After reading this essay you will learn about:- 1. Introduction to Acid Rain 2. Impacts of Acid Rain 3. Measuring 4. Monitoring.
Essay # Introduction to Acid Rain:
Acid rain is the term used to describe the deposition of acidic air pollution. Although some air pollutants fall directly back to Earth, a lot of it returns in rain, snow, sleet, hail, mist or fog, hence the term “acid rain”. When power stations, factories, houses and cars emit pollution into the air, it contains chemicals known as sulphur dioxide and nitrogen oxide.
These chemicals may either fall directly back to the Earth due to gravity, or they may mix with water (moisture) in the air to form acids. Once acids have formed, they can be transported long distances by the wind before being deposited in rain, snow or hail. This is what we commonly call acid rain.
Acid rain can have harmful impacts on the environment. It affects freshwater lakes and the wildlife that depend upon them. It also affects trees by harming leaves and soil, and it damages building made of limestone and marble.
During the 1970 and 1980s acid rain became a worldwide problem. In countries such as Britain and America, there are many power stations and factories that produce a large amount of pollution.
This pollution is released several hundred feet up through tall chimneys to keep the air at ground level cleaner. It is then blown by the wind deposited as acid rain in countries such as Canada, Norway, Sweden and Finland, which lie hundreds of miles downwind from the source of the pollution.
Once government became aware of the problem of acid rain, they introduced international laws to clean up pollution from power stations and factories. Clean technology was used to reduce the amount of sulphur dioxide and nitrogen oxide gases being released into the air.
We can all help reduce air pollution that causes acid rain. Some of the things we can do include using our car less, short journeys and walking or cycling instead, and saving more energy that we use at home, for heating, lighting and cooking.
Essay # Impacts of Acid Rain:
The effects of acid rain on buildings has been observed for 200 years because of air pollution. Buildings that had been standing in all types of weather for thousands of years suddenly began to decay rapidly. Acid rain can be especially damaging to buildings made of limestone and marble.
When acid rain falls on the buildings it slowly dissolves away the stonework. Ancient monuments are affected by acid rain more than modern buildings because they are often made of limestone or marble.
Consequently, these buildings may need constant up-keep. Even though acid rain has been reduced in recent years, buildings are still showing signs of damage. This is because the acid rain has permanently changed the stones from which the building is made.
Vehicle nitrogen emissions make a significant contribution to acid deposition. The major gases leading to the formation of acid deposition are sulphur dioxide (SO2), and nitrogen oxides (NOx). Vehicles do not produce much sulphur dioxide as petroleum contains very little sulphur.
In 1999, vehicles contributed 1% of the UK sulphur dioxide emissions whilst power stations being the major source of the total UK sulphur dioxide emissions contributed 65%. Nitrogen oxides from vehicles, however, are a major contributor to acid deposition. In 1999, road transport accounted for 44% of nitrogen oxides emissions in the UK.
A motor vehicle produces air pollutants when fuel is burnt to give mechanical power. In a totally efficient combustion process, hydrocarbons in fuel and oxygen will react to form carbon dioxide and water. However, the combustion process is never perfect; some of the hydrocarbon fuel is only partially burnt forming carbon monoxide and water, whilst some of the hydrocarbons are not combusted at all.
These can, and often are, emitted from the exhaust as unburned hydrocarbons. During the combustion process the temperature can reach 2500°C. At these temperatures nitrogen and oxygen from the air in the combustion chamber react to form nitrogen oxides.
Nitrogen oxides pollution from petrol-driven vehicles can be significantly reduced by fitting a catalytic converter to the exhaust system. This is a relatively low cost method of pollution control (around 350 pounds) which has little effect on vehicle performance and fuel consumption. All new cars sold in Britain from January 1993 onwards have catalytic converters.
b. Chimneys & Stacks:
In the 19th and early 20th century air pollution in cities used to be a terrible problem. High levels of smoke and sulphur dioxide pollution from coal burning in homes, industries and power stations caused a lot of illness and many deaths.
After the loss of 4,000 lives in December 1952 due to the Great London Smog, the Government demanded that any pollution released into the air should pass through tall chimneys or stacks, so that the air near ground level would be cleaner to breathe.
Since the 1950s the use of chimneys and stacks to disperse air pollution has improved air quality in towns and cities. Unfortunately, people soon realised that the air pollution was being blown far away from its source, sometimes to other countries downwind, where it fell as acid rain.
Since the 1980s, international laws and cleaner technology have reduced somewhat the amount of air pollution that comes from chimneys and stacks that is causing acid rain.
c. Freshwater Lakes:
Acid rain can affect freshwater lakes and the plants and animals which live in them. Although lakes can withstand a certain amount of acid rain, after a while, their acidity will increase. When this happens, the water in the lake can turn a clear blue due to a loss of organic matter which is usually dissolved in the water.
The range of plants and animals usually decreases. Some of the organisms affected by acidified water include leeches, snails, crayfish, many species of insect, salmon and trout. Others like rushes, pike and eel are more resistant to acidic water. To combat the effects of acid rain on freshwater lakes, lime can be sprayed onto the water surface. This reduces acidity and reduces the damage done to wildlife.
Acid rain comes from the pollution of the air with sulphur dioxide and nitrogen oxides when we burn coal, oil and gas in power stations to generate electricity or drive our cars.
Acid rain can be harmful to the environment, including wildlife, trees and lakes, and can damage buildings. Acid rain affects countries far away from the source of the air pollution. Sweden and Norway for example, receive a lot of acid rain because of air pollution coming from the UK.
d. Fossil Fuels:
Conventional power stations burn coal, oil or gas to produce electricity. Coal, oil and gas are called fossil fuels because they form over millions of years through the decay, burial and compaction of rotting vegetation on land (coal), and marine organisms on the sea floor (oil and gas). Burning fossil fuels in this way releases large quantities of sulphur dioxide and nitrogen oxides which can cause acid rain.
Coal is a solid fuel formed over millions of years by the decay of land vegetation. Over time, successive layer become buried, compacted and heated, a process through which the deposits are turned into coal. Coal is widely used in the generation of electricity because it is highly concentrated energy source.
However, it is not a particularly “clean” fuel, releasing more acidic pollution than either oil or gas. Coal was the first fossil fuel to be exploited on a large scale during the 19th century with the beginning of the Industrial Revolution. Before the commercial introduction of electricity, coal was primarily used in Industrial boilers to create steam energy to power machinery.
Oil is formed from the remains of marine microorganisms (microscopic animals and plants) deposited on the sea floor. As they accumulate over millions of years they gradually infiltrate the microscopic cavities of the sea floor sediment and rock where they decay. The resulting oil remains trapped in these spaces, forming oil reserves which can be extracted through large drilling platforms.
The use of oil increased significantly after the Second World War. In the early 1970s, approximately 40% of global fossil fuel use came from the oil, but during the 1990s this figure has decreased.
Improved energy efficiency has caused oil consumption to decline in many developed, industrialised countries, as well as shifts to other fuels such as natural gas and nuclear energy. Decreasing use of oil is also resulting from tougher environmental restrictions concerning its use in some regions. Consequently, natural gas has become the fastest growing energy resource.
The present global use of natural gas is approximately 20% of all fossil fuel use, and this figure is predicted to rise in the future. Natural gas provides an alternative to oil or coal in the provision of energy, and in terms of acidic pollution it is cleaner fuel. Some estimates indicate the reserves of natural gas may be available for up to 400 years.
Acid rain can harm trees and other plants. Many forests are dying in different countries of the world. The acid in polluted snow, sleet and fog, as well as rain, takes important minerals away from the soil. Without these minerals, trees and plants cannot grow properly.
Damaged trees lose their needles or leaves, and may have stunted growth and damaged bark. Conifer (evergreen) tree damaged by acid rain may turn a yellow or orange colour.
This makes it easier for fungi and insects to attack the tree, and the tree may die. Acid rain not only damages soil but can also block or damage little pores on leaves. These take in carbon dioxide from the air, which the trees need to make food to grow.
Soil is the basis of wealth upon which all land-based life depends. Acid deposition in known to wash essential nutrients from soils, and aluminium which is normally bound in soil may be released into ground water. Soil acidification may affect the health of trees and other vegetation.
Soils containing calcium and limestone are more able to neutralize sulphuric acid and nitric acid depositions than a thin layer of sand or gravel with a granite base. If the soil is rich in limestone or if the underlying bedrock is either composed of limestone or marble, then the acid rain may be neutralized.
The higher pH of these materials dissolved in water offsets or buffers the acidity of the rainwater producing a more neutral pH.
In regions where the soil is not rich in limestone or if the bedrock is not composed of limestone or marble, then no neutralizing effect takes place, and the acid rainwater accumulates in the bodies of water in the area.
This applies to much of the north-eastern United States where the bedrock is typically composed of granite. Granite has no neutralizing effect on acid rainwater. Therefore, over time, more and more acid precipitation accumulates in lakes and ponds. Such areas are catchments, are termed acid-sensitive (poorly buffered), and can suffer serious ecological damage due to acid rain.
To grow, trees and other vegetation need healthy soil to develop in. Long-term changes in the chemistry of some sensitive soils occur as a result of acid rain. As acid rain moves through the soils, it can strip away vital point nutrients such as calcium, potassium and magnesium through chemical reactions, thus posing a potential threat to future forest productivity. Furthermore, the number of microorganisms present in the soil also decreases as the soil becomes more acidic.
This further depletes the amount of nutrients available to plant life because the microorganisms play an important role in releasing nutrients from decaying organic material. Trees growing in acidified soil are more susceptible to viruses, fungi and insect pests. Other plants life may grow more slowly or die as a result of soil acidification.
Poisonous metals such as aluminium, cadmium and mercury are leached from soils through reacting with acids. This happens because these metals are bound to the soil under normal conditions, but the added dissolving action of acids causes rocks and small bound soil particles to break down. In addition, the roots of plants trying to survive in acidic soil may be damaged directly by the acids present.
Wildlife can be affected by changes in the environment caused by acid rain. Animals living in freshwater can be affected if the water becomes acidified. Some fish such as the salmon and trout are affected by acidic water, and may also be poisoned by toxic substances that have been washed out of the soil by acid rainwater. Frogs are also dependent upon freshwater for breeding and can be affected by acid rain.
Other animals affected by acid rain include those living in soils like earthworms, and those dependent upon them, like birds. Worms are affected by a build-up of poisonous metals in the soil as a result of acid rain.
Birds are not directly affected by acid rain, but by a change in their food supply because of acid rain. Some birds, like the osprey, feed on fish. Otters, too, may have their fish supply reduced if the waters in which they usually feed become acidified.
Acid rain also affects trees and plants, by damaging leaves and the soil which feeds them. A decrease in the amount of trees may cause further problems for wildlife that rely on them for shelter.
Essay # Measuring Acid Rain:
The acidity of acid rain is measured using the pH scale. It ranges from 1 to 14.
Substance like vinegar and lemon juice are acidic, and have a low pH. Distilled water is neutral with a pH of 7. Substances like blood and milk are alkaline and have a high pH. All rain is slightly acidic as it contains carbon dioxide, a gas found in air. Unpolluted rain usually has a pH of between 5 and 6. Acid rain has been found to have a pH as low as 3 and in some cases even lower.
Essay # Monitoring Acid Rain:
The simplest way to monitor the acidity of acid rain (from wet deposition) is to collect rain samples and to measure the pH of the water. Since 1987, such monitoring of acid rain has taken place in and around Greater Manchester in the UK, the Greater Manchester Acid Deposition Survey (GMADS). Rain collectors have been sited in Greater Manchester following strict criteria.
The collectors must be 100 m away from small point sources (such as domestic chimneys), 100 m from mobile sources (road traffic), 1 km from major roads, 5 km from large surface works, and 10 km from large point sources (such as power stations).
Across the UK, the Acid Deposition Monitoring Network monitors the composition and acidity of precipitation at 32 sites to provide an accurate measurement of pollutant deposition in rain and snow to asist in implementing a critical loads approach to environmental protection.
All precipitation samples are analysed for conductivity, pH, sulphur, nitrate and chloride concentration, and a variety of metal ions (ammonium, sodium, calcium, potassium, and magnesium).
Combining these measurements of acid deposition with the estimated critical loads in the forms of maps can highlight those areas where the tolerance to acidity is being exceeded, and where damage from acidification is most likely to be found.