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“Acid Rain, Causes and Effects”

Institute of Zoology, University of Punjab Lahore

Acid Rain, Causes and Effects
Summary:
Acid rain, also called acid precipitation or acid deposition, precipitation possessing
a pH of about 5
...
In acid-sensitive
landscapes, acid deposition can reduce
the
pH
of surface waters and
lower biodiversity
...
In acid-sensitive
areas, acid rain also depletes soil of important plant nutrients and buffers, such
as calcium and magnesium, and can release aluminum, bound to soil particles
and rock, in its toxic dissolved form
...

The phrase acid rain was first used in 1852 by Scottish chemist Robert Angus
Smith during his investigation of rainwater chemistry near industrial cities
in England and Scotland
...
It was not
until the late 1960s and early 1970s, however, that acid rain was recognized as a
regional environmental issue affecting large areas of western Europe and
eastern North America
...
As a global environmental issue, it is frequently
overshadowed by climate change
...


Acid Rain:
Definition:
Acid rain is 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
...


History:
Modern anthropogenic acid deposition began
in Europe and
eastern North
America after World War II, as countries in those areas greatly increased
their consumption of fossil fuels
...
In 1979 the Geneva Convention
on Long-range Transboundary Air Pollution created the framework for
reducing air pollution and acid deposition in Europe
...
This first agreement has been extended by several protocols since
its original inception
...
Work toward developing a Memorandum of
Intent between the U
...
and Canada to reduce air pollution and acid deposition
began in the 1970s
...
The SO2 emissions in
the United States and Canada peaked in the late 1970s, but they have subsequently
declined as a result of the adoption of government-mandated air pollution
standards
...
S
...
This development marked the beginning of further
significant SO2 reductions in the United States and resulted in an 88 percent
decline in SO2 emissions between 1990 and 2017
...

NOx emissions have exceeded SO2 emissions since about 1980, but they too have
fallen with the implementation of the Clean Air Act
...
The combined reductions of
SO2 and NOx emissions during this period led to a significant drop in acid
deposition, as well as sulfate (SO42) and nitrate (NO3) deposition
...

As a result of actions and agreements such as those described above, acid
deposition in both Europe and eastern North America has been significantly
reduced
...
S
...
Similar trends were also reflected in data collected at
measuring stations located across the eastern United States, which reported a
decrease of approximately 40 percent in H+ concentration between 1994 and
2008
...

Despite significant reductions in acid deposition, some European and North
American ecosystems impaired by acid deposition have been slow to recover
...
As a result, these soils are even more susceptible to
continued acid deposition, even at reduced levels
...

In contrast to Europe and North America, acid deposition is increasing in other
parts of the world
...
However, the introduction of stringent
emission controls in China in 2007 produced a 75 percent decline in the country’s
SO2 emissions by 2019, whereas India’s SO2 emissions continued to increase
...
The sulfuric and
nitric acids formed in the atmosphere fall to the ground mixed with rain, snow, fog,
or hail
...
The acidic particles and gases may deposit to surfaces
(water bodies, vegetation, buildings) quickly or may react during atmospheric
transport to form larger particles that can be harmful to human health
...

The amount of acidity in the atmosphere that deposits to earth through dry
deposition depends on the amount of rainfall an area receives
...


Chemistry of Acid Rain:
Acid rain is a popular expression for the more scientific term acid deposition,
which refers to the many ways in which acidity can move from
the atmosphere to Earth’s surface
...
Acid deposition also includes the dry deposition of acidic particles
and gases, which can affect landscapes during dry periods
...

Acidity is a measure of the concentration of hydrogen ions (H+) in a solution
...
Substances are
considered acidic below a pH of 7, and each unit of pH below 7 is 10 times more
acidic, or has 10 times more H+, than the unit above it
...
0 has a concentration of 10 microequivalents of H+ per litre, whereas
rainwater with a pH of 4
...

Normal rainwater is weakly acidic because of the absorption of carbon
dioxide (CO2) from the atmosphere—a process that produces carbonic acid—and
from organic acids generated from biological activity
...
Other
natural sources of acidification include the production of nitrogen oxides from the
conversion of atmospheric molecular nitrogen (N2) by lightning and the conversion
of organic nitrogen by wildfires
...
2
...
In
the United States, electric utilities produce nearly 70 percent of SO 2 and about 20
percent of NOx emissions
...
In the atmosphere, sulfuric and
nitric acids are generated when SO2 and NOx, respectively, react with water
...
In such areas
the pH of precipitation can average 4
...
5 annually, and the pH of individual
rain events can sometimes drop below 3
...
In addition, cloud water and fog in
polluted areas may be many times more acidic than rain falling over the same
region
...
In addition to acid deposition, NO x emissions along
with hydrocarbon emissions
are
key
ingredients
in
groundlevel ozone (photochemical smog) formation, which is one of the most widespread
forms of air pollution
...
Coal combustion is the leading
source of atmospheric mercury, which also enters ecosystems by wet and dry
deposition
...
) Acid
deposition of nitrogen derived from NOx emissions creates additional
environmental problems
...
This eutrophication (or over-enrichment) causes the overgrowth
of plants and algae
...

Eutrophication is considered to be a major environmental problem in lake, coastal
marine, and estuarine ecosystems worldwide
...
Sulphur and Nitrogen particles which get mixed with
water are found in two ways either man-made i
...

According to the Royal Society of Chemistry, which considers him the “father of
acid rain,” the word acid rain was invented in 1852 by Scottish chemist Robert
Angus Smith
...


The regular clean rain we experience, even though it is not clean i
...
The reaction occurring is
H2O (l) + CO2 (g) ⇌ H2CO3 (aq)
The pH value of regular rainwater is around 5
...
The
oxides of nitrogen and sulphur are blown away by the wind along with the dust
particles
...
Acid rain is essentially a byproduct of human activities which emit
oxides of nitrogen and sulphur in the atmosphere
...

Sulphur dioxide and nitrogen dioxide undergo oxidation, and then they react with
water resulting in the formation of sulphuric acid and nitric acid respectively
...

i
...

At pH lower than 5 most fish eggs will not hatch and lower pH can kill adult fish
...
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
...
e
...
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
...
e
...

ii
...
Some microbes
are unable to tolerate changes to low pH and are killed
...

The hydronium ions of acid rain also mobilize toxins, such as aluminium, and
leach away essential nutrients and minerals such as magnesium
...


iii
...
Most minor cases which do not result in fatality of plant life can be
attributed to the plants being less susceptible to acidic conditions and/or the acid
rain being less potent
...
Acidic water enters the
plant and causes important plant minerals to dissolve and get carried away; which
ultimately causes the plant to die of lack of minerals for nutrition

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