Physical basis of the greenhouse effect the wavelength shift
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Online at: http://www.umich.edu/~twod/energy/resources/greenhouse_lecture. Physical basis of the Greenhouse Effect -The “wavelength shift”-. Solar insolation calculation (doc file) Blackbody radiation, Absorption spectra Conservation of energy Energy & Environment 263.

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Physical basis of the greenhouse effect the wavelength shift l.jpg

Online at: http://www.umich.edu/~twod/energy/resources/greenhouse_lecture

Physical basis of the Greenhouse Effect-The “wavelength shift”-

Solar insolation calculation (doc file)

Blackbody radiation,

Absorption spectra

Conservation of energy

Energy & Environment 263


Black body radiation l.jpg
Black body radiation

  • Continuous spectra

400 500 600 700

Wavelength [nm, nanometers]

ColorScience.htm


Black body radiation3 l.jpg
Black body radiation

  • Continuous spectra – we see as white light

400 500 600 700

Wavelength [nm, nanometers]

ColorScience.htm


Black body radiation4 l.jpg
Black body radiation

  • Continuous spectra & human cones, rods

400 500 600 700

Wavelength [nm, nanometers]

Warning:

shows range

of three

types of cones,

but not

relative

sensitivities

(green

has ~ 10x

sensitivity

of red).

ColorScience.htm


Black body radiation5 l.jpg
Black body radiation

  • Continuous visible spectra – higher temp.

400 500 600 700

Wavelength [nm, nanometers]

ColorScience.htm


Black body radiation6 l.jpg
Black body radiation

Note peak shift  

And flatter shape

with lower Temperature

  • Continuous visible spectra -- lower temperature

400 500 600 700

Wavelength [nm, nanometers]

ColorScience.htm


Black body radiation7 l.jpg
Black body radiation

  • Continuous visible spectra -- lower temperature

400 500 600 700

Wavelength [nm, nanometers]

-- Wavelength vs. temp is Stephan-Boltzmann law

-- Peak is Wein’s law

-- Shape or ‘distribution’ of intensity with frequency is Plank’s Readiation Law … A big deal in Quantum Mechanics’ history (Einstein, Plank, et al)

-More on this & math later

ColorScience.htm


Black body vs atomic line spectra l.jpg
Black body vs. atomic line spectra

  • Continuous spectra – from bulk solids with complex modes

  • Atomic line spectra – discrete energy levels

400 500 600 700

Wavelength [nm, nanometers]

Hydrogen EMISSION line spectra

ColorScience.htm


Solar black body radiation l.jpg
Solar black body radiation

  • Solar spectra … ~5800 K at surface

  • Yellow-green at middle. Combo ~ white.

    But, some parts missing …

400 500 600 700

Wavelength [nm, nanometers]

ColorScience.htm


Blackbody radiation l.jpg
Blackbody radiation

400 500 600 700

Wavelength [nm, nanometers]

But, what we actually get from the sun is:

Hydrogen ABSORPTION spectra

ColorScience.htm


Slide11 l.jpg

  • Atomic physics:

  • ATOMISTIC

  • and QUANTUM

  • view of

  • micro-world

  • Larger jump

  • more energy

     bluer color

400 500 600 700

Hydrogen EMISSION line spectra

Hydrogen ABSORPTION spectra

Hydrogen emits/absorbs same energies.

ColorScience.htm


Slide12 l.jpg

Atomic physics:

ATOMISTIC

and QUANTUM

view of

micro-world

400 500 600 700

Hydrogen EMISSION line spectra

Hydrogen ABSORPTION spectra

Hydrogen emits/absorbs same energies.

ColorScience.htm


Greenhouse black body radiation l.jpg
Greenhouse: Black body radiation

Three concepts crucial to understand greenhouse effect:

  • Blackbody radiation is E&M radiation

    a) Continuous spectra

    b) Shifts with temperature

  • Physics of radiant energy


Greenhouse black body radiation14 l.jpg
Greenhouse: Black body radiation

Three concepts crucial to understand greenhouse effect:

  • Blackbody radiation is E&M radiation

    a) Continuous spectra

    b) Shifts with temperature

    2) Line Spectra of atoms (or bands of molecules)

    a) Discrete lines (bands)

    b) Emission and absorption at same energies

  • Physics of radiant energy


Greenhouse black body radiation15 l.jpg
Greenhouse: Black body radiation

Three concepts crucial to understand greenhouse effect:

  • Blackbody radiation is E&M radiation

    a) Continuous spectra

    b) Shifts with temperature

    2) Line Spectra of atoms (or bands of molecules)

    a) Discrete lines (bands)

    b) Emission and absorption at same energies

    3) Equilibrium temperature reached when

    earth’s emission = earth’s absorption.

    - Slight change in either -> colder or hotter earth


Greenhouse and wavelength shift l.jpg
Greenhouse: and “Wavelength shift”

  • Fourth issue: CO2 emissions and H2O already in atmosphere

  • Look in detail now Physics of radiant energy …

  • We’ll need couple students with calculators …

    (And remember Sun = 6000 K, earth = 288 K,

    sigma = 5.67 x 10-8 Watts m-2)

    Later: solar-earth spectra compared 


Slide17 l.jpg

Source: http://www.lenntech.com/The-greenhouse-effect.htm


Slide18 l.jpg

Source: http://www.lenntech.com/The-greenhouse-effect.htm


Slide19 l.jpg

Earth

shine

Source: http://www.lenntech.com/The-greenhouse-effect.htm


Slide20 l.jpg

Earth

shine

WATER VAPOR

“Water molecules, always abundant I air, absorb thermal IR light due to the H-O-H bending vibration, the peak in the spectrum for this absorption occurs at about 6.3 µm. Thus almost all the relatively small amount of outgoing IR in the 5.5-7.5 µm regions is intercepted by water vapor. There are other water vibrations the remove thermal infrared light of wavelength 12 µm and longer. In fact the water is the most important greenhouse gas in the earth’s atmosphere, though on a per molecule basis it is a less efficient absorber than is CO2. “

“The equilibrium vapor pressure of liquid water, and consequently the maximum concentration of water vapor in air, increases exponentially with temperature. Thus the amount of thermal IR redirected by water vapor will rise as a result of any global warming induced by the other greenhouse gases and will amplify the temperature increase. Since it comes about as an indirect effect of increasing the levels of other gases. Consequently, water is not usually listed explicity among gases whose increasing concentrations are enhancing the greenhouse effect.  Water in the liquid form droplets in clouds also absorbs thermal IR. “

Source: http://www.lenntech.com/The-greenhouse-effect.htm