CHEMISTRY PROJECT ON ACID RAIN
INTRODUCTION
The presence in the air of one or more contaminants in such a concentration and
of such duration as to cause a nuisance or to be injurious to human life, animal
life or vegetation.
:Atmospheric pollution is the presence of substances in the atmosphere that are
harmful to the health of humans and other living beings, or cause damage to
the climate or to materials. There are many different types of air pollutants,
such as gases (such as ammonia, carbon monoxide, sulfur dioxide, nitrous
oxides, methane and chlorofluorocarbons), particulates (both organic and
inorganic), and biological molecules. Air pollution may cause diseases, allergies
and even death to humans; it may also cause harm to other living organisms
such as animals and food crops, and may damage the natural environment (for
example, climate change, ozone depletion or habitat degradation) or built
environment (for example, acid rain). Both human activity and natural processes
can generate atmospheric pollution. Atmospheric pollution is a significant risk
factor for a number of pollution-related diseases, including respiratory
infections, heart disease, COPD, stroke and lung cancer.[1] The human health
effects of poor air quality are far reaching, but principally affect the body's
respiratory system and the cardiovascular system. Individual reactions to air
pollutants depend on the type of pollutant a person is exposed to, the degree of
exposure, and the individual's health status and genetics.[2] Indoor air pollution
and poor urban air quality are listed as two of the world's worst toxic pollution
problems in the 2008 Blacksmith Institute World's Worst Polluted Places
report.[3] Outdoor air pollution alone causes 2.1[4][5] to 4.21 million deaths
annually.[1][6] Overall, air pollution causes the deaths of around 7 million
people worldwide each year, and is the world's largest single environmental
health risk.[1][7][8] The scope of the air pollution crisis is enormous: 90% of
the world's population breathes dirty air to some degree. Although the health
consequences are extensive, the way the problem is handled is often haphazard
Acid rain, or acid deposition, is a broad term that includes any form of
precipitation with acidic components, such as sulfuric or nitric acid that fall to the
ground from the atmosphere in wet or dry forms. This can include rain, snow,
fog, hail or even dust that is acidic.
HISTORY
The corrosive effect of polluted, acidic city air on limestone and marble was
noted in the 17th century by John Evelyn, who remarked upon the poor
condition of the Arundel marbles.[5] Since the Industrial Revolution, emissions
of sulfur dioxide and nitrogen oxides into the atmosphere have increased.[6][7]
In 1852, Robert Angus Smith was the first to show the relationship between acid
rain and atmospheric pollution in Manchester, England.[8]
In the late 1960s, scientists began widely observing and studying the
phenomenon.[9] The term "acid rain" was coined in 1872 by Robert Angus
Smith.[10] Canadian Harold Harvey was among the first to research a "dead"
lake. At first, the main focus in research lay on local effects of acid rain.
Waldemar Christofer Brøgger was the first to acknowledge long-distance
transportation of pollutants crossing borders from the United Kingdom to
Norway.[11] Public awareness of acid rain in the US increased in the 1970s after
The New York Times published reports from the Hubbard Brook Experimental
Forest in New Hampshire of the harmful environmental effects that result from
it.[12][13]
Occasional pH readings in rain and fog water of well below 2.4 have been
reported in industrialized areas.[6] Industrial acid rain is a substantial problem
in China and Russia[14][15] and areas downwind from them. These areas all
burn sulfur-containing coal to generate heat and electricity.[16]
The problem of acid rain has not only increased with population and industrial
growth, but has become more widespread. The use of tall smokestacks to reduce
local pollution has contributed to the spread of acid rain by releasing gases into
regional atmospheric circulation.[17][18] Often deposition occurs a considerable
distance downwind of the emissions, with mountainous regions tending to
receive the greatest deposition (because of their higher rainfall). An example of
this effect is the low pH of rain which falls in Scandinavia.
WHAT IS ACID RAIN
Acid rain is the term used to describe the deposition of acidic air pollution.
Although some air pollutants fall directly back to Earth, a lot of it returns in rain,
snow, sleet, hail, mist or fog, hence the term "acid rain".
When power stations, factories, houses and cars emit pollution into the air, it
contains chemicals known as sulphur dioxide and nitrogen oxides. These
chemicals may either fall directly back to the Earth due to gravity, or they may
mix with water (moisture) in the air to form acids. Once acids have formed, they
can be transported long distances by the wind before being deposited in rain,
snow or hail. This is what we commonly call acid rain.
Acid rain can have harmful impacts on the environment. It affects freshwater
lakes and the wildlife that depend upon them. It also affects trees by harming
leaves and soil, and it damages buildings made of limestone and marble.
Once governments became aware of the problem of acid rain, they introduced
international laws to clean up pollution from power stations and factories. Clean
technology was used to reduce the amount of sulphur dioxide and nitrogen oxide
gases being released into the air.
There are two types of acid deposition, one is wet and the other is dry. Wet
deposition is the one, which involves acid rain or snow or dew whereas dry
deposition is when the particles such as polluting gases, dust particles and
gaseous elements are just absorbed by the surface of the Earth or the plant
bodies.
They are not converted into acids until and unless they are in contact with
water. In case of wet deposition the acids are removed from the atmospheric air
and are deposited on the surface of the earth.
COMPOSTION
Sulfuric acid, Nitric acid and carbonic acid are the major components of acid
rain.
The two strong acids present in the acid rain are nitrogen oxide and sulphur
dioxide. These two gases react with water in the atmosphere and oxygen in the
air to form sulphuric acid and nitric acid. Sulphur dioxide and nitrogen oxide are
the principal chemicals for acid rain. It can also influence humans since the acid
goes into fruits, vegetables and animals. In other words, we can get really sick if
acid rain doesn’t stop, and we eat those things. In general, the acid rain affects
men, but not directly.
Sulfuric Acid (H2SO4)
Sulfuric acid forms from sulfur dioxide (SO2). This occurs naturally though
volcanic eruptions (or the release of volcanic gases). Humans contribute to the
release of SO2 through combustion of fossil-fuels. The initial equation looks like
this:
SO2+OH⋅→HOSO2⋅
HOSO2 is an intermediary so it's immediately broken down through exposure to
oxygen forming a hydroperoxyl molecule/ radical (HO2⋅) and sulfur trioxide
molecule (SO3):
HOSO2⋅+O2→HO2⋅+SO3
SO3 is another intermediary and is immediately broken down into a sulfuric acid
molecule (H2SO4) when water (H2O) is present:
SO3(g)+H2O(l)→H2SO4(aq)
Voila! Sulfuric acid!
Nitric Acid (HNO3)
Nitric acid forms through the mixing of nitrogen dioxide (NO2) and a hydroxide
ion (OH⋅) in the atmosphere. Naturally NO2 comes from electrical discharges
such a lightening strikes. Humans increase the NO2 levels through burning of
gasoline and oil (typically from a vehicle). The chemical equation looks like this:
NO2+HO⋅→HNO3
Carbonic Acid
Carbonic acid forms from the mixing of carbon dioxide (CO2) and water (H2O).
Carbonic acid in the atmosphere is usually attributed to natural sources such as
the decomposition of dead plants and animals and not to industrial processes or
human consumption of hydrocarbons. The chemical equation looks like this:
H2O+CO2→H2CO3
FORMATION
In its purest state, rain water is like distilled water. It does not have carbon
dioxide dissolved in it. It is neutral, with a pH level of 7. As rain water falls
through the atmosphere, particles suspended in the air are dissolved in it.
These substances are generally dust, pollen grains and carbon dioxide (CO2),
sulphur dioxide (SO2) and nitrogen dioxide (NO2). Emissions of volcanoes and
lightning tend to decrease the pH level of acid rain, making it even more acidic.
CO2 combines with water to form carbonic acid (H2CO3),
H2O (1) + CO2 (g) = H2CO3 (aq)
Carbonic acid ionizes in water to form low concentrations of carbonate and
hydronium ions.
2H2O (1) + H2CO3 (aq) = CO2-3 (aq) + 2H3O+ (aq)
Carbonic acid is a weak acid. It brings down the pH of the rain water 6.5-5.2.
With pH levels ranging between 6.0—5.2, rain water is acidic, but to still not
dangerous. This is a reversible reaction.
The problem occurs when rain water combines with gaseous oxides of sulfur,
nitrogen and phosphoric and hydrochloric acid mists. The latter two and sulfur
are released into the atmosphere from automobile exhausts, industries and
electric power plants.
Nitrogen forms a major part of atmospheric composition. These chemicals bring
down the acid rain pH level to 5.6-3.5. Sometimes, the pH level can even
become as low as 2. This phenomenon of acidic rain water precipitation is called
acid rain.
CAUSES
Acid rain is a form of pollution that can cause of lot of damage to natural
ecosystems, to man-made objects, as well can harm to human health.
Human activity is the main cause of acid rain. Burning of fossil fuels is the
primary source of these gases. With increase in industrialization and number of
vehicles running on the roads, fumes that contain these gases are being added
to the atmosphere at such a rate that the excess of these gases can’t be
neutralized by natural processes.
For example, combustion of fossil fuel in vehicles and industries like iron and
steel, processing of crude oil and utility factories contribute to more than 70% of
the sulfur dioxide that is added to the atmosphere.
Almost 75% of oxides of nitrogen are released by similar processes. However,
natural phenomena like eruption of volcanoes, lightning, forest fires, rotting
vegetables and action of bacteria on the soil also release these gases. However,
their contribution amounts to less than 10% of the total amount.
Rapid industrialization is the main cause of increase in the incidence of acid rain
and precipitation with low pH value is common in industrialized nations.
However, an amusing acid rain fact is, that it need not occur at the same place
from where the gases that form acid rain, are released.
Sulphur dioxide and oxides of nitrogen are very light and they can be carried far,
away from the industries that actually spewed them. Hence, acid rain can also
be experienced in places that are not heavily industrialized.
Acid rain, more accurately acid precipitation, is the term used for describing
rainfall with a pH level lower than 5.6. This type of pollution is a matter of great
debate currently due to the potential of its causing environmental damages all
across the world. For the last decade acid rain has caused destruction to
hundreds of lakes and streams in many parts of the world, including the US,
Canada, and Europe.
The oxides of nitrogen, (Nox) and sulfur dioxide, (SO2) are the two main sources
of acid rain. Sulfur dioxide, which is a colourless gas, is given off as a byproduct
when fossil fuels that contain sulfur are burned. This gas is produced due to
various industrial processes, like the processing of crude oil, utility factories, and
iron and steel factories.
Natural means and disaster can also result in sulphur dioxide being released into
the atmosphere, such as rotting vegetation, plankton, sea spray, and volcanoes,
all of which emit about 10% sulphur dioxide. On the whole, industrial
combustion is responsible for 69.4% sulphur dioxide emissions into the
atmosphere, and vehicular transportation is responsible for about 3.7%.
Nitrogen oxide is the other chemical that acid rain is made up of. Any nitrogen
compound that contains oxygen atoms of any amount is known as oxides of
nitrogen. For example, nitrogen dioxide and nitrogen monoxide are oxides of
nitrogen.
These gases are produced in firing processes which involve extremely high
temperatures, e.g., utility plants and automobiles, as well as in chemical
industries, such as in the production of fertilizers. Five percent of nitrogen oxide
is emitted by natural processes like lighting, volcanic eruptions, forests fires, and
action of bacteria in the soil. Industrial processes emit 32% and vehicular
transportation is responsible for 43%.
EFFECTS( 2 PAGES)
i. Effects of Acid Rain on Plants:
The acid rain affects the crops as well as the vegetation. The effect of acid rain
on plants is grave. It not only damages the root, but also stops its growth and
brings an end to the life of a plant. The nutritive value of the soil is reduced to a
great extent as an effect of acid rain. Acid rain effects can be seen on the useful
micro-organisms which convert the decayed organic matter into essential
nutrients for the soil.
The consequence is that the micro-organisms are killed resulting in reducing the
availability of nutrients for the soil and plants. Also, the waxy layer of the leaves
is damaged which make the plant more and more susceptible to diseases. On
the whole, acid rain effects on plants make it difficult to survive in the extreme
climatic conditions like storm, drought and heavy rainfall.
It even affects the productivity and the process germination in the plants. The
acidity of the rain has also led to soil erosion by dissolving the forests and other
vegetation. It takes away the essential nutrients of the soil and releases
aluminum, which disables trees from sucking water from the soil.
ii. Effects of Acid Rain on Aquatic Life:
Apart from plants, acid rain also affects aquatic organisms adversely. A high
amount of sulfuric acid interferes with the ability of fish to take in nutrients, salt,
and oxygen. As far as freshwater fish is concerned, in order for them to stay
alive they need to have the ability of maintaining a balance between the
minerals and salts in their tissues..
Not only a large number of species are killed due to deposition of harmful
chemicals inside their body but it also affects the health of human beings on
consumption of different varieties of fish. These toxic chemicals also damage
hatchings and their reproduction process. Decrease in number of species as a
result of sudden deposition of acid is known as acid shock.
iii. Effects of Acid Rain on Humans:
Most of all, acid rain affects human health adversely. It has the ability of
harming us via the atmosphere as well as the soil where the food we eat is
grown. Acid rain results in toxic metals breaking from the chemical compounds
that occur naturally. Though toxic metals may be dangerous, but as long as they
exist in combination with other elements, they are not harmful.
Another adverse health effect of acid rain on humans is the respiratory problems
it causesPeople if get exposed to acid rain will suffer from skin blisters, irritation
and burns. Under high acidic condition, the skin gets burned. Scientists also say
that the risk of getting skin cancer is highly increased due to acid rain. The
health effect of acid rain also comes from other sources.
The harmful chemicals pass into human beings when they consume the plants
and animals. Many rural dwellers suffer from health problems due to
consumption of acidified drinking water directly from lakes and other water
bodies.
iv. Effects on Buildings and Monuments:
Acid rain causes severe damage to buildings and marble statues. Acid rain reacts
with the calcium carbonate (CaCO3) to form soluble calcium hydrogen carbonate
or calcium bicarbonate,
Ca(HCO3)2 -CaCO3 + Acid rain = Ca(HCO3) (aq)
Calcium bicarbonate is a powdery substance, which is easily washed away with
water or more specifically, rainwater. This is the way acid rain has partly eroded
many world-famous monuments and buildings like the Taj Mahal in India, St.
Paul’s Cathedral in London, and the Statue of Liberty in New York.
Acid rain can destroy stained glass windows in churches, bridges made of steel,
and railway tracks. It corrodes metal, ruins the paint colours, weakens leather
and forms a crust on glass surfaces.
v.Effects on forest
Acid precipitation on vegetation reduces the photosynthesis and growth also
increase the susceptibility to draught and disease, process called ‘dieback’ it
causes browning of leaf and fall off in addition, effects such as thinning of annual
growth ring and reduction in biomass (due to reduced growth), it also damage
the fine root system, affect root mycorrhiza (due to increase in Al and acidity)
and decrease the lichens, reduction of soil fertility as potassium
leached out of the soil, phosphorus is also reduced this reduces the fruit
production,
toxic metals such as zinc and aluminum accumulates, aluminum toxicity retard
root growth and causes loss of chlorophyll Young seed lings are more susceptible
than older plants Soil acidity can be overcome by addition
of lime, whereas alkalinity of limestone neutralizes the negative ions in acid
PERVENTION
The numbers of possible solutions for acid rain that are available to us are
aplenty. What matters more is to consciously enforce these solutions to stop acid
rain and to do soon a wide scale. People all over the world must be made aware
of the causes and effects of acid rain, and they should be thoroughly educated
about it. Solutions to stop acid rain can only be successful through mutual
cooperation.
Some methods to control acid rain are given below:
i. Reduce the use of fossil fuels. This would decrease the emission of nitrogen
and sulphur in the environment.
ii. One of the main causes of acid rain is a sudden drop in the pH levels of water
and that happens because of absorption of harmful gases by the atmosphere.
The best way to restore the pH balance of water is to limit the use of items,
which run on gasoline.
iii. Drivers should ease up as soon as the yellow light rather than slamming on
the brakes and they shouldn’t rush away as soon as the lights turn green. These
small practices help reduce the wastage of gasoline and also help people save a
lot of money on fuel.
iv. Always keep the vehicle tires inflated. Tires having proper pressure will
provide users with a better fuel economy.
v. Use cycles or should walk to cover small distances.
vi. One of the most fundamental acid rain solutions is to utilize fuels that burn
cleanlier or to burn coal more efficiently. This will greatly reduce the possibilities
of acid rain developing in the atmosphere.
vii. As far as industrial power plants are concerned, the best solution is to attach
devices known as ‘scrubbers’ in the chimneys of these plants. These scrubbers
reduce the amount of sulphur produced in the smoke by 90-95%.
viii. For industrial power plants, there are many more acid rain solutions that
must be enforced, as they are clearly the biggest contributors to the formation
of acidified water droplets in the atmosphere. Industries must regularly inspect
and clean all their emission equipment and chimneys and pipes.
ix. Fitting catalytic converters into the exhaust pipes of vehicles also reduces the
amount of sulphur dioxide produced by the vehicles.
x. We can make a lot of changes on a personal level as well, in order to combat
acid rain. We should restrict the use of our cars and vehicles and utilize other
modes of transportation on a more frequent basis. We should also remember to
turn off all our lights and electrical devices in case we are not using them.
All these acid rain solutions will be pointless unless people are informed and
educated about the adverse-effects and harms of acid rain. A widespread and
nationwide effort must be made to make people aware. Only after that is done
will all the acid rain solutions actually make a difference.
CONCLUSION
Acid rain is one of the world’s major environmental problems since 19th century
.Generally, rainfall that has a pH value less than 5.6 is considered as acid rain
.The two primary sources of acid rain are sulphur dioxide and nitrogen oxide.
Automobiles are the main source of nitrogen oxide emissions, and utility
factories are the main source for sulphur dioxide emissions. These gases
evaporate into the atmosphere and then oxidized in clouds to form nitric or
nitrous acid and sulphuric acid. It is formed when sulphur dioxides and nitrogen
oxides reacted with water during rain and as gases or fine. Acids rain is
described in terms of wet and dry depositions. The wet deposition refers to
acidic rain, fog and snow whereas dry deposition refers to acidic gases and
particles. This acid rain affects a variety of plants and animals (harmful to
aquatic life, harmful to vegetation, affects human health and transport) in our
environment. Acid rain deteriorates the marble, stone monuments and
architectures, corrode metal structures and fading paints .Moreover, when these
acids fall back to the earth they do not cause damage to just the environment
but also to human health. The pollutants in acid rain causes problem in human
respiratory systems. The pollutants attack humans indirectly through the foods
they consumed. They effected human health directly when humans inhale the
pollutants. The effects of acid rain can never be reversed. The sooner we realize
this the better it will be for all concerned. Several methods are used to reduce
the emission of SO2and NO such as reducing the sulphur content in fuels, using
scrubbers such as flue gas