Millions of people live in areas where smog, very small particles, and toxic pollutants pose serious health concerns. People exposed to high enough levels of air pollutants may experience breathing difficulties. Long-term exposure to air pollution can cause cancer and long-term damage to the immune, neurological, reproductive and respiratory systems. The Clean Air Act is the law that defines the EPA's responsibilities for protecting and improving the nation's air quality and the ozone layer. This page provides a link to the EPA's rules and regulations for each state.