Acid Rain - Definition, Effects, Disposition, Causes, and Prevention

Acid Rain is rainfall or any precipitation mixed with elements and gases that make them more acidic than normal. Acid rain effects include soil degradation, infrastructure corrosion, vegetation damage, health risks, etc. Acid rain causes acidification of the earth and surface water acid rain has detrimental effects on plants and animals along with the whole ecosystem and poses a serious threat to living beings. In this article, we will study acid rain definition, effects, causes, and prevention in detail.

What is Acid Rain?

Acid Rain Definition: Acid rain or acid deposition can be defined as any form of precipitation with acidic components (pH ≤ 5.2) such as sulfuric acid or nitric acid which includes rain, snow, sleet, hail, fog, and even dust that falls from the sky.

Acid rain or acid deposition is one of the serious consequences of air pollution. The word ‘Acid Rain’ was first coined by Scottish chemist Robert Angus Smith in 1852 during his investigation of the chemical properties of rainwater near industrial cities in England and Scotland. Acid deposition can be of two types, wet deposition and dry deposition. Wet depositions include rain, snow, fog, or mist with high amounts of sulfuric and nitric acid whereas dry depositions are dust and smoke that contain high amounts of sulfur dioxide and nitrogen oxides that settle down on the ground, or onto buildings, cars, and vegetation.

The emissions from industries, motor vehicles, heating boilers, and combustion of fossil fuel are responsible for developing acid rain. These emissions contain gases such as nitrogen oxides, sulfur dioxide, and sulfur trioxide, which combine with water and transform it into various acids like sulfurous acid, nitric acid, and sulfuric acid. This process can also occur naturally through volcanic eruptions.

Acid Rain Diagram

The labelled diagram of acid rain is given below:

Acid Rain Causes

Acid rain casues includes when emissions containing sulfur dioxide (SO₂) and nitrogen oxides (NO₂) react with water, oxygen, and other chemicals to form sulfuric and nitric acids in the atmosphere. These acids then mix with water and other materials and fall on the ground in the form of acid rain.

SO₂ + H₂O → H₂SO₄ ←→ H⁺ + HSO₄ ←→ 2H⁺ + SO₄^2-

NO₂ + H₂O → HNO₃ ←→ H⁺ + (NO₃)^-

Acid Rain can be caused by natural processes or man-made activities:

Natural Causes

Natural processes like volcanic eruptions produce sulfuric acid (H₂SO₄), nitric acid (HNO₃), and hydrochloric acid (HCl), and lightening and wildfires convert atmospheric molecular nitrogen (N₂) into nitrogen oxides which contribute to the formation of acid rain. Other natural causes include earthquakes, decomposing vegetation, and some microbial processes that produce sulfur dioxide and nitrogen oxides and release them into the atmosphere. However, the extent of acidification by any natural source is small and in most cases, it lowers the pH of precipitation not more than 5.2.

Man-Made Causes

The main man-made source includes the combustion of fossil fuel by power-production companies and industries which release sulfur into the air that combines with oxygen to form sulfur dioxide (SO2), exhausts from motor vehicles cause the formation and emission of nitrogen oxides into the air. Intensive livestock farming releases ammonia from the decomposition of organic matter which also contributes to the formation of acid rain. Ore smelting, coal-fired power generators, and the processing of natural gas, manufacturing industries, and oil refineries are the main sources of sulfur dioxide emission.

Types of Acid Rain

Acid rain can be wet or dry deposition:

Wet Deposition

When the acid rain contains water, it is called wet deposition. In wet deposition, the sulfuric and nitric acids form in the atmosphere and mix with rain, snow, fog, or hail and fall on the ground as acid rain.

Dry Deposition

When acid rain forms with dust or gases, it is called dry deposition. The acidic particles and gases may deposit on the surfaces of water bodies, vegetation, or buildings. These particles can also react during transport into the atmosphere and form larger particles very harmful to living beings. When the accumulated acidic particles are washed off the surface by the next rain, the rainwater becomes acidic and flows over the ground. This is very dangerous for wildlife and aquatic animals.

Acid Rain Effects

The pH of rain or any precipitation decreases as it combines with sulfuric acid and nitric acid. Thus, when it falls onto the ground or water bodies, it changes the chemical properties of the surface which has a dangerous impact on the ecosystems including all animals and plants. This acidification phenomenon of the environment has several adverse effects which are as follows:

• Ecological Effects: An ecosystem is a community of plants and animals along with their environment including the air, water, and soil which are interconnected with each other. If one part of an ecosystem i.e. one species of animal or plant or soil or water is affected, it will have an impact on others in the ecosystem.
• Effects on Fish and Wildlife: The adverse effects of acid rain are mostly observed in aquatic environments which include streams, lakes, and marshes. Acidic rainwater flows through the soil and leaches aluminum from soil clay particles into the water bodies which is harmful for aquatic animals including fishes and other wildlife.

👁 Effects-of-Acid-Rain-

• Effects on Plants: The areas affected by acid rain are found to have dead or dying trees. Acid rain removes minerals and nutrients from the soil which are essential for the growth of plants.
• Episodic Acidification: Melting acidic snow and heavy acidic rain can result in episodic acidification of lakes and waterbodies which normally do not have a high level of acidity.
• Nitrogen Pollution: Acid rain contains nitrogen which badly affects some ecosystems. For example, nitrogen in Acid Rain may cause nitrogen pollution in coastal waters which is partially responsible for declining fish and shellfish populations in those areas.
• Effects on Human Health: Acid rain effects on human does not directly affect health. However, the gases (SO₂ and NOx) and particles (sulfates and nitrate) present in the air that are responsible for acid rain are harmful to human health.
• Effects on Human-Made Structures: Acid rain also affects human-made structures such as historical structures, monuments, statues, gravestones, and buildings. Sulfur dioxide present in acid rain directly reacts with limestone in the presence of water to form gypsum. Thus it flakes off from the structures.

Real-life Examples of Acid Rain

Evidence of damages caused by acid rain has been found throughout the world. The world-famous structures that bear the signs of damage caused by acid rain include the Taj Mahal (India), Cologne Cathedral (Germany), Notre Dame Cathedral (France), the Colosseum (Italy), Westminster Abbey (England), Statue of Liberty (New York), Leshan Giant Buddha Mount Emei (China), Acropolis of Athens (Greece), Dampier Rock Art Complex (Australia) and Longmen Grottoes (China).

👁 Before-and-After-effects-of-acid-rain-on-the-India-Gate-

The Taj Mahal is made up of marble, which reacts with sulfuric acid in Acid Rain, causing pitting, decolorization, and loss of luster. The Colosseum in Rome shows signs of degradation from atmospheric sulfuric and nitric acids. London's Westminster Abbey shows signs of degradation from atmospheric sulfuric and nitric acids. The Statue of Liberty is made up of copper which appears green due to damage caused by Acid Rain. The Black Triangle, a border area shared by Germany, Poland, and the Czech Republic, is an example of an Acid Rain-affected forest area with dying plants.

👁 Before-and-After-effects-of-acid-rain-on-the-Taj-Mahal

Prevention of Acid Rain

To mitigate the problem of Acid Rain, the

Program (ARP) has been established to reduce the emission of sulfur dioxide (SO₂) and nitrogen oxides (NO_x), the primary precursors of Acid Rain. For this purpose, the ARP program has suggested some measures which are as follows.

• The water used by the factories should be filtered and detoxified before returning it to the rivers.
• The industries should reduce the emission of pollutant gases.
• The industries are encouraged to produce and use renewable energy instead of fossil fuels.
• More trees should be planted to absorb polluted air.
• People should reduce household energy consumption by turning off lights, computers, and other appliances when not in use and using energy-efficient lighting, air conditioners, heaters, refrigerators, washing machines, etc.
• People should be encouraged to use electric vehicles and other non-polluting vehicles, such as bicycles.
• Regulating the emissions coming from vehicles and buildings is an important step that can be done by restricting the use of fossil fuels and focusing on more renewable energy sources such as solar and wind power.

Conclusion - Acid Rain

Acid Rain is one of the most serious environmental problems that should be addressed to preserve our environment and balance the ecosystem. Acid rain causes and effects are important to understand and get a better knowledge on the topic. Implementing stricter regulations, promoting the use of renewable energy sources, and campaigning awareness about the harmful effects of emissions of pollutants are essential steps to mitigate the problems of Acid Rain.

Also Read:

• What are the Effects of Acid Rain on Taj Mahal?
• Rain - Definition, Causes, Importance, Acid Rain
• What is Atmospheric Pollution?