Even healthy young adults breathe less efficiently on days when the air is heavily polluted, especially if exercising outdoors. Particularly vulnerable to smog are people with heart or lung disease, the elderly and small children. The two main ingredients in smog that affect our health are ground-level ozone and fine airborne particles. NOx and VOC come from natural sources as well as human activities. NOx are nitrogen-oxygen compounds that include the gases nitric oxide and nitrogen dioxide, and are produced mostly by burning fossil fuels.
Human activities are responsible for the increases in ground-level ozone in recent years.
About 95 per cent of nitrogen oxides from human activity come from the burning of coal, gas and oil in motor vehicles, homes, industries and power plants. VOC come mainly from fuel combustion and from the evaporation of liquid fuels and solvents. Ozone not only affects human health, it can damage vegetation and decrease the productivity of some crops. It can also injure flowers and shrubs and may contribute to forest decline in some parts of Canada. Ozone can also damage synthetic materials, cause cracks in rubber, accelerate fading of dyes, and speed deterioration of some paints and coatings.