It is defined as the presence of chemicals and particulate in the atmosphere in quantities and pollution that are harmful to human health and environment. It occurs when the concentration of certain substances become high enough to cause the atmospheric environment to become toxic. Air pollution affects the human being very high because every human being inhales about 15-22 kg of air daily and if it polluted it will damage human health considerably.

Example: SO2, CO, Chlorofluoro-Carbon (CFC'S), Nitrogen oxide etc.