Coal, oil, and natural gas are called fossil fuels because they are the fossilised remains of plants and animals that lived hundreds of millions of years ago. Burning fossil fuels releases a chemical called Sulphur dioxide that causes approximately half the worlds acid rain. There are other sources that emit Sulphur dioxide, they are volcanoes, sea spray, rotting vegetables and plankton. When sulphur dioxide reaches the atmosphere, it oxidises to first form a sulphate ion. It then becomes sulphuric acid as it joins with hydrogen atoms in the air and falls back down to earth. Oxidation occurs the most in clouds and especially in heavily polluted air where other compounds such as ammonia and ozone help to catalyze the reaction, converting more sulphur dioxide to sulphuric acid. However, not all of the sulphur dioxide is converted to sulphuric acid. In fact, a substantial amount can float up into the atmosphere, move over to another area and return to earth unconverted.

Nitric oxide and nitric dioxide are also components of acid rain. Its sources are mainly from power stations and exhaust fumes. Like sulphur dioxide, these nitrogen oxides rise into the atmosphere and are oxidised in clouds to form nitric acid.

Other bad effects of Fossil Fuels are Global Warming, caused by the greenhouse effect.