(a) Pollutants: Air contains substances which are harmful to plants and animals. These harmful substances are called pollutants.
(b) Acid rain: When sulphur trioxide and nitrogen oxide present in the air mix with rainwater they form sulphuric acid and nitric acid respectively. Rainwater containing these acids is called acid rain.
(c) Global warming: An increase in the percentage of carbon dioxide, methane, nitrous oxide and chlorofluorocarbon traps the heat causing the temperature of the earth and its surroundings to rise. This is known as global warming.
(d) Smog: Oxides of nitrogen form a mixture of smoke and fog known as smog which affects our eyes too.
