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Acid deposition- commonly called acid rain- is caused by emissions of sulphur dioxide and nitrogen oxides. Although natural sources of sulphur oxides and nitrogen oxides do exist, more than 90% of the sulfur and 95% of the nitrogen emissions occuring in eastern North America are of human origin. These primary air pollutants arise from the use of coal in the production of electricitiy, from base-metal smelting, and from fuel combustion in vehicles. Once released into the atmosphere, they can be converted chemically into such secondary pollutants as nitric acid and sulfuric acid, both of which dissolve easily in water. The resulting acidic water droplets can be carried long distances by prevailing winds, returning to Earth as acid rain, snow, or fog.

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There are three main chemical reactions that are relevant to our acivity.

1. Combustion reaction:Combustion reaction describes what happens when the charcoal is burned with fire in presence of oxygen. The charcoal contains carbon, which becomes carbon dioxide when reacted with oxygen with heat. The carbon dioxide can easily be dissolved in water and form carbonic acid, which is explained in the next step. The below shows a balanced reaction of carbon dioxide formation.

C + O2 CO2

(12 kg C) + (32 kg O) (34 kg CO2)

2. Carbonic acid (H2CO3) formation:Carbon dioxide is a major product of coal combustion reaction. Carbon dioxide in atmosphere reacts with water. When CO2 gas dissolves in water molecules, carbonic acid forms. The below shows each chemical reactions that take place in formation of carbonic acid from carbon dioxide. Carbonic acid is a diprotic acid. It dissociates one protons to make bicarbonate and another proton to make carbonate.

CO2 + H2O H2CO3

H2CO3 H+ + HCO3-

HCO3- H+ + CO32-
* In the demonstration, carbon dioxide formed from burning charcoal will not change the concentration of carbonic acid in the water because the water is already saturated with CO2.

3. Sulfuric acid (H2SO4) formation:Coal contains many impurities and sulfur is one of them. When coal is burned the sulfur combines with oxygen and the sulfur oxides are released to the atmosphere. Sulfur dioxide (SO2) becomes sulfur trioxide (SO3) when reacting with oxygen in the air. This reacts with water molecules in the atmosphere to form sulfuric acid, a strong mineral acid. This makes rain acidic. In our demonstration, the smoke is transferred directly to the water in the beaker to form sulfuric acid. The below shows the chemical reactions that take place in formation of sulfur trioxide, which reacts with water to form sulfuric acid.

2 SO2 + O2 2 SO3

SO3 + H2O H2SO4

H2SO4 H+ + HSO4-

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Fossil fuel is an energy source that is used widely in the world. Examples are heating for houses, fueling automobiles, and other energy sources. Types of fossil fuels include coal, petroleum, and natural gas. In this activity we are focusing on the coal. Coal is a natural resource that forms with geological steps over millions of years. The first step of coal formation is the formation of what is called the peat, which is formed by decomposition of organisms. However, peat cannot be used as a fuel because it is too wet. The peat must have a protective layer of sediment on top so the moist is prevented and it becomes denser. Depending on the quality of coal, there are three different classifications (lowest to highest quality): lignite, bituminous, and anthracite. The quality depends on the amount of carbon in the coal. The higher quality coal burns more efficiently and cleanly. The coal powered power plants use it to generate electricity. The coal is burned to produce heat to boil water and steam. The steam turns a turbine connected to a generator, which generates electricity. Coal burning produces gases that contain primarily carbon, sulfur, nitrogen, hydrogen, and oxygen. We will focus on the sulfur oxides and carbon dioxidesâ€™ effects to the formation acid rain. The burning of charcoal and sulfur produces smoke similar to that of many coal-fired power plants. The smoke precipitates with water as acid rain, which is what we produced in the water in the beaker with the smoke dissolved in it. The acidity is apparent and we can see what it is capable of doing to the environment by observing the dissolving of a piece of chalk. 

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Fossil fuel is an energy source that is used widely in the world. Examples are heating for houses, fueling automobiles, and other energy sources. Types of fossil fuels include coal, petroleum, and natural gas. In this activity we are focusing on the coal. Coal is a natural resource that forms with geological steps over millions of years. The first step of coal formation is the formation of what is called the peat, which is formed by decomposition of organisms. However, peat cannot be used as a fuel because it is too wet. The peat must have a protective layer of sediment on top so the moist is prevented and it becomes denser. Depending on the quality of coal, there are three different classifications (lowest to highest quality): lignite, bituminous, and anthracite. The quality depends on the amount of carbon in the coal. The higher quality coal burns more efficiently and cleanly. The coal powered power plants use it to generate electricity. The coal is burned to produce heat to boil water and steam. The steam turns a turbine connected to a generator, which generates electricity. Coal burning produces gases that contain primarily carbon, sulfur, nitrogen, hydrogen, and oxygen. We will focus on the sulfur oxides and carbon dioxidesâ€™ effects to the formation acid rain. The burning of charcoal and sulfur produces smoke similar to that of many coal-fired power plants. The smoke precipitates with water as acid rain, which is what we produced in the water in the beaker with the smoke dissolved in it. The acidity is apparent and we can see what it is capable of doing to the environment by observing the dissolving of a piece of chalk. 

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While a small portion of the SO2 and NOX that cause acid rain is from natural sources such as volcanoes, most of it comes from the burning of fossil fuels.  The major sources of SO2 and NOX in the atmosphere are:

Burning of fossil fuels to generate electricity.  Two thirds of SO2 and one fourth of NOX in the atmosphere come from electric power generators.

Vehicles and heavy equipment.

Manufacturing, oil refineries and other industries.

Winds can blow SO2 and NOX over long distances and across borders making acid rain a problem for everyone and not just those who live close to these sources.

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Sulfur dioxide contributes to the formation of acid rain, which damages forests, crops, and buildings, and acidifies lakes, streams, and rivers, making them unsuitable for aquatic plant and animal life. Continued exposure to SO2 over an extended period of time can permanently alter the natural variety of plants and animals in an ecosystem.Sulfate particles are also the major cause of smog in many parts of the U.S.

In 2010, plant experts, scientists, environmentalists and ranchers said they believe sulfur dioxide pollution from coal-fired power plants is slowly killing vegetation across Texas. Sulfur dioxide has been known to kill vegetation in other parts of the country. In Texas, the deaths of pecan trees, oaks, elms and willows have been documented. In Central Texas, not far from a power plant operated by the Lower Colorado River Authority, pecan growers say thousands of trees have died and nut production has steadily decreased since the plant began operating in 1979. After consulting experts, the growers believe the plant's sulfur dioxide emissions are to blame. The U.S. Environmental Protection Agency has toured some of the farms and is reviewing the data.

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The burning of fossil fuels generates air pollution that scientists have determined is the major cause of acid rain. Power plants, along with factories and vehicles that also burn fossil fuels, all emit sulfur dioxide (SO2) and oxides of nitrogen (NOx). When combined with moisture in the atmosphere, these pollutants are returned to the earth as acids. This process is known as "deposition" and occurs when it rains or snows, but it can also occur when dust settles out of the atmosphere during dry periods.

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Coal-fired power plants are the largest human-caused source of sulfur dioxide, a pollutant gas that contributes to the production of acid rain and causes significant health problems, particularly through its role in forming particulates. Coal naturally contains sulfur, and when coal is burned, the sulfur combines with oxygen to form sulfur oxides. Although natural processes like volcanic eruptions, biological decomposition, and forest fires also produce sulfur dioxide, emissions caused by human activity far exceed natural production in developed countries.

The EPA estimates that more than 65%, or over 13 million tons per year, of SO2 production in the U.S. comes from electric utilities, 93 percent of which is produced by coal power plants. In China, the world’s largest consumer of coal, approximately 22.5 million tons of sulfur were released in 2004, and over 30% of the country now experiences acid rainfall.

Acid rain is rain saturated with chemicals like sulfur dioxide and nitrogen oxide, which causes acidification of lakes and streams and contributes to the damage of trees at high elevations and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's cultural heritage. Prior to falling to the earth, sulfur dioxide and nitrogen oxide gases and their particulate matter derivatives—sulfates and nitrates—contribute to visibility degradation and harm public health.

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What Causes Acid Rain?Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents.  The SO2 and NOX react with water, oxygen and other chemicals to form sulfuric and nitric acids.  These then mix with water and other materials before falling to the ground.

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What Causes Acid Rain?Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents.  The SO2 and NOX react with water, oxygen and other chemicals to form sulfuric and nitric acids.  These then mix with water and other materials before falling to the ground.

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Mercury: Coal plants are responsible for more than half of the U.S. human-caused emissions of mercury, a toxic heavy metal that causes brain damage and heart problems. Just 1/70th of a teaspoon of mercury deposited on a 25-acre lake can make the fish unsafe to eat. A typical uncontrolled coal plants emits approximately 170 pounds of mercury each year. Activated carbon injection technology can reduce mercury emissions by up to 90 percent when combined with baghouses. ACI technology is currently found on just 8 percent of the U.S. coal fleet.

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Mercury: Coal plants are responsible for more than half of the U.S. human-caused emissions of mercury, a toxic heavy metal that causes brain damage and heart problems. Just 1/70th of a teaspoon of mercury deposited on a 25-acre lake can make the fish unsafe to eat. A typical uncontrolled coal plants emits approximately 170 pounds of mercury each year. Activated carbon injection technology can reduce mercury emissions by up to 90 percent when combined with baghouses. ACI technology is currently found on just 8 percent of the U.S. coal fleet.

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Acid rain happens when gas pollutants such as nitrogen oxides and sulfur oxides react with water molecules in the atmosphere; the chemical reaction of sulfur oxide turning into sulfuric acid is described below. Sulfuric acid is delivered Earth when it precipitates with rain or snow. When it rains as an acid rain, this is called wet deposition of acid. Acidic rain is harmful to humans and environments. Acid rain can disrupt the aquatic ecosystem by affecting the reproduction and survival of aquatic organisms that cannot survive acidic conditions. Acid rain also damages soil by disabling some of the important organismsâ€™ ability to maintain healthy soil. Acid rain can cause toxins to spread in the soil and also leach away important minerals nutrients from soil.

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Coal burned in these power plants produce smoke that is released in mass amounts in the atmosphere. The power plants use coals that are not completely clean, so it contains impurities. Impure coal burning produces smoke that contains a lot of chemicals, which can harm the environment by producing acid rain. Carbon dioxide is produced in excess amounts. This gas is already present in our atmosphere but in excess amounts, it can cause global warming, increasing the global temperature abnormally. Sulfur oxides are another type of gas that is released with the smoke. When this is present in the atmosphere it can be one of the prime causes of acid rain on Earth. Acid rain in real life can be harmful for the plants and aquatic organisms in rivers and lakes.

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Sulfur dioxide (SO2): Coal plants are the United States’ leading source of SO2 pollution, which takes a major toll on public health, including by contributing to the formation of small acidic particulates that can penetrate into human lungs and be absorbed by the bloodstream. SO2 also causes acid rain, which damages crops, forests, and soils, and acidifies lakes and streams. A typical uncontrolled coal plant emits 14,100 tons of SO2 per year. A typical coal plant with emissions controls, including flue gas desulfurization (smokestack scrubbers), emits 7,000 tons of SO2 per year.

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Sulfur dioxide (SO2) becomes sulfur trioxide (SO3) when reacting with oxygen in the air. This reacts with water molecules in the atmosphere to form sulfuric acid, a strong mineral acid. This makes rain acidic.