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Byline: DR. S.M ALAM

Acid rain is a severe environmental problem and affects various regions of the world. It is harmful to the surroundings including lakes, streams, woodlands, and floras and faunas. It is fundamentally caused due to poisonous gases which are emitted from the Earth's surface in the atmosphere. It may be related to the acid deposition, which includes wet deposition and dry deposition.

Acidic rain, acidic fog, and acidic snow are elements of the wet deposits. If the acid chemicals present in the atmosphere travel into regions, which have wet weather, the acids can drop on the surface of the Earth through rain, snow, fog, or even mist. The acidic water flows on the ground surface and through the ground, which has a contrary effect on various plants and animals. The degree of the consequences count on many factors, including how much acid the water contains, and the type and chemistry of the soil, which gets in contact with the acidic water. It also harms fish, trees, and other living beings which are dependent on water.

In regions of dry atmosphere, the acid chemicals are mixed with dust or smoke, and drop on the Earth's surface in the form of dry depositions which sediment to the ground, and on skyscrapers, houses, cars, and trees. These deposits are then washed off by rains, after which the rainwater causes the acid chemicals to become more acidic. Around 50 per cent of the acidity in the air drops back on Earth by means of dry deposition.

Chemicals such as sulfur dioxide and nitrogen oxide are the chief reasons for acid rains which occur due to the reaction that takes place after burning fossil fuels such as coal. They have a ruinous effect on the environment, which includes woodlands, soil, fishes, and other living things. The bionomical effects are generally visible in water bodies such as lakes and watercourses. As the acid water flows through the watersheds, the aluminum which is present in the soil is discharged in the rivers and lakes situated in that watershed. As a result, the level of hydrogen lowers and that of aluminum increases, which can be instantly fatal to the fish.

Plants, human beings, and fish are mostly harmed by the deposition of acids on the ground and water. It has a bad effect on human health and may damage our lungs, and affects fish which die due to the acidic water.

However, there are some measures, which can be taken by human beings to prevent sources of acid rains. Smokestacks and exhaust pipes need to be kept clean, as all of the electrical energy is generated from burning fossil fuels such as coal, natural gas, and oil. Historical monuments and buildings also end up being damaged by these acid rains. Moreover, people need to be educated regarding the after-effects of acid rain over time. If the necessary steps are not taken, there is a possibility of the instances of acid rain rising enormously.

The term, 'acid rain' refers to a phenomenon in which falling rain sometimes can be acidic. This is a bad thing. Acid rain is a side effect from the burning large amounts of fossil fuels like coal and petroleum, and usually occurs over regions downwind from clusters of large, modern, industrial cities. Acid rain is a bad problem because it can result in the death of plants and animals in lakes and streams. In some places, acid rain has been linked to the death of many trees, threatening whole forests. The acids come from cars and fossil fuel- burning electrical power plants. Sulfur dioxide (SO2) and nitrogen dioxide (NO2) are the two main pollutants in the exhaust smoke that cause the acid rain problem.

They react with other substances in the atmosphere to make the acids found in acid rain. NO2 reacts to make nitric acid, and SO2 reacts to make sulfuric acid. Strong acids are very reactive. Weak acids are weakly reactive and neutral solutions have no reactivity. Without getting into the chemistry itself, we can understand the significance of the 'reactivity' of water solutions. Acid rain is an interesting and important environmental phenomenon, particularly considering its impact on natural ecosystems.

Unfortunately, with the rapid growth of human population and since industrial revolution, pollution impacts are getting worst. Motors, factories, and the use of fossil fuels to generate electricity, all contribute to the vast increase of air pollutants including sulphur dioxide, nitrogen oxides etc.

Nitrogen oxide mainly refers to the gaseous of nitrogen dioxide and nitrogen monoxide. The main sources of these gases are from the burning of fossil fuel and by lightning. When these gases are emitted into the atmosphere, they will react with the water molecules in the air to form acid rain.

The areas affected by acid rain are widespread and these areas may be very far away from the source. For example, the acidic gases emitted in the UK might be blown to Germany and Norway, precipitated as acid rain. The acidic gases emitted in Hong Kong may be blown to mainland China.

The impact of acid rain is widespread, and the impact location can be distance away from the source. Therefore, the overall impacts are severe. When acid precipitation falls on woodland, the soil within the woodland will become more acidic.

Acidic soil will have direct impaction soil organisms such as plants, animals, and even bacteria. The growth of vegetation relies on soil nutrients and pH. Plant growth may be inhibited when the soil pH is too high or too low, if the acidity of the soil is too high, death of vegetation may be the results. Although different vegetation has different toleration to soil pH, most of them can only survive within a narrow pH value. Therefore, if the acidity in the soil has changed, the diversity of vegetation will change relatively. Acid rain will also change the level of nutrients in the soil, as acidic water can dissolve or react with the minerals/nutrients. The dissolved minerals/nutrients will be lost through the runoff of water, leading to the lack of nutrients for plant growth. Eventually this nutrient-deficient land will lead to desertification.

Acid rain can have adverse impacts of plant tissues. The acid water will corrode and damage plant structure and as a result the malfunction of plant physiology, photosynthesis process cannot be carried out and the whole woodland ecology may eventually collapse. When the plants die, the soil cannot be consolidated and lead to soil erosion. Most of the landslide is due to the loss of vegetation.

Water is a precious resource on Earth. Life would not be existed without water. 2/3 of earth surface is covered by water, present mainly in oceans, lakes and rivers, and of two types: marine and fresh water. The impact of acid rain is not as significant in seawater than in freshwater. The volume of seawater is enormous and the top part of ocean water moves (due to tidal and wind). Therefore, when acid rain falls into seawater, it would be diluted. In addition, seawater contains vast quantities of alkaline substances (e.g. calcium carbonate from shells), which can react with acid rain to decrease its acidity.

On the other hand, when acid rain falls into the freshwater resources such as rivers and lakes, because these resources usually do not store huge volume of water, the impacts of acid rain are more significant, especially in lakes with still water. Acid water will store in lakes and accumulate every time of acid precipitation, eventually the acidity will be too high to kill most of the organisms in lake water. Although each aquatic species can tolerate acid rain to an extent, lack of calcium carbonate shells and the small volume of water account for the high acidity in some highland lakes and cause death.

Acid rain can cause damage to buildings, especially the ones built by limestone rocks. Surface of the buildings can be corroded by acid water and cause the loss of heritages such as historic buildings and statues. Apart from buildings, the caves within the limestone rocks are also caused by long-term exposure of acid rain. Corrosion caused by acid rain is not short-term (i.e. not happens in few hours or days), it takes a long time (generally speaking at least tens of years) to see a distinct damage caused by acid rain. There are many heritages round the world show evidences of acid rain corrosion.

Solutions: The best way to reduce acid rain is to reduce air pollution such as emission of acidic gases. However, it is difficult to stop pollutants with the advance of technology. Fossil fuel power plants are the critical sources for acid rain. One of the methods to achieve this is to neutralise the acidic gases before releasing into the atmosphere.
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Publication:Pakistan & Gulf Economist
Date:Oct 31, 2010

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