Health Effects of Ground Level Ozone

The ozone layer in the upper atmosphere is beneficial, protecting us from harmful ultraviolet radiation, However, ground-level ozone is bad for our health. We do not directly pollute the atmosphere with ozone. It is generated when emissions of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. Ozone accumulates around cities on hot summer days. Since NOx and VOCs can travel long distances, ozone also builds up in rural areas. In fact, about half of the NOx and VOCs in the province come from American sources.

Ontario Volatile Organic Compounds Emissions by Sector – 2012 Estimates

(Image and data from Government of Ontario, 2012: http://airqualityontario.com/science/pollutants/ozone.php)  Copyright Information: © Queen’s Printer for Ontario | Ontario.ca Queen’s Printer for Ontario


Ontario Nitrogen Oxides Emissions by Sector – 2012 Estimates

(Image and data from Government of Ontario, 2012:  http://airqualityontario.com/science/pollutants/nitrogen.php)  Copyright Information: © Queen’s Printer for Ontario | Ontario.ca Queen’s Printer for Ontario

Health Effects

Ozone Reduces Lung Function

People have difficulty breathing when ozone levels rise. It is not generally realized that in the summer, ozone impacts rural and suburban areas even more than cities in Southern Ontario. Ozone reduces lung function, even at levels equal to the one hour standard of 80 parts per billion (ppb). Studies of human subjects exposed for several hours to ozone in controlled chambers have shown a definite “dose-response” relationship: the greater the dose of ozone, the greater the reduction in pulmonary function. These have been summarized by Hazucha (1987)* and Larsen (1991)*. Current summer ozone levels in Ontario likely temporarily reduce lung function in sensitive people.

Ozone can put you in the hospital

More people are admitted to hospital for respiratory problems on or just after higher ozone days. This effect can be shown at low concentrations of ozone. Bates and Sizto’s classic 1983* study showed that as the concentration of ozone increased, so did the number of respiratory admissions in hospitals across Ontario. This effect is demonstrated most easily during hot summer months, ozone is particularly harmful to people with respiratory conditions such as asthma or chronic bronchitis etc. These groups are more likely to be admitted to hospital during higher ozone days. Numerous studies have shown effects with healthy individuals as well. Also, since ozone easily spreads as a result of urban pollution to rural areas, it affects everyone.

Ozone precursors also affect us

ozone admissions

Did you know?

  • The current Ontario Ambient Air Quality Criterion for ozone is 80 ppb (parts per billion) for a one hour period. In 1994, this figure was exceeded 740 times at 44 stations, mainly in southern Ontario.
  • An estimated 650 kilotonnes of VOCs and 500 kilotonnes of NOx are released in Ontario each year.
  • Off-road engines such as construction equipment, railway engines, 4×4, tractors and lawnmowers produce 15% of all NOx emissions.

What is being done?

The Canadian Council of Ministers of the Environment (CCME) has initiated a NOx / VOCs management plan with a goal of consistently meeting the current O3 criterion by the year 2005.

Ontario made public its “smog Plan” in June 1996. In partnership with industry, universities and environmental and health public interest group, and the province plans to reduce O3 exceedances by 75% and particles by 10%; both by the year 2015.

The Canada-US Air Quality Committee is working on a plan to reduce ambient O3 concentrations on both sides of the border.

What can you do?

PROTECT YOURSELF: If levels are high do not exercise vigorously outside. Go indoors if necessary.

BE INFORMED: Request information from local government, the Ministry of the Environment , Environment Canada, plant managers and environmental groups.

BE INVOLVED: Reduce your own emissions: use public transportation, car pool, walk, rollerblade or cycle. If you do drive, keep your car well-tuned. Practice energy conservation. By solvent-free household products. Start or join a citizen’s group. Write letters to the Minister of Environment and to your local MPP. Register complaints about air quality.

Hamilton-Wentworth Air Quality Initiative is a joint project of Environment Canada, Ontario Ministry of Environment and the City of Hamilton.