HOW ACID RAIN IS FORMED

             Acid Rain is a serious problem with disastrous effects. Every day this problem increases. Many believe that this issue is too small to deal with, but if the acid rain problem is not met with head on, the effects on people, plants, animals, and the economy will only worsen. In the following paragraphs you will learn what acid rain is, the effects it has on human life, animals, the economy, the economic costs, and what is being done to help to stop this problem. This topic is very important because acid rain effects everyone everywhere all over the world.

What is acid rain?

"Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.

Wet acid deposition refers to acid, fog and snow. It is the combination of two chemicals released into the atmosphere. These chemicals are sulphur dioxide (SO2) and nitrogen oxides (Nox). Natural sources such as volcanoes, sea spray, rotting vegetation and plankton are all contributors to acid rain, but burning fossil fuels, such as coal and oil which are referred to as dry emissions are largely to blame for more than half of the emissions into the world. Nationally, one hundred and twenty tons of sulfur dioxide and nitrogen dioxide are emitted into the air each day.

Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone.

A) How is acid rain formed?

When the sulfur dioxide reaches the atmosphere, it oxidizes to first form a sulfate ion. It then becomes sulfuric acid when it joins with hydrogen atoms in the air and falls back down to earth, usually in the form of rain, snow, or fog. Oxidation occurs the most in clouds and heavily polluted air where other compounds such as ammonia and ozone help to catalyze the reaction, converting more sulphur dioxide to sulphuric acid.

Nitric oxide and nitric dioxide are also components of acid rain. Its sources are mainly from electric power stations and exhaust fumes. Like sulphur dioxide, these nitrogen dioxides also rise into the air and are oxidized in the clouds to form nitric acid.

           

When the chemicals aren't absorbed into clouds, they can drift for miles and fall to the ground, resulting in Acid Deposition, or dry deposition. The generation of sulfur  dioxide in USA due to non environmental reason is depicted in under mentioned figure.

B) How Acidity of rain is measured?

Acid rain is measured using a scale called "pH." (potential Hydrogen). The pH scale measures how acidic a substance is. A pH less than 7 is acidic, the smaller the number on the pH scale, the more acidic the substance is.

           

Rain measuring between 0 and 5 on the pH scale is acidic and therefore called "acid rain".  Clean rain usually has a pH of 5.6. It is slightly acidic because of carbon dioxide which is naturally present in the atmosphere.