Acid rain is a serious problem with disastrous effects. Each day this serious problem increases, many people believe that this issue is too small to deal with right now this issue should be met head on and solved before it is too late. In the following paragraphs I will be discussing the impact has on the wildlife and how our atmosphere is being destroyed by acid rain.
Although there is very little data, the evidence indicates that in the last twenty to thirty years the acidity of rain has increased in many parts of the United States.
the United States annually discharges more than 26 million tons of suffer dioxide into the atmosphere. Just three states, Ohio, Indiana, and Illinois are responsible for nearly a quarter of this total. Overall, two-thirds of the suffer dioxide into the atmosphere over the United States comes from coal-fired and oil fired plants. Industrial boilers, smelters, and refineries contribute 26%; commercial institutions and residences 5%; and transportation 3%.
The outlook for future emissions of suffer dioxide is not a bright one. Between now and the year 2000, United States utilities are expected to double the amount of coal they
burn. The United States currently pumps some 23 million tons of nitrogen oxides into the atmosphere in the course of the year.
Transportation sources account for 40%; power plants, 30%; industrial sources, 25%; and commercial institutions and residues, 5%. What makes these figures particularly
distributing is that nitrogen oxide emissions have tripled in the last thirty years.
Acid rain is a cancer eating into the face of Eastern Canada and the North Eastern United States. One of the main causes of acid rain is sulphur dioxide. Natural sources which emit this gas are volcanoes, sea spray , rotting vegetation and plankton. However, the burning of fossil fuels, such as coal and oil, are largely to be blamed for approximately half of the emissions of this gas in the world. When sulphur dioxide reaches the atmosphere, it oxidizes to first form a sulfate ion. It then becomes sulphuric acid as it joins with hydrogen atoms in the air and falls back down to earth. Oxidation occurs the most in clouds and especially in heavily polluted air where other compounds such as ammonia and ozone help to catalyze the reaction, converting more sulphur dioxide to sulphuric acid. However, not all of the sulphur dioxide is converted to sulphuric acid. In fact, a substantial amount can float up into the atmosphere, move over to another area and return to earth unconverted. The following are the stoichiometric equations for the formation of sulphuric acid:
Nitric oxide and nitric dioxide are also components of acid rain. Its sources are mainly from power stations and exhaust fumes. Like sulfur dioxide, these nitrogen oxides rise into the atmosphere and are oxidized in clouds to form nitric acid. These reactions are also catalyzed in heavily polluted clouds where iron, manganese, ammonia and hydrogen peroxide are present.
In Canada, the main sulfuric acid sources are non-ferrous smelters and power
generation. On both sides of the border, cars and trucks are the main sources for nitric acid(about 40% of the total), while power generating plants and industrial commercial and residential fuel combustion together contribute most of the rest. In the air, the sulfur dioxide and nitrogen oxides can be transformed into sulfuric acid and nitric acid, and
air current can send them thousands of kilometers from the source. When the acids fall to the earth in any form it will have large impact on the growth or the preservation of
One of the direct effects of acid rain is on lakes and its aquatic ecosystems. There are several routes through which acidic chemicals can enter the lakes. Some chemical substances exist as dry particles in the air while others enter the lakes as wet particles such as rain, snow, sleet, hail, dew or fog. In addition, lakes can almost be thought of as the “sinks” of the earth, where rain that falls on land is drained through the sewage systems eventually make their way into the lakes. Acid rain that falls onto the earth washes off the nutrients out of the soil and carries toxic metals that have been released from the soil into the lakes. Another harmful way in which acids can enter the lakes is spring acid shock. When snow melts in spring rapidly due to a sudden temperature change, the acids and chemicals in the snow are released into the soils. The melted snow then runs off to streams and rivers, and gradually make their way into the lakes. The introduction of these acids and chemicals into the lakes causes a sudden drastic change in the pH of the lakes – hence the term “spring acid shock”. The aquatic ecosystem has no time to adjust to the sudden change.
Areas in Ontario mainly southern regions that are near the Great Lakes, such substances as limestone or other known antacids can neutralize acids entering the body of water
thereby protecting it. However, large areas of Ontario that are near the Pre-Cambrian Shield, with quartzite or granite based geology and little top soil, there is not enough
buffering capacity to neutralize even small amounts of acid falling on the soil and the lakes. Therefore over time, the basic environment shifts from an alkaline to a acidic one.
This is why many lakes in the Muskoka, Haliburton, Algonquin, Parry Sound and Manitoulin districts could lose their fisheries if sulphur emissions are not reduced
WHAT IS ACID RAIN?
Acidity is measured using a pH scale, with the number 7 being neutral. Consequently, a substance with a pH value of less than 7 is acidic, while one of a value greater than 7 is basic. It is also worthwhile to note that the pH scale is logarithmic; that is, a substance of pH of 6 is 10 times more acidic than another with a pH of 7. Generally, the pH of 5.6 has been used as the baseline in identifying acid rain, although there has been much debate over the acceptance of this value. Interestingly enough, a pH of 5.6 is the pH value of carbon dioxide in equilibrium with distilled water. Hence, acid ran is defined as any rainfall that has an acidity level beyond what is expected in non-polluted rainfall. In essence, any precipitation that has a pH value of less than 5.6 is considered to be acid precipitation.
The average mean of pH rainfall in Ontario’s Muskoka-Haliburton lake country ranges between 3.95 and 4.38 about 40 times more acidic than normal rainfall, while storms in Pennsilvania have rainfall pH at 2.8 it almost has the same rating for vinegar.
Already 140 Ontario lakes are completely dead or dying. An additional 48 000 are sensitive and vulnerable to acid rain due to the surrounding concentrated acidic soils.
ACID RAIN CONSISTS OF….?
Canada does not have as many people, power plants or automobiles as the United States, and yet acid rain there has become so severe that Canadian government officials
called it the most pressing environmental issue facing the nation. But it is important to bear in mind that acid rain is only one segment, of the widespread pollution of the
atmosphere facing the world. Each year the global atmosphere is on the receiving end of 20 billion tons of carbon dioxide, 130 million tons of suffer dioxide, 97 million tons
of hydrocarbons, 53 million tons of nitrogen oxides, more than three million tons of arsenic, cadmium, lead, mercury, nickel, zinc and other toxic metals, and a host of
synthetic organic compounds ranging from polychlorinated biphenyls(PCBs) to toxaphene and other pesticides, a number of which may be capable of causing cancer, birth defects, or genetic imbalances.
COST OF ACID RAIN
Interactions of pollutants can cause problems. In addition to contributing to acid rain, nitrogen oxides can react with hydrocarbons to produce ozone, a major air pollutant
responsible in the United States for annual losses of $2 billion to 4.5 billion worth of wheat, corn, soyabeans, and peanuts. A wide range of interactions can occur many unknown with toxic metals.
In Canada, Ontario alone has lost the fish in an estimated 4000 lakes and provincial authorities calculate that Ontario stands to lose the fish in 48 500 more lakes within the next twenty years if acid rain continues at the present rate.Ontario is not alone, on Nova Scotia’s Eastern most shores, almost every river flowing to the Atlantic Ocean is
poisoned with acid. Further threatening a $2 million a year fishing industry.
Acid rain is killing more than lakes. It can scar the leaves of hardwood forest, wither ferns and lichens, accelerate the death of coniferous needles, sterilize seeds, and weaken the forests to a state that is vulnerable to disease infestation and decay. In the soil the acid neutralizes chemicals vital for growth, strips others from the soil and carries them to
the lakes and literally retards the respiration of the soil. The rate of forest growth in the White Mountains of New Hampshire has declined 18% between 1956 and 1965, time of
increasingly intense acidic rainfall. Acid rain no longer falls exclusively on the lakes, forest, and thin soils of the Northeast it now covers half the continent.
There is evidence that the rain is destroying the productivity of the once rich soils themselves, like an overdose of chemical fertilizer or a gigantic drenching of vinegar. The damage of such overdosing may not be repairable or reversible. On some croplands, tomatoes grow to only half their full weight, and the leaves of radishes wither. Naturally it rains on cities too, eating away stone monuments and concrete structures, and corroding the pipes which channel the water away to the lakes and the cycle is repeated. Paints and automobile paints have its life reduce due to the pollution in the atmosphere speeding up the corrosion process. In some communities the drinking water is laced with toxic metals freed from metal pipes by the acidity. As if urban skies were not already gray enough, typical visibility has declined from 10 to 4 miles, along the Eastern seaboard, as acid rain turns into smogs. Among one of the serious side effects of acid pollution on humans is respiratory problems. The SO2 and NO2 emissions give rise to respiratory problems such as asthma, dry coughs, headaches, eye, nose and throat irritations. An indirect effect of acid precipitation on humans is that the toxic metals dissolved in the water are absorbed in fruits, vegetables and in the tissues of animals. Although these toxic metals do not directly affect the animals, they have serious effects on humans when they are being consumed. For example, mercury that accumulates in the organs and tissues of the animals has been linked with brain damage in children as well as nerve disorders, brain damage and death. Similarly, another metal, Aluminum, present in the organs of the animals, has been associated with kidney problems and recently, was suspected to be related to Alzheimer’s disease.
Acid particles are also deposited on to buildings and statues, causing corrosion. For example, the Capitol building in Ottawa has been disintegrating because of excess sulphur dioxide in the atmosphere. Limestone and marble turn to a crumbling substance called gypsum upon contact with the acid, which explains the corrosion of buildings and statues. In addition, bridges are corroding at a faster rate, and the railway industry as well as the airplane industry have to expend more money in repairing the corrosive damage done by acid rain. Not only is this an economically taxing problem caused by acid rain, but also a safety hazard to the general public.
There are three main sources of acid deposition: coal in electricity, base metal smelting, and fuel combustion in vehicles. There are several ways to reduce SO2 emissions and NOx emissions:
NOx emissions are reduced during combustion are reduced primarily by a process called Overfire Air. In this procedure, a portion of the total air required for the combustion process is diverted from the burners to an upper furnace. This causes the combustion to occur with less O2 than that required, hence slowing down the conversion of atmospheric nitrogen to NO. The process of Low NOx Concentric Firing operates under the same principal, but involves increases separation of the fuel air and secondary air.
The catalytic reduction system – This system involves the injection of ammonia gas upstream of the catalytic reaction chamber. This gas will react with NO by the following reaction:
It will react with NO2 by the following reaction:
The harmless nitrogen gas can then be released into the atmosphere.
1. Coal Cleaning – The cleaning of coal was originally used to reduce costs from transporting inert material and improving the quality and uniformity of the coal. However, it has been found to be useful in reducing sulfur content. The cleaning process is performed gravitationally and is dependent on the density of the sulfur. The process is therefore successful in removing pyritic sulfur (FeS2) due to its high specific gravity, and relatively unsuccessful in removing chemically bound organic sulfur. This method is therefore limited by its dependence on the percent of pyritic sulfur in the coal. The pyritic sulfur content varies from region to region, so those with the highest percentage will be in the highest demand.
2. Burning of Low Sulfur Coals – Some power plants have chosen to reduce their sulfur dioxide emissions by burning coal of low sulfur content. (Subbituminous coal is of lower sulfur content than bituminous coal.) A process is very expensive, due to the high demand for subbituminous coal.
1. FBC – Fluidized Bed Combustion – This process allows sulfur dioxide emissions to be reduced during the combustion process. A limestone or sand bed are crushed and fluidized. It is essential that a balance is established between the heat liberated within the bed from fuel combustion, and the heat removed by the flue gas as it leaves. The limestone is able to react with the SO2 and reduce emissions by over 90%.
1. Wet Flue Gas Desulfurization – This is a highly effective and cost efficient system of flue gas desulfurization. The wet scrubber is located downstream of the boiler, and consists of either limestone, lime, or sodium hydroxide. Limestone is the most popular choice and reacts with the gas by the following reaction:
CaCO3 + SO2 + H2O + O2„_ CaSO3 + CaSO4 + CO2 + H2O
The flue gas enters the absorber and is re-emitted after being scrubbed, at which time the waste solids are removed and disposed of.
2. Dry Scrubbing – The process of dry scrubbing involves the contact between drying gas and the atomized liquid (alkaline based). Upon contacting the flue gas, the drying gas will convert the atomized droplets into a dry product that can be separated and disposed of. The dry scrubbing process requires less power to complete than wet scrubbing.
Acid rain is very real and a very threatening problem. Action by one government is not enough. In order for things to be done we need to find a way to work together on this
for at least a reduction in the contaminates contributing to acid rain. Although there are right steps in the right directions but the government should be cracking down on
factories not using the best filtering systems when incinerating or if the factory is giving off any other dangerous fumes.
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