Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water
molecules in the atmosphere to produce acids. Governments have made
efforts since the 1970s to reduce the release of sulfur dioxide into the
atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes and sulfur dioxide is produced by volcanic eruptions. The chemicals in acid rain can cause paint to peel, corrosion of steel structures such as bridges, and erosion of stone statues.
Definition
"Acid rain" is a popular term referring to the deposition of wet
(rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying
particles and gases) acidic components. Distilled water, once carbon dioxide
is removed, has a neutral pH of 7. Liquids with a pH less than 7 are
acidic, and those with a pH greater than 7 are alkaline. "Clean" or
unpolluted rain has an acidic pH, but usually no lower than 5.7, because
carbon dioxide and water in the air react together to form carbonic acid, a weak acid according to the following reaction:
- H2O (1) + CO2 (g)
H2CO3 (aq)
Carbonic acid then can ionize in water forming low concentrations of hydronium and carbonate ions:
- H2O (l) + H2CO3 (aq) HCO3− (aq) + H3O+ (aq)
However, unpolluted rain can also contain other chemicals which affect its pH (acidity level). A common example is nitric acid produced by electric discharge in the atmosphere such as lightning.
[1] Acid deposition as an environmental issue (discussed later in the article) would include additional acids to H
2CO
3.
History
Trees killed by acid rain
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.
[2] Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides into the atmosphere have increased.
[3][4] In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England.
[5]
Though acidic rain was discovered in 1853, it was not until the late
1960s that scientists began widely observing and studying the
phenomenon.
[6] The term "acid rain" was coined in 1872 by Robert Angus Smith.
[7]
Canadian Harold Harvey was among the first to research a "dead" lake.
Public awareness of acid rain in the U.S increased in the 1970s after The New York Times published reports from the Hubbard Brook Experimental Forest in New Hampshire of the myriad deleterious environmental effects shown to result from it.
[8][9]
Occasional pH readings in rain and fog water of well below 2.4 have been reported in industrialized areas.
[3] Industrial acid rain is a substantial problem in China and Russia
[10][11] and areas downwind from them. These areas all burn sulfur-containing coal to generate heat and electricity.
[12]
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.
[13][14]
Often deposition occurs a considerable distance downwind of the
emissions, with mountainous regions tending to receive the greatest
deposition (simply because of their higher rainfall). An example of this
effect is the low pH of rain which falls in Scandinavia.
History of acid rain in the United States
Since 1998, Harvard University wraps some of the bronze and marble statues on its campus, such as this "Chinese stele", with waterproof covers every winter, in order to protect them from erosion caused by acid rain (or, actually, acid snow)
[15]
In 1980, the U.S. Congress passed an Acid Deposition Act.
[16]
This Act established an 18-year assessment and research program under
the direction of the National Acidic Precipitation Assessment Program
(NAPAP). NAPAP looked at the entire problem from a scientific
perspective. It enlarged a network of monitoring sites to determine how
acidic the precipitation actually was, and to determine long term
trends, and established a network for dry deposition. It looked at the
effects of acid rain and funded research on the effects of acid
precipitation on freshwater and terrestrial ecosystems, historical
buildings, monuments, and building materials. It also funded extensive
studies on atmospheric processes and potential control programs.
From the start, policy advocates from all sides attempted to
influence NAPAP activities to support their particular policy advocacy
efforts, or to disparage those of their opponents.
[16]
For the U.S. Government's scientific enterprise, a significant impact
of NAPAP were lessons learned in the assessment process and in
environmental research management to a relatively large group of
scientists, program managers and the public.
[17]
In 1991, DENR provided its first assessment of acid rain in the
United States. It reported that 5% of New England Lakes were acidic,
with sulfates being the most common problem. They noted that 2% of the
lakes could no longer support Brook Trout, and 6% of the lakes were
unsuitable for the survival of many species of minnow. Subsequent
Reports to Congress have documented chemical changes in soil and
freshwater ecosystems, nitrogen saturation, decreases in amounts of
nutrients in soil, episodic acidification, regional haze, and damage to
historical monuments.
Meanwhile, in 1989, the U.S. Congress passed a series of amendments
to the Clean Air Act. Title IV of these amendments established the Acid Rain Program, a cap and trade
system designed to control emissions of sulfur dioxide and nitrogen
oxides. Title IV called for a total reduction of about 10 million tons
of SO
2 emissions from power plants. It was implemented in two
phases. Phase I began in 1995, and limited sulfur dioxide emissions
from 110 of the largest power plants to a combined total of 8.7 million
tons of sulfur dioxide. One power plant in New England (Merrimack) was
in Phase I. Four other plants (Newington, Mount Tom, Brayton Point, and
Salem Harbor) were added under other provisions of the program. Phase II
began in 2000, and affects most of the power plants in the country.
During the 1990s, research continued. On March 10, 2005, EPA issued
the Clean Air Interstate Rule (CAIR). This rule provides states with a
solution to the problem of power plant pollution that drifts from one
state to another. CAIR will permanently cap emissions of SO
2 and NO
x in the eastern United States. When fully implemented, CAIR will reduce SO
2 emissions in 28 eastern states and the District of Columbia by over 70% and NO
x emissions by over 60% from 2003 levels.
[18]
Overall, the program's cap and trade program has been successful in achieving its goals. Since the 1990s, SO
2 emissions have dropped 40%, and according to the Pacific Research Institute, acid rain levels have dropped 65% since 1976.
[19][20] Conventional regulation was utilized in the European Union, which saw a decrease of over 70% in SO
2 emissions during the same time period.
[21]
In 2007, total SO
2 emissions were 8.9 million tons, achieving the program's long term goal ahead of the 2010 statutory deadline.
[22]
The EPA estimates that by 2010, the overall costs of complying with
the program for businesses and consumers will be $1 billion to $2
billion a year, only one fourth of what was originally predicted.
[19]
Emissions of chemicals leading to acidification
The most important gas which leads to acidification is sulfur dioxide. Emissions of nitrogen oxides which are oxidized to form nitric acid
are of increasing importance due to stricter controls on emissions of
sulfur containing compounds. 70 Tg(S) per year in the form of SO
2 comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires and 7–8 Tg(S) per year from volcanoes.
[23]
Natural phenomena
The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes. Thus, for example, fumaroles from the Laguna Caliente crater of Poás Volcano
create extremely high amounts of acid rain and fog, with acidity as
high as a pH of 2, clearing an area of any vegetation and frequently
causing irritation to the eyes and lungs of inhabitants in nearby
settlements.
[24] Acid-producing gasses are also created by biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur containing compounds is dimethyl sulfide.
Nitric acid in rainwater is an important source of fixed nitrogen for plant life, and is also produced by electrical activity in the atmosphere such as lightning.
Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.
[13]
Soils of coniferous forests are naturally very acidic due to the
shedding of needles, and the results of this phenomenon should not be
confused with acid rain.
Human activity
The coal-fired Gavin Power Plant in Cheshire, Ohio
The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, factories, and motor vehicles.
Electrical power complexes utilising coal are among the greatest
contributors to gaseous pollutions that are responsible for acidic rain.
The gases can be carried hundreds of kilometers in the atmosphere
before they are converted to acids and deposited. In the past, factories
had short funnels to let out smoke but this caused many problems
locally; thus, factories now have taller smoke funnels. However,
dispersal from these taller stacks causes pollutants to be carried
farther, causing widespread ecological damage.
Chemical processes
Combustion of fuels produces sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid.
[25]
Gas phase chemistry
In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction:
[5]
- SO2 + OH· → HOSO2·
which is followed by:
- HOSO2· + O2 → HO2· + SO3
In the presence of water, sulfur trioxide (SO
3) is converted rapidly to sulfuric acid:
- SO3 (g) + H2O (l) → H2SO4 (aq)
Nitrogen dioxide reacts with OH to form nitric acid:
- NO2 + OH· → HNO3
Chemistry in cloud droplets
When clouds are present, the loss rate of SO
2 is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets.
- Hydrolysis
Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series of equilibrium reactions:
- SO2 (g) + H2O SO2·H2O
- SO2·H2O H+ + HSO3−
- HSO3− H+ + SO32−
- Oxidation
There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulfuric acid. The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and manganese in the cloud droplets).
[5]
Acid deposition
Wet deposition
Wet deposition of acids occurs when any form of precipitation (rain,
snow, and so on.) removes acids from the atmosphere and delivers it to
the Earth's surface. This can result from the deposition of acids
produced in the raindrops (see aqueous phase chemistry above) or by the
precipitation removing the acids either in clouds or below clouds. Wet
removal of both gases and aerosols are both of importance for wet
deposition.
Dry deposition
Acid deposition also occurs via dry deposition in the absence of
precipitation. This can be responsible for as much as 20 to 60% of total
acid deposition.
[26] This occurs when particles and gases stick to the ground, plants or other surfaces.
Adverse effects
This chart shows that not all fish, shellfish, or the insects that they
eat can tolerate the same amount of acid; for example, frogs can
tolerate water that is more acidic (i.e., has a lower pH) than trout.
Acid rain has been shown to have adverse impacts on forests,
freshwaters and soils, killing insect and aquatic life-forms as well as
causing damage to buildings and having impacts on human health.
Surface waters and aquatic animals
Both the lower pH and higher aluminium concentrations in surface
water that occur as a result of acid rain can cause damage to fish and
other aquatic animals. At pHs lower than 5 most fish eggs will not hatch
and lower pHs can kill adult fish. As lakes and rivers become more
acidic biodiversity is reduced. Acid rain has eliminated insect life and
some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.
[27]
However, the extent to which acid rain contributes directly or
indirectly via runoff from the catchment to lake and river acidity
(i.e., depending on characteristics of the surrounding watershed) is
variable. The United States Environmental Protection Agency's (EPA)
website states: "Of the lakes and streams surveyed, acid rain caused
acidity in 75% of the acidic lakes and about 50% of the acidic streams".
[27]
Soils
Soil biology and chemistry can be seriously damaged by acid rain.
Some microbes are unable to tolerate changes to low pH and are killed.
[28] The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins such as aluminium, and leach away essential nutrients and minerals such as magnesium.
[29]
- 2 H+ (aq) + Mg2+ (clay) 2 H+ (clay) + Mg2+ (aq)
Soil chemistry can be dramatically changed when base cations, such as
calcium and magnesium, are leached by acid rain thereby affecting
sensitive species, such as sugar maple (Acer saccharum).
[30][31]
Forests and other vegetation
Effect of acid rain on a forest, Jizera Mountains, Czech Republic
Adverse effects may be indirectly related to acid rain, like the
acid's effects on soil (see above) or high concentration of gaseous
precursors to acid rain. High altitude forests are especially vulnerable
as they are often surrounded by clouds and fog which are more acidic
than rain.
Other plants can also be damaged by acid rain, but the effect on food
crops is minimized by the application of lime and fertilizers to
replace lost nutrients. In cultivated areas, limestone may also be added
to increase the ability of the soil to keep the pH stable, but this
tactic is largely unusable in the case of wilderness lands. When calcium
is leached from the needles of red spruce, these trees become less cold
tolerant and exhibit winter injury and even death.
[32][33]
Ocean acidification
Main article: Ocean acidification
Coral's limestone skeletal is sensitive to pH drop, because the calcium carbonate, core component of the limestone dissolves in acidic (low pH) solutions.
Human health effects
Acid rain does not directly affect human health. The acid in the
rainwater is too dilute to have direct adverse effects. However, the
particulates responsible for acid rain (sulfur dioxide and nitrogen
oxides) do have an adverse effect. Increased amounts of fine particulate
matter in the air do contribute to heart and lung problems including
asthma and bronchitis.
[34]
Other adverse effects
Effect of acid rain on statues
Acid rain can damage buildings, historic monuments, and statues, especially those made of rocks, such as limestone and marble,
that contain large amounts of calcium carbonate. Acids in the rain
react with the calcium compounds in the stones to create gypsum, which
then flakes off.
- CaCO3 (s) + H2SO4 (aq) CaSO4 (s) + CO2 (g) + H2O (l)
The effects of this are commonly seen on old gravestones, where acid
rain can cause the inscriptions to become completely illegible. Acid
rain also increases the corrosion rate of metals, in particular iron, steel, copper and bronze.
[35][36]
Affected areas
Places significantly impacted by acid rain around the globe include most of eastern Europe from Poland northward into Scandinavia,
[37] the eastern third of the United States,
[38] and southeastern Canada. Other affected areas include the southeastern coast of China and Taiwan.
[citation needed]
Prevention methods
Technical solutions
Many coal-firing power stations use flue-gas desulfurization
(FGD) to remove sulfur-containing gases from their stack gases. For a
typical coal-fired power station, FGD will remove 95% or more of the SO
2
in the flue gases. An example of FGD is the wet scrubber which is
commonly used. A wet scrubber is basically a reaction tower equipped
with a fan that extracts hot smoke stack gases from a power plant into
the tower. Lime or limestone in slurry form is also injected into the
tower to mix with the stack gases and combine with the sulfur dioxide
present. The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates.
In some areas the sulfates are sold to chemical companies as gypsum when the purity of calcium sulfate is high. In others, they are placed in landfill.
However, the effects of acid rain can last for generations, as the
effects of pH level change can stimulate the continued leaching of
undesirable chemicals into otherwise pristine water sources, killing off
vulnerable insect and fish species and blocking efforts to restore native life.
Fluidized bed combustion also reduces the amount of sulfur emitted by power production.
Vehicle emissions control reduces emissions of nitrogen oxides from motor vehicles.
International treaties
A number of international treaties on the long range transport of atmospheric pollutants have been agreed for example, Sulphur Emissions Reduction Protocol under the Convention on Long-Range Transboundary Air Pollution. Canada and the US signed the Air Quality Agreement in 1991. Most European countries and Canada have signed the treaties.
Emissions trading
Main article: Emissions trading
See also: Acid Rain Program
In this regulatory scheme, every current polluting facility is given
or may purchase on an open market an emissions allowance for each unit
of a designated pollutant it emits. Operators can then install pollution
control equipment, and sell portions of their emissions allowances they
no longer need for their own operations, thereby recovering some of the
capital cost of their investment in such equipment. The intention is to
give operators economic incentives to install pollution controls.
The first emissions trading market was established in the United States by enactment of the Clean Air Act Amendments of 1990. The overall goal of the Acid Rain Program established by the Act
[39] is to achieve significant environmental and public health benefits through reductions in emissions of sulfur dioxide (SO
2) and nitrogen oxides (NO
x),
the primary causes of acid rain. To achieve this goal at the lowest
cost to society, the program employs both regulatory and market based
approaches for controlling air pollution.
See also
- Basic precipitation
- List of environmental issues
- Lists of environmental topics
- Ocean acidification
- Rain dust (an alkaline rain)
Source: http://en.wikipedia.org/wiki/Acid_rain
Question :
1. Rain or any other form of precipitation that is unusually acidic is called
a. Acid rain
b. Sweet rain
c. Unusual rain
d. Usual rain
2. acid rain can have harmful effects on...., except
a. Plants
b. Aquatic animals
c. Infrastructure
d. Sun
3. The chemicals in acid rain can cause......
a. Heavy rain
b. Paint to peel
c. Usual rain
d. Unusual rain
4. Clean or unpolluted rain has an acidic pH, but usually no lower than
a. 5.7
b. 4.4
c. 2.2
d. 4.5
e. 5.4
5. The most important gas which leads to acidification is
a. Sulfur
b. Dioxide
c. Sulfur dioxide
d. Sulfur trioxide
e. Sulfur oxide
6. The principal cause of acid rain is
a. Sulfur and nitrogen
b. Sulfur
c. Oxygen
d. Nitrogen
e. Helium
7. The principal cause of acid rain is compounds from human sources below, except
a. Electricity generation
b. Factories
c. Motor vehicles
d. Human breath
8 Combustion of fuels produces
a. Sulfur dioxide
b. Sulfur dioxide and nitric oxides
c. Sulfur trioxide
d. Nitric oxide
e. Nitric trioxide
9. Combustion of fuels are converted into
a. Sulfuric acid and nitric acid
b. Usual acid
c. Unusual acid
d. Sulfuric acid
e. Nitric acid
10. The gases can be carried hundreds of ............ in the atmosphere before they are converted to acids and deposited
a. Meters
b. Centimeters
c. Kilometers
d. Milimeters
e. Nanometers
Answer : adbac adbac
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