Acid rain is caused by emissions of sulphur dioxide and nitrogen oxide which react with the water molecules in the atmosphere to produce acids. Some governments have made efforts to reduce the release of sulphur dioxide and nitrogen oxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes and sulphur dioxide is produced by volcanic eruptions. Acid rain has been shown to have adverse impacts on freshwaters and soils killing insect and aquatic life forms. It also causes paint to peel corrosion off steel structures such as bridges and weathering of stone buildings and statues as well as having impacts on human health. Acid rain is a popular term referring to the deposition of a mixture from wet and dry components. Once carbon dioxide is removed distilled water has a neutral pH of seven. Unpolluted rain can also contain other chemicals which affect its acidity level. A common example is nitric acid being produced by electric discharge in the atmosphere. The corrosive effect of polluted and acidic city air on limestone and marble was noted by John Evelyn who remarked upon the poor condition of the Arundel marbles. Since the Industrial Revolution emissions of sulphur dioxide and nitrogen oxides into the atmosphere have increased. Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester England. The term acid rain was coined by Robert Angus Smith. Harold Harvey was among the first to research a dead lake. At first the main focus in research lay on local effects of acid rain.