Sangeetha Pulapaka

Since the beginning of civilization, human beings have used various natural resources for their benefit. To make their life easier, they have produced facilities that use many of the Earth’s energy resources. On one side this kind of development makes our lives easier, but on the other hand it results into pollution by release harmful substance into environment. Acid rain is the most serious environmental problems emerged due to air pollution. Acid rain is particularly damaging to lakes, streams and forests, and the plants and animals that live in these ecosystems. Rain is one of the most essential ingredients for human and animal life. The water provided by rain allows all life on earth to survive. Although rain is naturally acidic, it is being increasingly acidified by pollution from homes, factories, power stations and cars. The term used to describe this problem is “acid rain”. Acid rain hasn’t just occurred in the last twenty to thirty years. This was over 100 years ago.For years ever since most of the world has been industrialized, the effects of pollution have plagued nations alike. Acid rain is one of the largest contributors to this industrialized form of pollution. 

Causes of acidification:

Sulphur dioxide (SO2) and oxides of nitrogen and ozone to some extent are the primary causes of acid rain. These constituents interact with reactants present in the atmosphere and result into acid deposition. The natural sources of sulphur pollutants are oceans and to much smaller extent from volcanic eruptions. The man-made sources of SO2 emissions are the burning of coal and petroleum and various industrial processes . Other sources include the smelting of iron and other metallic (Zn and Cu) ores, manufacture of sulphuric acids, and the operation of acid concentrators in the petroleum industry.The levels of NOx are small in comparison to SO2, but its contribution in the production of acid rain is increasing. The degree of acidity is measured by pH value, it is shorthand version of potential hydrogen. The pH of normal rainwater is also acidic; the reason is that water reacts to a slight extent with atmospheric carbon dioxide (CO_{2}) to produce carbonic acid.] CO_{2} + H_{2}O\rightarrow H_{2} CO_{3}(carbonic acid)


Small amount of nitric acid is also responsible for the acidity of normal rainwater, which is produced by the oxidation of nitrogen in presence of water during lightening storms.

2 N_{2 }+ 5O_{2} + 2H_{2}O 4 HNO_{3} (nitric acid) 

Chemical reactions during acid rain formation:

The chemical reaction that results in the formation of acid rain involves the interaction of SO2, NOx and O3. When the pollutants are vented into the atmosphere by tall smoke stakes, molecules of SO2 and NOx are caught up in the prevailing winds, where they interact in the presence of sunlight with vapours to form sulphuric acid and nitric acid mists. These acids remain in vapour state under the prevalent high temperature conditions. When the temperature falls, condensation takes the form of aerosol droplets, which owing to the presence of unburnt carbon particles will be black, acidic and carbonaceous in nature. 

Peroxy radicals react with formaldehyde, acetaldehyde and form formic and acetic acids and some other organic acids, contributing to 5-20% acidity in total acid rain load.