Acid rain

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Acid rain

Acid rain is a result of air pollution. When any type of fuel is burnt, lots of different chemicals are produced.

The smoke which come out of a car exhaust don't just contain the sooty grey particles that you can see - they also contains lots of invisible gases that can be even more harmful to our environment. Power stations, factories and cars all burn fuels and therefore they all produce polluting gases. Some of these gases (especially nitrogen oxides and sulphur dioxide) react with the tiny droplets of water in clouds to form sulphuric and nitric acids. Then from these clouds the rain falls as very weak acid - that's why it is known as "acid rain". The release of sulphur dioxide can also occur naturally when a volcano erupts. [1]

Sources of Acid Rain

Acid 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. 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, 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.

Pure water is neutral and has a pH of 7. Natural rain water is slightly acidic mainly because of dissolved CO₂ which produces carbonic acid or H₂CO₃:

H₂O(l) + CO₂(g) <==> H₂CO₃(aq)

The pH of unpolluted rainwater ranges from pH 5 to 6. Acid rain is rain water with a pH of less than 5. In some parts of the Northern Hemisphere the pH of the rain water has been as low as 2!

Acid rain is caused by industrial pollutants. The main industrial gases responsible are SO₂ and NOx (a mixture of NO and NO₂).

Major sources of industrial sulfur dioxide:

SO₂(g) comes from mining smelters and the burning of coal.

The roasting of minerals releases SO₂(g) from:

Metal sulfide + oxygen ==> Metal oxide + SO₂(g)

ii) Electrical power stations that burn coal produce sulfur dioxide from the sulfur impurities in the coal:

S(s) + O₂(g) ==> SO₂(g)

The SO₂(g) combines with water to produce sulfurous acid:

H₂O(l) + SO₂(g) ==> H₂SO₃(g)

Source of nitrogen oxides:

Sources of NOx are more widespread. Nitrogen is a diatomic molecule and is inert because its triple bond. However, at temperatures over 1300°C, nitrogen combines with oxygen to form nitrogen monoxide:

N₂(g) + O₂(g) => 2NO(g)

These high temperatures can be achieved by i) the internal combustion engine (human activity)

ii) lightning in the atmosphere (natural source)

The nitrogen monoxide slowly combines with oxygen to form soluble nitrogen dioxide gas:

2NO(g) + O₂(g) => 2NO₂(g)

Nitrogen dioxide readily dissolves in water producing a mixture of nitric and nitrous acids.

2NO₂(g) + H₂O(l) => HNO₃(aq) + HNO₂(g)

Acidic rain is mainly caused by atmospheric pollutants of sulfur dioxide and nitrogen oxides. [2]

The chemical formula of acidic rain is dependent upon the type of acids present. Acidic rain is a complex mixture of nitrous, nitric, sulfurous and sulfuric acids which all combine to lower the pH.

Effects of Acid Rain

Acid rain causes acidification of lakes and streams and contributes to the damage of trees at high elevations (for example, red spruce trees above 2,000 feet) 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 (SO₂) and nitrogen oxide (NO_x) gases and their particulate matter derivatives - sulfates and nitrates - contribute to visibility degradation and harm public health.

Acid rain looks, feels, and tastes just like clean rain. The harm to people from acid rain is not direct. Walking in acid rain, or even swimming in an acid lake, is no more dangerous. However, the pollutants that cause acid rain - sulfur dioxide (SO₂) and nitrogen oxides (NO_x) - do damage human health. These gases interact in the atmosphere to form fine sulfate and nitrate particles that can be transported long distances by winds and inhaled deep into people's lungs. Many scientific studies have identified a relationship between acid rain and increased illnesses, premature death from heart and lung disorders, such as asthma and bronchitis. acid rain chemical nitrogen

Reducing Acid Rain

There are several ways to reduce acid rain ranging from societal changes to individual action.

Understand acid deposition's causes and effects:

To solve the acid rain problem, people need to understand how acid rain damages the environment. They also need to understand what changes could be made to the air pollution. The answers to these questions help leaders make better decisions about how to control air pollution and therefore, how to reduce acid rain. Because there are many solutions to the acid rain problem, leaders have a choice of which options or combinations of options are best.

ь Clean up smokestacks and exhaust pipes:

Almost all of the electricity that powers modern life comes from burning fossil fuels such as coal, natural gas, and oil. Coal accounts for most SO₂ emissions and a large portion of NO_x emissions.

ь Use alternative energy sources:

There are other sources of electricity besides fossil fuels. They include nuclear power, hydropower, wind energy, geothermal energy, and solar energy. Nuclear and hydropower are used most widely in the United States, while wind, solar, and geothermal energy have not yet been harnessed on a large enough scale to make them economically-feasible alternatives. There are also alternative energies, such as natural gas, batteries, and fuel cells, available to power automobiles. All sources of energy have environmental costs as well as benefits. Some types of energy are more expensive to produce than others. Nuclear power, hydropower, and coal are the cheapest forms of energy today, but advancements in technologies and regulatory developments may change this 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.

ь Restore a damaged environment:

Acid deposition penetrates deeply into the fabric of an ecosystem, changing the chemistry of the soil and 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 pH is restored to normal. For example, while 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.

ь Look to the future:

As emissions from the largest known sources of acid deposition--power plants and automobiles--are reduced. 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. It may consider additional emission reductions from sources that have already been controlled, or methods to reduce emissions from other sources. Congress may also focus on energy efficiency and alternative energy. Implementation of cost-effective mechanisms to reduce emissions and their impact on the environment will continue to evolve.

ь 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. 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.

- Use electric appliances only when you need them.

- Use public transportation, better, walk or bicycle whenever possible.

- Buy vehicles with low NO_x emissions, and properly maintain your vehicle.

- Be well informed.

Literature

1. Wikipedia, the free encyclopedia. Retrieved February 7, 2012, from http://www.wiki.com

2. Common chemical formula. Retrieved March 7, 2012, from http://www.chemicalformula.org/book/export/html/3

3. United States Environmental Protection Agency. Retrieved March 7, 2012, from http://www.epa.gov/region1/eco/acidrain/causes.

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