Option D - Environmental Chemistry

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[edit] D.1 Primary Air Pollution

[edit] D.1.1

Sources of Pollutants:

CO (carbon monoxide) : Natural : Forest fires. Anthropogenic : Transportation industry (automobile exhaust), incomplete combustion of fossil fuels: eg. 2CH4 + 3O2 ---> 2CO + 4H2O

NOx (nitrogen oxides) : Natural : forest fires. Anthropogenic : Stationary combustion sources (factories and power plants), transportation.

N_2(g) + O_{2 (g)} ---> 2NO _(g)

2NO _(g) + O_{2 (g)} ---> 2NO_{2 (g)}

SO_x (sulfur oxides) : Natural : Volcanoes. Anthropogenic : Stationary combustion sources, industry, found in metal ores, coal.

S + O₂ ---> SO₂

2S + O₂ ---> 2SO₃

Particulates : Natural : Forest fires, volcanoes, windstorms, pollen, sea salts. Anthropogenic: Industry (smoke, cement, ash), domestic heating.

HC (hydrocarbons) : Natural : Living and decaying plants. Anthropogenic : Transportation (you can just invent your own equation)

[edit] D.1.2

Health Effects of P.A.P. (Primary Air Pollutants):

CO: Acute exposure causes headaches, dizziness and decreased physical performance. Chronic exposure causes stress on cardiovascular system and heart attack.

NOx : Acute exposure causes lung irritation. Chronic exposure causes bronchitis (persistent inflammation of bronchial tubes).

SOx : Acute inflammation of respiratory tract, asthma. Chronic emphysema (breakdown of alveoli in lungs), bronchitis

Particulates : Irritation of respiratory system, cancer.

HC : Some, such as benzene, are carcinogenic. Can also form toxic secondary pollutants e.g. PANs

[edit] D.1.3

Control and Prevention of P.A.P. :

Catalytic converters : Devices attached to a vehicle's exhaust system to convert CO and HC into water and carbon dioxide.

Scrubbers : Pollutant-laden air is passed through a mixture of water and lime, trapping particulates and sulfur oxide gases.

Filters : Cloth bags through which smoke is passed to stop particulates from flowing into the air (and more, see syllabus for details on which pollutants can be controlled by which methods).

[edit] D.2 Ozone Depletion

[edit] D.2.1

Evidence for ozone depletion :

A thin layer of ozone gas (O3) encircles the earth and prevents about 99% of the ultraviolet light (UV) from the sun from reaching the earth.

• Measurements made by British scientists at Halley Bay, Antarctica demonstrated the thinning of the ozone layer.
• Satellite measurements of the ozone layer over Antarctica revealed that there was a hole in the layer, the size of the United States. The ozone layer over Antarctica was depleted by more than 50% in 20 years (1965-1985)
• A similar hole was discovered above the Arctic, but smaller in size.
• Other data from satellites showed that the ozone layer was depleted even over non-polar regions (about 3%)

[edit] D.2.2

Formation and depletion of ozone (the natural process)

UV light strikes 0₃ molecules, which split apart. The products reunite, giving off heat and reforming ozone. The ozone layer continues renewing itself while converting UV light into heat (infrared radiation).

Balanced equations:
O₃(ozone) + UV light ----> O + O₂
O + O₂ ----> O₃ + Infrared radiation (heat)

[edit] D.2.3

[edit] Pollutants and Their Sources

CFC's : Propellants in spray cans (i.e. deodorant, insecticides, paint, aerosols), coolants in refrigerators, air conditioners, freezers and the production of Styrofoam.

NOx : High-altitude jets (supersonic transport (SST), commercial jets), detonation of nuclear weapons, fertilizers, volcanoes (minor).

[edit] Catalysts for ozone depletion

CFC's : React with stratospheric ozone. When CFC's are broken down, chlorine free radicals are produced These can react with more than 100,00 molecules of ozone. Thus depleting the ozone layer.

NOx : Nitric oxides react with ozone to form oxygen gas (O₂), thus interfering with the natural process of formation of ozone.

[edit] D.2.4

[edit] Environmental Effects of ozone depletion

Ozone depletion increases the amount of UV light that strikes the earth's surface. An excess of this type of light causes damage to living organisms, including:

• Eyes : Cataracts (blurred vision or blindness).
• Skin : Severe burns/cancer.
• Immune system: Weaker immune response makes organisms more susceptible to diseases.
• Crops: Interference with photosynthesis result in lower crop yields.
• Marine ecosystem: Plankton near surface die, which disrupts food chain.

[edit] CFC Alternatives

HCFC's and HFC's are used in place of CFC's because they are largely destroyed in the lower region of the atmosphere.

HCFC's : Composed of hydrogen, chlorine, fluorine and carbon. They contain chlorine, but most is destroyed in the lower atmosphere before reaching the stratospheric ozone layer (20 times less destructive than CFC's).

HFC's : Do not contain chlorine or bromine and therefore have no potential to depleting the ozone layer.

[edit] D.3 Global Warming

[edit] D.3.1

Evidence for global warming

Historically the level of carbon dioxide in the Earth's atmosphere had remained relatively stable until about 100 years ago. This was the time that the human race began burning fossil fuels at a high level (it's all our grandparents' and great-grandparents' fault!). In just over a century, industrial civilization has added 360 billion tons of carbon dioxide to our atmosphere. Carbon dioxide is very difficult to get rid of. The natural processes are very slow and we aren't intelligent enough to have invented our own way of doing it.

[edit] D.3.2

Main Gases involved (the gases that trap the heat near the Earth's surface and radiate it back):

CH₄, H₂O (water vapor), CO₂, chlorofluorocarbons (CFC's) and nitrous oxide. (You don't need to know the last two, but knowing them won't harm you).

Their Sources:

CH₄ : Paddy fields - It is produced by the bacterial decomposition of vegetation under water that occurs in flooded rice fields. Cattle - "ruminants" (because they "ruminate") i.e. cows. In the complicated process of digesting the grass the food is fermented, producing a large quantity of methane gas as a by-product which the cow expels.

H₂O : I mean, water vapour is always present in the atmosphere (the water cycle - you know what I mean, don't you?!?!?).

CO₂ : It is produced naturally by the decomposition of organic materials, growing plants, and weathering of rocks. While they are burning millions of trees in the tropical rain forest, not only are they suffocating us, and killing many species of animals, but they are also contributing to global warming.

CO₂ is also produced by the burning of fossil fuels such as coal, oil and natural gas in furnaces and coal fires, aircrafts and cars, industrial plants, etc. Fossil fuels are essentially stored carbon, left over from the bodies of plants and animals that died millions of years ago and were trapped underground and the burning process releases this carbon.

[edit] D.3.3

[edit] Influence of gases on global warming

The greenhouse theory proposes that the greenhouse gases are increasing in the atmosphere to such an extent that less reradiated energy is able to escape from the atmosphere. The greater quantities of greenhouse gases absorb this long-wave radiation, effectively trapping it. The energy is then reradiated into the lower atmosphere. The gases may be said to be acting like a blanket, absorbing more and more radiation in the atmosphere. In theory, this could lead to a progressive increase in temperatures and eventually to climatic change.

CH₄ : This gas is present in the atmosphere only in very small quantities, but it absorbs radiation more effectively than CO₂.

CO₂ : Naturally occurring CO₂ allows sunlight to pass through the atmosphere and heat the Earth, but also absorbs infrared radiation escaping from the Earth's surface and radiates it back to earth. This process helps maintain Earth's temperature. The increase of CO2 concentration in the air slows down the escape of heat resulting in global warming. Like almost anything in the world, a little carbon dioxide is good but too much may be devastating.

[edit] Effects of global warming

Oceans will absorb more heat energy, making hurricanes and typhoons more common.

There will be a change in ocean current patterns meaning the world's weather patterns will be altered significantly, producing flooding in some areas/droughts in others. Areas like USA and Canada will become warmer and drier and the agricultural plains might become too dry to support dry-land farming.

Melting of polar ice caps and glaciers would raise the sea level, flooding up to 20% of the world's land mass. (bye-bye Florida and especially Holland, which is already half-inside the sea - they just retrieved it by building canals!).

The construction of climate models is difficult because of feedback processes: The Earth warms -> more water evaporates -> more clouds form -> clouds reduce the amount of heat reaching Earth -> the warming trend will slow down OR The Earth warms -> polar ice caps melt -> ice reflects back sunlight instead of absorbing -> when ice decreases, warming speeds up.

[edit] D.3.4

Influence of particulates on temperature:

Particulates consist of smoke, ash, soot, dust, lead, and other particles from burning fuel. They come from industrial processes and motor vehicles that burn fossil fuel, burning wood, and dust from construction and agriculture. (see D.1 and D.8 for further details). This can form clouds that reduce visibility and cause a variety of respiratory problems. Particulates have also been linked with cancer. They also corrode metals, erode buildings and sculptures, and soil fabrics. They can also lower the temperature by reflecting sunlight

What else can be said about this?

More detail: They cool the earth by scattering short wave radiation from the sun and reflecting this radiation back into space.