Acid rain. Image representing the effects of acid rain on a statue. Acid rain is caused by the reaction in the atmosphere between water droplets and pollutant gases, notably sulphur oxide and oxides of nitrogen, which are mainly emitted by the burning of fossil fuels. Such reactions lead to the production of sulphuric acid and nitric acid which are brought down through the rain, increasing the acidity of soil and water in rivers and lakes. Statues are eroded by the acid depositions and many of Europe's older buildings are decaying at an unnatural rate.