The document discusses air pollution and its impacts on health. It defines air pollution as particles or gases in the air not normally present, including those from natural sources like fires and dust storms, and unnatural sources like vehicles and industry. It describes the Air Quality Index scale of 0-500 that indicates health risks from pollutant levels and provides protection guidelines. It then details the five major pollutants - carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter, and ground-level ozone - and their sources and health effects. The document concludes with a discussion of smog formation and some individual actions that can be taken to reduce pollution.