Greenhouse gases report

  1. I have been given a report and a part of it is on greenhouse gases. What do you think are some scientific factors/properties I should use in a comparison matrix of n2o,co2,ch4.

    I have read something about the shape of the molecule of an atom affecting the IR rays it can absorb. Also please include important background information I should cover.

    Thanks so much
    :)
     
  2. jcsd
  3. jambaugh

    jambaugh 1,800
    Science Advisor
    Gold Member

    Well that's sort of a wide open question. Who's your audience? Are you trying to motivate the politically? Educate the scientifically? Who gave you the report and what do they want? Why didn't they include the principle green house gas (for Earth's atmosphere), water vapor?
     
  4. School gave it to me. They were just examples of gases.
     
  5. jambaugh

    jambaugh 1,800
    Science Advisor
    Gold Member

    Well given the political agenda of they who select curriculum, as long as your report tells about how we're all gonna die due to the evil industrial emissions of green house gasses, you're sure to get an A, but if you want the science....

    Some background is to look at the thermal spectrum of light at different temperatures. The distribution of frequencies of light given off by any "black"body that is above absolute zero in temperature depends on its temperature. Earth's temps give the peak in the infra-red region. The sun's is in the yellow visible light region (which is why we evolved eyes to see that range and hence make it "the visible region".)

    The Earth can only shed heat energy by radiating it into space and gets its surface heat primarily from absorbed solar light. (Some geothermal to due to decaying radioisotopes in the crust and core and some tidal friction from the Moon and Sun tidally deforming the Earth as it rotates, but the balance is solar light).

    So you look at how the atmosphere isn't a "black body" or even a "grey body" but rather absorbs an emits light in a very frequency dependent way. You will want to find graphs for your report showing the emissivity spectrum of the major greenhouse gasses in the infrared region. As I said you'll see that water vapor is the principle green house gas in that it blocks emission of a major portion of the Earth's infrared radiation outward but not much of the visible light coming in from the sun. Of interest is how the other gasses add to or fail to add to what water vapor does.

    Naturally this is an involved topic and the "emission in one range absorption in another" description is very simplistic. I don't know how deep you want to go or are able to in time and audience education level. There are atmospheric dynamics and issues of how high in the atmosphere this occurs, how (and whether) there are amplifying effects (or attenuating ones) and saturation levels where adding more of one gas has either a magnified effect due to secondary behavior (i.e. interacting with water vapor) or whether there is a reduced overall effect (offset by increased circulation or cloud formation) or if there is a saturation effect... (you cannot block more than all of the radiation at a given frequency so adding more "black"to the "paint"has no effect.)

    Start with your favorite search engine and search "green house gasses" as well as the ones given. You'll be overwhelmed but get your list of gasses together you may want to include. Then search for images with "<specific gas> infrared emissivity" and see what you uncover.
     
  6. Thanks very much :)
     
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