Acid Rain

Acid Rain What is acid rain? Acid rain is the term for pollution caused when sulfur and nitrogen dioxides combine with atmospheric moisture. The term ‘acid rain’ is slightly misleading, and would be more accurate if deemed ‘enhanced acid rain’, as rain occurs acidic naturally. Acidity is measured on what is know as the pH scale. Fourteen is the most basic, seven is the most neutral, and zero is the most acidic. Pure rain has a pH level of 7, which is exactly neutral.

The acidity of rain is determined by the pH of pure water in reaction with atmospheric concentrations of carbon dioxide, resulting in carbonic acid. These particles partly dissociate to produce hydrogen ions and bicarbonate ions. A bicarbonate atom is an ion formed by one hydrogen atom, one carbon at atom, and three oxygen atoms, and is very effective in natural waters at neutralizing hydrogen ions and reducing acidity. The dissociation results in the natural acidity of pure rain, which is moderately acidic at a pH of 5.7. Rain less than 5.7 is considered ‘acid rain’, meaning it has reacted with acidic atmospheric gases other than carbon dioxide, such as sulfur dioxide and nitrogen dioxide.

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Sulfur dioxide is produced by electric utilities, industrial, commercial and residential heating, smelters, diesel engines and marine and rail transport, which creates sulfuric acid in rain. Nitrogen dioxide will also react with the rain, caused largely by transportation (cars, trucks, planes, etc.) and electric utilities, producing nitric acid. There is a certain degree of naturally occurring acidity in rain water. This acid is from reaction with alkaline chemicals, found in soils, lakes and stream, and can occasionally occur when a volcano erupts as well. Bacterial action in soils and degasing from oceanic plankton also contribute to the acidity found in rain.

More than 90% of the sulfur and 95% of the nitrogen emissions which occur in North America are due to the pollution created by humans.1 How Is Acid Rain Formed? Acid rain consists mainly of acids formed in the atmosphere. It consists of the oxides of sulfur, SO2 and SO3, and of nitrogen NO and NO2. Let us examine the major contributor to acid rain, sulfur oxides. Natural sources which emit sulfur dioxide include volcanoes, sea spray, plankton and rotting vegetation. Despite these natural occurrences, the burning of fossil fuels (such as coal and oil) can be largely blamed for the emissions. The chemical reactions begin as energy from sunlight, in the form of photons, hit ozone molecules (O3) to form free oxygen (O2), as well as single reactive oxygen atoms (O).

The oxygen atoms react with water molecules (H2O), producing electrically charged, negative hydroxyl radicals (HO). These hydroxyl radicals are responsible for oxidizing sulfur dioxide and nitrogen dioxide, which produces sulfuric acid and nitric acid. Some particles will settle to the ground (in the form of acid deposition) or vegetation can absorb some of the SO2 gas directly from the atmosphere. When sulfur dioxide comes in contact with the atmosphere, it oxidizes and forms a sulfate ion. It becomes sulfuric acid as it joins with hydrogen atoms in the air and falls down to earth. Oxidation occurs most in clouds, especially in heavily polluted air, where other compounds such as ammonia and ozone help to catalyze the reaction, increasing the amount of sulfur dioxide changing to sulfuric acid. Not all of the sulfur dioxide is converted to sulfuric acid, and it is not uncommon for a substantial amount to float up into the atmosphere, move to another area, and return to earth as sulfur dioxide, unconverted.

S (in fossil fuels) + O2 =* SO2 2 SO2 + O2 =* 2 SO3 Much of the sulfur dioxide is converted to sulfur trioxide in the atmosphere SO3 + H2O =* H2SO4 The sulfur trioxide can then dissolve within water to form sulfuric acid Nitric oxide and nitric dioxide are mainly from power plants and exhaust fumes. Similar to sulfur dioxide, reactions are heavily catalyzed in heavily polluted clouds where iron, manganese, ammonia and hydrogen peroxide are present. Also, the formation of nitric acid can trigger further reactions which release new hydroxyl radicals to generate more sulfuric acid. The following is a typical reaction, which is direct combination of nitrogen and oxygen at the high temperature inside a car engine. N2 + O2 + heat =* 2NO 2NO + O2 =* 2NO2 This nitrogen monoxide immediately reacts with oxygen and forms nitrogen dioxide in the following reaction 3NO2 + H2O =* 2HNO3 (aq) + NO The nitrogen will then dissolve in water in the atmosphere and produce nitric acid There are several other potential contributors to acid rain. These include oxidation by products of alkene-ozone reactions, oxidation by reactions of NxOy species and oxidation by peroxy radicals. Each of these reactions, however prove to be minor contributors and are rather insignificant.

How Is Acid Rain Harmful? Environmental Hazards Aquatic Ecosystems Acid rain has an effect on virtually all ecosystems it touches. Perhaps the most prominent, and equally as troubling is the harmful results it produces when in contact with lakes, streams and ponds. Scientists studying the effects of acid rain went to a lake about 135 km away from the Ontario- Manitoba border called Lake 223. This lake, so far north acid rain did not reach it, was extremely healthy, and was a perfect setting to explore the effects of acid rain on aquatic ecosystems. In 1974, scientists began to add sulfuric acid into the lake. The acid was added very slowly, and it was four years later when they saw a major change. The freshwater shrimp began to die out.

Fathead minnows stopped reproducing and began to vanish. As the scientists continued adding acid to Lake 223 in low amounts, large algae mats began to form and crayfish became unhealthy and died. Seven years after the beginning of the experiment, the lake trout stopped reproducing, and most of the fish species, leeches, crawfish and mayflies began to die. In 1984, the scientists stopped adding the acid. Without the addition of deadly sulfuric acid, the lake slowly began to recover. Some of the fish species began to recover, however some of the scientists estimated it would take one hundred years for the lake to fully recover, even without the addition of any more acid.

Fish can still live in a lake with a low acid level, however they will get sick and not grow to proper proportions. Often the fish will not reproduce, and eventually, as the acid level increases, all the fish will die. The acid will also ‘leach’ metals from the bottom of the lake. There are metals contained within the mud and rocks of the lake bottom, however they remain not dangerous as long as they are not released. The acid will draw out these harmful metals and dissolve them in the water, resulting in the deterioration and disappearance of a species. One of these damaging metals is aluminum, which will coat and burn the gills of the fish as it intakes the polluted water.

Some fish found in acidic lakes contain higher levels of mercury in their bodies, which is harmful to humans, resulting in the government telling society to limit the amount of fish they eat from certain lakes and rivers. If the numbers of one species or group of species changes in response to acidification, the ecosystem of the entire body of water is likely to be affected through the predator-prey relationships. Let us examine how acid rain is dangerous to fish. A freshwater fish’s respiration consists of a ‘trade’ of hydrogen ions (H+) in their blood for sodium ions (Na+) from the water around them. If the concentration of hydrogen ions in the water is increased, which is essentially what happens when pH falls, there are (proportionally) fewer sodium ions.

Fish are forced to absorb more hydrogen while finding it harder to obtain sodium. The acidity of their blood increases, while the salt content drops. An experiment involving brown trout showed that at a pH of 5.2 or lower, this process was fatal to this species, and is likely deadly to many other trout species. The following chart shows the steps typical to freshwater fish as the acidity increases. (Fig 1-1) ACIDITY LEVEL (pH) EFFECTS ON AQUATIC LIFE 7 Neutral, H+ and H- are in balance 6.8 Shells of clams and snails become thinner, due to lack of hazardous calcium ions in the water 6.6 The viability of eggs of the fathead minnow is reduced, rain can have and fewer eggs hatch 6.5 Lake trout begin to have difficulty reproducing, clams and snails become scarcer, green algae growth increases 6 Several clam and snail species disappear, several trout species populations decrease, the smooth newt is gone, smallmouth bass, walleyes and spotted salamanders have difficulty reproducing, several mayfly species cease to lay eggs 5.8 Copepods (a critical link of crustaceans in the marine food chain) are gone, crayfish have trouble regrowing exoskeleton after molting 5.7 Several algae species decrease, while filamentous green algae increases, plankton decreases 5.5 Rainbow trout, fathead minnows and smallmouth bass lose considerable population, walleyes, brook trout, roach, lake trout and shiners don’t reproduce, leeches and mayfly larvae vanish.

5.4 Crayfish reproductivity is impaired. 5 Snail and clams are extinct. All but one species of crayfish are extinct, brook trout, walleyes and most bullfrogs are gone, most fish species experience reproduction difficulties, zooplankton population begins to drop, green and green-blue algae mats have largely spread 4.8 Leopard frog numbers decline 4.5 Mayflies and stoneflies vanish, a slowing in growth rate and oxygen uptake of bacteria is notable 4.2 The common toad disappears 4 The oxygen output of Lobelia plants declines 75% 3.5 Virtually all clams, snails, frogs, fish and crayfish vanish 2.5 Only a few species of acid-tolerant midges, bacteria and fungi are alive 2 In practical terms, the lake is sterile Two hundred and twenty lakes in Ontario have been found acidified, meaning their pH is less that 5.1 year round.2 Terrestrial Plant Life It is much more difficult to solve the mystery of forest destruction compared to that of a lake. This is partially because trees live so much longer than fish do, and acid rain damage in trees may not show up for thirty or forty years. It is also very difficult to replicate forest conditions in a laboratory, such as insects, cold winters, pollution, elevation and abrupt changes in rainfall. Each of these conditions put stress on the trees and can be considered variables.

Many scientists are convinced that because of the complexity of a forest ecosystem, it is nearly impossible to prove the death of forests is due to pollution in the form of acid rain, but deduce from many experiments it is a main factor in forest destruction. Deciduous trees are like air filters, and screen particles that pass through the air around them …

Acid Rain

INTRODUCTION: Acid rain is a great problem in our world. It causes fish
and plants to die in our waters. As well it causes harm to our own race as
well, because we eat these fish, drink this water and eat these plants. It
is a problem that we must all face together and try to get rid of. However
acid rain on it’s own is not the biggest problem. It cause many other
problems such as aluminum poisoning. Acid Rain is deadly.

Acid rain is all the rain, snow, mist etc that falls from the sky onto
our planet that contains an unnatural acidic. It is not to be confused with
uncontaminated rain that falls, for that rain is naturally slightly acidic.

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It is caused by today’s industry. When products are manufactured many
chemicals are used to create it. However because of the difficulty and cost
of properly disposing of these products they are often emitted into the
atmosphere with little or no treatment.

The term was first considered to be important about 20 years ago when
scientists in Sweden and Norway first believed that acidic rain may be
causing great ecological damage to the planet. The problem was that by the
time that the scientist found the problem it was already very large.

Detecting an acid lake is often quite difficult. A lake does not become
acid over night. It happens over a period of many years, some times
decades. The changes are usually to gradual for them to be noticed early.

At the beginning of the 20th century most rivers/lakes like the river
Tovdal in Norway had not yet begun to die. However by 1926 local inspectors
were noticing that many of the lakes were beginning to show signs of death.

Fish were found dead along the banks of many rivers. As the winters ice
began to melt off more and more hundreds upon hundreds more dead fish
(trout in particular) were being found. It was at this time that scientist
began to search for the reason. As the scientists continued to work they
found many piles of dead fish, up to 5000 in one pile, further up the
river. Divers were sent in to examine the bottom of the rivers. What they
found were many more dead fish. Many live and dead specimens were taken
back to labs across Norway. When the live specimens were examined they were
found to have very little sodium in their blood. This is typical a typical
symptom of acid poisoning. The acid had entered the gills of the fish and
poisoned them so that they were unable to extract salt from the water to
maintain their bodies sodium levels.

Many scientist said that this acid poising was due to the fact that it
was just after the winter and that all the snow and ice was running down
into the streams and lakes. They believed that the snow had been exposed to
many natural phenomena that gave the snow it’s high acid content. Other
scientists were not sure that this theory was correct because at the time
that the snow was added to the lakes and streams the Ph levels would change
from around 5.2 to 4.6. They believed that such a high jump could not be
attributed to natural causes. They believed that it was due to air
pollution. They were right. Since the beginning of the Industrial
revolution in England pollution had been affecting all the trees,soil and
rivers in Europe and North America.

However until recently the loses of fish was contained to the southern
parts of Europe. Because of the constant onslaught of acid rain lakes and
rivers began to lose their ability to counter act their affects. Much of
the alkaline elements; such as calcium and limestone; in the soil had been
washed away. It is these lakes that we must be worried about for they will
soon become extinct.

A fact that may please fishermen is that in lakes/rivers they tend to
catch older and larger fish. This may please them in the short run however
they will soon have to change lakes for the fish supply will die quickly in
these lakes. The problem is that acid causes difficulties the fish’s
reproductive system. Often fish born in acid lakes do not survive for they
are born with birth defects such as twisted and deformed spinal columns.

This is a sign that they are unable to extract enough calcium from the
water to fully develop their bone. These young soon die. With no
competition the older,stronger can grow easily. However there food is
contaminated as well by the acid in the water. Soon they have not enough
food for themselves and turn to cannibalism. With only an older population
left there is no one left to regenerate themselves. Soon the lake dies.

By the late 1970s many Norwegian scientists began to suspect that it
was not only the acid in the water that was causing the deaths. They had
proved that most fish could survive in a stream that had up to a 1 unit
difference in PH. After many experiments and research they found that their
missing link was aluminum.

Aluminum is one of the most common metals on earth. It is stored in a
combined form with other elements in the earth. When it is combined it
cannot dissolve into the water and harm the fish and plants. However the
acid from acid rain can easily dissolve the bond between these elements.

The Aluminum is then dissolved into a more soluble state by the acid. Other
metals such as Copper (Cu), iron (Fe) etc can cause such effects upon the
fish as well however it is the aluminum that is the most common. For
example: CuO + H2SO4 ———-> CuSO4 + H2O
In this form it is easily absorbed into the water. When it comes in
contact with fish it causes irritation to the gills. In response the fish
creates a film of mucus in the gills to stop this irritation until the
irritant is gone. However the aluminum does not go always and the fish
continues to build up more and more mucus to counteract it. Eventually
there is so much mucus that it clogs the gills. When this happens the fish
can no longer breath. It dies and then sinks to the bottom of the lake.

Scientists now see acid, aluminum and shortages of calcium as the three
determining factors in the extinction of fish.

As well there is the problem of chlorine. In many parts of the world
it is commonly found in the soil. If it enters the fish’s environment it
can be deadly. It affects many of the fish’s organisms and causes it to
die. As well it interferes in the photosynthesis process in plants.

NaOH + HCl —-> NaCl + H2O
The carbon in the water can become very dangerous for fish and plants
in the water if the following reaction happens:
CaCO3 + 2HCl —> CaCl2 + H2CO3 then
H2CO3 —> H2O + CO2
The salt created by this reaction can kill. It interferes directly with
the fish’s nervous system.

Acid lakes are deceivingly beautiful. The are crystal clear and have a
luscious carpet of green algae on the bottom. The reason that these lakes
are so clear is because many of the decomposers are dead. They cannot break
down that material such as leaves and dead animals. These materials
eventually sink to the bottom instead of going through the natural process
of decomposition. In acid lakes decomposition is very slow. “The whole
metabolism of the lake is slowed down.”
During this same period of time the Canadian department of fisheries
spent eight years dumping sulfuric acid (H2SO4) into an Ontario lake to see
the effects of the decrease in the PH over a number of years. At the PH of
5.9 the first organisms began to disappear. They were shrimps. They started
out at a population of about seven million, but at the pH of 5.9 they were
totally wiped out. Within a year the minnow died because it could no longer
reproduce it’s self.

At this time the pH was of 5.8. New trout were failing to be produced
because many smaller organisms that served as food to it had been wiped out
earlier. With not enough food the older fish did not have the energy to
reproduce. Upon reaching the pH of 5.1 it was noted that the trout became
cannibals. It is believed this is due to the fact that the minnow was
nearly extinct.

At a pH of 5.6 the external skeletons of crayfish softened and they
were soon infected with parasites, and there eggs were destroyed by fungi.

When the pH went down to 5.1 they were almost gone. By the end of the
experiment none of the major species had survived the trials of the acid.

The next experiment conducted by the scientists was to try and bring the
lake back to life. They cut in half the amount of acid that they dumped to
simulate a large scale cleanup. Soon again the cuckers and minnows began to
reproduce again. The lake eventually did come back; to a certain extent;
back to life. THE NEW THEORY:
A scientist in Norway had a problem believing that it was the acid
rain on it’s own that was affecting the lakes in such a deadly way. This
scientist was Dr Rosenqvist.

“Why is it that during heavy rain, the swollen rivers can be up to
fifteen times more acid than the rain? It cannot be the rain alone that is
doing it, can it?” Many scientist shunned him for this however they could
not come up with a better answer. Soon the scientists were forced to accept
this theory.

Sulfuric acid is composed of two parts, know as ions. The hydrogen ion
is what make a substance acid. The other ion is sulphate. When there are
more hydrogen ions then a substance is acid. It is this sulphate ion that
we are interested in. When the rain causes rivers to overboard onto the
banks the river water passes through the soil. Since the industrial
revolution in britain there has been an increasing amount of sulphur in the
soil. In the river there is not enough sulphur for the acid to react in
great quantities. However in the soil there is a great collection of
sulphur to aid the reaction. When it joins the water the pH becomes much
lower. This is the most deadly effect of acid rain on our water!!! The
water itself does not contain enough sulphur to kill off it’s population of
fish and plants. But with the sulphur in the soil it does.

Acid rain is a big problem. It causes the death of our lakes, our rivers,
our wild life and most importantly us. As well it causes other problems
that are very serious as well such as the release of aluminium and lead
into our water supplies. We are suffering because of it. In Scotland there
are many birth defects being attributed to it. We must cut down the
releases of chemicals that cause it. But it will take time, even if we were
to stop today we would have the problem for years to come because of the
build up in the soil. Let’s hope we can do something.

Penguin Publishing House, 1987 , Pearce Fred Acid Rain. What is it and
what is it doing to us?
New York Publishers, 1989, William Stone Acid Rain. Fiend or Foe?
Lucent books, Inc. 1990, Steward Gail Acid Rain.