This document provides information about a chemistry course titled "Environmental Chemistry" that covers the topic of acid rain. It defines acid rain as caused by sulfur dioxide and nitrogen oxide emissions reacting with water and oxygen in the air to form acids. The document then discusses the natural and human sources of acid rain, how it is measured on the pH scale, its effects on water bodies, forests, aquatic life, and more. It also outlines strategies to control acid rain through policies like the Clean Air Act that have significantly reduced sulfur dioxide and nitrogen oxide emissions from power plants in the United States and Europe.

2.  Course Title: Environmental Chemistry
 Course Code: CHEM2111
 Topic: Acid Rain
 Prepared by: Dr. Rashida Bashir

3. Acid Rain
Acid rain is caused by a chemical reaction that begins when
compounds like sulfur dioxide and nitrogen oxides are released
into the air. These substances can rise very high into the
atmosphere, where they mix and react with water, oxygen, and
other chemicals to form more acidic pollutants, known as acid
rain.

4. 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.

5. 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 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.

6. Acidic deposits have been detected in glacial ice thousands of
years old in remote parts of the globe.
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.

7. Measurement of Acid Rain
The pH scale is used to measure the acidity or alkalinity of an
aqueous solution, is determined by the hydrogen ion content (H+).
This scale was invented by a Danish scientist called Sorenson in 1909.
The pH scale ranges from 0, which is strongly acid, to 14 which is
strongly alkaline, the scale point 7 being neutral. Examples of
solutions with differing pH values include car battery acid (pH 1),
lemon juice (pH 2), natural rain (pH 5-6), milk (pH 6), washing-up
liquid (pH 7), seawater (pH 8), milk of magnesia (pH 10) and
ammonia (pH 12).

8. The pH scale is logarithmic relationship rather than linear, and
so there is a ten fold increase in acidity with each pH unit, such
that rainfall with
pH 5 is ten times more acidic than pH 6,
pH 4 is 100 times more acidic than pH 6
pH 3 is 1000 times more acidic than pH 6.

9. Normal rain has a pH value of between 5.0 and 5.5, this is
slightly acidic due to the presence of carbon dioxide in the
atmosphere which forms weak carbonic acid in water. It is not
uncommon for acidified rainwater to have a pH of 4, about 30
times as acidic as normal rainwater.
Types of Acid Rain:
1- Wet Deposition
2- Dry Deposition

10.  Wet Deposition:
Wet deposition refers to acidic rain, fog, and snow. As this acidic
water flows over and through the ground, it affects a variety of
plants and animals.
• Dry Deposition:
Dry deposition refers to acidic gases and particles. About half of
the acidity in the atmosphere falls back to earth through dry
deposition

11. History
 The term acid rain was coined in 1852 by Scottish chemist
Robert Angus Smith, Royal Society of Chemistry, called him the
"father of acid rain." He wrote about his findings in 1872 in the
book “Air and Rain: The Beginnings of a Chemical
Climatology”
 In the 1960s and early 1970s, acid rain became recognized as a
regional environmental issue

12. 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. 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.

13. Occasional pH readings in rain and fog water of well
below 2.4 have been reported in industrialized areas.
Industrial acid rain is a substantial problem in China
and Russia and areas downwind from them. These
areas all burn sulfur-containing coal to generate heat
and electricity.

14. Major Sources of Acid Rain
 Rotting vegetation and erupting volcanoes release some
chemicals that can cause acid rain.
 The biggest sources are coal-burning power plants, factories,
oil refineries and automobiles. Sulfur dioxide (SO2) and
nitrogen oxides (NOx) are released into the atmosphere. Those
air pollutants react with water, oxygen, and other substances to
form sulfuric and nitric acid. That mix with precipitation and
fall to the ground.

15. The reaction takes place in the following manner.
 SO2 + H2O → H2SO3 (Sulphurous acid)
 SO2 + O3 (Ozone) → SO3 + O2
 SO3 + H2O → H2SO4 (Sulphuric acid)
 2NO + O2 → 2NO2
 2NO2 + H2O → HNO3 (Nitric acid) + HNO2(Nitrous acid)
The sulphuric acid and nitric acid remain in vapours state at
high temperature. The condensation begins at low temperature
together with the rain, fog or snow, increases its acidity

17. Major contributors in Acid Rain
 Natural processes 10% SO2
 industrial combustion 69.4% SO2
 vehicular transportation 3.7% SO2
 Natural processes (lightning, volcanic eruptions, forest fires,
action of bacteria) 5% NOx
 Industrial processes 32% NOx
 vehicular transportation 43% NOx

18.  According to the EPA. Two thirds of sulfur dioxide and one
fourth of nitrogen oxide found in the atmosphere come from
electric power generators.

20. Geographic distribution of acid rain
Wet deposition samples can be measured to determine chemical
concentrations in almost any area. The National Atmospheric
Deposition Program (NADP) at the Wisconsin State Laboratory
of Hygiene, University of Wisconsin-Madison, maintains five
networks with more than 350 deposition monitoring sites. The
NADP National Trends Network has 250 sites in the U.S.
located far from the point sources of pollution. Each site has an
automated precipitation collector and gage to gather samples
only during rain or snowfall.

21. The areas of greatest acidity (lowest pH values) are located in
the North-eastern United States. This pattern of high acidity is
caused by the large number of cities, the dense population, and
the concentration of power and industrial plants in the North-
east.
In addition, the prevailing wind direction brings storms and
pollution to the Northeast from the Midwest, and dust from the
soil and rocks in the Northeastern United States is less likely to
neutralize acidity in the rain.

22. Weekly samples are collected and sent to the NADP for analysis. The
network measures acidity and calcium, magnesium, sodium,
potassium, sulfate, nitrate, chloride, and ammonium ions. Data are
available online at http://nadp.slh.wisc.edu/. These monitoring efforts
support research and policy on air quality issues.
NADP monitoring data show that wet sulfate deposition has decreased
an average of 30 percent since the early 1990s in the eastern United
States. The largest decreases occurred in Maryland, New York,
Virginia, West Virginia. Nitrogen deposition has decreased as well, but
to a lesser extent.

23. Effects of Acid Rain
Acid rain has serious implications for continuation of life on this
planet. The main acid rain problems are:
1- Effects on Water Bodies:
 Rivers and lakes have a pH ranges between 6 and 8. Acid rain
in these water bodies altered the chemical environment which
may be a threat for the survival of flora and fauna. Soil with
poor buffering capacity may release aluminum ions from the soil
which is toxic for aquatic life forms.

24. Effects on Soil and Forests:
 Acid rain is being cited as one of
the major causes of degradation of
the forests at higher altitudes of the
Appalachian Mountains from Maine
to Georgia. Forests are affected
directly as well as indirectly by acid
rain.

25.  Acid rain changed soil acidity. In its bid to neutralize, soil
releases substances that are toxic for trees growing on it.
 Acidic water also dissolve nutrients in the soil before they can
be absorbed by flora growing on the forest floor.
3- Effects on Aquatic Flora and Fauna
Acid rain can directly effect on the aquatic life, as the high
amount of sulphuric acid and nitric acid levels in acid rains are
directly consumed by aquatic animals and plants.

26. The harmful acids affect the ability of fish to take in nutrients,
salt, and oxygen.
 Many bacteria and blue green algae are killed due to
acidification. This disrupting the whole ecological balance.
 Acidic water can also leach aluminium from the soil. This
runoff carry dissolved aluminium to lakes, rivers and streams.
This cause death of fish by clogging its gills and deprives it of
oxygen.

27.  Acid rains affect the pH level of the water which reduces the
absorption capacity of essential nutrients of the aquatic life. This also
hampers the reproduction process in fish leading to weak or brittle
eggs.
4- Effects on Human beings:
 Acidification effect human nervous system, respiratory system and
digestive system.
 Acid contaminates with potable water and enter man’s body. The
heavy metals released by acid rain may cause potential threat to
human health

28. 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 pH lower than 5
most fish eggs will not hatch and lower pH 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 State.

29. 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".

30. Lakes hosted by silicate basement rocks are more acidic than
lakes within limestone or other basement rocks with a carbonate
composition (i.e. marble) due to buffering effects by carbonate
minerals, even with the same amount of acid rain

32. 5- Effect on terrestrial ecosystem:
 Demineralization of soil occurs. Cation like Ca2+, Mg2+, Na+, K+ are
leached away and replaced by acid cations such as Al3+ ions.
 Nitrogen fixation ability of nitrifying bacteria diminishes rapidly
below pH 6.
 Acidification of soil adversely affects soil fauna and lead to reduced
forest productivity.
 Acid rain has retarded the growth of vegetables such as pea, beans,
radish, spinach, carrot etc.

33.  Continuous chronic exposure to low levels of acidic water causes
diffuse chlorosis in the leaves of the plants.
5- Effect of Acid rain on Building material:
 1. Acid rain causes extensive damage to buildings and structural
material of marble, limestone, salts etc. The attack of acid in marble is
termed as Stone leprosy.
CaCO3 + H2SO4→CaSO4 + H2O + CO2
 2. Acid rain corrodes houses, monuments, statues, bridges, fences
and railing that require huge cost for maintenance every year.
 3. Acid precipitation causes damage to steel, oil based paints and
automobile coatings. It disintegrates textile and paper etc.

34. Control Measure:
 In the U.S., the Clean Air Act of 1990 targeted acid rain, putting in
place pollution limits that helped cutoff sulfur dioxide emission 88
% between 1990 and 2017.
 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 were added under other provisions of the
program.

35. Phase II began in 2000, and affects most of the power plants in
the country.
• When fully implemented, CAIR will reduce SO2 emissions in
28 eastern states and the District of Columbia by over 70%
and NOx emissions by over 60% from 2003 levels.

36.  During the 1990s, research continued. On March 10, 2005, the
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 SO2 and NOx in the eastern
United States.
 U.S. emission of nitrogen dioxide down 50 percent in the
same time period.

37. Overall, the program's cap and trade program has been
successful in achieving its goals. Since the 1990s, SO2
emissions have dropped 40%, and according to the Pacific
Research Institute, acid rain levels have dropped 65% since
1976.Conventional regulation was used in the European Union,
which saw a decrease of over 70% in SO2 emissions during the
same time period.

38. In 1980, the US Congress passed an Acid Deposition Act. 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.

39. Strategy:
The numbers of possible solutions for acid rain :
 One of the most fundamental acid rain solutions is to utilize
fuels that burn more cleanly, or to burn coal more efficiently.
 The best solution for the industrial power plants is to attach
devices known as ‘scrubbers’ in the chimneys. These scrubbers
reduce the amount of sulfur produced in the smoke by 90 – 95%.

40.  Vehicles and cars must be required to comply with very tight and efficient
emission standards. Fitting catalytic converters into the exhaust pipes also
reduces the amount of sulfur dioxide produced by the vehicles.
 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 is to achieve significant
environmental and public health benefits through reductions in emissions of
sulfur dioxide (SO2) and nitrogen oxides (NOx), 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

41. Thank You