ENVIRONMENTAL IMPACT OF ACID RAIN
Acid rain is a wide spread term used to describe all forms of acid precipitation (rain, snow, hail and fog) Atmospheric pollutants particularly oxides of sulphur, oxides of Nitrogen and carbonic acid can cause precipitation to become more acidic when converted to sulphuric and Nitric acids hence the term acid rain.
Acid deposition, acid rain and acid precipitation all relate to the chemistry of air pollution and moisture in the atmosphere. Scientists generally use the term acid deposition but all three terms relate to the same issue (acid precipitation, Acid deposition and Acid rain). The term acid rain was first used by (Robert Augus Smith, 1870) a scientist working in the 1870s. The problem of acid rain is hence not a new one but the nature of the problem has changed from being a local problem for towns and cities to being an international problem (Johnson, 1972).
In Smith’s (1870) time, acid rain fall was both in towns and cities whilst today pollution can be transported thousand of kilometers due to the introduction of tall chimneys dispersing pollutants high into the atmosphere. Precipitation is naturally acidic because of carbon dioxide in the atmosphere. The burning of fossil fuels such as (coal, oil and gases) produces sulphur dioxide and Nitrogen oxides which can increase the acidity of rain or other precipitation. Sources of sulphur dioxide and oxide of Nitrogen may be natural such as volcanoes, oceans, biological decay and forest fires, or may arise from combustion sources. The increasing demand for electricity and the rise in the number of motor vehicles in recent decades has meant that emissions of acidifying pollutants have increased dramatically from human sources particularly since (1950s).
Emissions of such pollutants are heavily concentrated in the northern hemisphere, especially in Europe and North America in 1970s. As a result precipitation is generally acidic in these countries. In the 1970s and 1980s Scandinavian countries began to notice the effect of acid deposition on trees and freshwater. Much of the pollution causing this damage was identified as being transported from other more polluting countries. Acid rain became an international concern.
Acid rain is determined by the hydrogen ion content (H+) of the rain water pH. This scale was invented by a Danish Scientist in (1909) it is called Sorenson. The pH scale ranges from O, which is strongly acid, to 14 which is strongly alkaline the scale point 7 being neutral. The pH scale is logarithmic rather than linear, so there is a ten fold increase in acidity with each pH unit, such that rainfall with pH5 is ten times more acidic than pH6 rainfall with pH4 is 100 time more acidic than pH6 and rainfall with pH3 is 1000 time more acidic than pH6 (Baso, 1996).
Acid rain became particularly prominent as a media issue during the (1980s). However during the (1970s) many countries started to notice changes in fish population in lakes and damage to certain trees. By the late 1970s concern led to international effort to identify the cause and effect of long range (transboundary). Transport of air pollutants, and thus during the (1980s) much research was conducted in Europe and Northern America.
1.2 WHAT IS ACID RAIN
Acid rain is a broad term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amount of nitric and Sulfuric acid, (Berresheim, 1995). The precursors, or chemical forerunners of acid rains formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO2) and Nitrogen oxide (NO2) resulting from fossil fuel combustion.
In the United States, roughly 2/3 of all SO2 and ¼ of all NO2 come from electric power generation that relies on burning fossil fuel, like coal.
Acid rain occurs when these gases react in the atmosphere with water vapour, oxygen, and other chemicals to form various acidic compounds. The result is a mild solution of Sulfur acid and Nitric acid. When Sulfur dioxide and Nitrogen oxide are released from power plants and other sources, prevailing winds blow these compounds across states and national borders, sometimes over hundred of miles.
Wet deposition refers to acidic rain, fog and snow if the acid chemicals in the air are blown into areas where the weather is wet. The acids can fall to the ground in the form of rain, snow, fog or mist. As this acidic water flows over and through the ground it affects a variety of plants and animals.
The series of the effects depends on several factors including how acidic the water is, the chemistry and buffering capacity of the soil involved and the type of fish, trees and other living things that rely on the water.
In areas where the weather is dry, the acid chemicals may become in corporated into dust or smoke and fall to the ground through dry deposition sticking to the ground building, homes, cars and trees. Dry deposition gases and particles can be washed from these surfaces by rain storms, leading to increased runoff. This runoff water makes the resulting mixture more acidic. About half of the acidity in the atmosphere falls back to earth through dry deposition.
1.3 CAUSES OF ACID RAIN
Acid rain is mainly caused by these substances that are being released into the air: (Hottmann, 1982).
Carbon dioxide (Co2): Carbon dioxide is released by burning coal, oil and natural gas, if you inhale carbon dioxide, then since it is toxic, it can cause you to have to breathe more than usual, unconsciousness and other serious health problems.
Carbon Monoxide: Carbon monoxide is released by burning gasoline, oil and wood. When carbon monoxide enter your body, it goes into the blood-stream and when this happens, it will slow down the delivery of oxygen to the rest of the body causing dizziness, headaches, fatique and ultimately death, if the situation is not arrested quickly enough.
Chlorofluorocarbons (CFCs): These are the chemical that are used in industry, refrigeration, air-conditioning system and consumer products. Whenever CFCs are released into the air, they reduce the stratospheric ozone layer. The stratospheric ozone layer protects earths surface from the harmful rays of the sun.
Lead: Lead is released by house and car paint as well as the manufacturing of lead batteries, fishing lures, certain parts of bullets some ceramic ware, water pipes and fixtures. In young children, lead can cause nervous system damage and learning problems.
Nitrogen oxides (NO): Nitrogen oxides are released into the air by burning fuels such as gasoline and coal.
When Nitrogen oxides combine with Volatile Organic Compounds, they can cause breathing difficulty in people who have asthma, coughs in children and general illness in your respiratory system.
Ozone: Ozone is released by motor vehicles, industries, burning coal, gasoline and other fossil fuels, and in the chemicals that are in hairspray and paints. When ozone is close to the ground, it can cause chest pain, irritated respiratory tract, or persistent cough, can make unable to take deep breaths, and can make you more likely to get lung infections.
Sulphure dioxide (SO2): Sulphure dioxide are released by burning coal, paper production and melting metal sulphure dioxide can harm vegetation, harm metal and cause lung problems, which include breathing problems and permanent lung damage.
Volatile Organic Compounds (VOCs): VOCs are released into the air by burning gasoline, wood, coal, or natural gas, solvents, plants, glues and other products that are used at work or at home.
The scale is used to measure the acidity or alkalinity of an aqueous solution and is determined by the hydrogen ion content (H+). This scale was invented by a Denish Scientist called Sorenson in (1909). The scale ranges from zero, which is strongly acid to 14 which is strongly alkaline. The scale point 7 being neutral example of solution with differing pH values include carbattery acid (pH) lemon juice (pH2). Natural Lemon Juice (pH2) bear (pH4) Natural rain (pH5-6) milk (pH6) washing-up liquid (pH7) seawater (pH5) milk of Magnesia (pH10) and Ammonia (pH12).
The pH scale is logarithmic rather than linear and so there is a ten fold increase in acidity with each pH unit, such that rainfall with pH is ten time more acidic than pH6, rainfall with pH4 is 100 time more acidic than pH6 and rainfall with pH3 is 1000 time more acidic than pH6. (Geophy, 1992).
Rainfall acidity is measured in pH units normalor “unpolluted” rainfall has a pH of 5-6 this is slightly acidic due to the presence of carbon dioxide in the atmosphere which form weak carbonic acid in water it is not uncommon for acidified rain water to have a pH of 4 about 30 time as acidic as normal rain water.