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2012-02-12 15:13:00

Chemistry Questions
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  1. Define greenhouse effect.
    the natural process by which atmospheric gases trap a major portion (80%) of the infrared radiation by the Earth. (p108)
  2. List 3 greenhouse gases and their atmospheric lifetimes and global warming potential
    • 1) Carbon dioxide (CO2) has an estimated atmospheric
    • lifetime of 50-200yrs with a global warming potential of 1

    • 2) Methane (CH4) has an estimated atmospheric
    • lifetime of 12 with a global warming potential of 21

    • 3) Nitrous Oxide (N2O) has an estimated atmospheric
    • lifetime of 120 with a global warming potential of 310

  3. What is albedo?
    Albedo is the ratio of electromagnetic radiation reflected from a surface relative to the amount of radiation incident on it. In short, albedo is a measure of the reflectivity of a surface, the higher the number the reflective the surface. Earth has an average albedo of 0.39. (p135)
  4. What is carbon capture and storage?
    Carbon capture and storage is a process that involves separating CO2 from other combustion products and storing in a variety of geological locations. If properly done, the stored CO2 cannot reach the atmosphere and contribute to global warming. (p143)
  5. Why is ozone (O3) both necessary and an air pollutant?(Chapter 2)
    Ozone (O3) is a pollutant in the troposphere where it produced by human activity, but in the stratosphere, ozone plays a protective role shielding the Earth from damaging solar radiation. Therefore, ozone is necessary to keep life on Earth healthy. (p65-6)
  6. How does Antartica contrast with the North Pole?
    Antarctica is also totally surrounded by water (as contrasted with the north pole which has landed geographic features on many sides around it) and therefore meteorologically isolated from air at higher latitudes during the winter.
  7. What is a south polar vortex?
    An isolated air mass swirling over Antarctica. In the air of the polar vortex, the temperatures drop to very low levels in the stratosphere, below 80 degrees below zero C.
  8. What are polar stratospheric clouds (PSC)? How do the conribute to ozone?
    At south polar vortex temperatures, chemicals present in the stratosphere freeze out. It is the chemical reactions that occur on the PSCs that result in the large decrease in ozone during each spring over Antarctica that we called the Antarctic ozone hole.
  9. How is HCl, hydrogen chloride formed?
    Chlorine radicals abstract a hydrogen from the Methane (CH4) that is present in the stratosphere.
  10. How is HC1 in the aqueos from? In the gaseous?
    HC1 is a strong completely dissociate acid in aqueous solution, but in the dry gas phase of the stratosphere, exists as a stable, undissociated molecule and is a stable "chlorine radical catcher," or reservoir species.
  11. What are 2 other reactions that can form HCl?
    • Hydroxyl radical plus chlorine monoxide or hydroperoxy
    • radical plus chlorine radical:

    • OH + ClO ---> HCl + O2
    • HO2 + Cl ----> HCl + O2
  12. What is C1ONO2, chlorine nitrate?
    • Another reservoir species, this stable molecule is the product of a reaction between nitrogendioxide and chlorine monoxide, and like hydrogen chloride, acts to sequesteractive chlorine radicals from the ozone destruction cycle:
    • ClO + NO2 -> ClONO2
  13. What are PSCs made up of?
    Nitric acid and water crystals (most prominent for the clouds forming at about -70 degrees C) mixed with more water containing crystals (which form at temperatures below - 80 degrees).
  14. What are these clouds two negative effects on ozone?
    • These clouds have two negative effects on ozone:
    • 1) they sequester oxides of nitrogen (as nitric acid) which could react with chlorine monoxide to form the chlorine nitrate reservoir species (see immediately above)
    • 2) they act as an active site on which a very slow gas phase reaction can go very quickly heterogeneously (gases reacting on solid surfaces). This reaction can be viewed as:

    HCl + ClONO2 -- on ice -> Cl2 (gas) + HNO3 (ice)

    • This reaction releases molecular chlorine into the
    • stratospheric gas phase during the winter and thereby helps to remove chlorine
    • reservoir species.
  15. Why are ozone layers depleted in the Spring?
    When the sun starts to shine on the polar stratosphere at the beginning of spring, the chlorine gas is photolyzed back to chlorine radicals which can enter into the catalytic destruction of ozone. The result is that at the beginning of the spring (~October over Antarctica) the ozone in the stratosphere is depleted to less than 20% of its winter levels
  16. Key ingredients to make an Ozone Hole:
    1. Chlorine: Manmade CFCs

    2. Cold: Antarctic Polar Vortex

    3. Seasons: Dark and Light seasons

    4. Clouds: Polar Stratospheric Clouds

    5. UV radiation: Springtime sunlight