Acid Rain occurs when contaminants in the atmosphere, such as nitrogen oxides and sulphur oxides, combine with precipitation and fall with the rain. There are two types of acid deposition namely: wet deposition and dry deposition. Acid rain harms humans, causes allergies and irritation, and is estimated to be associated with roughly 550 premature deaths each year. Acid Rain also destroys historical monuments, buildings, and other structures. Thus there is an urgent need to adopt measures to control acid rain. Acid rain can be controlled by reducing the amount of sulphur dioxide and oxides of nitrogen released into the atmosphere, switching to cleaner fuels, treating waste gasses, and neutralizing acids. This article will explain to you Acid Rain which will be helpful in preparing the Environment Syllabus for the UPSC Civil Service exam.

What is Acid Rain?

• Acid Rain, as the name implies, is the precipitation of acid in the form of rain in the most basic sense.
• Acid rain is made up of highly acidic water droplets that form as a result of air pollution, particularly the disproportionate amounts of sulfur and nitrogen produced by cars and manufacturing operations.
• There are two types of acid deposition: wet and dry.
• Any type of precipitation that removes acids from the atmosphere and deposits them on the earth's surface is known as wet deposition.
• Dry deposition of harmful particles and gasses adheres to the ground through dust and smoke in the absence of precipitation.

Acid Deposition

• Acid rain is a type of acidic deposition, which can take many different forms.
• They are broadly divided into two main categories: wet deposition and dry deposition.
• Rain, sleet, snow, or fog that has been more acidic than usual is referred to as wet deposition.
• Dry deposition refers to acidic gas and particles.
• Dry deposition results in the return of around half of the atmosphere's acidity to the planet.

Types of Acid Deposition

Wet Deposition

• What we most frequently associate with acid rain is wet deposition.
• Sulfuric and nitric acids that have generated in the atmosphere combine with rain, snow, fog, and hail as they fall to the ground.
• Numerous plants and animals are impacted as this acidic water permeates the ground and runs over it.
• Gases and particles are removed from the atmosphere by precipitation in two ways:
• rain-out, which is when particles are incorporated into cloud drops that fall to the ground, and
• washout, which happens when materials beneath a cloud are dragged down by rain or snow that falls.

Dry Deposition

• The acid compounds are deposited through dry deposition in locations with dry weather.
• The gases and acidic particles may instantly settle on surfaces (water bodies, vegetation, or buildings) or they may react while being transported through the atmosphere to produce larger particles that may be dangerous to human health.
• Rainstorms' runoff can remove dry depositions of gases and particles from these surfaces.
• The quantity of acidity in the atmosphere that falls as a dry deposition to the soil depends on how much rain falls in a given area.

*To know more about the topic, click this link Types of Acid Deposition

Sources of Compounds Causing Acid Rain

Sulphur and Nitrogen are the key culprits in causing acid rain. They are emitted into the atmosphere due to both natural and anthropogenic causes.

Sulphur

• Natural Sources: Sulphur is naturally found in seas and oceans, and is emitted during volcanic eruptions and biological processes such as the decomposition of organic matter in the soil.
• Man-made Sources: Anthropogenic sources of sulphur include the burning of coal (60% of SO2) and petroleum products (30% of SO2).and
• The process of smelting of metal sulfide ores to get the pure metals also release sulphur into the atmosphere.
• Sulphur is also released into the atmosphere as a byproduct of the industrial manufacture of sulfuric acid in the fertilizer, chemical, and metallurgical sectors.

Nitrogen

• Natural Sources: The natural sources of emission of nitrogen include lightning, volcanic eruption, and biological activities.
• The biological activities include the decomposition of microorganisms, nitrogen fixation, uptake, mineralization, nitrification, and denitrification.
• Anthropogenic Sources: Forest fires, Combustion of oil, coal, and gas are the man-made causes for the release of nitrogen.

Formic acid

• Formaldehyde (HCHO) and formic acid (HCOOH) is released into the atmosphere as a result of the burning of biomass as a result of forest fires.
• Formaldehyde undergoes photo-oxidation in large amounts, forming formic acid in the environment.
• These are three main compounds that cause the acidification of rain in the atmosphere.

These three substances are the principal ones responsible for the acidity of rain in the atmosphere.

*To know more about the topic, click this link Sources of Compounds Causing Acid Rain

Characteristics of Acid Rain

Composition

• Nitrogen oxide and sulphur dioxide are the two powerful acids found in acid rain.
• Sulfuric acid and nitric acid are created when these two gases interact with atmospheric water and oxygen.
• Thus the main chemical components of acid rain are sulphur dioxide and nitrogen oxide.
• The majority of the SO2 and NOX that contribute to acid rain originates from burning fossil fuels, however, a tiny amount comes from natural sources like volcanoes.

Acidity

• The pH scale is a scale that is used to measure acidity. The range of this scale is 0 to 14.
• The most acidic value is 0 and the most alkaline value is 14.
• A pH of between 5 and 6 would describe unpolluted rain.
• The acidity of the air can rise to a pH of 4 as a result of increased nitrogen oxide and sulphur dioxide pollution.
• The atmosphere can transport acid rain across enormous distances.

Common Characteristics of Acid Rain Areas

Some characteristics are present in areas that are vulnerable to acid rain attacks:

• They are mainly found in the northern hemisphere's industrialised belt.
• They are frequently mountainous and/or highland regions that receive abundant rainfall and snowfall.
• They have several lakes and streams, as well as an additional area that is covered in flora, due to the amount of water.
• They frequently have thin soils and glaciated bedrock because they are uplands.

*To know more about the topic, click this link Characteristics of Acid Rain

Difference Between Normal and Anthropogenic Acidified Lakes

*To know more about the topic, click this link Difference Between Normal and Anthropogenic Acidified Lakes

Impact of Acid Rain

Impact on Soil

• In the soil, the interchange of hydrogen ions with nutritional cations such as potassium and magnesium causes nutrient leaching, leaving the soil infertile.
• This is accompanied by a decrease in soil organism respiration.
• The pace of decomposition is slowed by an increase in ammonia in the soil due to a decrease in other nutrients, and the nitrate level in the soil is also observed to be lower.
• Acid rain has a lower impact on soil in India since Indian soils are typically alkaline and have a good buffering capacity.

Impact on Wildlife

• Acid rain's effects on wildlife aren't often visible, making documentation a challenge.
• However, acid rain has been shown to have a number of direct and indirect consequences on the fertility and survival of wildlife populations.
• It has been proposed that acid rain can indirectly affect wildlife by allowing metals bound on soils and sediments to be released into the aquatic environment, where toxic substances may be ingested by animals, such as birds, that feed in such an environment.
• It has been presented that acid rain can indirectly affect wildlife by allowing metals bound on soils and sediments to be released into the aquatic environment, where toxic substances may be ingested by animals, such as birds, that feed in such an environment.

Impact on Humans

• Acid rain has a lot of negative effects on human health.
• The most evident are foul odours, impaired visibility, and skin, eye, and respiratory system irritation.
• Chronic bronchitis, lung emphysema, and cancer are some of the direct impacts.
• Increased levels of harmful heavy metals such as manganese, copper, cadmium, and aluminium contribute to the negative impacts on human health.
• When acid rain falls at higher elevations, it creates a dense acidic fog that hangs low in the atmosphere, obstructing visibility.
• Acid rain has a significant impact on environmental balance in addition to its impacts on air quality.
• As trees and crops can be harmed by acid rain that falls directly on them, acidic rain leads to ruined harvests.
• The fishing industry suffers because of an imbalance in the availability of fish.

Damages Buildings

• Acid rain causes harm to buildings and structures by dissolving stone or corroding metal exposed to the elements.
• Metals, limestone, and marble were frequently utilized as building materials exposed to rain and fog before people became aware of the difficulties created by acid rain.
• Acid rain can dissolve calcium carbonate or calcium-based chemicals found in some of these products.
• Sandstone is more resistant to acid rain, yet it is susceptible to black surface deposits over time.

*To know more about the topic, click this link Impact of Acid Rain

Acid Rain - Global Scenario

• These characteristics are prevalent in most of Scandinavia, Canada, the North and Northeastern States, and Northern Europe (especially West Germany and upland Britain).
• The Adirondack Mountains in New York, the Great Smoky Mountains, sections of Wisconsin and Minnesota, and the Colorado Rockies are just a few of the hotspots for acid rain located on either side of the Atlantic.

Acid Rain - India

• In the past, there have been numerous instances of acid rain in India, however, they were only occasional.
• Acid rain has been observed in India, including in the industrial Mumbai neighbourhoods of Chembur and Colaba, close to the Singrauli Super Thermal Power Plant (average pH value: 5.3), and in the Silent Valley and Bhubaneswar rural areas.
• The National Capital Region of Delhi's Panipat has recently received reports of acid rain, along with more recent reports from Kalyan, Chembur, Sinhagad, and Delhi.
• Although it has been noted that Pune's rainfall has an alkaline pH, its value has been trending downward.
• The primary cause is an increase in sulphate and nitrate ions and a decrease in calcium ions.
• With time, the pH level of the rain in the Agra and Delhi regions has also decreased.
• For the previous three decades, IITM has been conducting acid rain investigations.
• In the north and northwest of India, the pH levels are higher (pH>7.0).
• The northeastern and southern regions of India are a little lower (6.0 pH 7.0).
• The only good news for India is that it is uncertain that acid rain will occur.
• This is due to the country's generally alkaline-rich soils and tropical climate, which neutralize the contaminants.

Measures to Control Acid Rain

Reducing the Amount of Sulphur Dioxide and Oxides of Nitrogen

• Scientists have devised a variety of methods for reducing the quantity of sulphur dioxide generated by coal-fired power plants.
• One alternative is to use coal with lower sulphur content. Another technique is to "wash" the coal in order to remove some sulphur.
• Scrubbers, which remove sulphur dioxide from gasses leaving the smokestack, can be installed at the power plant.
• Because nitrogen oxides are produced during the combustion of coal and other fossil fuels, some power plants are altering their coal-burning processes.

Cleaner Cars

• Automobiles and trucks are key polluting sources that generate acid rain.
• While a single car does not emit a lot of pollution when all of the cars on the road are joined together, it produces a lot of pollution.
• As a result, automakers must limit the number of nitrogen oxides and other pollutants generated by new vehicles.
• A catalytic converter is such a type of technology used in automobiles.
• This piece of equipment has been used to minimize the number of nitrogen oxides generated by automobiles for over 20 years.
• Cleaner fuels, such as natural gas, are also available in certain new cars.
• Low-emission automobiles are those that emit fewer pollutants and are therefore better for the environment.

Flue Gas Desulphurization

• Flue-gas desulfurization (FGD) is a set of technologies for removing sulphur dioxide (SO2) from fossil-fuel power plant exhaust flue gasses, as well as other sulphur oxide-producing processes like waste incineration.
• Most FGD systems have two stages: one for removing fly ash and another for removing SO 2.
• The removal of both fly ash and SO2 in a single scrubbing vessel has been attempted.
• Thus these systems greatly help in reducing SO2 emissions.

*To know more about the topic, click this link Measures to Control Acid Rain

Conclusion

Numerous areas of North America and Western Europe were destroyed by acid rain in the 1970s. Since then, countermeasures taken in these areas have gradually helped contain the issue to some extent. Recent studies have shown that acid rain poses an equally serious threat to developing nations like India and China as it did to some of the developed nations in the past. Even the latter has a long way to go before fully recovering from the earlier occurrences of extremely acidic rain.

FAQs

MCQs

1. Which of the following pollutants is primarily responsible for the formation of acid rain?

A) Carbon dioxide
B) Sulfur dioxide
C) Methane
D) Ozone

2. What is the pH range of water that is considered to be acid rain?

A) 5.6 to 6.5
B) 4.0 to 5.5
C) 2.0 to 4.0
D) Below 5.6

3. Which of the following is a direct consequence of acid rain?

A) Erosion of building materials
B) Increased agricultural yield
C) Reduced risk of respiratory diseases
D) Decreased pollution levels

4. How does acid rain affect aquatic life?

A) Increases biodiversity
B) Reduces oxygen levels in water
C) Increases water temperature
D) Enhances water clarity

5. Which of the following is NOT a consequence of acid rain?

A) Soil degradation
B) Harm to plant growth
C) Improvement in air quality
D) Damage to aquatic ecosystems

GS Mains Questions and Model Answers

Q1: Discuss the causes and consequences of acid rain. How can its effects be mitigated through environmental policies?

Answer: Acid rain is primarily caused by the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) from industrial activities, vehicles, and power plants. These pollutants mix with water vapor in the atmosphere to form sulfuric and nitric acids, which fall as acid rain. The consequences of acid rain include soil degradation, damage to plant life, and the acidification of water bodies, which harms aquatic life. Additionally, acid rain erodes buildings and monuments, especially those made of limestone and marble. To mitigate the effects of acid rain, environmental policies should focus on reducing emissions through stricter regulations on industries and vehicles, promoting the use of cleaner technologies, and adopting renewable energy sources. International cooperation and agreements like the Gothenburg Protocol, aimed at reducing transboundary air pollution, are also critical in addressing acid rain.

Q2: Evaluate the impact of acid rain on ecosystems and human health. What are the key measures to reduce acid rain?

Answer: Acid rain has a significant impact on ecosystems by altering the pH of soil and water, which can lead to the loss of biodiversity. It affects plant growth by leaching essential nutrients from the soil, which weakens plants and makes them more vulnerable to diseases. Aquatic ecosystems are severely impacted by acid rain, as it lowers the pH of water bodies, reducing oxygen levels and causing the death of many aquatic species. While acid rain itself does not directly harm human health, the pollutants that cause it, such as sulfur dioxide and nitrogen oxides, can cause respiratory problems, including asthma and bronchitis. To reduce acid rain, governments must focus on reducing emissions from industries and vehicles through better emission controls and the use of cleaner technologies. International agreements, public awareness, and stricter environmental standards are essential to address this issue effectively.

Q3: Analyze the role of international agreements in reducing the occurrence of acid rain. How successful have these agreements been?

Answer: International agreements have played a key role in reducing the occurrence of acid rain by setting limits on sulfur and nitrogen emissions. The 1999 Gothenburg Protocol, part of the Convention on Long-range Transboundary Air Pollution, is one of the most significant agreements that aimed to reduce the emissions of acid rain-causing pollutants. These agreements require countries to reduce their sulfur and nitrogen oxide emissions, which directly impact the formation of acid rain. The success of these agreements has been evident in countries like the United States and Canada, where emission reductions have led to a significant decrease in acid rain. However, there are challenges in achieving global cooperation, particularly in developing countries where industrial growth is still a priority. Overall, international agreements have been effective, but their success depends on continued global cooperation and implementation of policies aimed at reducing air pollution.

Previous Year Questions on Acid Rain

1. UPSC CSE Prelims 2020:

Question: Which of the following pollutants causes acid rain?

A) Carbon dioxide
B) Sulfur dioxide
C) Ozone
D) Methane

Answer: (B) Sulfur dioxide

Explanation: Sulfur dioxide (SO2) is the primary pollutant responsible for the formation of acid rain. It reacts with water vapor in the atmosphere to form sulfuric acid, which falls as acid rain.

2. UPSC CSE Mains 2019 (GS Paper 1):

Question: Discuss the environmental impacts of acid rain and suggest measures to prevent it.

Answer: Acid rain has numerous harmful effects on the environment, including soil degradation, damage to plant life, and acidification of water bodies, which harms aquatic life. It also accelerates the erosion of building materials, particularly limestone and marble. To prevent acid rain, measures include reducing sulfur dioxide and nitrogen oxide emissions from industries, power plants, and vehicles, promoting the use of renewable energy, and enforcing stricter environmental regulations. International agreements, such as the Gothenburg Protocol, have been successful in reducing emissions, but continued global cooperation is necessary to mitigate the effects of acid rain effectively.