The document discusses different types of air pollution sources and pollutants. It describes the four main types of air pollution sources as mobile sources like vehicles, stationary sources like power plants, area sources like cities, and natural sources like dust. It then classifies air pollutants as primary pollutants emitted directly into the air or secondary pollutants formed from atmospheric reactions between primary pollutants. Finally, it provides details on some common gaseous pollutants like carbon monoxide, nitrogen oxides, and sulfur oxides and particulate pollutants of different sizes.