All you need to know about acid rain

Acid rain refers to any precipitation (rain, fog, mist, snow) that is more acidic than normal. Acid rain is caused by atmospheric pollution from acidic gases such as sulphur dioxide and oxides of nitrogen emitting from burning of fossil fuels. Acid rain is formed when the air that contains acidic gases emitted mostly from power plants industries and automobiles, combines with the rain drops. The acid rain affects ecosystems in diverse ways Causes of acid rain...

Human activities

Human activities are the main cause of acid rain. Over the past few decades, humans have released so many different chemicals into the air that they have changed the mix of gases in the atmosphere. Power plants release the majority of sulfur dioxide and much of the nitrogen oxides when they burn fossil fuels, such as coal, to produce electricity. In addition, the exhaust from cars, trucks, and buses releases nitrogen oxides and sulfur dioxide into the air. These pollutants cause acid rain.

Reactions in the environment

Nature depends on balance, and although some rain is naturally acidic, with a pH level of around 5.0, human activities have made it worse. Normal precipitation—such as rain, sleet, or snow—reacts with alkaline chemicals, or non-acidic materials, that can be found in air, soils, bedrock, lakes, and streams. These reactions usually neutralise natural acids. However, if precipitation becomes too acidic, these materials may not be able to neutralise all of the acids. Over time, these neutralising materials can be washed away by acid rain.

Harmful effects of acid rain

Acid precipitation affects both aquatic and terrestrial organisms. It also damages buildings and monuments.

Effects on aquatic life

The pH of the surrounding or medium is very important for metabolic processes of aquatic organisms. The eggs or sperms of fish, frogs and other aquatic organisms are very sensitive to pH change. Acid rain kills their gametes affecting the life cycles and productivity and causes death or inability to increase in numbers, affecting aquatic food chains in acidic water bodies, causing severe ecosystem imbalances. Acidic lake waters may kill bacteria/microbes/planktons and the lakes become unproductive and life less. Such acidic and lifeless ponds/lakes adversely affect fisheries and livelihood.

Effect on terrestrial life

Acid rain damage cuticle of plant leaves resulting etiolation of foliage. This in turn reduces photosynthesis. Reduced photosynthesis accompanied by leaf fall reduces plant and crop productivity. Acidic medium promotes leaching of heavy metals such as aluminum, lead and mercury. Such metals when percolate into ground water, affect soil microflora/ micro fauna. The soil becomes lifeless. Absorption of these toxic metal ions by plants and micro organisms affects their metabolism.

Effects on forests

Acid rains damage forests and kill vegetation and causes severe damage to the landscape.

Effects on buildings and monuments

Many old, historic, ancient buildings and works of art/textile etc. are adversely affected by acid rain. Limestone and marble are destroyed by acid rain. Smoke and soot cover such objects. They slowly dissolve/flake away the surfaces because of acid fumes in the air. Many buildings/monuments such as Taj Mahal in Agra have suffered from acid rain. Strategies to cope with acid rain Any procedures that shall reduce minimise or halt emission of sulphur and nitrogen oxides into the atmosphere shall control acid rain. Use of low sulphur fuel or natural gas or washed coal (chemical washing of pulverized coal) in thermal plants can reduce incidences of acid rain.

A c a s e S t u d y

The forests in North America, Canada, Europe and Japan were affected by acid rain. Production of some vegetables, such as peas and beans, potato, raddish etc, may be reduced by acid rain, growth of pine; eucalyptus etc. may also be impeded. There may be harmful effects of acid rain on some animals also. It has been observed that breeding of moths is impeded by acid rain. In many places of the world, acid rain has reduced the number of different types of birds. In India, the water of the lake of Bharatpur Bird Sanctuary is turning acidic in contact with sulphur dioxide gas of the air; as a result the migratory birds are coming to this place in fewer numbers.

Acid rain may turn acidic the water of ponds, rivers, lakes etc. In such acidic water, the eggs of the fish may be destroyed, the physiological processes of the fish may also be affected and as a result the water reservoir may be fishless ultimately. If the soil below the water and at the sides of the water sources (lake, pond etc.) be basic in nature, the effects of acid rain on the aquatic animals may not be that much serious, but if such soil contains some acid soluble metals which are detrimental to the fish and other aquatic animals, the effects may be fatal.

For example Manganese or Aluminium form, the soil may dissolve in acidic water and may be harmful to the fish. Mercury compounds may also mix with acidic water and may thus cause danger to the aquatic animals. In fact, many lakes have become fishless as a result of acid rain. The effects of acid rain on the public health and on the animals may be dangerous. Acid rain contains mainly two acids – sulphuric acid and nitric acid – which are harmful to the lungs and the respiratory system; they may cause lung cancer, and damage the digestive and nervous systems.

There may be several other dangerous air pollutants other than acid in the acid rain which may also be harmful to public health.Due to acid rain, some heritage buildings and monuments of architectural and historical importance are in danger in different parts of the world. The acid attacks marble, limestone etc. of which such architectures are made of. In India, a few years back, signs of corrosion on the walls of Taj-Mahal were observed.

According to environmentalists this was due to the presence of sulphur dioxide in high concentrations in the air of Agra which reacted with the moisture of air forming sulphuric acid and corroded the marble of the walls of Taj-Mahal. Sulphur dioxide emitted from the petroleum refinery situated on the other side of the Jamuna River was held primarily responsible for such corrosion.

This ‘stone-cancer’ of Taj-Mahal has since been checked through adoption of suitable control measures. As the concentration of sulphur dioxide is increasing in the air of Delhi, there may be a danger of corrosion of the Red Fort and similar other historical buildings and monuments made up of stones. In Calcutta also, architectures such as the marble-built Victoria Memorial Hall may be in similar danger in the near future.