Acid Rain: Effects and Reduction


The release of sulfur dioxide and nitric oxide into the atmosphere causes a reaction with oxygen and ozone to yield sulfuric and nitric acid in which the rate is increased further in the presence of sunlight. The deposition of these two compounds onto the Earth’s surface is the phenomenon known as acid rain. Although the term “acid rain” is widely used, it is but a subcategory under acid precipitation, therefore a more general and accurate description is needed.

To emphasize why that is, let us introduce the two types of acid depositions: wet and dry. The portion of these compounds that dissolves in cloud droplets and precipitates in the form of rain, snow, sleet, hail, fog or mist, is known as a wet deposition. The portion that gets integrated with dust and smoke during dry weather which then gets deposited on the ground in the form of particles and gases is known as dry deposition. Runoff water washes them away where it eventually combines with the acid precipitations, which yield a solution that is even more acidic. Dry depositions account for 20 to 60% of all forms of depositions and are just as damaging to the environment as wet depositions.

Therefore the term “acid deposition” is a more suitable portrayal for this procedure. The acidity is measured using the PH scale, which ranges from 0 to 14, 7 being neutral (drinking water) and 0 being most acidic. The acidity of rain has a varied PH scale. Normal rain has an acidity of around 5 to 6, because carbon dioxide in the air dissolves in the molecules of water, releasing hydrogen ions, thereby increasing its acidity. When the PH falls below 5.6, it is considered acid rain.

The typical value of acid depositions is roughly around 4. The record of the lowest acid precipitation measure was as low as 1.6 in North America, which is close to the acidity of the vinegar. Another way of measuring acidity is by comparing the number of molecules in the atmosphere relative to one another, enabling scientists to determine the quantities of the harmful compounds present. As for the sources of nitric oxide and sulfur dioxide emissions, scientists have found that approximately 65% of the compounds released into the atmosphere originate from manmade sources such as fossil fuel combustion (mainly from coal-burning electrical power plants) and the smelting of sulfide ores.

The towering pillars span a height of more than 300 meters, dispersing the smog far downwind. The nitric oxide and sulfur dioxide compounds may drift hundreds of kilometers before reacting and depositing on the ground. The principal source of nitric oxide emissions is from vehicles, about 60%.

Kitchen ovens, heaters, and engines can also release nitric oxide. The remaining 35% of both sulfur dioxide and nitric oxide originate from natural sources which include the smoke from erupting volcanoes, forest fires, bacteria, electrical discharges and decaying vegetation. This paper seeks to: describe the effects of acid rain on surface waters and aquatic animals, forests, and automotive coatings, materials (such as metals, paint and limestone), visibility and human health; and the efforts that should be advanced by society and individuals reduce acid rain (1)

Effects of Acid Rain

Our knowledge of the effects of acid rain is well documented, but we know much less of what the real effects are on the environment and our health. The effects of acid depositions on aquatic ecosystems and animals vary depending on the degree of tolerance. The more robust the species, the more acidity it can tolerate before dying. A decreasing trend in the population of fish in aquatic ecosystems is usually visible when the PH falls below 6.

A lake has a lower diversity of algae at low PH, and the multiplication of rooted plants becomes compromised. Further, the number of invertebrates and the decomposition of organic matter diminish, and fungi begin to replace bacteria. This disrupts the equilibrium of the lake. An organism that can resist an increase in acidity can nevertheless become extinct if its prey is victimized by it.

This section describes the specific effects of acid rain on surface waters and aquatic animals, forests, automotive coatings, materials (such as metals, paint and limestone), visibility, and human health (1).

Effects of acid rain on surface waters and aquatic animals

The ecological effect of “acid rain is most clearly seen in the aquatic, or water environments, such as streams, lakes, and marshes” (1). The acid water that ends up in the water bodies often results from the surface runoff or direct acid rain on water surfaces. Acid rain usually impacts negatively on water bodies that are situated in watersheds that have soils with limited capacity to neutralize acidic compounds. “Lakes and streams become acidic when the water in them and the surrounding soil cannot buffer the acid rain enough to neutralize it” (2). The affected lakes are often characterized by chronic low pH levels.

The acid rain produces a sequence of effects that often “harm or kill individual fish, reduce fish population numbers, completely eliminate fish species from the water body, and decrease biodiversity” (2). The flow of water from acid rain through the soil in a watershed is often accompanied by the release of aluminum from the soil into the lakes and streams (1). Thus the decrease in the pH of the streams and lakes is accompanied by increase in aluminum concentration. Both decreased “pH and increased aluminum levels are directly toxic to fish and other aquatic life” (2). In addition, reduced pH levels and the rise in aluminum concentration may lead to chronic stress that may result in death but lead to diminished body weight.


For many years some forests were observed to grow at slower rates than others. The “leaves and needles often turn brown and fall off when they should be green and healthy” (3). Several types of research have been conducted and revealed that the above effects are caused by acid rain. Acid rain has “now been implicated in forest soil degradation in many areas” (2). The effects caused by acid rain together with other stressors in the environment such as pollution and diseases have impacted negatively on the affected forests.

The soil may sometimes neutralize some acid rain but persistent acid rain makes the soil become more acidic. The “differences in soil buffering capacity are important reasons as to why some areas that receive acid rain show a lot of damage, while others that receive about the same amount of acid rain are less damaged” (1). However, soil buffering does not protect the trees from the effects of acid rain.

Acid rain damages the leaves of trees and thus limits the nutrient supply but does not result in the direct death of the trees. However, the death of the trees usually occurs when the effects of acid rain are complemented by other stressors in the environment.

Automotive coatings

In the past years, “there were numerous reports of damage to automotive paints and coatings” (3). The typical damage is found on horizontal surfaces and usually has an irregular shape. The automotive industry arrived at a general agreement that the damage was being caused by some form of “environmental fallout” (2). Laboratory investigation and other case studies have revealed that acid rain damages automotive coatings. In addition, “chemical analyses of the damaged areas of some exposed test panels indicate elevated levels of sulfate, implicating acid rain” (1). It is often difficult to differentiate damage caused by acid rain from one that results from other environmental fallouts.

However, specialists can differentiate them using detailed chemical analysis (2). Acid rain damage on automotive coating is more often observed on vehicles that have fresh paints. Moisture plays a vital role in causing the damage and thus vehicles should be hand dried after washing.

Materials (e.g., metals, paint and limestone)

Acid rain and “the dry deposition of acidic particles contribute to the corrosion of metals and the deterioration of paint and stone” (3). This has significantly contributed to diminishing value of premises that are important to society. Maintenance costs also increase when dry acidic chemicals are constantly deposited on buildings. Thus there have been concerted efforts to identify ways through which acid rain-related damage to materials can be reduced. For instance, the automotive industry has come up with acid-resistant paints to be used on vehicles in the acid rain-prone areas (1).


“Sulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions contribute to visibility impairment” (1). This implies individuals who live in the areas that are prone to acid rains do see as far as they should. In the eastern part of the US it has been identified that sulfates contribute 50 to 70 % of the poor visibility and thus affect the recreation in the various national parks such as the Shenandoah and the Great Smoky Mountains (2). A program has been rolled out to mitigate the effects of acid rain on visibility and improve the visual range by up to 30%. The program is expected to use a considerable amount of resources but will lead to improved visibility in the national parks.

Human health

The water that results from acid rain often looks, feels, and states like water from clean rain (1). Acid rain does not cause direct harm to human beings. Human health is usually affected by the pollutants that lead to acid rain. “Sulfur dioxide and nitrogen oxides interact in the atmosphere to produce nitrate and sulfate particles which can be transported long distances by the wind and inhaled deep into the lungs” (2). Researches conducted reveals that an increase in the level of the particles results in increased instances of early death due to lung and heart diseases. The health concerns have resulted in increased efforts to regulate the amount of sulfur dioxide ad nitrogen dioxides (3).

Reducing Acid Rain

There are several ways through which acid rain reduction can be achieved. This is more commonly referred to as acid deposition and ranges from changes in society to individual initiative (1). It is important to reduce the deposition of acid not only in the areas that are affected by acid rain but all over the world. This is important so as to preserve the integrity of natural habitats as well a minimize the damage to man-made structures (1).

For one to contribute to the reduction of acid rain, he/she needs to understand the acidification processes. Scientists from various institutions study the acidification process to identify the causes of acidification. Ordinary individuals should be able to understand the ways acid rain causes damage to the environment. The following simple steps show how individuals can contribute to the reduction of acid rain. The first option is “through the removal of sulfur oxide from coal by washing and using devices like scrubbers to chemically remove the sulfur oxide” (2). Secondly, there is catalytic conversion equipment that is fitted on vehicles to reduce nitrogen oxides (1). The third approach is to make use of other alternative sources of energy rather than fossil fuels which emit the pollutants responsible for acid rain.

All the efforts towards reduction of the acid rain are aimed at restoring the ecosystem and this may take years to fully recover. Some of the useful ways through which environmental restoration can be achieved are through the addition of lime or limestone into acidic lakes to cancel out the acidity (2).

People can also act in their individual capacity to reduce the effects of acid rain. However, a substantial reduction can only be achieved through collaborative measures taken by millions of people. Individuals “can contribute directly to energy conservation since energy production contributes to much of the deposition challenges” (3).


This paper sought to: describe the effects of acid rain on surface waters and aquatic animals, forests, and automotive coatings, materials (such as metals, paint and limestone), visibility and human health; and the different efforts that should be advanced by the society and individuals reduce acid rain (3). It has been established that acid rain leads to low pH levels in aquatic environments. The effects of acid rain on aquatic life are more often associated with toxic levels of aluminum which accumulate from the surrounding soil; Acid rain affects forests by destroying leaves and thus interfering with the important process of food manufacture (2).

Acid rain does not however result in the death of trees on its own. The trees only die when other stressors such as plant diseases are involved; it has also been established that acid remain damages automotive coating and other materials through chemical reactions that result in altered appearance; The sulfates and nitrates that result from pollutants that cause acid rain are a major contributing factor to visibility impairment; finally, it has been found that acid rain has a profound impact on the health of individuals. The inhalation of nitrate and sulfate particles can lead to serious lung conditions.

Several different methods can be advanced to reduce acid rain. People must understand the process of acid rain formation to adequately take measures that can improve the situation. Some physical methods such as coal washing can be used to remove sulfur dioxide (1). However, the best results can be achieved by using alternative sources of energy and energy conservation practices.


  1. U.S Environmental Protection Agency. 2007. Web.
  2. Burtraw D., Krupnick, A., and Mansur, E., The cost and Benefits of reducing Acid Rain, Resources for the future Washington, 1997.
  3. Rodhe, H., Environmental Science and Technology, 36, 2006, 4382-8.