Lecture 2 Flashcards
What are the 4 regions the atmosphere id divided into? Why does air temperature increase with altitude above the troposphere?
The troposphere (0-10 km), stratosphere (10-50 km), mesosphere (50-80 km) and thermosphere (80-110 km). Air temperature increases with altitude above the troposphere, as the ozone layer is located there within the stratosphere. Due to ozone’s ability to absorb heat in the form of radiation from the sun’s rays, through absorption the ozone creates it’s on source of heat which forms the stratosphere that is responsible for keeping earth warm.
Oxygen’s percentage in the atmosphere is about 21%. What processes are responsible for it’s presence and stability? What happens to oxygen inside the stratosphere?
Within the oxygen cycle photosynthesis and respiration are responsible for it’s presence and stability. Oxygen that finds its way into the stratosphere is turned to ozone through many processes with radiation from the sun.
What role does ozone play in the earth’s atmosphere?
Ozone functions as a radiation shield for earth. Ozone absorbs harmful uv radiation originating from the sun. Ozone also is a component inside the ozone layer, which is responsible for keeping the earth warm.
What is photodissociation?
Photodissociation is the process by which molecules absorb photon light and are thus ruptured, splitting two molecules into separate neutral ones.
How is ozone made inside the stratosphere?
diatomic oxygen molecules are split via photodissociation. The new free radicals now react with the diatomic oxygen in the stratosphere to form O3 (Ozone).
Where is the highest rate of ozone formation? Where is most of the world’s ozone found?
The highest rate of ozone formation is found at about 50k at the stratopause. Around 90% of earth’s ozone can be located in the stratosphere.
Explain the chemical equilibrium of atmospheric ozone.
Absorption of light radiation also triggers the decomposition of O3. The concentration of ozone in the atmosphere is constant, this means the rate of decomposition must equal the rate of production of ozone. Ozone when formed via a free radical and diatomic oxygen molecule contains excess energy which must be released, ozone releases some of this energy by colliding with a molecule.
Explain the chapman cycle.
- The O2 molecule is broken via photodissociation.
- O2 bonds with O to form a high energy O3.
- O3 is broken via photodissociation into O2 and O, this happens simultaneously with step 2, thus the rate of formation = rate of O3 destruction.
- O3 bonds with O to form 2O2.
Concentration of ozone in the stratosphere is very low, however it is enough to filter out solar radiation ranging from 200-300 nm.
What is a consequence of lower concentrations of ozone. What year did satellite monitoring of ozone begin? What was found?
If concentrations of the ozone lower, the earth will be exposed to more harmful UV radiation. Satellite monitoring of ozone began in 1978, it was discovered that a “hole” is inside the ozone layer above Antarctica.
What are CFCs and why are they harmful to the earth’s ozone?
CFCs also called Freons are anthropogenic chemicals that contain chlorine, fluorine and carbon and are responsible for depletions of the ozone layer.
Give some examples of what CFCs are used for. How are they named.
CFCs because of their chemical stability, low toxicity and valuable physical properties are versatile and stable in the lower atmosphere and have been used in refrigeration, air conditioning and foam blowing. CFCs are referred to with numbers, E.g: CFC-11, etc.
Explain how a CFC can break down ozone using equations.
CFCs are relatively inert and, thus doesn’t change much when reaching the stratosphere. When exposed to the uv radiation between 175-220 nm CFCs are photodissociated and a free chlorine molecule is formed.
Equation:
CFCl3 -> CFCl2 + Cl
Chlorine catalyzes the decomposition of ozone. The oxygen atoms orignate from the photodissociation of O and O3.
Chlorine attacks ozone and breaks it apart into Chlorine monoxide and O2, thus destroying O3.
Equation:
Cl + O3 -> ClO + O2
This chlorine monoxide is able to react with a free oxygen atom, thus releasing chlorine and forming O2.
Equation:
ClO + O -> Cl + O2
The net result is the net removal of O3 from the stratosphere.This chlorine atom is now free to attack and destroy another ozone molecule. This cycle can continue thousands of times before it is removed via methods like HCl moving back into the troposphere and dissolving in water.
What efforts have been put in place to limit the use of CFCs?
Limits were set in 1992, when reps of 100 nations agreed to ban the production and use of CFCs in 1996, exceptions for “essential uses.”. Since then the hole in the ozone has begun to repair itself.
What substances have repalced CFCs and why?
HCFCs: Haloalkane containing hydrogen, chlorine and flourine atoms.The carbon-hydrogen bonds in HCFCs are able to be attacked by reactive radicals and atoms in the troposphere and decompose to a significant extent there. However, they still diffuse into the stratosphere and deplete significant ozone.
HFCs: A haloalkane containing hydrogen and flourine atoms. Due to it’s (C-H) bonds it undergoes decomposition in the troposphere. It’s ozone depleting capacity is 0, as it contains no (C-Cl) bonds. HFCs are used commonly in 1,1,1,2-tetrafluoroethane (used in refrigeration and air conditioning). It’s more espensive and less efficient than the CFCs it replaces.
