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Module 4

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  • Created by: Emma P
  • Created on: 11-04-11 10:23

The greenhouse effect- global warming

when the term greenhouse gases is used by the media, it is often used negatively.

However, without greenhouse gases, our planet would be around 35' colderadn covered in ice. This has alot more to do with greenhouse gases than the planet's proximety to the sun.

the earth recieves the majority of its energy in the form of electromagnetic radiation from the sun. Most of this radiation is from the visible region of the e.m. spectrum, with a small amount being either ultraviolet or infared.  The incoming radiation is relatively unaffected by the gases in the earth's atmosphere and passes straight through to the surface.  The solar energy is then absorbed and some is released back into the atmosphere as longer-wave infrared radiation.

Most infared emmited by the Earth's surface goes back into space. However, certain gasesin the atmosphere(CFC's) absorb some of the infa red radiation. It is then re-emmited as energy, with some passing back towards the Earth. This process effectively traps most of the heat in the lower atmosphere.

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Diagram to show the greenhouse effect

(http://www.seai.ie/images_upload/Schools/Secondary_Schools/Subjects/Geography_LC/Greenhouse_Effect_/greenhouseeffect.jpg)

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Greenhouse gases

·       Occur naturally in the atmosphere

 For example,    

  • Water vapour from evaporation of lakes and oceans  
  • Carbon Dioxide from volcanic eruptions, respiration of animals and the burning or decay of living matter     
  •  The third most abundant greenhouse gas in Methane, although found in smaller quantities than Carbon Dioxide, methane makes a much greater contribution to the greenhouse effect than the same amount of CO2  
  •  Methane is emitted during the production of coal, natural gas and oil .  A product of rotting organic waste in landfill sites, released from certain animals, such as Cows, as a by-product of digestion. i.e. farting  
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How do gases absorb radiation?

Carbon dioxide is a linear molecule.   (http://upload.wikimedia.org/wikipedia/commons/d/dc/Carbon-dioxide-3D-balls.png)  The Carbon dioxide molecule can absorb infrared radiation ,causing the molecule to vibrate.

Eventually the vibrating molecule emits some of this energy in the form of radiation. This can then be absorbed by another greenhouse gas molecule or at the earth's surface.

Water vapour and Methane absorb energy in a similar process:

  • In H2O, the O-H bonds absorb infrared radiation
  • In CH4, the C-H bonds absorb infrared radiation

The greenhouse effect of a gas depends not only on its connection in the atmosphere, but also on its ability to absorb infrared radiation

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Vibration and roation models

(http://www.windows2universe.org/physical_science/chemistry/co2_molecule_vibrate_modes_sm.gif)

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Climate change- How science works:(

Global warming is happening!!

  • Ice caps are melting
  • The earth is getting hotter- more heat waves/ droughts
  • More frequent storms and floods

This is caused by the combustion of coal, natural gas and oil which release millions of tonnes of Carbon dioxide into the atmosphere every year.

Global warming produces unpredictable changes, such as

  • Rivers overflowing
  • lower crop yields
  • storms and hurricanes                                                                       These changes are the reason why governments signed the Kyoto agreement. It meant that countries would do more to reduce their greenhouse emissions, for example by making cleaner cars and producing a strategy for future reductions
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An inconvenient truth

(http://www.treehugger.com/polar-bear-in-london-thames-river.JPG)

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Solutions to the greenhouse effect

In order to reduce the large amount of greenhouse gas producing fuels being burned, alternative energy supplies are used.

For example,

  • Wind turbines
  • Solar panels
  • Nuclear plants
  • Tidal power

carbon capture storage is an immediate method to prevent Carbon dioxide from being released into the atmosphere. A power station burns methane from natural gas(http://www.middleschoolchemistry.com/img/content/multimedia/chapter_6/lesson_1/combustion_of_methane.jpg)

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Storage of carbonates

Mineral storage aims to store carbon dioxide in stable minerals.CO2 would be trapped by converting it into a carbonate rock.  In this process, CO2 is reacted with metal oxides to produce stable carbonates.

CaO(s) + CO2(g)CaCO3(s)

MgO(s) + CO2(g)MgCO3(s)

This process occurs naturallly but is very slow. A power station using mineral storage would neeed 60-180% more energy than one without CCS. Therefore, more research is needed if this is to become a feesable option.

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The Ozone layer

Ozone, O3, is a molecule consisting of three Oxygen

(http://www.globalwarmingart.com/images/8/81/Ozone_Molecule_VdW.png)Environmentally, ozone can either be good or bad, depending on where it is found.

  • Bad: Ozone found near to the Earth's atmosphere in the troposphere is an air pollutant with harmfuleffects on the respiratory systems of animals.
  • Good: Ozone found in the upper atmosphere in the stratosphere protects living organisms by preventing the harmful ultraviolet lights from reaching the Earth's surface.
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(http://www.cec.org/ods/images/prn_cecods_ozone_e.png)

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The Ozone layer

The ozone layer is found in the region of the atmosphere called the stratosphere, about 10-50Km above the earth's surface.

Ultraviolet radiation from the sun has a wavelength of between 270 and 400 nm. The ozone filters out the shorter wavelengths, i.e. less than 320 nm.

These shorter wavelengths would be very damaging to life.

The ozone converts Ultraviolet radiation into heat and consequently, the ozone is at a higher temperature than other parts of the upper atmosphere.

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The Ozone-Oxygen cycle

Ultraviolet (uv) radiation

Ozone is continuosly being formed and broken down in the stratosphere by the action of UV radiation. There are three different types of UV radiation:

  • UV-a (320-400nm)- reaches the Eath's surface. it has less energy than shorter wavelenghts of UV and is not as damaging.
  • 
  • UV-b (280-320nm) radiation- can cause sunburn and sometimes genetic damage, which can result in skin cancer if exposure to UV-b is prolonged
  • UV-c (200-280nm)- is entirely screened out by the ozone layer

alhough Ozone screens out most UV-b, some does reach the Earth's surface. Any decrease in the Ozone layer would allow more UV-b radiation to reach the surface, causing increased genetic damage to living organisms.

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"Diagram" to show absorption of UV radiation by th

(http://www.theozonehole.com/images/index.39.jpg)

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Formation of Ozone

The first step in the formation of Ozone is the absorption of UV radiation with a wavelength of length of less than 240nm by (http://www.zath.co.uk/wp-content/uploads/2010/02/o2-mobile-network-logo.jpg)molecules. This is high-energy radiation, capable of breaking an(http://www.zath.co.uk/wp-content/uploads/2010/02/o2-mobile-network-logo.jpg) molecule into (http://kitchenscience.sci-toys.com/two_oxygens.jpg)two oxygen atoms.

 (http://www.zath.co.uk/wp-content/uploads/2010/02/o2-mobile-network-logo.jpg)+(radiation less than 2400nm) (http://getclickbankcodebonusesnow.com/images/redarrow.jpg) 2O                              The O atoms then react with(http://www.zath.co.uk/wp-content/uploads/2010/02/o2-mobile-network-logo.jpg)molecules to form Ozone molecules,(http://www.skunkworks-ost.com/web_images/ozone-molecule.jpg) This process generates heat. The heat is absorbed by air molecules in the stratosphere, raising the temperature. Ozone is formed mainly in the upper atmosphere.                                                                        

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(http://www.quality-drinking-water.com/image-files/ozone_formation.jpg)

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How the Ozone layer works

The Ozone molecules formed in the above rection then absorb UV with wavelengths between 240 and 310nm.

(http://www.skunkworks-ost.com/web_images/ozone-molecule.jpg)molecules are converted back to (http://www.zath.co.uk/wp-content/uploads/2010/02/o2-mobile-network-logo.jpg)molecules and O atoms. this reverse of the reaction that forms Ozone.  (http://www.cs.stedwards.edu/~wright/text/ozone1.gif)

The atomic Oxygen produced immediatly rects with other (http://www.zath.co.uk/wp-content/uploads/2010/02/o2-mobile-network-logo.jpg)molecules to rerform Ozone.(http://www.muchapedia.com/image-files/ozone-creation.jpg)

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(http://ozone.meteo.be/meteo/download/en/1568998/image/scaletomax-0-0/ozone_formation.png)

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Comments

RoxR

thank you very much i found this helpfull not just for exams but general class work....

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