Impacts of Acid Rain on Soils

Soil is the basis of wealth upon which all land-based life depends.
The damage that occurs to ecosystems from acidic deposition is dependent on the buffering ability of that ecosystem. This buffering ability is dependent on a number of factors, the two major ones being soil chemistry and the inherent ecosystem sensitivity to acidification. Indirect damage to ecosystems is largely caused by changes in the soil chemistry. Increasing soil acidity can affect micro-organisms which break down organic matter into nutrient form for plants to take up. Increasing soil acidity also allows aluminium (a common constituent of soil minerals) to come into solution. In its free organic form, aluminium is toxic to plant roots and can lock up phosphate, thereby reducing the concentrations of this important plant nutrient.

What Effect Does the Soil and Underlying Bedrock Have on Acid Rain?
Soils containing calcium and limestone are more able to neutralise sulphuric 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 neutralised. This is because limestone and marble are more alkaline (basic) and produce a higher pH when dissolved in water. The higher pH of these materials dissolved in water offsets or buffers the acidity of the rainwater producing a more neutral pH.

Acid Sensitive Areas
In regions where the soil is not rich in limestone or if the bedrock is not composed of limestone or marble, then no neutralising 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 neutralising effect on acid rainwater. Therefore over time more and more acid precipitation accumulates in lakes and ponds.

The water bodies most susceptible to change due to acid precipitation are those whose catchments have shallow soil cover and poorly weathering bedrock, for example granite and quartzite. These soil types are characterised by the absence of carbonates that could neutralise acidity. The run-off water from such areas is less buffered than from areas such as limestone catchments, with an adequate level of carbonate. Such catchments and waters are termed acid-sensitive (poorly buffered), and can suffer serious ecological damage due to artificially acidified precipitation from air masses downwind of major emissions.

Notable high-risk areas in Canada and the United States are the Canadian Shield, the Adirondack Mountains, the Laurentians, the Appalachians, and the Green Mountains of Vermont. These areas are vulnerable because of their high elevations, small watersheds, and naturally acidic soils. Different types of bedrock contain variable amounts of alkaline chemicals. Regions with bedrock containing less alkali have a lower capacity for reducing acidity, and thus are more sensitive to acid deposition.

Effects of soil on vegetation
When acid rain falls, it can affect forests as well as lakes and rivers. To grow, trees need healthy soil to develop in. Acid rain is absorbed into the soil making it virtually impossible for these trees to survive. As a result of this, trees are more susceptible to viruses, fungi and insect pests.
Long-term changes in the chemistry of some sensitive soils may have already occurred as a result of acid rain. As acid rain moves through the soils, it can strip away vital plant nutrients through chemical reactions, thus posing a potential threat to future forest productivity.

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 hydrogen ions causes rocks and small-bound soil particles to break down.
Plant life in areas where acid rain is common may grow more slowly or die as a result of soil acidification. In the Green Mountains of Vermont and the White Mountains of New Hampshire in the United States 50% of the red spruce have died in the past 25 years. There has also been noted a reduced amount of growth in existing trees as measured by the size of growth rings of the trees in these areas.

These effects occur because acid rain leaches many of the existing soil nutrients from the soil. The number of micro-organisms 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 micro-organisms play an important role in releasing nutrients from decaying organic material. In addition, the roots of plants trying to survive in acidic soil may be damaged directly by the acids present. Finally, if the plant life does not die from these effects, then it may be weakened enough so that it will be more susceptible to disease or other harsh environmental influences like cold winters or high winds.

Critical Loads
Environmental response to pollutants depends on many factors. Some regions cope with acidification better than others, having larger 'critical loads'. Critical load refers to the greatest assault that an ecological system can withstand before showing measurable degradation.

Scientists determine critical load by examining rock and soil type, land use and rainfall. If soil is fertile with a pH greater than 4.5, and rainfall is relatively low, the critical load will be high. The terrain can withstand moderately large additions of acidity without undue suffering. Conversely, in low pH soils, acidification mobilises toxic aluminium ions. If coniferous forests predominate, or if land is devoted to rough grazing, the result is a low critical load. Even minor acid deposition is undesirable.

There are very few long-term UK monitoring studies of soil acidification and none of soil biota. Chemical data are available from a few specific sites, from a small number of regional studies and from three national studies. From the limited information available, the National Expert Group on Transboundary Pollution has concluded that there is evidence that acid deposition has resulted in widespread acidification of acid sensitive soils in the UK. Further critical loads modelling research suggests that soil recovery from acidification may take many years or even decades.

Acid Rain – Is It A By-Product of Global Warming?

Acid rain: two words that are not very pretty. Instead of the romantic rain that most of us would like to imagine, acid rain brings to mind frightening images of a future wrought with pollution and other problems. But what is acid rain and what is it caused by? And is acid rain really a by-product of global warming? The short answer is both yes and no. Acid rain has causes that are rooted both in nature and in the human activity that is causing the effects of global warming to become more pronounced.

In scientific terms, acid rain refers to any kind of precipitation, including mist, snow, fog, and of course, rain, that is more acidic than normal. Most rain is naturally a bit acidic, but acid rain contains an above average level of acid in it. Generally speaking, acid rain is caused by emissions of sulfur dioxide and nitrogen oxides that react with hydroxyl radicals and water vapor that exist in many industrial environments. When this combination exists, the acid rain may come down as either dry acid deposition or, when it is mixed with water, it is known as acid rain.

What is most acid rain composed of? Acid rain as it falls in the eastern part of North America and parts of Europe is composed mostly of sulfuric acid and nitric acid. How do these things make up acid rain? Acid rain generally occurs when the burning of fuels produces sulfur dioxide and nitrogen oxides. These different oxides get into our atmosphere because of both natural environmental activity as well as human activity. When these oxides reach the troposphere, they become oxidized by the hydroxyl radicals in the atmosphere that then break down the oxides into sulfuric and nitric acids. These acids will usually break down readily into water that is then brought down in the form of precipitation, or acid rain.

So is acid rain a by-product of global warming? It is not so simple. Many natural sources are also a part of acid rain. Many tons of sulfur is released into the earth's atmosphere each year from natural sources, including volcano eruptions, microbial processes, and sea sprays. Nitrogen oxides are also released into the earth's atmosphere in a natural manner, including from burning, lightning, the burning of biomass, and many microbial processes.

However, in a sense, acid rain is indeed a type of by-product of global warming because human activity often is responsible for some kinds of acid rain. It is estimated that human beings release up to 100 to 130 million tons of sulfur dioxide into the atmosphere. Human beings are also estimated to be responsible for roughly 60 to 70 million tons of the nitrogen oxides that are released into the earth's atmosphere each year. Most acid rain occurs in highly industrialized areas where these oxides are released into the earth's atmosphere on a regular basis. However, human activity has caused more oxides to be released into the earth's atmosphere in certain concentrated areas. Thus, human activity is definitely a strong factor in the occurrence of acid rain, especially in highly concentrated areas.

The effects of acid rain are becoming recognized as a growing problem, especially around highly industrial areas. Areas that have been highly industrialized for more than 100 years are considerably more susceptible to experiencing acid rain. However, all parts of the world are susceptible to some kind of acid rain. Acid rain is especially having an effect on many fragile ecosystems, including many of the earth's aquatic ecosystems. Acid rain can also have a devastating effect on forests.

Normally while rain travels through the air, it dissolves floating chemicals and washes down particles that are suspended in air. At the start of its journey raindrops are neutral (pH = 7). In clean air, rain picks up materials that occur naturally such as dust, pollen, some CO₂ and other chemicals produced by lightening or volcanic activities. These substances make rain slightly acidic (pH = 6), which is not dangerous. However, when rain falls through polluted air, it comes across chemicals such as gaseous oxides of sulphur (SO_x), oxides of nitrogen (NO_x), mists of acids such as hydrochloric and phosphoric acid, released from automobile exhausts industrial plants, electric power plants etc.

These substances dissolve in falling rain making it more acidic than normal with pH range between 5.6 -3.5. In some case, it's pH gets lowered to the extent of 2. This leads to acid rain. The term acid rain is used here to describe all types of precipitation, namely, rain, snow, fog and dew more acidic than normal.

Chemistry of acid rain

In the natural processes of volcanic eruptions, forest fires and bacterial decomposition of organic oxides of sulphur and nitrogen, production and reductions of gases naturally tend to an equilibrium. Power plants, smelting plants, industrial plants, burning of coal and automobile exhausts, release additional sulphur dioxide, nitrogen oxides and acidic soot, causing pollution. Sulphur dioxide and nitrogen dioxide interact with water vapours in presence of sunlight to form sulphuric acid and nitric acid mist.

The formed sulphuric acid and nitric acid remain as vapour at high temperatures. These begin to condense as the temperature falls and mix with rain or snow, on the way down to the Earth and make rain sufficiently acidic.

Harmful effects of acid rain

SO_x, NO_x mixed with water as acid rain causes plant, animal and material damage. Some of the significant ill effects of acid rain are:

Damage to animals

Acid rain chemically strips waterways of necessary nutrients and lowers the pH to levels where plants and animals cannot live. Most of the aquatic animals cannot survive when the pH is less than 4. Some species of fish, such as salmon, die even when the pH is less than 5.5. Certain species of algae and zooplankton are eliminated at pH less than 6. A reduction in the zooplankton and bottom fauna ultimately affects the food availability for the fish population. The problem is most severe downwind of industrial areas where fishing and tourism are major sources of income such as in Norway and Sweden.

Damage to plants

Acidic water is dangerous to plants. Sulphuric and nitric acid rain washes nutrients out of the soil, damages the bark and leaves of trees and harms the fine root hairs of many plants which are needed to absorb water. Leaf pigments are decolorized because acid affects green pigment (chlorophyll) of plants. Agricultural productivity is also decreased. Several non-woody plants, such as barley, cotton and fruit trees like apple, pear, etc., are severely affected by acid rain. Since the acid concentration increases near the base of clouds by density, high altitude trees and vegetation may be exposed to pH levels as low as 3. Unique areas such as the Black Forest in Germany and sugar maples in Vermont (USA) are particularly threatened.

Material damage

Metallic surfaces exposed to acid rain are easily corroded. Textile fabrics, paper and leather products lose their material strength or disintegrate by acid rain.

Building materials such as limestone, marble, dolomite, mortar and slate are weakened on reaction with acid rains because of the formation of soluble compounds.

Thus, acid rain is dangerous for historical monuments.

Acid Rain & Heart Disease

Acid rain is the deposition of acidic components in rain, snow, fog, dew or dry particles that come from sulfur dioxide and nitrogen oxides. These dangerous chemical pollutants can have a severe impact on human health, including pulmonary disorders and heart disease. Much research is being done to combat acid rain for the sake of the environment, aquatic life and human health.

Process of Acid Rain

The process of depositing air pollutants on the Earth's surface is known as atmospheric deposition. These pollutants are derived from natural sources, such as forest fires and volcanoes, or from anthropogenic (man-made) sources, such as electric power plants and automobiles. Atmospheric deposition is both wet and dry. Wet deposition is precipitation (for example, rain and snow), and dry deposition is the settling, impaction, or adsorption of particles in dry weather. If wet deposition is acidic, it is known as acid rain.

Measuring Acid Rain

Because acid rain looks, feels and tastes like clean water, pH measurements are taken to determine its acidity. According to the U.S. Environmental Protection Agency, pure water has a pH of 7.0, and normal rain has a pH of about 5.6. Water is considered acid if the pH is less than 7.0 and alkaline if the pH is greater than 7.0. The lower the pH, the greater is the acidity of the water.

Causes of Acid Rain

Air pollution is the principal cause of acid rain. The burning of fossil fuels, such as coal and oil, from electric power generators forms sulfur dioxide. Automobile fumes cause nitrogen oxides to form. These gases are released into the atmosphere and travel with the wind for hundreds of miles from the originating city to the countryside, harming not only Earth's forests and lakes, but also the health of humanity.

Link Between Acid Rain and Heart Disease

When you breathe the air pollutants (sulfur dioxide and nitrogen oxides) that cause acid rain, symptoms including coughing, shortness of breath, chest tightness, and chest pain can occur. The formulated particles can penetrate deep into the lungs and aggravate heart disease. The high levels of sulfur dioxide and nitrogen oxides associated with acid rain are particularly harmful to senior citizens and people with existing heart disease. As a result of these airborne particles, hospital admissions for heart disease are on the rise as well as higher morbidity rates from this ailment.

Acid Rain Phenomenon

Introduction:

Acid rain is a very dangerous weather phenomenon that can harm an area to a great extent. Usually raindrops carry some amount of acid in it. When the amount of acid goes beyond the normal range, then the rainfall is called acid rain. Acid rain is a result of extreme pollution in certain places on the earth. Acid rain can destroy many things of nature such as various living objects as well as non-living objects. However, acid rain sometimes remains unrecognized and the particular place suffers from this dangerous natural outburst for years.

• The Reason behind Acid Rain:

Acid rain is a result of pollution that includes acidic gases emerged from the factories and vehicles of a place. The level of sulfur dioxide and nitrogen oxide increases in the atmosphere, thus increasing the acidic level in the raindrops.

Acids rain makes the entire atmosphere poisoned in a certain place. It raises the acidic level of the soil. Thus the water bodies like lakes, ponds, streams, etc. are affected. The chemical balance of these water bodies gets disturbed and water becomes poisonous for living beings. Places like Europe, North America, Canada, etc. are mostly affected by the acid rain.

From the above discussion it is clear that the level of sulfur dioxide and nitrogen oxide must be decreased in the atmosphere to stop the menacing effects of acid rain. For this people have to be careful while using their vehicles. Fossil fuels should not be used in cars. In factories also some pollution control equipments must be used to reduce the emission of poisonous gases.

When did acid rain start?

Acid rain is not

new. It was first discovered in England in 1872. Smoke from coal was the cause. Coal and oil smoke are still a problem, 120 years later.

What should rain be like?

The only place on earth where pure water is found is in a laboratory. Rain water always contains small amounts of impurities. These impurities come from dust particles or are absorbed from the gases in the air.

How is acid rain formed?

Acid rain is caused by the release of the gases SO2 (sulphur dioxide) and NOX (nitrous oxides). The main sources of SO2 in South Africa are coal-fired power stations and metal working industries. The main sources of NOX emissions are vehicles and fuel combustion

Acid rain can increase the acidity of lakes, dams and streams and cause the death of aquatic life.

Acid rain can increase the acidity of soil, water and shallow groundwater.

Acid rain erodes buildings and monuments. Acid particles in the air are suspected of contributing to respiratory problems in people.

- Acid rain can dissolve rock as deep as 98 ft. (30m)

- Erosion is fastest in steep rainy areas and semiarid areas with little vegetation.

- Heartburn is caused by excess hydrochloric acid in the stomach.

- The rate of erosion for the whole of the world land area is estimated to be 3.3 in. (8.6cm) every 1000 years.

- pH or potential of hydrogen indicates the number of hydrogen ions a substance forms.

- The word “ACID” comes from the Latin word for “sour”

Rain Water

Rainwater naturally contains a weak acid called carbonic acid. However, the burning or fossil fuels produces gases, such as sulfur dioxide. When this combines with rain water it produces sulfuric-acid and ingredient or acid rain. Acid rain damages trees or lake life.

What Are the Best Acid Rain Solutions?

Acid rain solutions focus on both prevention, and on helping to deal with the environmental ramifications once the acid rain does take place. So little can be done after the fact to improve the environment that the best acid rain solutions often focus on making sure it never happens in the first place. To do this, it is first necessary to identify the causes of acid rain together with processes that can be changed to aid in prevention.

Acid rain is caused by sulfur emissions, which are put into the air through the burning of coal, often used for energy. Other sources of sulfur in the atmosphere include volcanoes and decomposing vegetation. Despite the fact these natural sources do exist, it is generally agreed that anthropogenic causes are the main sources of acid rain. This may make acid rain solutions easier to identify simply because if humans have caused it, then logically they should have the ability to change it.

The best acid rain solutions focus on power plants and coal used in the production of energy. Technologies exist that can remove sulfur from the emissions coming out of coal plant. Low-sulfur varieties of coal can also be used to reduce sulfur emissions. Often, a combination of these acid rain solutions provides the best way to minimize the problem.

The installation of scrubbers can help prevent as much as 95 percent of sulfur emitted by a carbon-fired electric power plant. The scrubbers work by spraying water with lime through the gas emission produced from burning the coal. The lime interacts with the sulfur dioxide, creating a sludge that is then captured and stored. The problem with this method is that retrofitting existing power plants with the technology is usually very expensive. It is cheaper if the technology is installed as the power plant is being built, and the inclusion of the technology is now required in many countries when new power plants are erected.