Air pollution is the introduction of particulates, biological molecules, or other harmful materials into the Earth's atmosphere, possibly causing disease, death to humans, damage to other living organisms such as food crops, or the natural or built environment. An air pollutant is a substance in the air that can have adverse effects on humans and the ecosystem. The substance can be solid particles, liquid droplets, or gases. A pollutant can be of natural origin or man-made. Major primary pollutants produced by human activity include, sulphur oxides,, nitrogen oxides, carbon monoxide, volatile organic compounds, particulates, persistent free, toxic metals, such as lead and mercury, chlorofluorocarbons, ammonia, odors, and radioactive pollutants.
Air pollution effects various different health problems, such as cardiovascular disease, cystic fibrosis, lung disease, and different cancers. Moreover, children living in cities with high exposure to air pollutants are at increased risk of developing asthma, pneumonia and other lower respiratory infections.