A, Stieb D, Sanborn MD, Weir E. Identifying and managing adverse environmental health effects: 2. Outdoor air pollution. CMAJ 2002;166(9):1161-7