A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. The primary greenhouse gases in Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. The main chemicals in air pollution that create acid rain are sulfur dioxide and nitrogen . Acid rain usually forms high in the clouds where sulfur dioxide and nitrogen oxides react with water, oxygen, and oxidants. This mixture forms a mild solution of sulphuric acid and nitric acid. Chlorofluorocarbons (CFCs) and other halogenated ozone depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion.