Acid Rain

        Acid rain is basically defined as any kind of precipitation that has a pH-level lower than 5.5 (≤ 5.5), meaning that is more acidic than the usual precipitation. Precipitation is by nature already slightly acidic, because of the natural carbon dioxide in our atmosphere gets dissolved into the rain. The aqueous solution of CO2 is than Carbonic acid, H2CO3: Co2 + H2O ↔ H2CO3. H2CO3 is as an aqueous solution not stable, and thus it ionizes into water, forming the ions H3O+ and HCO3-: CO2 + H2O ↔ HCO3- + H3O+.When the precipitation, which can be for example rain, snow or fog, has a pH-level lower than 5.5 it is considered acidic and is due to human output of nitrogen and sulphur compounds. They both go through many complex steps until they become sulphuric acid (H2SO4) and Nitric acid (HNO3), which one would find in Acid rain. sulphuric acid originates from its compound. The sulphur dioxide reacts with Oxygen to make sulphur trioxide: 2SO2 +O2 ->  2SO3. Than the sulphur trioxide reacts with water to make sulphuric acid: SO+ H2O -> H2SO4. Nitric acid is made when nitrogen dioxide reacts with water, which also makes nitrous acid. The pH-level of an acidic rain cloud can reach up to 2.6. In areas with a lot of industry the pH-level will be about 4; in Los Angeles the most acidic precipitation had a pH-level of 3. However, in some parts of the world, such as north Australia, natural emissions of the vegetation can make the pH sink to 4.4.  

The cause of nitrogen oxide, sulphur dioxide, ammoniac and other compounds being in our rain is the burning of fossil fuels. Humans release about 3.5 million tons of SO2 into our atmosphere a year. Especially when coal and petroleum is burned, a lot of SO2 –released. Power plants, cars, ships und planes are all sources of NO and SO2. The main natural  contributor to acid rain are volcanoes.  They release about 230 billion metric tons (230 teragrams) of carbon dioxide a year. How much percent of the emissions caused by humans and how is caused by nature depends on the area. In cities up to 90% of the emissions can be caused by humans, but in other regions it could be 50% to 50%.The acid rain is global problem and has many different affects all around the world. The damage to buildings is only one of them. The acidic rain gets into the stone of the building and starts a chemical reaction, in which the stone starts to decompose. This makes the buildings more fragile to water, frost and other things that the stone would normally be able to withstand. The acid rain has destroyed many precious memorials that were made out of natural stone. The acid rain destroys the whole outer layer of the stone, which will make the fine carvings into the stone vanish. Limestone and marble are especially affected by acid rain, because they consist out of calcium carbonate. The calcium carbonate reacts with the dissolved acids than form plaster, which gets flakes after every new rain fall: CaCO3 + H2SO4 → CaSO4 + CO2 + H2O.

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The restoration of damaged building takes a lot of time and money. For example the restoration of the Westminster Abbey in London cost up to 10 million pounds. They had to peal of the damaged outer layer of the stone and than treat the new healthy outer layer of stone with a special fluid that is supposed to stop the acid rain from getting on into the stone again. (1,3, 4, 8) 

        In Scandinavia the acid rain has been destroying the nature for decades. Many lakes are acidic, meaning that they have an unusually low pH-level caused by the acid ...

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