The document defines air pollution as particles or gases found in air that are not part of its normal composition, including natural sources like forest fires and unnatural sources from human activities that burn fossil fuels. It describes the Air Quality Index scale of 0-500 that indicates potential health effects from different levels of air pollution. The five major pollutants are identified as carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter, and ground-level ozone, and their sources and health impacts are summarized. Photochemical smog is defined as a combination of gases, water vapor, and dust formed when sunlight reacts with vehicle and industrial exhaust. Ways to reduce air pollution are suggested.