Essay, Research Paper: Acid Rain


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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. STATISTICS 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. Presently,
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. CAUSES 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:
S (in coal) + O2_ SO2 2 SO2 + O2_ 2 SO3 SO3_ + H2O H2SO4 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 certain wildlife. NO DEFENSE 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
substantially. 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. THE DYING 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. EFFECTS 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. PREVENTION 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: 1. Reducing NOx emissions: During Combustion 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. After Combustion 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: 4NO +
4NH3 + O2_ 4N2 + 6H2O It will react with NO2 by the following reaction: 2NO2
+ 4NH3 + O2_ 3N2 + 6H20 The harmless nitrogen gas can then be released into
the atmosphere. 2. Reducing SO2 emissions: Before Combustion 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. During Combustion 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%. After Combustion 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. FINAL THOUGHTS 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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