Pollution in the atmosphere.
Sulfur Dioxide + Oxides of Nitrogen.

This site created by Stephanie, Jean and Clemson covers the following topics:

◦ Sources of Sulfur Dioxide.
◦ Sources of Nitrogen oxides.
◦ Reactions releasing sulfur dioxide into the atmosphere.
◦ Reactions releasing nitrogen oxides into the atmosphere.
◦ The evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen.
◦ Industrial origins of sulfur dioxide.
◦ Industrial origins of Oxides of Nitrogen.

The evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen

Evidence suggests that atmospheric concentration of oxides of sulphur and nitrogen have increased in the last 200 years. This is shown by:

• Quantitative analysis of air bubbles trapped in Antarctic ice core samples acquired and provided by the CSIRO and the Australian Antarctic Division.
• Measurement of carbon isotopes in old trees
• Acid rain
• Photochemical smog

Acid rain forms due oxides of sulphur and nitrogen reacting with the water in the atmosphere. The effects of acid rain has resulted in damage to buildings made of carbonates, such as concrete, mortar, limestone and marble, as it causes such structures to gradually dissolved away. Acid rain also damages forests and aquatic life. Therefore, an increase in the incidence of acid rain suggests oxides of sulphur and nitrogen has increased.

The CSIRO and the Australian Antarctic Division has drilled holes in the Antarctic to obtain ice core samples. By analysing the amount of oxides of sulphur and nitrogen at different levels, these ice core samples indicate that there has been an increase in the atmospheric concentration of the oxides.

Photochemical smog is a mixture of pollutants that are formed when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight, creating a brown haze above cities. The worsening of such smogs shows that oxides of nitrogen and sulphur have increased.

There is difficulty in acquiring accurate evidence to show increases in the concentration of nitrogen and sulphur oxides. While atmospheric CO₂ concentrations are about 360 parts per million (ppm), concentrations of SO₂ and NOx are only about 0.001 ppm in populated parts of the Earth. The instruments capable of measuring very low concentrations, like those for SO₂, have only been available since the 1970s. Thus long term trends have not yet been formed, and an accurate analysis can not be made.

Nitrogen dioxide form nitrogen ions, just as sulphur dioxide form sulphur ions. Both of these are soluble in water. This means that they easily travel around the biosphere and hydrosphere, making them difficult to study.

Since the Industrial Revolution in the 1800’s there has been and increase in SO₂ and NO_x pollution. This is due to the burning of fossil fuels, and the exponential increase in the use of automotive vehicles. Although the causes of these oxides can be measured, the oxides themselves in the atmosphere are hard to monitor.

Accurate measures of atmospheric oxides of sulphur and nitrogen currently do not exist. Even if there were accurate measures, there is no data to compare them to, as they have only been detected around the 1970s. However, there is adequate indirect evidence to show that there has been a significant increase in the atmospheric concentrations of oxides of nitrogen and sulphur.

Industrial origins of oxides of nitrogen

• Electricity supply
• Mining
• Oil and gas extraction
• Manufacturing industries
• Petroleum manufacturing.


The main human activity that generates large amounts of nitric oxide is combustion in power plants, cars and trucks. High temperatures in internal combustion engines produce nitric oxide:

N2 (g) + O2 (g) → 2NO (g)


Reasons for concern

Health effects
Low levels of oxides of nitrogen can irritate eyes, nose, throat and lungs. This may possibly lead to coughing, shortness of breath, tiredness and nausea. Exposure to oxides of nitrogen can also result in a build up of fluid in the lungs for 1-2 days after exposure. High levels of oxides of nitrogen can cause rapid burning, spasms and swelling of tissues in the throat and upper respiratory tract, reduced oxygenation of tissues, and possibly even death.

Environmental effects
Excessive levels of the oxides of nitrogen, predominantly nitrogen dioxide (NO2), can cause death in plants and roots and damage the leaves of many agricultural crops. Nitrogen dioxide is the damaging component of photochemical smog, and also participates in ozone layer depletion. Excessive levels increase the acidity of rain, and thus lower the pH of surface and ground waters and soil. This in turn can have harmful effects, possibly even death, on a variety of biological systems.

When dissolved in rain, it forms acid rain:
2NO2 (g) + H2O (l) → HNO3 (aq) + HNO2 (aq)


Acid rain can damage the environment in many ways:
• The decay and deterioration of constructions and buildings particularly those made of calcium carbonate.
• Further ions, eg. aluminum – can be harmful to plant and animal life and these are locked in insoluble compounds. Soils that are acidic can boost this solubility, which releases toxic ions.
• Some plants cannot endure acidic soils. Its growth can be affected and also this can cause defoliation.
• A range of animals are sensitive to the acidity levels of their environment (especially rivers and lakes). The increase of acidity levels can affect their reproduction or even kill them.
• Hydrogen sulfate from the sulfuric acid can leak out vital plant chemicals from the soil.



Evaluation
• The release of oxides of sulphur and nitrogen must be controlled, as they are harmful not only to humans but also the environment. • The destruction of the natural environment can lead to a change in ecosystems. • The result of these oxides leads to acid rain which also damages the man-made environment resulting in financial costs. • Damage to vegetation and other animals can have various economic consequences. • Social costs of health problems related to these oxides are immeasurable.

The industrial origins of sulfur dioxide:

• Emitted from coal-burning power plants,
• Metal smelting of sulfide-containing ores.
• Wood pulping and paper manufacturing,

Coal contains 0.5% of sulfur on average, in the form of metallic sulfides. In the combustion process sulfur is converted to sulfur dioxide:
S (in compound) + O2 (g) → SO2 (g)

Combustion of fossil fuels in power plants
4FeS2 (s) + 11O2 (g) → 2Fe2O3 (s) + 8SO2 (g)

Smelting sulphide ores
2ZnS + 3O2 → 2ZnO + 2SO2

Reasons for Concern

Health effects
Exposure to concentrations of 10 to 50 parts per million for 5 to 15 minutes causes irritation of the eyes, nose and throat, choking and coughing.
Exposure of the eyes to liquid sulfur dioxide, (from, for example an industrial accident) can cause severe burns, resulting in the loss of vision. On the skin it produces burns. Other health effects include headache, general discomfort and anxiety Children, the elderly, and people with asthma, cardiovascular disease or chronic lung disease (such as bronchitis or emphysema) are at increased risk. Repeated or prolonged exposure to moderate concentrations may cause inflammation of the respiratory tract, wheezing and lung damage. It has also proved to be harmful to the reproductive systems of experimental animals and caused developmental changes in their newborn.


Environmental effects
Sulfur dioxide is a potent and poisonous chemical that visibly damage the structure and appearance numerous plant species including valuable pines, legumes, red and black oaks, white ash, alfalfa and blackberry. This extent of the damage becomes apparent after a low exposure of 0.12 ppm for 8 hours. Visible injury can be obtained on plants of intermediate sensitivity after being exposed to .30ppm for 8 hours. In some instances, high levels of exposure to sulfur dioxide are beneficial for a limited range of plant species especially those growing in sulfur deficient soils. Low concentrations of sulfur dioxide can harm plants and trees and reduce crop productivity. Higher levels, and especially the acidic deposits from acid rain, will adversely affect both land and water ecosystems.

When dissolved in rain, it forms acid rain
SO2 (g) + H2O (l) → H2SO3 (aq)


Oxides of nitrogen contribute to the formation of photochemical smog which is a serious problem in big cities especially in USA and Europe. If these oxides are inhaled by humans, could cause severe illnesses such as asthma and bronchitis.


Other effects
Other effects of sulfur dioxide include accelerated corrosion of metals through the formation of sulfuric acid, damage stone and masonry, paint, various fibres, paper, leather, and electrical components.

Sources of nitrogen Oxides:

Natural sources of nitrogen oxides

Naturally-occurring processes that contribute to the emission on nitrogen oxides:

· Volcanic activity

· biological decay

· lightening

lightening.

Industrial sources of nitrogen oxides

Industrial processes which contribute to nitrogen oxide emissions:

· fuel combustion

· combustion of coal

· Agricultural fertilization

· Crop residue burning

· Adipic Acid Production

· Nitric Acid Production

crop burning.

Sources of Sulfur Dioxide:

Natural sources of sulfur dioxide:
Sulfur dioxide may be emitted into our atmosphere through a variety processes that occur naturally such as:

• Natural decomposition of vegetation, on land and in oceans.
• Volcanic activity and hot springs.
• Forrest fires.

volcanic activity.

forrest fire.

Industrial sources of sulfur dioxide
As well as natural sources, there is also a wide range of industrial processes that contribute to the emission of sulfur dioxide such as:

• Coal-burning power plants.
• Wood pulping and paper manufacturing.
• Metal smelting of sulfide-containing ores.
• Textile bleaching
• Food preserving and wineries
• Fumigation activities
• Fossil-fuel combustion

fossil fuel burning.

coal-fired power plant.

Reactions releasing nitrogen oxides into the atmosphere:

» Nitric oxide can be produced at very high temperatures – lightning, internal combustion engines which produce nitrogen monoxide, nitric oxide or nitrogen(II) oxide with temperatures above 1300^oC

N₂ + O₂ →2NO

» Nitric oxide can be formed with slow reaction with further oxygen to produce nitrogen dioxide.

2NO + O₂ → 2NO₂

» By water being the product, nitric oxide can be industrially prepared by catalytic oxidation of ammonia.

4 NH₃ + 5 O₂ → 4 NO + 6 H₂O

» Nitric oxide can be prepared in the laboratory by the reaction of concentrated nitric acid on copper.

3Cu+ 8HNO₃→ 3Cu(NO₃) ₂ + 2NO +4H₂O

» Nitrogen dioxide forms nitric oxide and oxygen when heated.

2NO₂ → 2 NO + O₂

» Manufacturing production of nitric acid from ammonia. The nitric acid decomposes to nitrogen dioxide.

4 HNO₃ → 4 NO₂ + 2H₂O + O₂

» Nitrogen monoxide reacts with oxygen in the air and forms acidic nitrogen dioxide (nitrogen(IV)oxide)

2NO + O₂ →2NO₂

Reactions releasing sulfur dioxide into the atmosphere:

» Iron (II) sulfate; commercially prepared from dilute sulfuric acid.

Dilute sulfuric acid – used to clean iron sheets before galvanizing.

When iron (II) sulfate is heated to 300^oC it decomposes into iron (III) oxide, sulfur dioxide and sulfur trioxide.

2 FeSO₄ → Fe₂O₃ + SO₂ + SO₃

» When hydrogen sulfide is oxidized during the decomposition of an organic matter or substance, it produces sulfur dioxide and water.

2 H₂S (g) + 3 O₂ (g) → 2 H₂O (g) + 2 SO₂ (g)

» By burning sulfur, sulfur dioxide is formed.

S₈ + 8 O₂ → 8 SO₂

» Sulfur dioxide is released by smelters in the process of sweltering sulfide ores such as copper, lead or zinc. The ore is heated in air and changes to a metal oxide which releases sulfur dioxide.

2ZnS + 3O₂ →2ZnO + 2SO₂

» Sulfur dioxide can be prepared in the laboratory by heating copper turnings with concentrated sulfuric acid. The two products are copper sulfate and water.

Cu (s) + 2 H₂SO₄ (aq) → CuSO₄ (aq) + SO₂ (g) + 2 H₂O (l)

» When sulfite such as sodium sulfite is mixed with dilute acid – sulfur dioxide is formed.

Na₂SO₃(s ) + 2 HCl(aq ) → 2 NaCl(s ) + SO₂(g ) + H₂O(l )

» Often, the sulfur in natural gases, coal or petroleum is burnt, the combustion produces sulfur dioxide.

S + O₂ →SO₂