Rain Acidification (Acid Rain)
Natural rain is slightly acidic due to the presence of various acids in the air that are washed out by rain. However, a number of man-made emissions are either acid or they are converted to acid by processes in the air. Examples of such emissions are sulphur dioxide (which becomes sulphuric acid) and nitrogen oxide (which becomes nitric acid).
As a result, the acidity of rain can be substantially increased. In a number of areas (such as large areas of Sweden), the soil and water have a limited capacity to neutralize these added acids. If water becomes too acid, an increasing number of aquatic species are harmed. If the soil becomes too acid, the ability of plants to grow and thrive is harmed.
An acidification indicator is derived by assuming that 100% of an emission is converted to acid and falls into a sensitive area. The acidity of each emission is converted into equivalent amounts of sulphur dioxide. All emissions are then added into an overall acidification indicator score that represents the total emission of substances that may form acids.
To interpret the acidification indicator, it is important to realize that the site where an emission takes place relative to a sensitive area is important. Also, acid falling into the sea is easily neutralized. Newer acidification indicators are being developed to include these variables as well as the buffering or neutralizing capacity of soils. Additional investigation to better understand the environmental meaning of the indicator is suggested.
As a result, the acidity of rain can be substantially increased. In a number of areas (such as large areas of Sweden), the soil and water have a limited capacity to neutralize these added acids. If water becomes too acid, an increasing number of aquatic species are harmed. If the soil becomes too acid, the ability of plants to grow and thrive is harmed.
An acidification indicator is derived by assuming that 100% of an emission is converted to acid and falls into a sensitive area. The acidity of each emission is converted into equivalent amounts of sulphur dioxide. All emissions are then added into an overall acidification indicator score that represents the total emission of substances that may form acids.
To interpret the acidification indicator, it is important to realize that the site where an emission takes place relative to a sensitive area is important. Also, acid falling into the sea is easily neutralized. Newer acidification indicators are being developed to include these variables as well as the buffering or neutralizing capacity of soils. Additional investigation to better understand the environmental meaning of the indicator is suggested.