This valley, which includes the City of Vancouver, is bordered by the Coastal Mountains to the north and the Cascade Mountains to the southeast. Motor vehicles in the Vancouver area are the major source of NOx and VOC emissions. Cross border pollution contributes between 50 and 90 percent of this region's smog problem. 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.
Health studies have focused on two groups of airborne particles that have proven harmful, even at very low levels. These very fine particles cause the greatest concern. They penetrate deep into the lungs, where they cause irritation and can exacerbate lung disease. Recent studies in Ontario and 16 Canadian cities have demonstrated that hospital admissions for respiratory problems increase with increases in smog levels, and that air pollution may be related to premature deaths from respiratory disease. Other studies on animals have indicated that ozone exposure decreases the lungs' ability to ward off disease.