6.4 Acid Deposition

The combustion of fossil fuels produces sulfur dioxide and oxides of nitrogen as primary pollutants. These gases may be converted into secondary pollutants of dry deposition (such as ash and dry particles) or wet deposition (such as rain and snow)

The impacts of acid deposition may be limited to areas downwind of major industrial regions but these areas may not be in the same country as the source of emissions.

The possible effects of acid deposition on soil, water and living organisms include:

• direct effect—for example, acid on aquatic organisms and coniferous forests

• indirect toxic effect—for example, increased solubility of metal (such as aluminium ions) on fish

• indirect nutrient effect—for example, leaching of plant nutrients.

Pollution management strategies for acid deposition could include:

• altering human activity—for example, through reducing use, or using alternatives to, fossil fuels; international agreements and national governments may work to reduce pollutant production through lobbying

• regulating and monitoring the release of pollutants—for example, through the use of scrubbers or catalytic converters that may remove sulfur dioxide and oxides of nitrogen from coal-burning powerplants and cars.

Clean-up and restoration measures may include spreading ground limestone in acidified lakes or recolonization of damaged systems—but the scope of these measures is limited.