Acid Rain

What it is:

• the deposition of acidic components in rain, snow, dew, or dry particles.

• more accurate term is "acid precipitation."

• defined as any type of precipitation with a pH that is unusually low

The Causes:

• occurs when sulfur dioxide and nitrogen oxides are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds

• then fall to earth as rain, snow, mist, dry dust, hail, or sleet.

• Dissolved carbon dioxide dissociates to form weak carbonic acid giving a pH of approximately 5.6 at typical atmospheric concentrations of CO2

• Therefore a pH of less than 5.6 has sometimes been used as a definition of acid rain

The Effects:

• increases the acidity of the soil, and affects the chemical balance of lakes and streams

• accelerates weathering in carbonate rocks and accelerates building weathering

• contributes to acidification of rivers, streams, and forest damage at high elevations

• When the acid builds up in rivers and streams it can kill fish

Problems:

• large fraction of which are formed from the same gases as acid rain (sulfur dioxide and nitrogen dioxide), have been shown to cause illness and premature deaths such as cancer and other deadly diseases

• killing off insect and aquatic lifeforms as well as causing damage to buildings and having possible impacts on human health

• cause damage to certain building materials and historical monuments

• cause weathering on ancient and valuable statues and has caused considerable damage

• sulfuric acid in the rain chemically reacts with the calcium compounds in the stones (limestone, sandstone, marble and granite) to create gypsum, which then flakes off

• commonly seen on old gravestones where the acid rain can cause the inscription to become completely illegible

• causes an increased rate of oxidation for iron

• Visibility is also reduced by sulfate and nitrate in the atmosphere

Solutions:

• many coal-burning power plants use Flue gas desulfurization (FGD) to remove sulfur-containing gases from their stack gases

• wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower

• Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulfur dioxide present

• calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates.

• international treaties on the long range transport of atmospheric pollutants have been agreed

• even more benign regulatory scheme involves emissions trading

• every current polluting facility is given an emissions license that becomes part of capital equipment. Operators can then install pollution control equipment, and sell parts of their emissions licenses

Essay

All rain is slightly acidic, but the term Acid Rain is used to describe rain that has mixed with a range of industrial pollutants and become far more acidic that it could normally become.

Air borne pollutants such as sulphur dioxide, nitrogen oxides and assorted hydrocarbons react in the air with sunlight and water to form nitric acid, sulphuric acid and assorted other mineral acids and ammonium salts.

The resultant acidic water can be carried thousands of miles by the wind before it falls to earth as rain, snow, fog or as dry particles which settle out due to gravity.

The biggest source of the 'acid rain' chemicals that pollute the atmosphere is the burning of fossil fuels. Fossil fuels were created from organic ( animal and plant ) material that died millions of years ago.

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