Sonal Patel        Geography Coursework

Acid Rain

Task 1 – Formation and effects of acid rain

a)        Acid rain is a term used to describe wet forms of acid pollution that can be found in rain, snow, fog or water vapour. This type of rainfall usually has a lower pH (below 5.6 average) when acidic. It is formed when secondary pollutants formed from the oxidation of nitrogen oxides of sulphur dioxide are released into the atmosphere. These substances react with the surroundings and react with other gases in the atmosphere to form acids, which can eventually incorporate with water vapour in the clouds to form sulphuric and nitric acids.

The major substances which produce acid rain is sulphur dioxide (SO2) and nitrogen oxides (NOx). Natural and human actions are responsible for the production of these pollutants. The natural processes are mainly unavoidable and include decomposition of organic matter, volcanic eruptions that release sulphur dioxide and degassing from oceanic plankton. The volcanic eruption in Philippines in 1991 resulted in a temporary decrease of global temperatures for more than two years.

Acid rain has been recognised for centuries but it was not known until the 19th century that these were linked with human actions. It is known to be caused from emissions released into the atmosphere from factories burning fossil fuels such as coal and oil. In the Victorian times, coal fires released huge amounts of sulphurous fumes through the chimneys as well. Harmful substances are also released from exhaust fumes which contain sulphur dioxide and nitrogen oxide which form acids in the atmosphere.

Dry acid deposition can be formed when sulphuric acid in the atmosphere condenses which can result in fogs, mists and hazes over urban areas.

b)        The table showing the acidity of commonly occurring substances in order starting from the most alkaline:

Acidic substances such as sulphuric acid can react easily with metals such as potassium. When it reacts it can be dangerous and can burn and destroy the metal completely. Acidity is measured using a pH scale from 1 to 14.An alkaline substance would about 9 to 14 and an acid substance 1 to 4. Neutral substances are of pH value 7. The acid in acid rain is very weak and dilute as it is mixed with a large amount of water in the atmosphere. That is why it cannot actually burn us. Acid rain with a pH value below 2 can be considered 5000 times more acidic than normal rainwater and this has occurred in West Virginia in 1978. Normal rainfall is normally slightly acidic as it is mixed with carbon dioxide, oxides of sulphur and oxides of nitrogen, which occur naturally in the air forming weak acids.

c)        On the next page…

d)        The type of soil a plant grows in can determine the growth for the plant. Many soils have properties which can decrease an impact on it such as being able to neutralize acids. This is because they have a lot of lime in them which is alkali and can neutralize these acids. Soils made of siliceous minerals or weathered bedrock are not so good at this job. In these kinds of soils the increase in acidity can result in leaching of several important nutrients such as calcium, potassium and magnesium. Leaching occurs as a form of filtration of useful nutrients from soils. A deficiency in these nutrients can result in poor root and stem growth.

        The increase in mobilisation of toxic metals can interfere in the active uptake of nutrients into the roots which can eventually damage them. These metals include Lead (Pb), copper (Cu), cadmium (Cd) and aluminium (Al). Reductions in soil pH can prevent the growth of germinating seeds and the growth of young seedlings. Many significant soil organisms require the correct pH to survive. Acid rain can result in a pH of below 6.0, therefore destroying these organisms. This can then result in decomposition which is known to release vast amounts of sulphur products which could form more acid rain.

        Acid rain releases metals into the soils, which can be transferred through the roots, and into the plant. Some of these plants could be vegetables which would later be consumed by humans. The results of acidification on the top soil can lead to reduced intake of water and nutrients, damage to fine root hairs and decomposition slowed down thus less nutrients for plants. The decline of trees in areas such as Scandinavia and Brazil have resulted in nutrients such as Magnesium and Calcium being washed away as there is no canopy to protect the undergrowth. This has now led to soil erosion and loss of humus in soils. The infertile soil has resulted in this decline of plant growth in these areas.

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Task 2 – Changes in UK emissions

a)        The greatest source of sulphur dioxide in 1981 was in power stations with nearly 3000 tonnes of emissions. The greatest source of sulphur dioxide in 1991 was in power stations as well with just over 2500 tonnes of emissions. The greatest source of nitrogen oxides in 1981 was in power stations with nearly 1000 tonnes of emissions. The greatest source of nitrogen oxides in 1991 was road transport with nearly 1500 tonnes of emissions.

b)        In the 1990’s more technology was introduced and the population increased so more vehicles were ...

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