Pollution

Fossil fuels – Acid Rain What is acid rain? Acid rain is the popular name for a variety of processes which all involve deposition of acidic materials in the form of rain, snow, dry particles such as soot and gases. It is more correctly termed acid deposition. Rainwater before the industrial Revolution had a pH range between 6 to 7.6 The rain that falls on central Europe today is a lot more acidic with an average of ph 4.1. The pH scale is logarithmic so that rain of Ph 4 is 100 times more acidic than rain of pH6. 0 = maximum acidity 7 = neutral point in the middle of the scale 14 = maximum alkalinity (the opposite of acidity)   Sources of acid rain. Sulphur and nitrogen from the oxidization of fossil fuels mainly contribute to acid rain.

Move your mouse over the pH levels to find items of this acidity/alkalinity.

1. Burning of fossil fuels
   S + O₂ forms SO₂        N + O₂ forms NO₂

2. This further oxidizes in the clouds
   SO_{2 +} O₂ forms SO₄^2-       NO_{2 +} O₂ forms NO₃^-

3. These reactions are catalysed by ozone, ammonia, and by unburnt hydrocarbons. These then go into solution.
   SO₄^2- + 2H⁺ forms H₂SO₄ (sulphuric acid)
   NO₃^- + H⁺ forms H_NO₃ (nitric acid)

These two make up ACID rain.

Effects of acid rain.

Acid rain has a number of effects that include the corrosion and subsequent erosion of buildings and statues made from limestone but the most important are the environmental problems caused when it falls on forests, lakes and rivers and soil.

1. Forests

   The leaching effect of acid rain removes Ca²⁺ and Mg²⁺ from the soil which then results in the poor development of the layer that binds cells together in plant tissue (middle lamella) and chlorophyll for photosynthesis. Plants also take up more aluminium ions (Al³⁺) which can be toxic. In addition to this, atmospheric SO₂ and NO₂ damage the photosynthetic spongy and palisade mesophyll cells of the leaves. All this leads to poor growth and death of trees. Trees suffering in this way are also stressed and less tolerant to frost and fungal infections.
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2. Lakes and rivers

   SO₄^2- displaces Al³⁺ from the soil. These aluminium ions wash into water and interfere with the gill function of fish. A sticky mucus accumulates and limits the uptake of oxygen which can result in the death of the fish. Changes in pH also cause the exoskeletons of invertebrates such as crustacea to become soft.
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3. Soil

   In soil, acid rain dissolves and washes away nutrients needed by plants. It also dissolves out toxic substances, such as aluminium. These toxins can then pollute water or poison plants that absorb them. Alkaline soils can neutralize acid deposition but others, especially thin mountain soils derived from granite, cannot.
    

What can society do to prevent acid rain?

The  US EPA (Environment Protection Agency) has a detailed list on their website
Follow these links to the EPA website to find out more about:

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What Society Can Do About Acid Deposition

There are several ways to reduce acid deposition, more properly called acid deposition, ranging from societal changes to individual action.

• Understand acid deposition's causes and effects
• Clean up smokestacks and exhaust pipes
• Use alternative energy sources
• Restore a damaged environment
• Look to the future
• Take action as individuals

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