Acid Rain

We all know about the rain. But what is an acid rain? Why do we need to know about acid rain? The rain was always acidic but in 1852 English chemist Robert Angus Smith described the relationship between the acidity in the rain and air pollution. But the so called phenomenon was closely observed in 1960s only after it had become an major environmental issue.

An acid rain is when the acidity of the normal rain gets much higher than the normal value. Naturally the rain is acidic due to the compounds in the air. There are gasses such as CO₂(carbon dioxide) , SO₂( sulfur dioxide) and NO₂ (nitrogen dioxide) in the atmosphere. When it rains the these gasses make H₂CO₃ (carbonic acid), H₂SO₄ (sulfuric acid) and HNO₃ (nitric acid) and relatively.

That is why you should never drink rain water directly

After the industrial revolution many industries that used human power had converted into the machines. Specially in the 19^th century many factories were opened and most of them were run by machines that used coal as fuel. Soon crude oil and its variations (Diesel and Petrol) were introduced. They were specially used in motor vehicles. Coal was still in use to generate electricity. But somehow the amount of coal and crude oil that would be used in factories and day today work increased with the time.

Photo by **Kamil Szerlag** from **Pexels**

Both coal and crude oil are mostly hydrocarbons but oxygen sulfur can be found. To use the coal or crude oil derivatives such as diesel or petrol, they are burned. So the sulfur in the compound turns into sulfur dioxide. In the previous decades the amount of sulfur found in the diesel were very high. So without any knowledge the air pollution was increased over time.

When burning these coal or oil sulfur in them would convert into SO₂ and it is released into the atmosphere in high amounts. So the amount of sulfuric acid that forms in the atmosphere is also increased. That means the acidity of the rain is increased.

Not only these but there are other human activities that cause acid rain such as animal farms.

The Effect of the Acid Rain

What happens when the acidity is increased?

Acid rains have adverse effect on forests. We do not hold umbrellas over trees so they are exposed to the rain. Specially the forests in the high altitudes, which are most of the time covered in clouds or fog. Clouds or fogs are more acidic than the rain. Not only the forests anything that is not covered can have bad effects due to acid rain. Specially the water bodies such as reservoirs and the organisms living in them. Even the buildings get their life span shortened.

Buildings and statues that of importance, which are thousands of years old could actually completely be destroyed as the time goes on. Historic monuments that are made of limestone or marble contain a large amount of calcium carbonate (CaCO₃), which reacts with the acids in the rain.

P^H is a scale used to measure the acidity or alkalinity of a compound.

When the acidity in a lake increases the P^H level of the lake decreases. When the P^H level is decreased under 5 then most fish eggs would not hatch. Also the acidic water can kill the fishes too. Not only the fishes the whole biodiversity in the lake decreases as the acidity increases. Most aquatic organisms prefer P^H level 6.5-8. And when it changes they just die.

On a global scale acid rains have less effect on the ocean. But the shallow waters might change the acidity and the biodiversity could decrease over the time. Specially the corals in the shallow water areas tends to die completely in a very short time period.

The microbial organisms in the soil cannot tolerate the acidic environment. When the acidity of the soil increases it also effects the trees as well. Trees will eventually die due to the high acidic levels in the absorbed water which would change the P^H in the plant with the time. The soil P^H level that is optimum to the plants to grow varies from 5.5-7. When the P^H level in the soil decrease then the availability of the nutrients that a plant need to grow will decrease causing the plant to die even before it starts to grow.

In what parts the acid rains have been reported?

The Black Triangle which covers the areas in Germany, Poland and Czech Republic has reported heavy acid rains during the 1970s. Within this area some forests have completely destroyed. Some parts of the eastern United States have reported the most acidic rains due to emissions from Midwestern coal-burning power plants. The situation was o bad that still about 90% of the freshwater streams are still acidic. After the 2000 the acid rains have been reported in India and China due to the rapid industrialization.

The coal burning factories in the eastern Europe were put under strict rules and regulations in the Geneva Convention held in 1979 in order to reduce the acidity of the rain. In 1970 the Clean Air Act was introduced in US as a result of the devastation situation. Because of these acts and regulations the severity of the acid rains have decreased over the time but not completely gone.

There are natural phenomena such as volcanic eruption and lightning that release SO₂ and NO₂ into the atmosphere. They are beyond control but what we could do is minimize the emission of such gases into the air because of the human activities or we can find an alternative method of doing things. Because soon enough we all might have to face the acid rain and its consequences.

So far the rain does not have any bad effect towards the humans because the acid in the rain is too diluted but who knows if we did not pay attention then one day we will not be able to enjoy the rain. So let’s be extra careful about what we throw into the environment.