Acid Rain - Causes, Effects and Solutions

Acid Rain

Formation, Aftermath, Countermeasures

1. Acid Rain - What is it?

According to a German Webpage,..

The phenomenon of acid rain has been known since ancient times: for example, it was observed in ancient Rome where trees died near Galena metal processing factories.


But it was not until the late 1950s / early 1960s, that the spread of acid rain in Europe has been observed. 

Rain is determined acid or sour, when the pH-level of the water is under 5.6. Now when you look at a pH-scale you should think that it should already be acidic having a pH-level that is under 7.0 , but in fact it is proven that "normal" rain is already acid. That is because of the reaction between rainwater and carbon dioxide. The carbon dioxide (produced by our emissions) reacts with water to carbonic acid : CO2 + H2O H2CO3

2. The Chemical Aspect

Due to the facts above, CO2 emissions cannot be the cause of acid rain, so responsible for a pH-level less than 5.6 have to be other particles.

The pollutants, that cause the water to get acidic are nitric oxide/nitrogen monoxide ; nitrogen dioxide and sulphur dioxide . These Chemicals are also present in nature (soil,volcanoes,etc.) , but the majority is produced by us, humans, in everyday situations like traffic, households and especially by burning fossil fuels in power stations.

Nitrogen oxides :  2 NO2+ H2O          HNO2  + HNO3

2 HNO2  + O2           2 HNO3

Sulphur oxides : SO2  + H2O            H2SO3

Easy explanation of the process

All these processes take place in the troposphere, that means, from the lowest atmospheric layer up to an altitude of 10-12 km.

3. Effects

Acid rain affects soil, water, plants and buildings. When acid rain meets basic ground, eg Calcareous soil, the acid can be neutralized immediately. The, in the soil present, bicarbonate anions react with the protons of the acid.

In slightly acidic soils a so-called cation exchange takes place: Certain metal ions such as Calcium and magnesium ions replace the protons of the acid: they are captured by the sulfate ion, and washed out with this from the ground. The hydrogen ions remain in the soil and are neutralized by bicarbonate ions.

However, the buffering capacity of the soil can eventually be exhausted; then the acid is passed on to the groundwater, streams, rivers and lakes. If the water contains no basic ions that can neutralize the acid, this water becomes acidic. Results in the receipt of vegetation, changes in life forms, or even the complete extinction of these waters.

Acid rain can wash out poisonous minerals and heavy metal ions from rocks in the soil. For example, aluminum, cadmium or lead cations. This can also pass through the soil into water. But they can also be absorbed by plants as nutrients and thus poison the plants.

Acid rain, as just described, washes the nutrients out and the plants suffer in these areas of a nutrient deficient. In addition, acid rain also acts directly on the plants through the leaves. Overall consequences are that plants are susceptible to diseases, flower colours are bleached and it can even cause the death of the plants.

Also buildings are not spared from the harmful influence of acid rain

Acid rain is particularly aggressive to sand and limestone. This is associated with a crystal magnification, so the building starts crumbling.

CaCO3 + H2SO4               CO2  + H2O + CaSO4

An example of how expensive the restoration of such damaged buildings can be: For Westminster Abbey in London, about 10 million British pounds were spent until 1990 to eliminate the damage of acid rain.

5. Remedies

The first remedy to stop the effects of acid rain, was that the chimneys of factories / plants were built higher- with the result that the pollutants were equally disposed.

Then they began to install filter systems in factories / plants. In Germany, a decree to reduce emissions of sulfur dioxide and nitrogen oxides from power plants was adopted in 1983. With success. Pollutant emissions from large industry were severely restricted. In order to reduce the damage to plants and soil, the forests are limed in some places.

However, the traffic and a very large number of households emit pollutants. Although now they start to install catalysts in vehicles. Nevertheless, the use of fossil fuels in engines, household, power stations should be restricted. One measure would be here to expand public transportation networks and other  renewable energies to promote.