WILL MCINTYRE / SCIENCE PHOTO LIBRARY WILL MCINTYRE / SCIENCE PHOTO LIBRARY
Acid rain damage to trees. Damaged and dying trees in a conifer forest due to the effects of acid rain. Acid rain is caused by gaseous pollutants dissolving in the water as it falls. The main acid rain pollutants are nitrogen oxides from car exhausts and sulphur oxides from the burning of coal by power stations and industry. Normal rain has a pH of 5.6 but the gases acidify it to a pH of 4-4.5. Aquatic organisms are also affected as lakes and streams are acidified. Trees are also affected by ozone, a poisonous form of oxygen, which is emitted by car exhausts too. Photographed in the Appalachian Mountains, USA.
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