Definition of Acid Rain

Definition of Acid Rain
Precipitation that has a pH of less than that of natural rainwater (which is about 5.6 due to dissolved carbon dioxide).
It is formed when sulphur dioxides and nitrogen oxides, as gases or fine particles in the atmosphere, combine with water vapour and precipitate as sulphuric acid or nitric acid in rain, snow, or fog.

Causes of Acid Rain
Natural Sources
Emissions from volcanoes and from biological processes that occur on the land, in wetlands, and in the oceans contribute acid-producing gases to the atmosphere
Effects of acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe

Causes of Acid Rain
The principal cause of acid rain is from human sources
Industrial factories, power-generating plants and vehicles
Sulphur dioxide and oxides of nitrogen are released during the fuel burning process (i.e. combustion)
MSN Encarta

Formation of Acid Rain

Formation of Acid Rain
When water vapour condeses, or as the rain falls, they dissolve in the water to form sulphuric acid (H2SO4) and nitric acid (HNO3).
While the air in cleaned of the pollutants in this way, it also causes precipitation to become acidic, forming acid rain

Affected Areas
Industrial acid rain is a substantial problem in China, Eastern Europe and Russia and areas down-wind from them.
Acid rain from power plants in the Midwest United States has also harmed the forests of upstate New York and New England.
This shows that the effects of acid rain can spread over a large area, far from the source of the pollution

Effects of Acid Rain
Harmful to aquatic life
Increased acidity in water bodies
Stops eggs of certain organisms (e.g. fish) to stop hatching
Changes population ratios
Affects the ecosystem

Effects of Acid Rain
Harmful to vegetation
Increased acidity in soil
Leeches nutrients from soil, slowing plant growth
Leeches toxins from soil, poisoning plants
Creates brown spots in leaves of trees, impeding photosynthesis
Allows organisms to infect through broken leaves

Effects of Acid Rain

Effects of Acid Rain
Accelerates weathering in metal and stone structures
Eg. Parthenon in Athens, Greece; Taj Mahal in Agra, India

Effects of Acid Rain
Affects human health
Respiratory problems, asthma, dry coughs, headaches and throat irritations
Leeching of toxins from the soil by acid rain can be absorbed by plants and animals. When consumed, these toxins affect humans severely.
Brain damage, kidney problems, and Alzheimer's disease has been linked to people eating "toxic" animals/plants.

Preventive Measures
Reduce amount of sulphur dioxide and oxides of nitrogen released into the atomosphere
Use less energy (hence less fuel burnt)
Use cleaner fuels
Remove oxides of sulphur and oxides of nitrogen before releasing
Flue gas desulphurization
Catalytic Converters

Preventive Measures
Use cleaner fuels
Coal that contains less sulphur
"Washing" the coal to reduce sulphur content
Natural Gas

Preventive Measures
Flue Gas Desulphurisation (FGD)
Removes sulphur dioxide from flue gas (waste gases)
Consists of a wet scrubber and a reaction tower equipped with a fan that extracts hot smoky stack gases from a power plant into the tower
Lime or limestone (calcium carbonate) in slurry form is injected into the tower to mix with the stack gases and reacts with the sulphur dioxide present

Preventive Measures
Produces pH-neutral calcium sulphate that is physically removed from the scrubber
Sulphates can be used for industrial purposes
Scrubber at work

Preventive Measures
Use other sources of electricity (i.e. nuclear power, hydro-electricity, wind energy, geothermal energy, and solar energy)
Issue of cost