Dr. V.K.Maheshwari, M.A(Socio, Phil) B.Sc. M. Ed, Ph.D
Former Principal, K.L.D.A.V.(P.G) College, Roorkee, India
The term ‘Acid Rain’ was first used by Robert Angust Smith in 1872. “literally” it means the presence of excessive acids in rain waters.
The term acid rain is used to describe all precipitation/or deposition, which is more acidic than normal. It results, when gaseous emissions of particularly SOx and NOx interact with water-vapor and sunlight and are chemically converted to strong acidic compounds such as sulphuric acids, sulphurous acid, Nitric acid and nitrous acids. When these compounds (acid gases or acid particles) along with other organic and inorganic chemicals are deposited on the earth’s as aerosols and particulate, the deposition is called as Dry deposition and when these are carried to the earth’s surface by precipitation (rain drops, snow, fog or dew) the deposition is called as wet deposition. History of Acid Rain
The gases responsible for acid deposition are normally a by-product of electric power generation and the burning of coal. As such, it began entering the atmosphere in large amounts during the Industrial Revolution and was first discovered by a Scottish chemist, Robert Angus Smith, in 1852. In that year, he discovered the relationship between acid rain and atmospheric pollution in Manchester, England.
Although it was discovered in the 1800s, acid deposition did not gain significant public attention until the 1960s and the term acid rain was coined in 1972. Public attention further increased in the 1970s when the New York Times published reports about problems occurring in the Hubbard Brook Experimental Forest in New Hampshire.
Acidic deposition occurs in two ways: wet and dry.
Wet Deposition
Wet deposition refers to acidic rain, fog, and snow. If the acid chemicals in the air are blown into areas where the weather is wet, the acids can fall to the ground in the form of rain, snow, fog, or mist. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depends on several factors, including how acidic the water is; the chemistry and buffering capacity of the soils involved; and the types of fish, trees, and other living things that rely on the water.
Dry Deposition
In areas where the weather is dry, the acid chemicals may become incorporated into dust or smoke and fall to the ground through dry deposition, sticking to the ground, buildings, homes, cars, and trees. Dry deposited gases and particles can be washed from these surfaces by rainstorms, leading to increased runoff. This runoff water makes the resulting mixture more acidic. About half of the acidity in the atmosphere falls back to earth through dry deposition.
Sources of Acid Rain:
Sources of sulphur dioxide and oxides of nitrogen may be natural such as volcanoes, oceans, and biological decay and forest fires.
Acidification of environment is a man made phenomenon. There is now no doubt that most acids come from human activities from cars, homes, factories and power stations etc. The increasing demand for electricity and the rise in the number of motor vehicles in recent decades has increased emissions of acidifying pollutants .
Measurement of Acid Rain
Acid rain refers to the presence of strong mineral acids like sulfuric acid, Nitric acid and in some locations even hydrochloric and hydrofluoric acids which bring down the pH in the atmospheric precipitation.
Acid rain is measured using a scale called “pH.” The lower a substance’s pH, the more acidic it is. . (The pH scale ranges from 0, which is strongly acid, , and strongly alkaline, is 14, the scale point 7 is neutral.). Pure water has a pH of 7.0. Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3.
Acid rain’s pH, and the chemicals that cause acid rain, are monitored by two networks, both supported by EPA. The National Atmospheric Deposition Program measures wet deposition, and its Web site features maps of rainfall pH (follow the link to the isopleth maps) and other important precipitation chemistry measurements.
Effects of Acid Rain
The ecological impact of acid rain is quite serious. It is likely to produce irreversible changes. The harmful effects caused by the acid deposition can be categorized under on water bodies, soil, vegetation, health and materials.
• Lakes and streams are no longer able to sustain many kinds of aquatic life
• Under continual acid precipitation, a lake gradually loses its buffering capacity against acidity, pH value of its waters begins to drop, and its ecosystems are threatened
• Spawning waters are threatened
• Acid-heavy water leaches important plant nutrients out of the ground
• Activities of heavy metals such as cadmium and mercury contaminate water supplies
• Status and tables made of bronze, limestone, marble, and sandstone are slowly wearing away Acid rain causes extensive damage to buildings and structural materials of Marble, Limestone, Slate and mortar etc. In Greece and Italy, invaluable stone statues have been partially dissolved by acid rain. The Taj Mahal is one of the seven wonders of the world is in the increasingly danger of being destroyed by the constituents of polluted atmosphere, especially due to the pollutants released from the nearby Mathura Refinery.
• Mountain forest- those closest to the acidic clouds best illustrate the long-term effects of acid rain; growth is stunted, leaves and needles drop inexplicably, frailer species die
• The nutrients are most essential for the plant growth. Also the activity of symbiotic nitrogen fixing bacteria present in the nodules of leguminous family is inhibited, thereby destroying the fertility of the soil. Thus agriculture production is greatly affected by the acidification of farmlands. . Human health can also be affected by acidification of air, water and food while the consumption of low PH water in itself in dangerous, it can also release heavy metals from the pipes of the distribution system into the potable water supply. This acidification can play havoc with human nervous system Respiratory system and Digestive system by making the person an easy prey to neurologist diseases. Sulphur (IV) oxide and nitrogen oxide emissions have been linked to increases in occurrence of asthma, heart disease, and lung disease, primarily among children and the elderly.
- Acid deposition also has an impact on architecture and art because of its ability to corrode certain materials. As acid lands on buildings (especially those constructed with limestone) it reacts with minerals in the stones sometimes causing it to disintegrate and wash away. Acid deposition can also corrode modern buildings, cars, railroad tracks, airplanes, steel bridges, and pipes above and below ground.
Remedial Measures of Acid Rain:
There are several ways to reduce acid deposition, more properly called acid deposition, ranging from societal changes to individual action.
Understanding acid deposition’s causes and effects
To understand acid deposition’s causes and effects and track changes in the environment, scientists from EPA, state governments, and academic study acidification processes. They collect air and water samples and measure them for various characteristics like pH and chemical composition, and they research the effects of acid deposition on human-made materials such as marble and bronze. Finally, scientists work to understand the effects of sulphur dioxide (SO2) and nitrogen oxides (NOx) – the pollutants that cause acid deposition and fine particles – on human health.
To solve the acid rain problem, people need to understand how acid rain causes damage to the environment. They also need to understand what changes could be made to the air pollution sources that cause the problem. The answers to these questions help leaders make better decisions about how to control air pollution and therefore how to reduce – or even eliminate – acid rain. Since there are many solutions to the acid rain problem, leaders have a choice of which options or combination of options is best. The next section describes some of the steps that can be taken to reduce, or even eliminate, the acid deposition problem.
Clean up smokestacks and exhaust pipes
Almost all of the electricity that powers modern life comes from burning fossil fuels like coal, natural gas, and oil. acid deposition is caused by two pollutants that are released into the atmosphere, or emitted, when these fuels are burned: sulphur dioxide (SO2) and nitrogen oxides .
Coal accounts for most US sulphur dioxide (SO2) emissions and a large portion of NO2 emissions. Sulphur is present in coal as an impurity, and it reacts with air when the coal is burned to form SO2. In contrast, NO2 is formed when any fossil fuel is burned.
There are several options for reducing SO2 emissions, including using coal containing less sulfur, washing the coal, and using devices called scrubbers to chemically remove the SO2 from the gases leaving the smokestack. Power plants can also switch fuels; for example burning natural gas creates much less SO2 than burning coal. Certain approaches will also have additional benefits of reducing other pollutants such as mercury and carbon dioxide. Understanding these “co-benefits” has become important in seeking cost-effective air pollution reduction strategies. Finally, power plants can use technologies that don’t burn fossil fuels. Each of these options has its own costs and benefits, however; there is no single universal solution.
Similar to scrubbers on power plants, catalytic converters reduce NOx emissions from cars. These devices have been required for over twenty years in the US, and it is important to keep them working properly and tailpipe restrictions have been tightened recently. EPA has also made, and continues to make, changes to gasoline that allows it to burn cleaner.
Use alternative energy sources
Reduce/avoid use of fossil fuels by encouraging use of renewable energy sources like solar energy, wind and hydroelectric power etc .Use alternative methods for power generation
There are other sources of electricity besides fossil fuels. They include: nuclear power, hydropower, wind energy, geothermal energy, and solar energy. Of these, nuclear and hydropower are used most widely; wind, solar, and geothermal energy have not yet been harnessed on a large scale in this country.
There are also alternative energies available to power automobiles, including natural gas powered vehicles, battery-powered cars, fuel cells, and combinations of alternative and gasoline powered vehicles.
All sources of energy have environmental costs as well as benefits. Some types of energy are more expensive to produce than others, which means that not all Americans can afford all types of energy. Nuclear power, hydropower, and coal are the cheapest forms today, but changes in technologies and environmental regulations may shift that in the future. All of these factors must be weighed when deciding which energy source to use today and which to invest in for tomorrow.
Restore a damaged environment
One of the simplest solutions to the problem is to neutralize the acid with lime. But it is quite expensive, especially when large areas of water bodies have to limed. Further large scale lime treatment may create its own ecological problems.
Acid deposition penetrates deeply into the fabric of an ecosystem, changing the chemistry of the soil as well as the chemistry of the streams and narrowing, sometimes to nothing, the space where certain plants and animals can survive. Because there are so many changes, it takes many years for ecosystems to recover from acid deposition, even after emissions are reduced and the rain becomes normal again. For example, while the visibility might improve within days, and small or episodic chemical changes in streams improve within months, chronically acidified lakes, streams, forests, and soils can take years to decades or even centuries (in the case of soils) to heal.
However, there are some things that people do to bring back lakes and streams more quickly. Limestone or lime (a naturally-occurring basic compound) can be added to acidic lakes to “cancel out” the acidity. This process, called liming, has been used extensively in Norway and Sweden but is not used very often in the United States. Liming tends to be expensive, has to be done repeatedly to keep the water from returning to its acidic condition, and is considered a short-term remedy in only specific areas rather than an effort to reduce or prevent pollution. Furthermore, it does not solve the broader problems of changes in soil chemistry and forest health in the watershed, and does nothing to address visibility reductions, materials damage, and risk to human health. However, liming does often permit fish to remain in a lake, so it allows the native population to survive in place until emissions reductions reduce the amount of acid deposition in the area.
Look to the future
As emissions from the largest known sources of acid deposition – power plants and automobiles-are reduced, EPA scientists and their colleagues must assess the reductions to make sure they are achieving the results Congress anticipated. If these assessments show that acid deposition is still harming the environment, Congress may begin to consider additional ways to reduce emissions that cause acid deposition. They may consider additional emissions reductions from sources that have already been controlled, or methods to reduce emissions from other sources. They may also invest in energy efficiency and alternative energy. The cutting edge of protecting the environment from acid deposition will continue to develop and implement cost-effective mechanisms to cut emissions and reduce their impact on the environment.
Take action as individuals
It may seem like there is not much that one individual can do to stop acid deposition. However, like many environmental problems, acid deposition is caused by the cumulative actions of millions of individual people. Therefore, each individual can also reduce their contribution to the problem and become part of the solution. One of the first steps is to understand the problem and its solutions.
Individuals can contribute directly by conserving energy, since energy production causes the largest portion of the acid deposition problem. For example, you can:
• Turn off lights, computers, and other appliances when you’re not using them
• Use energy efficient appliances: lighting, air conditioners, heaters, refrigerators, washing machines, etc.
• Only use electric appliances when you need them.
Keep your thermostat at 68 F in the winter and 72 F in the summer. You can turn it even lower in the winter and higher in the summer when you are away from home.
• Insulate your home as best you can.
• Carpool, use public transportation, or better yet, walk or bicycle whenever possible. Car pools and mass transit help; so do fuel-efficient cars and trucks
• Buy vehicles with low NO2 emissions, and maintain all vehicles well. Be well-informed.
• One simple way to draw attention to the problem is by monitoring the acid levels in the rainfall in your own backyard. The tools required for at-home testing are simple, and thought the results may not stand up in a scientific laboratory; they should give an indication of whether or not there are high levels of acid in your community s rainfall.
Because of these problems and the adverse effects air pollution has on human health, a number of steps are being taken to reduce sulphur and nitrogen emissions. Most notably, many governments are now requiring energy producers to clean smoke stacks by using scrubbers which trap pollutants before they are released into the atmosphere and catalytic converters in cars to reduce their emissions. Additionally, alternative energy sources are gaining more prominence today and funding is being given to the restoration of ecosystems damaged by acid rain worldwide.