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Ontario's Doctors : What you need to know about smog

How does smog impact health?

Smog also has an impact on the health care system with increased visits to doctor’s offices and emergency departments, as well as hospital admissions.

OMA Smog-Wise health tips

Smog Myths and Medical Facts

Smog Myth:  If it’s smoggy, all sporting events and outdoor activities should be cancelled.

Medical Fact – In most cases the benefits of physical activity outweigh the dangers of smog for healthy adults and children alike. Use your common sense, monitor your activities and those of your family. Reduce your exertion, schedule rest breaks and stay hydrated, but pay special attention to those with pre-existing health conditions. Toning down outdoor activities may be appropriate in the smog, eliminating them altogether is seldom necessary.

Smog Myth:  If I’m healthy, I’m safe because smog only affects asthmatics.

Medical Fact – Smog affects everyone, however, children, seniors, people with pre-existing lung or heart conditions and people who work and exercise outdoors are more vulnerable. Although smog makes asthmatics and others with respiratory conditions ill every year, smog-related deaths are more often the result of cardiac causes than respiratory ones. This is of particular concern because many people with heart problems are often unaware of their condition.

Smog Myth:  Air conditioners can contribute to pollution, so everyone should turn theirs off.

Medical Fact - Although air conditioners can contribute to smog, they are also an important defence against the combined effects of heat, allergens and pollution. If you have a known cardiac or respiratory condition, or are suffering the effects of dirty air, getting into a cool, clean environment is recommended.

The Ontario Medical Association launched the OMA Smog-Wise Information Program in 2003 and continues to update this advice to its patients on how to protect themselves from smog’s ill effects.

For more information on the OMA Smog-Wise Information Program visit our Smog/Air Pollution site.

How to be Smog-Wise

Few things are as important as the air we breathe, but our breathing is compromised by smog. Smog is a complex mixture of pollutants, mainly ground-level ozone, fine particulate matter and other gases. 

Ground-level ozone is different from the stratospheric “ozone layer”, which protects us from the sun's harmful ultraviolet rays. At ground-level, ozone gas is toxic to the respiratory system, and is the pollutant that has historically triggered most of the smog alerts in Ontario. Fine particulates are tiny specks of either liquid or solid particles, which are suspended in the air. They consist of soot and acids, which can lodge deep in our lungs. Nitrogen and sulphur oxides, ammonia and other gases contribute to the formation of both ozone and these smog particles.

The main sources of the man-made chemicals that make up smog are automobile emissions, coal-burning power plants and other heavy industries. They are emitted locally and from sources as far away as the United States and drift across the Ontario landscape on the prevailing winds.

Since polluted air masses cover large areas, and usually move slowly, the smog problem is not only confined to cities and industrial centres. Smog builds up in both urban and rural areas, blanketing southern Ontario, from Windsor to the Quebec border, along the Lake Huron shoreline, and as far north as Sudbury and North Bay. High smog readings, often called smog episodes, can last for just a few hours or for days at a time.

We are most familiar with elevated smog concentrations in the summer, on hot, sunny days, because that is when ozone is at its worst. Ground-level ozone concentrations tend to increase in the late afternoon and evening, after the component emissions have “cooked” in the hot sun. Elevated concentrations of fine smog particles  can happen at any time of the day or year. It is still however most common during the summer months. Nitrogen dioxide levels, one of the drivers of the new AQHI, are often worse where there is more traffic and subsequently can peak during rush hour.

Ground-level ozone is invisible, but particulate matter often gives the air the hazy appearance that we associate with a smoggy day. The yellowish-brown colour in the sky on polluted days is the result of nitrogen dioxide.  

The Ontario Ministry of the Environment provides hourly reports  on the AAQI in the summer and provides three-day air pollution forecasts. When smog levels are forecast to be high, the ministry issues a smog alert, which is widely reported via television, radio and newspapers. Smog alerts are targeted at the general population, so for those of you who are most vulnerable (e.g., asthmatics and heart patients) there can be significant health impact at lower pollution concentrations, i.e., less smog will trigger a physical reaction.

It is important to not be confused by the different names used for a smog alert. It is also sometimes called a Smog Watch, Smog Warning, Air Quality Advisory, or Air Quality Alert. Some of these terms refer to different forecast timeframes, so it is important to note the day for which the alert is being issued and to plan accordingly, but they all mean that you should take precautions.

Smog alerts are often accompanied by health advice on the possible risks associated with smog exposure, and although it is important to pay attention to these health warnings, they are not fully protective for all parts of the population. It is important that those who are vulnerable to the effects of smog, pay heed to these warnings, but remember that this system is not perfect. The combined effects of these different pollutants on our cardiac and respiratory systems may not have been factored in to these warnings. We also know that many people are affected at smog concentrations below the designated "poor air" or “high risk” level on the indexes. There is no threshold for smog's health effects, so don't mistake smog concentrations below the smog 'alert' level as “safe”.

Unfortunately, a smog alert mechanism has not yet been built into the Air Quality Health Index. The smog alert has proven beneficial in engaging society as a whole about increased smog concentrations. Like extreme weather alerts, the issuance of an alert creates news and focus, providing media outlets with something to report. The existing alert, the AQI’s Smog Advisory, is issued when the AQI is forecast to reach the poor air level. Although vulnerable populations should pay attention to and respond to smog forecasts  below the actual alert level, the alert is a very important engagement mechanism for higher smog readings.If the AQHI was ever to replace the AQI in Ontario, the smog alert mechanism could be lost.

It is now accepted that smog affects a range of cardio-respiratory health problems. Smog increases the number of people affected by asthma, it increases the number of asthma attacks and makes them worse.

Smog over-burdens the heart, but can also cause relatively minor irritation of the eyes and throat. Smog's health impact includes increased doctor’s office visits, trips to the emergency department, hospital admissions, and even premature death.

The health evidence against smog continues to grow stronger all of the time. Recent studies have shown that athletic kids living in polluted cities are more likely to develop asthma, have linked smog particles to lung cancer, and found that increased concentrations of these particles increases heart attack risk. Although everyone can be affected by smog, some groups are much more sensitive. These include individuals with cardiac conditions such as heart failure and arterial sclerosis, or respiratory diseases such as asthma, emphysema and chronic bronchitis. Any elderly individual may also be at increased risk. Children are at greater risk than adults because they take more breaths and, in summer, generally spend more time active outdoors. Adults who are exercising outdoors, such as joggers and cyclists, as well as outdoor workers, may also be at increased risk because they draw more polluted air through their lungs.

Heat and humidity, which are often a problem at the same time as smog, add synergistically to the stress on the cardio-respiratory system from smog, especially in those with pre-existing cardiac and respiratory compromise.

How to better inform and protect yourself

To protect yourself from smog you must become aware of when smog levels are high.

Join the Smog Alert Network HERE

AQI readings are available on the Ministry of the Environment's Air Quality in Ontario web site (http://www.airqualityontario.com). Daily AQI values and forecasts are also available from the Ministry of the Environment by calling (416) 246-0411 in Toronto, and toll-free at 1-800-387-7768 (English) or 1-800-221-8852 (French). AQHI readings for the Greater Toronto Area are available from Environment Canada’s AQHI site ( http://www.ec.gc.ca/cas-aqhi/).

You can also listen and watch for the smog advisories in local weather reports on the TV or radio, but also pay attention to the weather itself. If a hot and hazy day is forecast, the air quality is not likely to be very good, whether a smog alert has been called or not.

If you can't access a weather report, it is easy to get a basic sense of the air quality for yourself. In general, the hotter it is - the worse the ozone level; the hazier - the worse the smog particle concentrations. Foggy haze on rainy days isn't usually as bad because rain washes some of the pollution out of the atmosphere.

Since individual health responses to smog vary widely, it is important to pay attention to your breathing and the breathing of those in your care. The fact that you are breathing freely does not mean that young children and the elderly will respond to these pollutants in the same way.

Common sense suggests that very hot, hazy days are not the best days for outdoor exertion even if smog was not a factor, so taking the precaution of limiting strenuous activity can reduce your exposure and help in a number of ways. If you feel the immediate effects of air pollution, trust what your body is telling you and don't push yourself beyond a comfortable physical limit.

Some pollutant concentrations, like nitrogen dioxide, can be elevated in high traffic areas, so avoiding busy roadways may reduce smog’s impact on you.

We are still learning more about the short and long-term effects of smog, but we do know that reducing your exposure on high pollution days is appropriate preventative medicine.

A clean and cool environment is the most comfortable place to be on smoggy days. Putting off strenuous outdoor activities until it feels more comfortable makes good health sense too.