Acid rain is special type of rain with a PH value less than 5.7. Acid rain is usually caused by nitric and sulfuric acids in air pollution. Fossil fuels such as coal with sulfur can produce SO2 when burning and SO2 reacts with the water in the cloud and becomes acid. When it rains, the rain then becomes acidic. Not only burning coal, the burning of any other fossil fuel (like gasoline in automobiles) that contains sulfur will cause acid rain. So, many countries have managed to perform desulfurization on fossil fuels before they use it. Desulfurization is a chemical process that can eliminate the sulfur in fossile fuels. Because of environmental protection, low quality coal has been banned in most countries.

The clouds that are made up of acidic vapor can drift really far away. It is possible that the "acid cloud" produce in England goes to France and the acid rain drops in France. Because of this negative effect on our neighbor contries, it is our responsibility to minimize the possibity to produce air polllusion and use green energy.