The air pollution that human beings create by burning fossil fuels returns to the earth in the form of acid rain. Acid rain is essentially a product of aggressive industrialisation, mostly in developed countries. The frequency, intensity and spread of industrialisation are leading to disastrous consequences. Acid rain is caused both by natural as well as man-made disasters.

What is Acid Rain?

Any precipitation or deposition having a pH lower than 5.6 as a result of contact with airborne particles that may harm the flora and fauna if it falls, is called acid rain.

The phrase acid rain was first used in 1852 by Scottish chemist Robert Angus Smith during his examination of rainwater chemistry near industrial cities in England and Scotland. The phenomenon became an important part of his book Air and Rain: The Beginnings of Chemical Climatology (1872).

However, it was not until the late 1960s and early 1970s that acid rain was comprehended as a regional environmental issue affecting large areas of Western Europe and eastern North America. Acid rain also occurs in Asia and parts of Africa, South America, and Australia. As a global environmental issue, it is frequently overshadowed by climate change.

Acid rain is also caused naturally by lightning, volcanic eruptions, and by forest fires.

Formation of acid Rain

When rain falls across polluted air, containing several acid-forming substances in higher concentrations, acid rain is formed.
Among the chemicals frequently occurring in polluted air at higher-than-normal concentrations are sulphur oxide and nitrogen oxide. In some cases, hydrochloric acid vapour and mists of phosphoric acid and other acids may also be present. These gases dissolve in the falling rain, making it more acidic. As now as we see they pollute snow and fog as well.

Sources of Acid Rain

According to United Nations Environment and health studies, Acid Rain has both natural as well as man-made sources. But the main source of acid rain is emissions resulting from the combustion of fossil fuels by automobiles, factories, and power plants.
A large portion of sulphur and nitrogen oxides are produced from the burning of fossil fuels like coal and petroleum.

Impact of acid Rain

1. Impact on buildings and monuments
Acid rain is corrosive. It has a corroding effect on buildings, monuments, and other metal and rock structures. In this corrosion, sulphur dioxide plays the main role. The structures containing limestone or marble rocks are easily corroded by acid and it is called Marble Cancer.

The case study of Marble Cancer on Taj Mahal:

Marble cancer is the phenomenon occurring in the Taj Mahal. Polluted fumes coming from the Mathura refinery were two times the normal level in Agra. This had a corrosive effect on the marble of the Taj Mahal and thus this phenomenon has now been named the cancer of marble.
The Supreme Court in 1994 ordered the closure of the oil refineries and other industries implicated in corroding the Taj Mahal with their acid emissions.

2. Impact on human health

Acid rain is related to several human hazards. These are irritation in the eyes, reduced visibility and disorders in the respiratory system. Respiratory disorders include pulmonary emphysema and bronchitis. It sometimes leads to lung cancer.

But according to the US Environmental Protection Agency, “Swimming in an acidic lake or walking in an acidic puddle is no more harmful to people than swimming or walking in clean water.” While acid rain cannot burn your skin, it is linked to several indirect health effects.

3. Impact on trees
Soil can undergo chemical changes and release toxic metals in the forms that can be absorbed by plants. Acid rain also causes deficiency of vital nutrients in soil making it less fertile degradation of the plant communities by acid rain can include damage to leaves, loss of productivity and sometimes loss of sensitive plants.

In the 1970s and ’80s, forested areas in central Europe, southern Scandinavia, and eastern North America showed alarming signs of forest dieback and tree mortality. A 1993 survey in 27 European countries revealed air pollution damage or mortality in 23 per cent of the 1,00,000 trees surveyed. The dieback was likely the result of many factors, including acid rain deposition.

4. Impact on lakes and rivers:

Several direct and indirect effects of acid rain on lakes and rivers have been recognised. The acid build-up in lakes and rivers disrupts the reproductive processes of aquatic animals. Though the effect of acid rain is mostly seen in aquatic organisms, wildlife is also being affected through the food chain.

According to a New York research on acid rain, effects on water bodies shows that the number of fish species drops from five lakes with a pH of 6.0 to 7.0 to only one in lakes with a pH of 4.0 to 4.5. Other organisms are also negatively affected. Because of these acidified water bodies, there is a huge loss of different plant and animal species.

Acid Rain in developing countries

Although acid rain was first noticed in developed countries, examples of acid rain and its harmful effects are beginning to become common in developing countries also. It is a significant problem in the US, Canada, Germany, Scotland, Brazil, India, China, etc. Industrialised areas of Indonesia, Malaysia, the Philippines and Thailand will also experience heavy acid rain deposition in a few years.

In India, the first report of acid rain came from Bombay in 1974. Lowering of soil pH is reported in some parts of India like the northeast, coastal regions of Karnataka, Kerala, Odisha and in Bihar and West Bengal.

The Institute of Chemical Technology, Hyderabad points to a concern about acid rain over oceans. In winter, when the wind blows from land to the oceans in South Asia, it carries effluents from India, China, and Japan. The alkaline dust suspension is heavy and not carried that far. So, the rains in the Indian Ocean and the Arabian Sea and the Bay of Bengal have become acidic.

Control of Acid Rain

The first and foremost measure to control acid rains is control over pollution, mainly air pollution.

Several emission-reducing equipment like scrubbers, electrostatic precipitators, etc. can be used for reducing air pollution.
The practice of adding a neutralising agent to the acidified water to increase the pH is one of the important measures to control the acid rain.

Controlling acid rain requires local government and international participation. Laws should be formulated by the government to regulate emissions.

Increasing public awareness about the problem is the first step toward finding some solutions to the problem of acid rain.