15 de octubre del 2000
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Cambio Climático
Proyecto de soporte a negociación ambiental

Cambio Climático

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sobre temas globales de seguridad humana
Programa de las Naciones Unidas para el Desarrollo
Programa de las Naciones Unidas para el Medio Ambiente

Lluvia ácida en Japón/ UNEP-Select
Acid rain in Japan / UNEP-Select

Acid Rain

Acid rain is a significant environmental and economic concern for many regions around the world. This section explains what acid rain is, where it comes from, and what its effects are.


1 What causes acid deposition?

-Acid deposition, commonly called acid rain, is caused by emissions of sulphur dioxide and nitrogen oxides. Although natural sources of sulphur oxides and nitrogen oxides do exist, more than 90% of the sulphur and 95% of the nitrogen emissions occurring in eastern North America are of human origin. These primary air pollutants arise from the use of coal in the production of electricity, from base-metal smelting, and from fuel combustion in vehicles. Once released into the atmosphere, they can be converted chemically into such secondary pollutants as nitric acid and sulphuric acid, both of which dissolve easily in water. The resulting acidic water droplets can be carried long distances by prevailing winds, returning to Earth as acid rain, snow, or fog.

2 Is acid deposition always wet?

-No. The acids can be transformed chemically into sulphur dioxide gas or into sulphur and nitrogen salts. In this form they are deposited 'dry', causing the same damage as when they land dissolved in rain or snow. In this form they can also do internal damage to plants as they are taken up from the soil.

3 Is natural precipitation acidic?

-Yes. Water solutions vary in their degree of acidity. If pure water is defined as neutral, baking soda solutions are basic (alkaline) and household ammonia is very basic (very alkaline). On the other side of this scale, there are ascending degrees of acidity; milk is slightly acidic, tomato juice is slightly more acidic, vinegar is mediumly acidic, lemon juice is still more acidic, and battery acid is extremely acidic.

4 How does acid deposition affect human health?

-We eat food, drink water, and breathe air that has come in contact with acid deposition. Canadian and U.S. studies indicate that there is a link between this pollution and respiratory problems in sensitive populations such as children and asthmatics. Acid deposition can increase the levels of toxic metals such as aluminum, copper, and mercury in untreated drinking water supplies.

5 How does acid deposition affect aquatic ecosystems?

-The interactions between living organisms and the chemistry of their aquatic habitats are extremely complex. If the number of one species or group of species changes in response to acidification, then the ecosystem of the entire water body is likely to be affected through the predator-prey relationships of the food web. At first, the effects of acid deposition may be almost imperceptible, but as acidity increases, more and more species of plants and animals decline or disappear.

6 How does acid deposition affect terrestrial plant life?

-Both natural vegetation and crops can be affected:

  • It can alter the protective waxy surface of leaves, lowering disease resistance.
  • It may inhibit plant germination and reproduction.
  • It accelerates soil weathering and removal of nutrients.
  • It makes some toxic elements, such as aluminum, more soluble. High aluminum concentrations in soil can prevent the uptake and use of nutrients by plants.

Source: The Primer on Environmental Citizenship.