Thursday, March 28, 2013

History on the effect of the Acid Rain

  1. In Sweden, over 18,000 lakes have become so acidic due to acid rain that all the fish have died. Some success has been achieved by dumping vast quantities of rocks like limestone into the lakes, because these rocks destroy the acid, but for most of the lakes it will be many years after we stop producing acid rain before the water returns to normal.
  2. In what used to be called West Germany the government discovered that more than 70,000 square kilometers of forests had died because of acid rain. In the old East Germany, the damage was even worse due to factories creating much more pollution. It is not always the country that produces the pollution that suffers from the acid rain. For example, industrial pollution from the United Kingdom is blown across the sea and falls as acid rain over Norway and Sweden.
  3. Acid rain is not just a European problem; it occurs around the world. In North America thousands of lakes along the eastern coast are so acidic that fish cannot survive any longer, and at least 10 percent of the lakes in the Adirondack region have a pH value of five or less. ( A pH of 7 is neutral, pure water. Lower values are acidic, higher values are alkaline. )
  4. In the Appalachian Mountains a World Resources Institute report in the late 1980's stated that the acidity of clouds on the mountains was 100 times greater than it would be if it wasn't polluted. In consequence, trees were dying.
     With all this damage, why do we still produce so much pollution and continue tolerating acid rain? Well, it's basically because governments don't consider it important enough. They believe that other things are more important, such as making sure that industry continues to grow and that the prices of goods are kept as low as possible. Making factories cleaner costs money, and unless everyone does it, the clean factories wont be able to make goods as cheaply as the dirty ones,and will make less money.

Developed countries also make huge profits from the exploitation and sale of the fuels that produce the pollution. The technology exists to run all our cars and lorries on other 'cleaner' fuels, but the oil companies wouldn't want that to happen, and neither would the governments that tax the oil companies! 

What is the relationship between Sulphuric Acid and Acid Rain?

 Acid rain takes place as a direct result of the natural cleaning process of the atmosphere. The tiny droplets of water which form clouds confine within them the suspended solid particles and gases in the atmosphere. Among these gases are sulfur oxides and nitrogen oxides which are them chemically converted into sulfuric and nitric acids. Other than this some sulfuric acid may also be formed directly in the droplets of water from the reaction of sulfur dioxide and hydrogen peroxide.
Some of the effects caused by acid rain and the sulfuric acid present in it are:

• The acid may react with buildings and marble made structure by reacting with the Calcium carbonate and this reaction forms Calcium bicarbonate which is soluble and hence causes the structures, buildings etc to deteriorate.  

• Acid rain can filter aluminum from the soil and make it get mixed with ground water, lakes or rivers. This can poison fish and many plant roots. 

•Acid rain disrupts the process of photosynthesis, hence causing damage to plant life 

•If the acid rain is highly concentrated, it slows down the production of chlorophyll and at high concentration it may kill plants.

The relationship between Acid Rain and Corrosion?

Acid rain is the mixing of different harmful gases such as sulfur and nitrogen and when they mix with rain they form acid rain.The main causes of these harmful gases are cars,various factories and powerplants.Due to the harmful emissions acid rain is formed.As population increases so do all these harmful emissions.One of the main contributors that lead to acid rain are coal powerplants.As to why the corrosion,well when sulfuric acid and the calcium compounds in various buildings and monuments mix together they lead to the creation of gypsum which eventually flakes off leading to corrosion.Acid rain also has many diverse effects on the environment.
When  petroleum burns, it  produces oxides of nitrogen and  that rise up into the atmosphere.  There they get mixed by wind and undergo chemical reactions with sunlight and moisture. After some days,  the sulfuric acid and nitric acid particles fall as acid rain. So not only sulphuric acid is involved but nitric acid also plays an important role. Due to acidic features acid rain eats into the stone surfaces at once. These particles settle into crevices and molding, and
the damage they create comes later. When rain comes in contact with the deposits  corrosion is there.

What can the Acid Rain do to the soil and water?


Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pHs and are killed.The enzymes of these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins, e.g. aluminium, and leach away essential nutrients and minerals.
2H+ (aq)+ Mg2+ (clay) 2H+ (clay)+ Mg2+(aq)
Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).
Acid rain has many adverse effects on plant life. It may be direct or indirect. It stunts the growth of plants. The worst adverse effect is that acid rain seriously damages the soil biology.Only a few microbes consume acids. The enzymes of there microbes change shape by the acid. To retain the pH of the soil lime stone can be used.

Surface waters and aquatic animals

Both the lower pH and higher aluminum concentrations in surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals. At pHs lower than 5 most fish eggs will not hatch and lower pHs can kill adult fish. As lakes and rivers become more acidic biodiversity is reduced. Acid rain has eliminated insect life and some fish species, including the brook trout in some lakes, streams, and creeks in geographically sensitive areas, such as the Adirondack Mountains of the United States.However, the extent to which acid rain contributes directly or indirectly via runoff from the catchment to lake and river acidity (i.e., depending on characteristics of the surrounding watershed) is variable. 


Acid rain was first described by an English man in 1872. He was a chemist and was first to note that rain that fell had a high percentage of acidity which effected man, animal and plants. It is now the most controversial form of air pollution in the developed world.
Rain clouds
Acid rain is a form of pollution which became a serious environmental problem in the large urban and industrial areas of North America, Europe and Asia. Any precipitation that contains a heavy concentration of Sulphuric Acid (H2SO4) and Nitric Acid (HNO3) is generally called acid rain. Automobile industries, electrical power plants and some other industrial operations that burn fossil fuels and emit the gases like sulphur dioxide (SO2) and nitrogen oxide (NO2) into the environment. In the air the gases meet with water vapour available in clouds to reform Sulphuric Acid and Nitric Acid. This acid rain or highly acidic precipitation from those clouds may contaminate lakes and streams, thereby, harming the fishes and other aquatic species. It also causes a great harm to vegetation including agricultural crops and plants and trees. Now-a-days acid rain or acid precipitation has become a threatening problem for the environment and humankind.

Acid rain is rain that has been made acidic by certain pollutants in the air. Acid rain is a type of acid deposition, which can appear in many forms. Wet deposition is rain, sleet, snow, or fog that has become more acidic than normal. Dry deposition is another form of acid deposition, and this is when gases and dust particles become acidic. Both wet and dry deposition can be carried by the wind, sometimes for very long distances. Acid deposition in wet and dry forms falls on buildings, cars, and trees and can make lakes acidic. Acid deposition in dry form can be inhaled by people and can cause health problems in some people.
What is acidity?
Acidic and basic are two ways that we describe chemical compounds. Acidity is measured using a pH scale. A pH scale runs from zero (the most acidic) to 14 (the most basic or alkaline). A substance that is neither basic or acidic is called "neutral", and this has a pH of 7.

Sources of Acid RainAcid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain. Sulfur dioxide and nitrogen oxides dissolve very easily in water and can be carried very far by the wind. As a result, the two compounds can travel long distances where they become part of the rain, sleet, snow, and fog that we experience on certain days.
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.
Acid Rain is Caused by 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 neutralize natural acids. However, if precipitation becomes too acidic, these materials may not be able to neutralize all of the acids. Over time, these neutralizing materials can be washed away by acid rain. Damage to crops, trees, lakes, rivers, and animals can result.

Why is Acid Rain Harmful?

Tree affected by acid rainAcid Rain Can Cause Health Problems in People
Air pollution like sulfur dioxide and nitrogen oxides can cause respiratory diseases, or can make these diseases worse. Respiratory diseases like asthma or chronic bronchitis make it hard for people to breathe. The pollution that causes acid rain can also create tiny particles. When these particles get into people’s lungs, they can cause health problems, or can make existing health problems worse. Also, nitrogen oxides cause ground-level ozone. This ground-level ozone causes respiratory problems, like pneumonia and bronchitis, and can even cause permanent lung damage. The health effects that people have to worry about are not caused by the acid rain, but are caused when people breathe in these tiny particles or ozone. Swimming in an acidic lake or walking in an acidic puddle is no more harmful to people than swimming or walking in clean water.
Acid Rain Harms Forests
Acid rain can be extremely harmful to forests. Acid rain that seeps into the ground can dissolve nutrients, such as magnesium and calcium, that trees need to be healthy. Acid rain also causes aluminum to be released into the soil, which makes it difficult for trees to take up water. Trees that are located in mountainous regions at higher elevations, such as spruce or fir trees, are at greater risk because they are exposed to acidic clouds and fog, which contain greater amounts of acid than rain or snow. The acidic clouds and fog strip important nutrients from their leaves and needles. This loss of nutrients makes it easier for infections, insects, and cold weather to damage trees and forests.
Acid Rain Damages Lakes and StreamsWithout pollution or acid rain, most lakes and streams would have a pH level near 6.5. Acid rain, however, has caused many lakes and streams in the northeast United States and certain other places to have much lower pH levels. In addition, aluminum that is released into the soil eventually ends up in lakes and streams. Unfortunately, this increase in acidity and aluminum levels can be deadly to aquatic wildlife, including phytoplankton, mayflies, rainbow trout, small mouth bass, frogs, spotted salamanders, crayfish, and other creatures that are part of the food web.
This problem can become much worse during heavy downpours of rain or when the snow begins to melt in the spring. These types of events are known as episodic acidification.
Acid Rain Damages Buildings and Objects
Acid rain can also have a damaging effect on many objects, including buildings, statues, monuments, and cars. The chemicals found in acid rain can cause paint to peel and stone statues to begin to appear old and worn down, which reduces their value and beauty.
What is Being Done?

Capitol BuildingNow that you know why acid rain is a problem, you might be wondering what’s being done to control it. Regulations and new technologies are helping reduce acid rain.
EPA’s Acid Rain Program
Power plants generate the electricity we use every day. Unfortunately, power plants also produce large amounts of nitrogen oxides and sulfur dioxide—the pollutants that cause acid rain—when they burn fossil fuels, especially coal, to produce energy. Congress passed a law called the Clean Air Act Amendments of 1990, and this law said that EPA should start the Acid Rain Program. The program limits, or puts a cap on, the amount of sulfur dioxide that power plants can release into the air and issues allowances to the power plants to cover their sulfur dioxide emissions. It also reduces the amount of nitrogen oxides that power plants can release.
Reducing Pollution
Scientists have found different ways to reduce the amount of sulfur dioxide released from coal-burning power plants. One option is to use coal that contains less sulfur. Another option is to “wash” the coal to remove some of the sulfur. The power plant can also install equipment called scrubbers, which remove the sulfur dioxide from gases leaving the smokestack. Because nitrogen oxides are created in the process of burning coal and other fossil fuels, some power plants are changing the way they burn coal.
Other Sources of Energy
A great way to reduce acid rain is to produce energy without using fossil fuels. Instead, people can use renewable energy sources, such as solar and wind power. Renewable energy sources help reduce acid rain because they produce much less pollution. These energy sources can be used to power machinery and produce electricity.
Cleaner Cars
Cars and trucks are major sources of the pollutants that cause acid rain. While one car alone does not produce much pollution, all the cars on the road added together create lots of pollution. Therefore, car manufacturers are required to reduce the amount of nitrogen oxides and other pollutants released by new cars. One type of technology used in cars is called a catalytic converter. This piece of equipment has been used for over 20 years to reduce the amount of nitrogen oxides released by cars. Some new cars can also use cleaner fuels, such as natural gas. Cars that produce less pollution and are better for the environment are often labeled as low emissions vehicles.
What Can You Do?
People carpooling to reduce the creation of acid rain.Government agencies and scientists are not the only ones that can take action to stop acid rain. You can become part of the solution, too!
Understand the Problem
The first step you can take to help control acid rain is to understand the problem and its solutions. Now that you have learned about this environmental issue, you can tell others about it. By telling your classmates, parents, and teachers about what you learned on this site, you can help educate them about the problem of acid rain. You CAN make a difference!
Conserve Energy
Since energy production creates large amounts of the pollutants that cause acid rain, one important step you can take is to conserve energy. You can do this in a number of ways:
  • Turn off lights, computers, televisions, video games, and other electrical equipment when you're not using them.
  • Encourage your parents to buy equipment that uses less electricity, including lights, air conditioners, heaters, refrigerators, and washing machines. Such equipment might have the Energy Star label.
  • Try to limit the use of air conditioning.
  • Ask your parents to adjust the thermostat (the device used to control the temperature in your home) when you go on vacation.
Minimize the Miles
Driving cars and trucks also produces large amounts of nitrogen oxides, which cause acid rain. To help cut down on air pollution from cars, you can carpool or take public transportation, such as buses and trains. Also, ask your parents to walk or bike with you to a nearby store or friend’s house instead of driving.

Air Pollution Affects Plants, Animals, and Environments

Air pollution does not only damage the air; it also damages environments on Earth’s surface and their inhabitants. Plants and animals are harmed by air pollution. Sometimes it is the pollutants themselves that cause damage. Other times pollutants combine and change the resources that plants and animals depend upon such as water, soil, and nutrients. Read on to learn more about the ways that air pollutants can damage environments and the living things within them.

Acid rain harms living things
When an air pollutant, such as sulfuric acid combines with the water droplets that make up clouds, the water droplets become acidic. When those droplets fall to the ground as rain or snow, the acidity of the water can have damaging effects on the environment. When acid rain falls over an area, it can kill trees and harm animals, fish, and other wildlife. Acid rain destroys the leaves of plants. When acid rain infiltrates into soils, it changes the chemistry of the soil making it unfit for many living things that rely on soil as a habitat or for nutrition. Acid rain also changes the chemistry of the lakes and streams that the rainwater flows into, harming fish and other aquatic life.

The thinning ozone layer harms living things
Air pollutants called chlorofluorocarbons(or CFCs) destroy ozone molecules in the stratosphere. This has left places in the layer where the ozone is thin. These areas of thin ozone are called ozone holes. The ozone layer, located in the stratosphere layer of Earth’s atmosphere, shields our planet from the Sun’s ultraviolet radiation. Ultraviolet radiation causes skin cancer and damages plants and wildlife. In recent decades the number of CFCs released into the atmosphere has decreased significantly due to an agreement between the nations of the world called the Montreal Protocol. Although it takes a long time to see the impact, the ozone holes might someday be smaller.

Tropospheric ozone harms living things
Ozone molecules in the troposphere damage lung tissues of animals and prevent plant respiration by blocking the openings in leaves, called stomata, where respiration occurs. Without sufficient respiration, a plant is not able to photosynthesize at a high rate and will not be able to grow. Ozone is also able to enter the stomata and decay plant cells directly.

Global warming harms living things
Our planet is currently warming much more rapidly than expected because of additional greenhouse gasses that are released into the atmosphere from air pollution. When fuels are burned, some of the pollutants released, such as carbon dioxide, are greenhouses gasses. Through the process of photosynthesis, plants convert carbon dioxide into oxygen and use the carbon to grow larger. However, the amount of carbon dioxide released by burning fuels is far greater than plants can convert. Cutting down forests exacerbates the problem.

Global warming is changing climate globally and is causing significant changes to various regions of the world. For example:

    * Polar ice melt and permafrost melt are causing changes in the habitat and resources for plants and animals living in polar ecosystems.
    * Ocean warming, rising sea levels, increasing runoff, and coral diseases are causing change in shallow marine ecosystems such as coral reefs.
    * Less rainfall in the dry interiors of continents due to global warming is limiting water resources for plants and animals.

Some air pollutants harm plants and animals directly. Other pollutants harm the habitat, food or water that plants and animals need to survive. Read on to learn more about how air pollutants harm plants and animals.

Acid rain harms living things
When acidic air pollutants combine with water droplets in clouds, the water becomes acidic. When those droplets fall to the ground, the acid rain can damage the environment. Damage due to acid rain kills trees and harms animals, fish, and other wildlife. Acid rain can destroy the leaves of plants like in the picture at the left. When acid rain soaks into the ground, it can make the soil an unfit habitat for many living things. Acid rain also changes the chemistry of the water in lakes and streams, harming fish and other aquatic life.

The thinning ozone layer harms living things
Air pollutants called chlorofluorocarbons(or CFCs) have destroyed parts of the ozone layer.The ozone layer, located in the stratosphere layer of Earth's atmosphere, shields our planet from the Sun's ultraviolet radiation. The areas of thin ozone are called ozone holes. Ultraviolet radiation causes skin cancer and damages plants and wildlife.

Tropospheric ozone harms living things
Ozone molecules wind up near the Earth's surface as a part of air pollution. Ozone molecules near the ground damages lung tissues of animals and prevent plant respiration by blocking the openings in leaves where respiration occurs. Without respiration, a plant is not able to photosynthesize at a high rate and so it will not be able to grow.

Global warming harms living things
Our planet is currently warming much more rapidly than expected because additional greenhouse gasses are being released into the atmosphere from air pollution. When fuels are burned, some of the pollutants released are greenhouses gasses. Through the process of photosynthesis, plants convert carbon dioxide into oxygen and use the carbon to grow larger. However, the amount of carbon dioxide released by burning fuels is much more than plants can convert.

Global warming is causing changes to the places where plants and animals live around the world. For example:

    * Near the poles, ice and frozen ground are melting. This causes changes in the habitat and resources for plants and animals living there.
    * Ocean warming, rising sea levels, runoff, and coral diseases are causing change in shallow marine environments such as coral reefs.
    * Global warming is causing less rain to fall in the middle of continents. This makes these areas very dry and limits water resources for plants and animals.

Acid rain harms living things
Did you know that air pollution can change the rain? And all living things need rain for water to drink, or to swim within. The rain changed by air pollution is called acid rain. Acid rain kills trees and harms animals. Acid rain can destroy the leaves of plants like in this picture. When acid rain soaks into the ground, it can make the soil unhealthy for many living things. Acid rain also changes the water in lakes and streams, harming fish and other aquatic life.

Ozone holes harm living things
Some air pollutants have damaged parts of the ozone layer high in the atmosphere. The ozone layer protects our planet from the Sun's harmful rays. The areas of thin ozone are called ozone holes. These strong rays from the Sun cause skin cancer and damage plants and wildlife.

Ozone near the ground harms living things
Pollution releases ozone near the ground. Ozone molecules near the ground hurt the lungs of animals and people and prevent plants from breathing by blocking the openings in leaves where they breathe. Without breathing, a plant is not able to grow.

Global warming harms living things
Our planet is currently warming quickly. The extra warmth is caused by greenhouse gasses from air pollution. Greenhouse gasses are released into the atmosphere when fuels are burned. Plants can make some of the greenhouse gasses into oxygen in the air and carbon to grow their leaves, stems, and trunks larger. However, the amount of greenhouse gasses released in air pollution is much more than plants can use.

Global warming is causing changes to the places where plants and animals live around the world. For example:

    * Near the poles, ice and frozen ground are melting. This causes changes in the habitat and resources for plants and animals living there.
    * Ocean warming, rising sea levels, runoff, and coral diseases are causing change in shallow marine environments such as coral reefs.
    * Global warming is causing less rain to fall in the middle of continents. This makes these areas very dry and limits water resources for plants and animals.

Tuesday, March 5, 2013

Acid Rain

 In October 1998, U.S. Senator Daniel Patrick Moynihan testified before Congress on acid rain. A longtime champion of the issue, Moynihan stated that "As far back as the 1960s, fishermen in the Adirondacks began to complain about more than 'the big one that got away.' Fish, once abundant in the pristine, remote Adirondack lakes, were not just getting harder to catch. They were gone."

The issue of acid rain emerged in the United States in the mid-1970s. At the time, little was known about the magnitude and distribution of acid rain or about its impacts on terrestrial (land-based) and aquatic ecosystems . However, many believed that acid rain and the air pollutants that caused it posed a threat to forests, aquatic life, crops, structures (e.g., buildings), cultural artifacts (e.g., statues and monuments), and human health.

Since the 1970s, acid rain has been addressed in the United States through hundreds of millions of dollars of research, passage of laws, and implementation of regulatory programs. However, Senator Moynihan's 1998 remark is stark testimony to the fact that acid rain continues to have a negative effect on natural resources, and addressing the problem is an enduring public policy dilemma.
Sources and Forms of Acid Rain

Rain, snow, sleet, and other forms of precipitation are naturally slightly acidic because of chemical reactions with carbon dioxide and other naturally occurring substances in the atmosphere. But this natural acidity can be increased by human-induced air pollution. Acid deposition or "acid rain" occurs when emissions of sulfur dioxide (SO 2 ) and oxides of nitrogen (NO x ) in the atmosphere react with water, oxygen, and oxidants to form mild solutions of sulfuric acid or nitric acid. Sunlight increases the rate of most of these reactions. These compounds fall to Earth and are deposited in either wet form (e.g., rain, snow, sleet, and hail), known as wet deposition, or dry form (e.g., particles, gases, and vapor), known as dry deposition. Cloud or fog deposition, a form of wet deposition, occurs at high elevations and in coastal areas.

In the United States, nearly two-thirds of annual SO 2 emissions and just over one-fifth of NO x emissions are produced by electric utility plants that burn fossil fuels . Transportation sources (e.g., cars, trucks, and other vehicles) account for more than half of NO x emissions. Ammonia emissions derive largely from livestock waste and fertilized soil. Industrial combustion 

 A sign in Nova Scotia, Canada proclaims the potential effect of acid rain on a local river and its salmon runs. Acidified waters can be harmful or even deadly to salmon populations.
and industrial processes are the other major categories of emission sources. Acid rain is a regional problem because prevailing winds can transport SO 2 and NO x emissions over hundreds of kilometers, sometimes crossing state, national, and international borders.

Wet Deposition.

Wet deposition of sulfur and nitrogen compounds is commonly known as acid rain, although it also takes the form of snow, sleet, clouds, or fog. Wet deposition is intermittent because acids reach the Earth only when precipitation falls. Nevertheless, it can be the primary pathway for acid deposition in areas with heavy precipitation.

The eastern United States receives more acidic precipitation than the rest of the country, with the greatest rates occurring in Ohio, West Virginia, western Pennsylvania, upstate New York, New England, and other northeastern areas. Because nitrogen compounds can remain stored in snow until it melts, nitrate concentrations in lakes and streams can increase dramatically during seasonal or episodic acidification, particularly in the Northeast, resulting in toxic impacts on aquatic organisms.

Acidic compounds can reach plants, soil, and water from contact with acidic clouds as well. Although cloud deposition affects only a limited number of locations, it can provide a relatively steady source of acids in comparison with wet deposition, particularly at high altitudes. As a result, trees such as the red spruce have declined in areas of significant cloud deposition.

Dry Deposition.

Dry deposition occurs when acidic gases and particles in the atmosphere are deposited directly onto surfaces when precipitation is not occurring. Dry-deposited gases and particles can also be washed from trees and other surfaces by rainstorms, making the combination more acidic than the falling rain alone. Dry deposition is the primary acid deposition pathway in arid regions of the West, such as Joshua Tree National Park.

Effects on Aquatic Ecosystems

The ecological effects of acid rain are most clearly seen in aquatic environments, particularly streams and lakes. Acid rain mainly affects sensitive bodies of water that are located in watersheds whose soils have limited ability to neutralize acidic compounds. The ability of forest soils to neutralize acidity, referred to as buffering capacity, results from chemicals in the soil that neutralize some or all of the acidity in rainwater. Buffering capacity depends on the thickness and composition of the soil as well as the type of bedrock beneath the forest floor.

Lakes and streams become acidic ( pH decreases) when the water itself and its surrounding soil cannot neutralize the acidity in the rain. Differences in soil buffering capacity are an important reason that some areas receiving acid rain show damage, whereas other areas receiving about the same amount of acid rain do not appear to be harmed.

Several regions in the United States contain many of the surface waters sensitive to acidification. They include the Adirondacks and Catskill Mountains in New York State, the mid-Appalachian highlands, the upper Midwest, and mountainous areas of the western United States. In areas such as the northeastern United States, where soil buffering capacity is low, some lakes have a pH value of less than 5. With a pH of 4.2, Little Echo Pond in Franklin, New York was one of the most acidic lakes reported as of 2002.

Ecosystem Impacts.

Acid rain is not the sole cause of low pH in lakes and streams. There are many natural sources of acidity that can drive down pH to low levels (as low as 4) even in the absence of acid rain: for example, organic acid inputs or mineral veins in underlying geologic materials. Similarly, natural sources of buffering capacity such as limestone bedrock can push pH to as high as 8. Notwithstanding these natural influences in specific locations, lakes and streams generally have pH values from 6 to 8. Hence, reductions in pH due to human-induced acid rain create an imbalance in the chemistry and ultimately the entire ecosystem of a lake or stream.

Acid rain causes a cascade of effects that harm or kill individual fish, reduce fish populations, completely eliminate fish species from a waterbody, and decrease biodiversity . As acid rain flows through soils in a watershed, aluminum and other metals are released from soils into the lakes and streams located in that watershed. Thus, as a lake or stream becomes more acidic (has lower pH), aluminum levels increase. Both low pH and increased aluminum levels are directly toxic to fish. In addition, low pH and increased aluminum levels cause chronic stress that may not kill individual fish but may make fish less able to compete for food and habitat.

The impact of declining pH varies because not all aquatic organisms can tolerate the same amount of acid. For example, frogs are better able than trout to tolerate somewhat acidified water. Generally, the young of most species are more sensitive to environmental conditions than adults.

As pH levels decline, acid-sensitive species may attempt to migrate to better habitat, or, if blocked from migration, will likely die. At pH 5 and below, most fish species disappear, and ecosystem-level processes are affected. Some acid lakes and streams contain no fish. 

Acidified lakes and streams can be treated with agricultural lime in an attempt to counteract the acidity. Such temporary and localized measures are not as effective as emissions reductions in addressing the long-term and geographically widespread ecological impacts of acid rain.

Effects on Forests and Soils

Acid rain has been implicated in forest and soil degradation in many areas of the eastern United States, particularly high elevation forests of the Appalachian Mountains from Maine to Georgia. Acid rain does not usually kill trees directly. Instead, it weakens trees by damaging their foliage, limiting the nutrients available to them, or exposing them to toxic substances slowly released from the soil. Quite often, injury or death is a result of acid rain in combination with other environmental stressors, such as insects, disease, drought, or very cold weather.

Chemicals in watershed soils that provide buffering capacity (such as calcium and magnesium) are also important nutrients for many species of trees. As forest soils receive year after year of acid rain, these chemicals are washed away, depriving trees and other plants of essential soil nutrients. At the same time, acid rain causes the release of dissolved aluminum into the soil water, which can be toxic to trees and plants. The chemicals that provide buffering capacity take many decades to replenish through gradual natural processes, such as the weathering of limestone bedrock.

Trees also can be damaged by acid rain even if the soil is well buffered. Mountainous forests often are exposed to greater amounts of acidity because they tend to be surrounded by acidic clouds and fog. Essential nutrients in foliage are stripped away when leaves and needles are frequently bathed in acid fog, causing discoloration and increasing the potential for damage by other environmental factors, especially cold weather.

Effects on Human Health and Human Environments

The pollutants that cause acid rain also damage human health. These gases interact in the atmosphere to form fine sulfate and nitrate particles that can be inhaled deep into the lungs. Scientific studies show relationships between elevated levels of fine particles and increased illness and premature death from heart disease and lung disorders, such as bronchitis. In addition, nitrogen oxides react in the atmosphere to form ozone , increasing risks associated with lung inflammation, such as asthma.

Sulfates and nitrates in the atmosphere also contribute to reductions in visibility. Sulfate particles account for 50 to 70 percent of decreased visibility in eastern U.S. national parks, such as the Shenandoah and the Great Smoky Mountains. In the western United States, nitrates and carbon also play roles, but sulfates have been implicated as an important source of visibility impairment in some national parks, such as the Grand Canyon.

Wet and dry acid deposition contribute to the corrosion of metals (such as bronze) and the deterioration of paint and stone (such as marble and limestone). These effects seriously reduce the value to society of buildings, bridges, cultural objects (such as statues, monuments, and tombstones), and automobiles.
1990 Clean Air Act Amendments: Title IV

In 1990, the U.S. Congress took action intended to address acid rain issues, passing the Clean Air Act Amendments (CAAA) (42 U.S.C. 7651). The purpose of the Acid Rain Program (Title IV of the 1990 amendments) was to address the adverse effects of acid rain by reducing annual emissions of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x )—the main air pollutants that cause the problems—from stationary power generation sources.

Implemented by the U.S. Environmental Protection Agency starting in 1995, the program consists of two major components. The SO 2 emission reduction program employs a two-phase cap-and-trade approach to reduce total annual SO 2 emissions by 10 million tons below 1980 levels by 2010 (roughly a 40-percent reduction in total emissions). When the SO 2 emission reduction is fully implemented in approximately 2010, electric utility emissions will be capped at 8.95 million tons per year (representing approximately a 50-percent reduction in emissions from this sector).

The NO x emission reduction program aims to reduce annual NO x emissions from coal-fired electric utility boilers by 2 million tons below what they would have been without Title IV. The NO x component of the program does not include a cap on NO x emissions or any emissions trading provisions.
Emissions Trading.

In establishing the Acid Rain Program, Congress chose to utilize an innovative environmental management approach known as capand-trade, or emissions trading, to reduce SO 2 emissions. Emissions trading is a departure from more traditional "command and control" regulatory approaches in which the government commands industry to install particular control technologies at specific plants in order to reduce pollution. Because emissions trading allows industry the flexibility to reduce pollution from sources that can achieve reductions least expensively, large amounts of emissions are reduced at lower costs, with less administrative burden and fewer lengthy lawsuits, than if sources were regulated individually.

The approach first sets an overall cap (maximum amount of emissions) that policymakers believe will achieve the desired environmental effects. Affected sources are then allocated emission allowances that permit them to emit a certain amount of a pollutant. The total number of allowances given to all sources cannot exceed the cap.

Sources are not told how to reach the emissions goal established by the number of allowances they are given. They may reach their goal through various means, including buying allowances from sources that are able to reduce emissions more cost effectively and so have excess allowances to sell. The only requirements are that sources completely and accurately measure and report all emissions and then turn in the same number of allowances as emissions at the end of the yearly compliance period. If emissions exceed allowances, a source faces expensive fines and other penalties.

Cap-and-trade is effective for the following reasons:

    * The mandatory cap always protects the environment. Even as the economy grows, or as new sources enter the industry, total emissions cannot exceed the cap.
    * Complete and consistent emissions measurement and reporting by all sources guarantee that total emissions do not exceed the cap and that individual sources' emissions are no higher than their allowances.
    * The design and operation of the program is simple, which helps keep compliance and administrative costs low.

Effectiveness of the Acid Rain Program

In terms of SO 2 emissions reductions, the results of the Acid Rain Program have been dramatic—and unprecedented. From its 1995 inception to 1999 (completion of Phase I), annual SO 2 emissions from the largest, highestemitting sources dropped by nearly 5 million tons from 1980 levels. These reductions were an average of 25 percent below required emission levels, resulting in early achievement of human health and environmental benefits. In 2001, SO 2 emissions from power generation were more than 6.7 million tons below 1980 levels.

Emissions of NO x have been reduced by 1.5 million tons from 1990 levels (about 3 million tons lower than projected growth). Because the NO x component of the program includes no cap, there is no guarantee that NO x emissions will stay at these low levels; without a cap, emissions may increase as power generation increases.

Because of the reduction in SO 2 emissions, acidity of rainfall in the eastern United States has dropped by up to 25 percent. As a consequence, some sensitive lakes and streams in New England are showing signs of recovery. Further, sulfate concentrations in the air have decreased, leading to improved air quality and associated benefits to public health, such as fewer irritations or aggravations to respiratory conditions (e.g., asthma and chronic bronchitis). Finally, visibility has improved in some parts of the eastern United States, including areas with scenic vistas, such as Acadia National Park in coastal Maine.

Although the Clean Air Act has had positive effects, emissions and acid deposition remain high compared to background conditions. The rate and extent of ecosystem recovery from acid deposition are directly related to the timing and degree of emissions reductions. Research suggests that deeper emissions cuts will lead to greater and faster recovery from acid deposition in the northeastern United States.

Effects of Acid Rain

Acid rain, like its name suggests, is rainfall that is highly acidic, much more so than normal precipitation. Acid rain is usually a result of human air pollution such as emissions of sulfur and nitrogen compounds. These compounds react with those in the atmosphere causing acids to be produced and in turn causing precipitation to be acidic in nature. A major public concern due to its ability to damage property, not to mention its negative impact on both aquatic and land animal and plant life, many steps have been taken to reduce acid rain’s effect on the environment.

The main cause of acid rain is human consumption. The burning of fossil fuels from numerous sources such as factories, power plants, and automobiles create the gases that lead to acid rain. Power plants that operate with the burning of coal are recognized as being some of the worst sources of acid rain. Although acid rain is usually considered a modern phenomenon, it does occur naturally, though on a lower scale. Emissions from burning volcanoes and from natural biological processes, such as methane emissions from cattle are some of the more common natural causes.

Acid rain is known to cause significant damage to property due to its chemical compound. It eats away at marble and limestone which are often used in the construction of government buildings and monuments as well as gravestones in cemeteries. Metals (iron for instance) are also affected by the alkaline present in acid rain.

The negative impact of acid rain is evident in ecosystems. Acid rain changes the PH levels of rivers and lakes. Animals such as fish are very susceptible to changes in PH and therefore are unable to survive if the change is too drastic. Plankton and invertebrates are put even more at risk. Acid rain in water environments can also affect plant life. On land, acid rain damages forests in high altitudes and also lowers the fertility of soil as important nutrients and minerals are removed from it. These impacts on different aspects of the environment have a trickling down effect that negatively influence entire ecosystems.

Since the recognition of acid rain as an important public concern, many steps have been taken to decrease its occurrence. The National Acidic Precipitation Assessment Program was created in the United States to monitor the effects of acid rain on the environment. Western countries in Europe and North America have taken significant measures to reduce the harmful emissions that are the cause of acid rain. Changes such as stricter emissions regulations for motor vehicles and emissions trading which create economic incentives for factories to decrease their pollution.

Acid Rain does continue to be a global problem. Asia is currently the region in the world that is most affected by it. Lax or nonexistent emissions regulations, especially in China, contribute to this. To address this problem, global treaties such as the Sulphur Emissions Reduction Protocol and the Nitrogen Oxide Protocol have been enacted. Stricter emissions laws both nationally and internationally as well as the introduction of alternative energy sources will no doubt help to prevent acid rain in the future.

Introduction to the Hydrosphere

Acid Precipitation

Acidic pollutants can be deposited from the atmosphere to the Earth's surface in wet and dry forms. The common term to describe this process is acid deposition. The term acid precipitation is used to specifically describe wet forms of acid pollution that can be found in rain, sleet, snow, fog, and cloud vapor. An acid can be defined as any substance that when dissolved in water dissociates to yield corrosive hydrogen ions. The acidity of substances dissolved in water is commonly measured in terms of pH (defined as the negative logarithm of the concentration of hydrogen ions). According to this measurement scale solutions with pHs less than 7 are described as being acidic, while a pH greater than 7.0 is considered alkaline (Figure h-1). Precipitation normally has a pH between 5.0 to 5.6 because of natural atmospheric reactions involving carbon dioxide. For comparison, distilled water, pure of any other stubstances, would have a pH of 7.0. Precipitation is considered to be acidic when its pH falls below 5.6 (which is 25 times more acidic than pure distilled water). Some sites in eastern North America have precipitation events with pHs as low as 2.3 or about 1000 times more acidic than natural.
Figure h-1: The pH scale. A value of 7.0 is considered neutral. Values higher than 7.0 are increasingly alkaline or basic. Values lower than 7.0 are increasingly acidic. The illustration above also describes the pH of some common substances.

Acid deposition is not a recent phenomenon. In the 17th century, scientists noted the ill effects that industry and acidic pollution was having on vegetation and people. However, the term acid rain was first used two centuries later when Angus Smith published a book called 'Acid Rain' in 1872. In the 1960s, the problems associated with acid deposition became an international problem when fishermen noticed declines in fish numbers and diversity in many lakes throughout North America and Europe.

Acid Deposition Formation

Acid deposition can form as a result of two processes. In some cases, hydrochloric acid can be expelled directly into the atmosphere. More commonly it is due to secondary pollutants that form from the oxidation of nitrogen oxides (NOx) or sulfur dioxide (SO2) gases that are released into the atmosphere (see Figure                         h-2). Reactions at the Earth's surface or within the atmosphere can convert these pollutants into nitric acid or sulfuric acid. The process of altering these gases into their acid counterparts can take several days, and during this time these pollutants can be transported hundreds of kilometers from their original source. Acid precipitation formation can also take place at the Earth's surface when nitrogen oxides and sulfur dioxide settle on the landscape and interact with dew or frost.
Emissions of sulfur dioxide are responsible for 60-70% of the acid deposition that occurs globally. More than 90% of the sulfur in the atmosphere is of human origin. The main sources of sulfur include:
  • Coal burning - coal typically contains 2-3% sulfur so when it is burned sulfur dioxide is liberated.
  • The smelting of metal sulfide ores to obtain the pure metals. Metals such as zinc, nickel, and copper are all commonly obtained in this manner.
  • Volcanic eruptions - although this is not a widespread problem, a volcanic eruption can add a lot of sulfur to the atmosphere in a regional area.
  • Organic decay.
  • Ocean spray.
After being released into the atmosphere, sulfur dioxide can either be deposited on the Earth's surface in the form of dry deposition or it can undergo the following reactions to produce acids that are incorporated into the products of wet deposition (Figure h-2):

SO2 + H2O »»» H2SO3
H2SO3 + 1/2O2 »»» H2SO4

Figure h-2: Several processes can result in the formation of acid deposition. Nitrogen oxides (NOx) and sulfur dioxide (SO2) released into the atmosphere from a variety of sources call fall to the ground simply as dry deposition. This dry deposition can then be converted into acids when these deposited chemicals meet water. Most wet acid deposition forms when nitrogen oxides (NOx) and sulfur dioxide (SO2) are converted to nitric acid (HNO3) and sulfuric acid (H2SO4) through oxidation and dissolution. Wet deposition can also form when ammonia gas (NH3) from natural sources is converted into ammonium (NH4).


Some 95% of the elevated levels of nitrogen oxides in the atmosphere are the result of human activities. The remaining 5% comes from several natural processes. The major sources of nitrogen oxides include:
  • Combustion of oil, coal, and gas.
  • Bacterial action in soil.
  • Forest fires.
  • Volcanic action.
  • Lightning.
Acids of nitrogen form as a result of the following atmospheric chemical reactions (see Figure h-2 above):

NO + 1/2O2 »»» NO2
2NO2 + H2O »»» HNO2 + HNO3
NO2 + OH »»» HNO3

Finally, the concentrations of both nitrogen oxides and sulfur dioxides are much lower than atmospheric carbon dioxide which is mainly responsible for making natural rainwater slightly acidic. However, these gases are much more soluble than carbon dioxide and therefore have a much greater effect on the pH of the precipitation.

Effects of Acid Deposition
Acid deposition influences the environment in several different ways. In aquatic systems, acid deposition can effect these ecosystems by lowering their pH. However, not all aquatic systems are effected equally. Streams, ponds, or lakes that exist on bedrock or sediments rich in calcium and/or magnesium are naturally buffered from the effects of acid deposition. Aquatic systems on neutral or acidic bedrock are normally very sensitive to acid deposition because they lack basic compounds that buffer acidification (see Figure h-3). In Canada, many of the water bodies found on the granitic Canadian Shield fall in this group. One of the most obvious effects of aquatic acidification is the decline in fish numbers. Originally, it was believed that the fish died because of the increasing acidity of the water. However, in the 1970s scientists discovered that acidified lakes also contained high concentrations of toxic heavy metals like mercury, aluminum, and cadmium. The source of these heavy metals was the soil and bedrock surrounding the water body. Normally, these chemicals are found locked in clay particles, minerals, and rocks. However, the acidification of terrestrial soils and bedrock can cause these metals to become soluble. Once soluble, these toxic metals are easily leached by infiltrating water into aquatic systems where they accumulate to toxic levels.
Figure 8h-3: Lake acidification begins with the deposition of the byproducts acid precipitation (SO4 and H ions) in terrestrial areas located adjacent to the water body. Hydrologic processes then move these chemicals through soil and bedrock where they can react with limestone and aluminum-containing silicate minerals. After these chemical reactions, the leachate continues to travel until it reaches the lake. The acidity of the leachate entering lake is controlled by the chemical composition of the effected lake's surrounding soil and bedrock. If the soil and bedrock is rich in limestone the acidity of the infiltrate can be reduced by the buffering action of calcium and magnesium compounds. Toxic aluminum (and some other toxic heavy metals) can leach into the lake if the soil and bedrock is rich in aluminum-rich silicate minerals.

In the middle latitudes, many acidified aquatic systems experience a phenomenon known as acid shock. During the winter the acidic deposits can buildup in the snowpack. With the arrival of spring, snowpack begins to melt quickly and the acids are released over a short period of time at concentrations 5 to 10 times more acidic than rainfall. Most adult fish can survive this shock. However, the eggs and small fry of many spring spawning species are extremely sensitive to this acidification. 

The severity of the impact of acid deposition on vegetation is greatly dependent on the type of soil the plants grow in. Similar to surface water acidification, many soils have a natural buffering capacity and are able to neutralize acid inputs. In general, soils that have a lot of lime are better at neutralizing acids than those that are made up of siliceous sand or weathered acidic bedrock. In less buffered soils, vegetation is effected by acid deposition because:
  • Increasing acidity results in the leaching of several important plant nutrients, including calcium, potassium, and magnesium. Reductions in the availability of these nutrients cause a decline in plant growth rates.
  • The heavy metal aluminum becomes more mobile in acidified soils. Aluminum can damage roots and interfere with plant uptake of other nutrients such as magnesium and potassium.
  • Reductions in soil pH can cause germination of seeds and the growth of young seedlings to be inhibited.
  • Many important soil organisms cannot survive is soils below a pH of about 6.0. The death of these organisms can inhibit decomposition and nutrient cycling.
  • High concentrations of nitric acid can increase the availability of nitrogen and reduce the availability of other nutrients necessary for plant growth. As a result, the plants become over-fertilized by nitrogen (a condition known as nitrogen saturation).
  • Acid precipitation can cause direct damage to the foliage on plants especially when the precipitation is in the form of fog or cloud water which is up to ten times more acidic than rainfall.
  • Dry deposition of SO2 and NOx has been found to affect the ability of leaves to retain water when they are under water stress.
  • Acidic deposition can leach nutrients from the plant tissues weakening their structure.
The combination of these effects can lead to plants that have reduced growth rates, flowering ability and yields. It also makes plants more vulnerable to diseases, insects, droughts and frosts. 

The effects of acidic deposition on humans can be divided into three main categories. Acid deposition can influence human health through the following methods:

  • Toxic metals, such as mercury and aluminum, can be released into the environment through the acidification of soils. The toxic metals can then end up in the drinking water, crops, and fish, and are then ingested by humans through consumption. If ingested in great quantities, these metals can have toxic effects on human health. One metal, aluminum, is believed to be related to the occurrence of Alzheimer's disease.
  • Increased concentrations of sulfur dioxide and oxides of nitrogen have been correlated to increased hospital admissions for respiratory illness.
  • Research on children from communities that receive a high amount of acidic pollution show increased frequencies of chest colds, allergies, and coughs.
Acid deposition also influences the economic livelihoods of some people. Many lakes and streams on the eastern coast of North America are so acidic that the fish decline significantly in numbers. The reduced fish numbers then influence commercial fishermen and industries that rely on sport fishing tourism. Forestry and agriculture are effected by the damage caused to vegetation. In some areas of eastern North America and Europe, large die-backs of trees have occurred. 

Finally, acid deposition effects a number inanimate features of human construction. Buildings and head stones that are constructed from limestone are easily attacked by acids, as are structures that are constructed of iron or steel. Paint on cars can react with acid deposition causing fading. Many of the churches and cathedrals in Europe are under attack from the effects of acidic deposition.