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This is the depositing of acid that leads to increasing damage to buildings and vegetation as a result of human actions. It was first noted in the mid 1800's, but did not become a major concern until the 1980's.
Acid can be deposited in two ways:
Dry deposition: This occurs close to the source, (usually no further away than 5km) as a result of gas and aerosol emissions. Impacts largely on buildings.
Wet deposition: Impacts much further away from the source, and often crosses international borders (UK 'exports' acid rain to Sweden.) Nitrogen Dioxide and Sulphur Dioxide, are given off from transport, burning of fossil fuels, forest, fires, biological decay and volcanic eruptions. These rise into the atmosphere where they mix with water vapour to producing clouds and acid rain.
Both of these processes are shown in the diagram below:
A problem is that it is not only the producers of acid rain, who suffer from its consequences, especially when gases are found in the upper troposphere. As the prevailing wind direction for the UK is from the Southwest much of the acid rain we produce is carried away over the North Sea to Scandinavian Countries. If precipitation is in a form other than rain, pollution may not be immediately apparent as it will be held in snow/ice.
The table below outlines the main consequences of acid rain:
|Vegetation/Soil||Much initial concern focused on the death of coniferous trees in Scandinavia. As rain falls to the ground (or snow melts) toxins are released into the soil. Tree roots become damaged, and soil deficient in nutrients. The ability of vegetation to withstand bacteria and disease is vastly reduced.|
|Lakes||Acid rain has led to acid levels in lakes in Scandinavia being especially high. The number of fish in lakes in Norway has fallen dramatically since the 1950's. A change in the balance of salt intake results in the gills of fish becoming clogged, thus reducing their ability to take in oxygen.|
|Water Supply||Aluminium is washed into lakes and reservoirs from the surrounding land, often leading to algae bloom which again upsets the ecosystem and kills fish. Some evidence suggests a link between increased levels of aluminium in water and Alzheimer's disease.|
|Buildings||Acid deposition encourages more rapid weathering of buildings via carbonation.|
The approaches can look at reducing the emissions that lead to acid rain, or take measures that reduce its impact.
|International, Political||Establish International agreements to reduce Gas emissions which lead to acid rain, for example, 1988 UK agreed Large Combustion Plants Directive with other EU countries, setting out limits for emission of sulphur dioxide and nitrogen dioxide.|
|Technological approaches||Addition of lime to lakes, reducing their acidity. Removal of sulphur from coal and oil prior to burning. Use of low sulphur coal in power stations. Adopting 'greener energy sources'|
It is important to see that most work on tackling problems is limited to MEDC's where they have the fiancees available. The problem is growing in LEDC's.