Elderly people and those with heart or lung disease such as asthma, emphysema and chronic bronchitis are particularly sensitive to air pollutants. When pollution levels are high, sensitive people may experience symptoms after only one or two hours outdoors. Children and active adults are also at a greater risk because they typically spend more time outdoors.
Children tend to be more sensitive than adults because they breathe faster.
Exposure to ozone can irritate the nose and throat and cause chest tightness, coughing and wheezing. Increases in ozone levels in Canada have been linked to increased mortality, emergency hospital visits and admissions for respiratory problems. In sensitive people, the stress of ozone exposure can be particularly damaging. There is also evidence that ozone heightens the sensitivity of asthmatics to allergens. The smaller the particle, the deeper into the lungs it can penetrate.