1. In this presentation you will:
Explore the properties of acid rain, its causes and consequences.
ClassAct SRS enabled.

2. Acid rain, together with the greenhouse effect, is nowadays one of the more serious environmental concerns of the industrialized world.
Acid rain changes the natural pH balance of large ecosystems, damaging or weakening natural habitats and plantations, affecting flora and fauna.
In this lesson you are going to see what acid rain is, what it does, what causes it and what are its consequences.
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3. What is acid rain?
Some polluting molecules contaminating the atmosphere like nitrogen oxides (NOX), sulphur dioxides (SO2) and ammonia (NH3) are acidic and create acids when mixed with rain water. +
NO2
H2O
These substances, when released into the air in large quantities by industrial processes and car exhausts, increase the acidity of rain water to a pH below 5 and this is known as acid rain. +
HNO2
HNO3
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4. The Global Problem of Acid Rain
What is acid rain?
Natural unpolluted rain is slightly acidic with a pH around 5.6 as a result of carbon dioxide gas dissolved from the air.
Pacific Ocean
Indian Ocean
Atlantic Ocean
South America
North America
Europe
Africa
Asia
Australia
In many areas of the world the atmosphere is contaminated by acidic substances that provoke rain with pH values up to 4 and 3.
In some areas with acid fog, pH can reach values up to 2.3 (about 1000 times more acidic than natural rain), similar to those in lemon or vinegar.
The Global Problem of Acid Rain
Acid rain
Polluted air emissions leading to acid rain
Sensitive soils, potential problems
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5. Question 1 What is acid rain?
A) Water precipitations with a pH level below 5.
B) Water precipitations with a pH level above 5.

6. Causes The main cause of acid rain is human industrial activity.
During recent decades, different types of chemicals have been released to the atmosphere, which have progressively changed its gaseous components.
SO2 - Industry
SO2 - Other
NOX – Road Transport
NOX – Power Stations
NOX – Industry
NOX – Other
SO2 – Power Stations
Power plants burn enormous quantities of fossil fuels to generate electricity, making them the main sources of sulphur dioxide and nitrogen oxide released into the air.
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7. Causes
Pollution from power plants and combustion engines in vehicles contribute to the rising levers of chemical contaminants in the atmosphere.
Sulfur Dioxide (SO2)
Nitrogen Oxide (SO2)
SO2 & NOX
Acid Snow
Acid Rain
This chemicals can reach high levels in the atmosphere, where they mix and react with water, oxygen and other chemical elements like ozone.
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8. Causes
Contaminating chemicals in the atmosphere react with water, oxygen and other chemical elements to form sulfuric acid and nitric acid that we know as acid rain:
SO3+H2O → H2SO4
2NO2+H20 → HNO3 + HNO2
Sulfur Dioxide (SO2)
Nitrogen Oxide (SO2)
SO2 & NOX
Acid Snow
Acid Rain
The sulphur dioxide and the nitrogen oxide dissolve very easily in water and can be transported long distances when they become part of rain water, snow and fog.
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9. Question 2 Is the following statement true or false?
'Contaminating chemicals like sulfur dioxide and nitrogen oxide produced by power plants and combustion engine vehicles, react with the water in the atmosphere to form sulphuric acid and nitric acid'.
Answer True or False.

10. Dry deposition
Nearly half the acidic atmospheric contamination occurs from a direct deposition of acid pollutants as small particles, on plants and soils.
This type of acid contamination is called dry deposition and occurs in dry areas with minimal precipitations.
Sulfur Dioxide (SO2)
Nitrogen Oxide (SO2)
SO2 & NOX
Dry Deposition
The wind takes these dry particles over buildings, soils, crops and even to the air we breathe.
We could even ingest some of these contaminants when we eat food which has been in contact with polluted dust and gas.
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11. pH Natural Balance Nature depends on balance.
Normal precipitation - such as rain, sleet, or snow - reacts with alkaline chemicals, or non-acidic materials, that can be found in air, soils, bedrock, lakes, and streams.
pH 5
Buffer Material
These reactions usually neutralize natural acids.
pH 6
Neutralizing materials are called buffers since they ‘absorb’ or neutralize some degree of acidity.
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12. pH Natural Balance
If precipitation becomes too acidic due to human contamination or in mediums with a smaller buffer capacity, they may not be able to neutralize all of the acids and the drop in pH can destroy the ecological balance.
pH 3.5
pH 4
Over time, these neutralizing materials can be washed away by acid rain resulting in damage to crops, trees, lakes, rivers and animals.
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13. Question 3 Is the following statement true or false?
'The natural acidity of rain water is neutralised by alkaline chemicals found in air, soils, bedrocks, lakes and streams'.
Answer True or False.

14. Consequences
Acid rain causes alterations in water habitats like rivers and lakes, in animals, in plants and in soils by unbalancing their nutrients.
Acid rain affects some man-made constructions, such as buildings and monuments, since over time, it dissolves some of the materials these are built with.
Acid rain directly affects man too, since it may increase the mercury levels of the water that we drink and create high levels of nitrogen oxides in the air, obstructing breathing systems.
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15. Water Habitats
Acid rain effects are most evident in water habitats like springs, lakes and rivers, since rain water that falls on land will eventually flow into them.
Fish and other types of aquatic animals and plant life are the most vulnerable to the changes in pH levels that acid rain causes in their habitats, substantially reducing the population of some of these species and, in some cases, even making them disappear.
The first concerns about acid rain were raised in the 1950’s when scientists found that the population of trout in some areas of the Scandinavian countries were drastically falling due to changes in the pH levels of the lakes and rivers.
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16. Question 4 Is the following statement true or false?
'Fish and other water species are particularly resistant to pH changes in their habitats'.
Answer True or False.

17. Land Plants Acid rain can also damage and destroy plants.
Some species are more sensitive to acid rain than others. Among the most sensitive are lichens, mosses, fungus, and aquatic plants.
Lichen
Moss
Fungus
Aquatic Plants
Some plants are directly affected by acid rain since it strips away the waxy protective layer of leaves and causes alterations in the metabolism processes, like photosynthesis.
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18. Land Plants
As result of the alterations caused by acid rain, plants lose leaves and suffer a gradual weakening process, becoming more vulnerable to plagues, diseases and water deficiency.
This makes it very difficult to demonstrate that the real cause of a forest’s death is pollution, since there are different agents other than pollution that actually kill the plants.
However, in cases with highly contaminating concentrations, there are clear symptoms of defoliation and discoloration that can be related to acid contamination.
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19. Question 5
Which of the following plants are particularly sensitive to acid rain?
A) Lichens
B) Mosses
C) Fungus
D) Aquatic plants
E) All of the above

20. Man Under Acid Rain Acid rain affects humans too.
The toxic materials released into water by acid rain can cause poisonous levels of mercury in the fish we eat.
Acidic drinking water reacts with water pipes dissolving the metal, causing damage to the kidneys and liver.
The effects of acid rain may affect people directly too. High levels of nitrogen oxides in the air obstruct breathing systems, raising the cases of pneumonias and bronchitis.
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21. Man’s Constructions and Acid Rain
Acid rain accelerates the corrosion process of exposed metals like bronze and other metals used in construction.
Buildings and monuments, particularly those made with limestone, chalk or marble are very vulnerable to the ravage of acid rain, which reacts with the calcium carbonate of the stone, dissolving it away.
Many ancient ruins and other monument have disappeared or are in a degradation process due to damage from acid rain.
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22. Question 6
Which of the following construction materials are particularly sensitive to acid rain?
A) Clay and slate.
B) Steel and aluminium.
C) Limestone, chalk and marble.
D) Wood.

23. Question 7 Which of the following are mayor consequences of acid rain?
A) Alterations in water habitats.
B) Degradation of man made constructions and monuments.
C) Risks for human health.
D) All of the above.

24. Summary After completing this presentation you should be able to:
Show knowledge and understanding of what acid rain is.
Show knowledge and understanding of the causes of acid rain.
Show knowledge and understanding of the natural pH balance.
Show knowledge and understanding of the consequences of acid rain.
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