Name “ acid rain ” was for the first time used by Robert Angus Smith in 1870
Elle describes since all the acid forms of precipitations meteoritic (Pluie, Neige, Brume S and Brouillard S, Grêle, Neige, Rosée, Smog S and Aérosol S, etc), which even degrade destroy ecosystem S and/or certain fragile old buildings.

The Acidité of these repercussions has to some extent of the natural origins (proximity of sulfur volcanic emissions) but especially anthropic (Industrie, Thermo plants, Chauffage, Transport S, etc).

The normal rains have a pH of 5,6. one speaks about acid rains when their pH is lower than 5,6. " rains sèches" (solid repercussions of aerosols) being able to be even more dangerous and to produce strong acids while combining for example with the dew. The acidification of the air has consequences mediatized on the forest, but it affects also our health, the buildings and perhaps of many animal species.

The acid rains constitute the phenomenon resulting from air pollution by sulfur oxides (SO2) produced by the use of fossile fuels rich in sulfur as of the nitrogen oxides (Nox) which are formed during any combustion of the atmosphere. Of another products such as carbon dioxide (CO2) and the acids hydrofluoric act much less on the formation of the acid rains. These gases are primarily due to the fossil matter combustion by the Man, but also to the volcanic eruptions, the lightning, the biological decomposition, the oceans, forest fires… With regard to, the human action on our environment, the factories, the heating and the motor vehicle traffic are the main causes.

Mechanisms of formation

Once introduced into the atmosphere, the acid vapors travel to the liking of the airstreams sometimes on thousands of kilometers. They react with water to form nitric Acid , sulphuric Acid and carbon Dioxide . Fogs and fogs, and the dewdrops can absorb some.

Geographical distribution

The principal production zones of pollutants initially were the fields and industrial of the northern hemisphere, of which the the Ruhr, the Lombardy, old French and English mining countries. Carried by the dominant winds, a good part of the acid rains of Scandinavia result from the pollutants accumulated by the masses from air coming from the sea when they flew over the England, the France and the Germany. In China, the areas of South-east are particularly touched by the acid rains; the emissions of oxides of nitrogen and sulfur dioxide are 8 to 9 times higher in China than in the developed countries. The acid rains also touch Japan. China is the first transmitter of oxide of nitrogen and sulfur dioxide of the world.

Consequences of the acid rains

The acidity of the lakes prevents the normal development of the species and the plants which they shelter. The flora is weakened, resists less better the diseases and the rigorous winters. The acidified grounds poison the trees, weaken them, and can kill them in the serious cases. The base of the food chain is also touched, as all the animals which depend on it. The watery birds and mammals are touched in particular.

Effects on the flora

The trees are not directly destroyed, but the nutritive elements contained in the ground are dissolved and carried by the rains. The acid rains kill also the micro-organisms, which leaves a dirty ground, without new produced nutritive elements. The sheets are damaged (black task or chestnut), and cannot practice the Photosynthèse more. Defoliation deprives the tree of sugar. Certain chemical substances can also be slowly released in the ground and poison the trees. Their roots, trying to survive in a corroded ground, can also be directly attacked by the acid. All that led to a reduction in the resistance of the flora, and thus to an increase in mortality at the time of epidemic, difficult climatic conditions, etc

The resistant sheets of the Résineux are burned in the most polluted zones. The mountainous forests, bathing in the fog and the clouds, receive even more acid than the forests of plain, these forms of pollution being besides rather often more acid than the dry deposits.

Impacts on the buildings

The acidity of the rains can accelerate the natural erosion of many materials, in particular limestones, as well as the corrosion of certain metals (lead which holds the stained glasses). The stones limestones tender, some Marble S and Tuffeau X are most sensitive there. That was initially noticed in Europe on many cathedrals whose stone quickly degraded end of the 19th century at the years 1990, for example in England for the cathedrals such as York Minster and the Abbaye of Westminster. Many other buildings and built elements of the world heritage were tackled these last years by the acidity of the air, of which for example Taj Mahal in India and the Colisée in Rome, especially in the industrial areas.

Effects on the animal terrestrial life

The effects on the terrestrial animal life plausible and probable, but are badly determined fault of studies. Certain Scandinavian lakes in years 1980-1990 had become so acid that the fish and shellfish disappeared there. Some were the subject of lime discharge to plug their pH. The effects can be direct by attack of the skin, of the cuticules, mucous membranes and bodies respiratory by the acid pollutants of the air, or by external contact or intern with polluted water. (As one sees it in the film microcosmos, of many insects the dewdrops drink). Indirect, differed effects and cascades about it on the ecosystems and the network trophic exists, obvious for example when whole populations of trees die.

The chlorides, fluorides and heavy metals can better circulate and accumulate in the ground acidified on levels which are toxic for the invertebrates which live in the ground. The species sensitive to metals are substituted by those which are more tolerant. Thus, the species with the soft bodies such as the ground worms and the nematodes seem to be more easily affected by the concentrations raised out of metals (except enchytraéidés which resist it better).

In addition, the invertebrates play a big role in the decomposition of the refuses on the ground of the forests. However, while the refuses accumulate there, the release of the biogenic salts is delayed and the availability of the nutritive elements to the plants is reduced. The herbivores are finally affected when the quantity or the quality of their food provisioning decreases.

Moreover, although the birds and the mammals are not directly affected by the acidification of water, they are there indirectly by changes in the quality and the quantity of their food resources. In Scotland, for example, the otters are rather rare around the brooks and of the acid rivers because their principal provisioning, the fish, is reduced.

Moreover, calcium is an essential component for the mammals and the birds and an adequate dietetic provisioning their is crucial during the reproduction. Indeed, the birds need calcium for the good formation of the egg shells and for the skeletal growth their offspring, as well as the mammals, which need some for the skeletal development their fetuses.

Lastly, much of invertebrate species, which contain high calcium concentrations, such as molluscs and shellfish, are very sensitive to the level of pH and are among the first to disappear during the acidification of the marshy grounds.

Answers

The acid rains are a “total pollution” and constitute for this reason an international problem. In 1988, a treaty (Convention on transborder pollution in the long run; Convention one Length-Arranges Transboundary Pollution) limited the nitrogen oxide emissions to their level of 1987.

In Europe, the Economic commission is concerned with question, with European standards and main roads which allowed a strong reduction in the acid pollution of the air of years 1980 the years 2000.

The level of released pollutants is adapted to the critical load (maximum level of pollutants being able to be tolerated) of the medium, even less. Filters or purifiers of air are installed on the polluting factory chimneies. The catalytic pot is obligatory, with results discussed for certain parameters.

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