1. Air pollution is one of the greatest risks to human health and the environments. It turns clear, odorless air into hazy smelly air that harms health, kills plants, and damages property. While often invisible, pollutants in the air create smog and acid rain, cause cancer or other serious health problems, diminish the protective ozone layer in the upper atmosphere, and contribute to the potential for world climate change.
2. Smog and other types of air pollution can lead to or aggravate respiratory, heart, and other health problems. Both gases and particulates burn people's eyes and irritate their lungs. Particulates can settle in the lungs and worsen such respiratory diseases as asthma and bronchitis. Some experts believe that particulates may even help cause such diseases as cancer, emphysema, and pneumonia. In cities throughout the world, long periods of heavy air pollution have caused illness and death rates to increase dramatically.
3. Acid rain – caused by sulfur dioxide and nitrogen oxides combining with moisture in the air – limits the ability of lakes to support aquatic life, may damage trees and plants, and erodes building surfaces and national monuments.
4. The air inside our homes and offices is another area for concern. A growing body of scientific evidence indicates that indoor air can be more seriously polluted than the air outside. Radon, asbestos, lead-based paint, tobacco smoke and other "air toxics" cause serious health effects, such as damage to respiratory or nervous systems.