Citywide problems: Ambient air pollution
In those cities with high air pollution levels and a combination of geography and weather that prevents pollutants from dispersing, ambient air pollution can pose a significant health risk to rich and poor alike. That risk is compounded in cities where air pollution regulations or enforcement is weak. Worldwide, an estimated 1.1 billion urban residents are exposed to particulate or sulfur dioxide levels in excess of the guidelines set by the World Health Organization (WHO).
