How is Acid Rain Formed?

Acid rain refers to rain or other forms of precipitation with a low pH level.


Acid rain is defined as any form of precipitation that has an unusually low level of pH, which is caused by the release of sulfur dioxide and nitrogen oxide into the atmosphere. The rain has harmful effects on plants, marine animals, and infrastructure. Since the 1970s, some governments have made efforts to ensure that there are reduced emissions of the two gases into the atmosphere. Although the gasses can be released naturally through lightning strikes and volcanic activities, it does not happen often. Acid rain has harmful impacts on trees, water, and soil, and can endanger the lives of humans, insects, and aquatic animals. The rain also causes paint to peel, and can lead to the corrosion of steel structures and the weathering of stone buildings and statues.

How is Acid Rain Formed?

Acid rain is a product of the chemical reaction of sulfur dioxide and nitrogen oxide that is released with water, oxygen, and other chemicals into the atmosphere. Sulfur dioxide and nitrogen oxide readily dissolve in water and can be carried several miles by the wind. After traveling for a long distance, the two compounds become part of rain, sleet, snow or fog. Power plants emit sulfur dioxide and nitrogen oxide when fossil fuels such as coal are burned to produce electricity. Similarly, the exhaust from cars, trucks, and buses releases sulfur dioxide and nitrogen oxide into the air.

Effects of Acid Rain

i) Effects of Acid Rain on Animals

In aquatic settings such as the ocean, lakes, streams, and marshes, the ecological effect of acid rain is evident due to the danger it presents to fish and wildlife. As it flows through the soil, acidic rainwater can leach aluminum from clay soil particles and flow into streams and lakes. The more acid that is introduced into the ecosystem, the more aluminum is released. Although some plants and animals can endure acidic waters and direct measures of aluminum, others are acid-sensitive and will die if pH levels are low. The young of most species are more sensitive to ecological conditions than mature species. At a pH level of 5, most fish eggs will not survive, and at lower pH levels adult fish can die.

ii) Effects of Acid Rain on Plants

Dead or dying trees are common in areas affected by acid rain. Acid rain leaches aluminum from the soil and the aluminum may be detrimental to plants and animals. The rain also eliminates minerals and nutrients from the soil that trees need to grow. At high altitudes, acidic fog and clouds might strip nutrients from the foliage of trees, leaving them with brown or dead leaves. This can cause difficulties in the absorption of sunlight, which makes trees fragile and less likely to endure freezing temperatures.


Nature depends on balance, and although some rain is naturally acidic, with a pH level of about 5.0, human activities have made it worse. Ordinary precipitation reacts with basic chemicals or non-acidic materials which are found in air, rocks, soils, streams, and lakes. These reactions usually neutralize natural acids. However, if rain becomes too acidic, these chemicals may not be able to neutralize all of the acids. Over time, these neutralizing chemicals can be washed away by acid rain.

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