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 vapor and precipitate as sulphuric acid or nitric acid in rain, snow, or fog.

Causes of Acid Rain

• 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
• 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)

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

• Increased acidity in water bodies
• Stops eggs of certain organisms (e.g. fish) to stop hatching
• Changes population ratios
• Affects the ecosystem
• 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
• Accelerates weathering in metal and stone structures E.g. Parthenon in Athens, Greece; Taj Mahal in Agra, India
• 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 atmosphere
• 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
• Use cleaner fuels
• Coal that contains less sulphur
• "Washing" the coal to reduce sulphur content
• Natural Gas
• Flue Gas De-sulphurization (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
• Produces pH-neutral calcium sulphate that is physically removed from the scrubber
• Sulphates can be used for industrial purposes
• Use other sources of electricity (i.e. nuclear power, hydro-electricity, wind energy, geothermal energy, and solar energy)
• Issue of cost
• Liming
• Powdered limestone/limewater added to water and soil to neutralize acid
• Used extensively in Norway and Sweden

Expensive, short-term remedy

• Use an alternative energy source such as batteries, solar & wind power, electricity and the like. Fossil fuel emissions cause pollution and acid rain and are expensive and non-renewable. Another great energy source is manpower; consider walking or biking to work or school.
• Plant a tree. These are finally something we don't seem to have enough of. The tree will absorb some of the polluted air and put out clean, fresh oxygen.