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Understanding Radiation Mechanisms for Energy Transfer and Mass Flux

Explore the intricate processes of energy flux, mass transfer, and radiation mechanisms involving electromagnetic waves, particles, blackbody radiation laws, and selective absorption by atmospheric gases. Learn about the formation and depletion of ozone, greenhouse gases, scattering phenomena, and radiation measurement techniques. Delve into the principles of thermal devices, photoelectric cells, and photochemical sensors for studying radiation.

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Understanding Radiation Mechanisms for Energy Transfer and Mass Flux

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  1. Radiation Mechanisms of Energy Transfer Mass flux- Energy flux-

  2. Radiation: 1. Electromagnetic wave

  3. Radiation: 2. particles (photons) Photons have no mass, and travel at the speed of light Energy of a photo h=6.626068 x10-34 m2 kg / s

  4. Laws of blackbody radiation 1. Plank’s law 6000K 300K 2. Wien’s displacement law

  5. Gray body:

  6. Gray body: Radiative equilibrium temperature

  7. Absorbtivity Reflectivity Transmissivity

  8. What Happens to Incoming Solar Radiation Selective absorption and emission of atmospheric gases 1. Energy level of atoms or molecules Quantum jump: transition between different energy levels 2. Different energy form of a molecule or atom

  9. a. Rotational energy CO Rotational energy transition can happen as long as a photon’s wavelength is shorter than 1 cm, usually associated with microwave wavelength. b. Vibrational energy Polar molecule has permanent dipole Non-polar molecule does not have permanent dipole.

  10. Vibrational energy level transition requires a photon's wavelength shorter than 20 micrometer, usually in the infrared band. Vibration and rotation sometimes combine together to form vibration- rotation mode, the transition between vibration-rotation modes also involves certain frequencies.

  11. c. Photodissociation Solar ultraviolet photon For photodissociation to occur, the wavelength of a photon must be in the ultraviolet band. To dissociate Oxygen the wavelength of radiation must be shorter than 200 nm. Ozone is a loosely bonded molecule. To dissociate a Ozone molecule, the frequency of a photon can be as low as 300 nm.

  12. d. Electronic excitation 1st Shell 2nd Shell Electrons may be excited from one shell to another shell by a photon with a sufficiently high energy level. The wavelength is usually shorter than 1 micrometer. e. Photoionization To photoionize a molecule requires the radiation with a wavelength shorter than 100 nm. Photoelectron

  13. M Electronic excitation Photoionization overlap What gases absorb shortwave radiation? Ozone What gases absorb and emit longwave radiation? Clouds water vapor CO2 Ozone Methane

  14. Ozone 10-50 km (stratosphere) Formation of Ozone Sustaining Ozone Depletion of Ozone

  15. Ozone Ozone Depletion

  16. The Ozone Hole Ozone concentration drops sharply over Antarctica

  17. 1. Polar winter leading to the stronger circumpolar wind belt (polar vortex) to isolate the cold air within it. The Ozone Hole Cold air -80C Polar vortex 2. As the cold temperatures persist over the polar, polar stratospheric clouds form. 3. Chlorine reservoir species HCl and ClONO2 become very active on the surface of polar stratospheric clouds.

  18. Atmospheric gases absorb all energy at wavelengths emitted from surface except for 8-11 micron window known as Atmospheric Window. Oxygen, ozone, carbon dioxide, water vapor are great absorbers of IR radiation.

  19. Trace gases, other important greenhouse gases CFC-11 CFC-12 HCFC-22

  20. Rayleigh Scattering The scattering from molecules and very tiny particles (< 1 /10 wavelength) is predominantly Rayleigh scattering.

  21. Mie Scattering The scattering from relatively large particles (> 1 wavelength) is predominantly Mie scattering, which is not strongly wavelength dependent and produces a sharper and more intense forward lobe

  22. Red Sunset

  23. Making Radiation Measurements There are three ways to make radiation measurements. • Thermal sensitive devise • Photoelectric cell (photodiode) • Photochemical sensor What is the basic operating principle for the thermal devise? • How could we use a plate to measure broadband radiation? Illuminate the surface with a bright light, or sun light…

  24. 2. What besides radiation will affect temperature of the plate? Convection and conduction 3. how could their effect on the temperature of the plate be removed? Using a glass dome

  25. What is the basic operating principle for the photoelectric cell? A device that converts light into electricity. Phototube is an electron tube in which electrons are excited and emitted by light. The simplest phototube is composed of a cathode coated with a photosensitive material. Light falling upon the cathode causes the liberation of electrons, which are then attracted to the positively charged anode, resulting in a flow of electrons (i.e., current) proportional to the intensity of the light. Solid-state photodetector is the photoconductor whose resistance changes when it is exposed to light. The solid-state photodetector is small, inexpensive, and uses little power.

  26. What is the basic operating principle for the photochemical sensor? The photochemical sensor utilizes materials that tend to have chemical reaction due to the absorption of light (including visible, ultraviolet, and infrared). The light excites atoms and molecules (shifts some of their electrons to a higher energy level) and thus makes them more reactive. The bleaching of dyes or the yellowing of paper by sunlight is a good example of photochemical reaction. It is harnessed by plants in photosynthesis and by humans in photography. Broadband Radiation Instruments: Shortwave K Longwave L Total Q = K + L

  27. Upward stream and a downward stream of radiation = -solar incident = reflected solar = emission from sun’s face = emission from atmosphere Net radiation Spectral Radiation Instruments:

  28. What are solar radiation measurements? Direct (beam), diffused (sky), and global (total)

  29. Pyranometer measures global-solar shortwave radiation Solar radiation curve outside atmosphere Solar radiation curve at the sea level Curve for balckbody at 50000K Pyranometer sensor

  30. Solar radiation irradiance measurements on a clear day

  31. Shaded Pyranometer measures diffuse solar radiation The pyranometer has a black thermopile sensor protected by two concentric hemispherical optically ground covers. The detector is independent of wavelength of radiation over the solar energy spectrum. Both the pyranometer and the shading disk are mounted on an automated solar tracker to ensure that the pyranometer is continuously shaded.

  32. Pyrometer — measures global longwave radiation Fixed pyrometer High speed pyrometer Protable pyrometer Video pyrometer

  33. Pyrheliometer measures direct beam used with a solar tracking system to keep the instrument aimed at the sun. A pyrheliometer is used in the same setup with a pyranometer.

  34. Pyrradiometer measures net radiation For exact determination of net radiation in short- and longwave radiation range (0.3 to >30 um) with two separately working receivers. The CN1-R Net Pyrradiometer measures the net total radiation flux (solar, terrestrial, and atmospheric) downward and upward through a horizontal surface.

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