ABSTRACT
The acidity of rain is measured by its pH representing the balance of hydrogen and basic ions in solution. Rain acidity reflects its chemical composition, of which carbon dioxide is a principal component. The importance of sulphur dioxide gas in generating acidity in rain was first recognized quite early in the last century by Adam Smith, a pollution inspector in industrial Manchester. The commonly expressed view that “acid rain” is synonymous with “polluted rain” is misleading. Many types of evidence are available for assessing the effects of acidification and their time-scales; alone, any single method has evident deficiencies in providing a scientific “proof.” A proportional change in surface water acidity with change in deposition is rather uncertain given the diversity of hydrological and geological conditions at any site. Direct demonstration of surface water acidification has been achieved by direct acid additions to a pristine lake in Ontario, Canada, demonstrating rates of acidification and recovery.
