Acidic particles and gases can also deposit from the atmosphere in the absence of moisture as dry deposition. The acidic particles and gases may deposit to surfaces water bodies, vegetation, buildings quickly or may react during atmospheric transport to form larger particles that can be harmful to human health.
When the accumulated acids are washed off a surface by the next rain, this acidic water flows over and through the ground, and can harm plants and wildlife, such as insects and fish. The amount of acidity in the atmosphere that deposits to earth through dry deposition depends on the amount of rainfall an area receives.
For example, in desert areas the ratio of dry to wet deposition is higher than an area that receives several inches of rain each year. Unlike wet deposition, dry deposition is difficult and expensive to measure. When acid deposition is washed into lakes and streams, it can cause some to turn acidic.
Assume that a very large quantity of magnesium sulfite, relative to the amount of water, is produced. Acid rain triggers a number of inorganic and biochemical reactions with deleterious environmental effects, making this a growing environmental problem worldwide. Marble and limestone have long been preferred materials for constructing durable buildings and monuments. Marble and limestone both consist of calcium carbonate CaCO 3 , and differ only in their crystalline structure.
Limestone consists of smaller crystals and is more porous than marble; it is used more extensively in buildings. Marble, with its larger crystals and smaller pores, can attain a high polish and is thus preferred for monuments and statues.
Although these are recognized as highly durable materials, buildings and outdoor monuments made of marble and limestone are now being gradually eroded away by acid rain. How does this happen? A chemical reaction Equation 9 between calcium carbonate and sulfuric acid the primary acid component of acid rain results in the dissolution of CaCO 3 to give aqueous ions, which in turn are washed away in the water flow.
This process occurs at the surface of the buildings or monuments; thus acid rain can easily destroy the details on relief work e. The degree of damage is determined not only by the acidity of the rainwater, but also by the amount of water flow that a region of the surface receives. Regions exposed to direct downpour of acid rain are highly susceptible to erosion, but regions that are more sheltered from water flow such as under eaves and overhangs of limestone buildings are much better preserved.
The marble columns of the emperors Marcus Aurelius and Trajan, in Rome, provide a striking example: large volumes of rainwater flow directly over certain parts of the columns, which have been badly eroded; other parts are protected by wind effects from this flow, and are in extremely good condition even after nearly years!
Even those parts of marble and limestone structures that are not themselves eroded can be damaged by this process Equation 9. When the water dries, it leaves behind the ions that were dissolved in it.
When a solution containing calcium and sulfate ions dries, the ions crystallize as CaSO 4 l 2H 2 O, which is gypsum. Gypsum is soluble in water, so it is washed away from areas that receive a heavy flow of rain. However, gypsum accumulates in the same sheltered areas that are protected from erosion, and attracts dust, carbon particles, dry-ash, and other dark pollutants.
This results in blackening of the surfaces where gypsum accumulates. An even more serious situation arises when water containing calcium and sulfate ions penetrates the stone's pores. When the water dries, the ions form salt crystals within the pore system.
Dry acid rain is especially common in areas which receive a low rainfall, such as deserts[sc:3]. When acid rain reaches the earth, it has many ecological effects. Not only does it affect the area where it falls, but it flows across the land, polluting waterways, lakes, and even groundwater. Most ecosystems are affected in some way when touched by acid rain, but the greatest impact occurs in freshwater aquatic environments[sc:4]. It also can have a noticeable effect on woodlands, alpine ecosystems, and in places where the soil is naturally acidic.
A range of human infrastructure is damaged every year as acid rain erodes and dissolves[sc:5]. Since acid rain is caused by human pollution , the only way to stop it from happening and reduce its effects is to stop polluting. Everyone can play a role: conserving electricity will mean that less fossil fuels need to be burnt, meaning that less pollutants will be emitted.
If you regularly drive places, you could consider walking or cycling, since motor vehicles are the second major source of the pollutants causing acid rain[sc:6]. These reactions usually neutralize natural acids. However, if precipitation becomes too acidic, these materials may not be able to neutralize all of the acids. Over time, these neutralizing materials can be washed away by acid rain.
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