Both Atlantic Canada and the Windsor-Quebec Corridor inherit the polluted air of industrialized urban centres along the Eastern United States. Periods of smog can last several days, and often occur when pollutants are trapped over a region on hot, sunny days. Weather, climate and land surfaces also affect smog levels. Rain can clean the air of the pollutants that cause smog. But this may result in polluted rain water or acid rain.
Wind can blow smog away.
If cities are surrounded by hills or mountains, the air flow is trapped and smog levels may increase. This is the case in the Lower Fraser Valley, around Vancouver. In most of Canada, smog problems are particularly bad on hot, sunny days. Because smog formation depends on temperature and sunlight, the afternoons and early evenings of hot days are peak smog periods. By late in the day, the sun's rays have baked the exhaust from motor vehicles and industries.