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Lecture 4

# CHM310- Lecture 4.docx

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Department
Chemistry
Course
CHM310H1
Professor
Jon Abott
Semester
Winter

Description
CHM310 – Lecture 4 Green House Effect Recap  Calculating the energy of the Black Body  The earth is warmed by solar radiation coming in  Solar constant radiation coming in reaching the side of the atmosphere,  Shadow Area: The amount of sunlight that reaches the earth, it is the area which gets cut out form the earth  If anything emits as a black body it emits as a stepfan Boltzman Constant. Sigma*T^4  EinE out 1. Sunlight comes into the earth, - visible light (Short wave light) 2. Then the earth absorbs it, and emits IR light (Long wave light) 3. IR coming off from the earth is being absorbed by the gases that are infrared active 4. The atmospheric layer above then starts acting as a black body 5. It is to presume that the Black Body absorba radiations and emits them. 6. The black body atmosphere is a little thin bod of gas. It absorbs only the IR passing through it. It doesn’t absorb visible light. 7. Let’s assume this is a very thin layer which srriunds the earth. 8. We’ve got as much energy s its going down 9. Atmosphere is cooler than the ground, but its not that much cooler than the ground, so they emit IR radiation 10. Some of these radiation hits back to outer space. If an alien in mars or anywhere can see as if IR is coming from the Atmospheric layer. If you are looking from earth you can see as if IR is coming down from the atmospheric layer 11. This is the green house effect. The emission of IR radiation from the atmospheric layers. 12. The IR radiation emitting downwards is reabsorbed by the earth. 13. So in addition to the source of energy, 1) Calculate the surface temperature of the earth when there is an atmospheric layer a) We are going to use two equations b) One for the planet c) One for the atmosphere 2) For the planet a) Can write the same exact situation as before, except the only thing which would have changed would be the temperature. We should be solving for the temperature i) E = E in out ii) Solar constant * (1- albedo) (shadow area) = (sigma T^4) (Emission Area) iii) If we did this calculation again for the planet we have to end up with 255K as the temoerature for the atmosphere iv) For the sun they don’t have any idea what the temperature is for the surface. They can only see the tempreture coming from the atmos. Layer b) For the Atmosphere i) Assume that the atmosphere is a black body ii) Assumes that its transparent iii) in= Eout iv) Absorbs all the energy that comes from the earth v) The earth is emitting as a BB
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