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test 2 review

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Department
Chemistry
Course
Chemistry 2210A/B
Professor
Kay Calvin
Semester
Fall

Description
Chem 2210A StudyGuide for Test # 2 Chapter 5 Wavelength regions of incoming radiation (from the sun) and outgoing (from t he Earth). - emission wavelength = temperature based - 2897/T (in K) = wavelength peak (in nm) - from the sun = wavelengths UV, visible and IR ....peak in visible (400-750nm) - from the earth = wavelengths IR (energy absorbed from sun, less emitted hence IR) - 50% of sun radiation absorbed (20% IR absorbed by water, CO2; UV absorbed by ozone and O2) Albedo; what is it and how does it vary with surface? - Ability to reflect light - 30% reflected back into space (70% stay absorbed) = albedo; clouds, snow, ice all reflect light - water/soil better at absorbing - rate of emission of light increases as temperature is raised Greenhouse Effect and Enhanced Greenhouse Effect; how are they different? D escribe the processes in general terms. Greenhouse Effect: greenhouse gases (such as CO2, water vapour) capture IR radiation and either re-emits it as IR, or after absorbing emits it as heat. Random and warms air near surface...natural billions of years Enhanced Greenhouse Effect: not so natural, increasing concentration of trace gases in air that absorb IR light , increase surface temperature well beyond 15 degrees What are the major greenhouse gases? What is feedback? What is the atmosp heric window and what is its significance? 1. CO2 : absorbs at 2.46nm (asymmetrical stretch) + 15nm (bend) In spring/summer because of growth of vegetation, CO2 extracted from air CO2 + H2O  O2 + polymeric CH2O Fossil fuels from home heating added in winter Forests cleared for wood or land, wood burned = CO2 2. Water Vapour: 2.7 (asymmetrical) + 6.3 bending absorbs through bending (less IR light than CO2 per molecule) Increase in temperature = more water vapour = more warming POSITIVE FEEDBACK 3. CH4: bending vibrations (7.7nm), lifetime less than 10 years; 90% of CH4 removed by OH sink; CH4 + OH*  CH3* + H20 (first reaction = CH4  CH20 CO CO2) *** per molecule 20x more efficient at absorbing IR Methane trapped in ice, 2CH20  CH4 + CO2 4. N2O (nitrous oxide) : absorbs IR at 8.6 (bending) and 7.8 (stretching); no sink, last 120 years; produced by nitrification and denitrification 5. CFCs – C-F: 9um  in window! Heating from IR counteracts cooling happening in stratosphere when break down ozone; long lifetime 6. Tropospheric ozone: short lived, absorbs in window, photochemical smog 7. SF6 (sulfur hexafluoride): long lived, good absorber Feedback: Positive: event produces a result that further amplifies the result Negative: system whose output reduces subsequent output Atmospheric Window: IR light from 8-13um escapes atmosphere efficiently , gases that absorb in this region = further enhance greenhouse effect Amount of light absorbed by particles is linearly proportional to conc bc logarithmic but if C=0 then linear (directly proportional) Interaction of light with particles and aerosols; what is the effect of these inter actions on climate change. - particles can absorb and reflect light - reflection: back into space (scattering); back towards surface (backscattering) - aerosols especially sulfate aerosols reflect strongly hence cooling ! - soot particles absorb strongly hence warm air! o Absorb light energy, either releases as IR light or heat (warm air) - Small dro
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