The document discusses air pollution and the air quality index (AQI). It defines air pollution as particles or gases found in air that are not part of its original composition, including natural sources like forest fires and unnatural sources like emissions from cars, homes and factories burning fossil fuels. It describes the AQI scale from 0-500 and the health effects at different levels. It then discusses the five major pollutants - carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter and ground level ozone - and their sources and health impacts. The document concludes with suggestions for reducing air pollution.