Ultraviolet Absorption

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Ultraviolet Absorption

• by
• Richard L. Miller

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UV Absorption Topics

• UV Light
• Absorption
• Ozone Layer
• Sunscreen
• Sunglasses

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UV Light

• The UV region of light from the sun
• 100nm to 400nm
• Bands
• UVA 320-400nm
• UVB 270-320nm
• UVC 100-270nm
• Characteristics of each band
• UVA (90 of UV light at sea level)
• UVB (responsible for the redness seen in the
  skin)
• UVC (filtered out in stratosphere)

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Absorption

• Absorption - In absorption, the frequency of the
  incoming light wave is at or near the vibration
  frequency of the electrons in the material. The
  electrons take in the energy of the light wave
  and start to vibrate. What happens next depends
  upon how tightly the atoms hold on to their
  electrons. Absorption occurs when the electrons
  are held tightly, and they pass the vibrations
  along to the nuclei of the atoms. This makes the
  atoms speed up, collide with other atoms in the
  material and then give up as heat the energy
  they acquired from the vibrations.

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Ozone Layer

• Location of ozone layer
• The stratosphere starts around 10 km above sea
  level
• The stratosphere ends around 50 km above sea
  level
• 90 of ozone is in the stratosphere
• Chemical reactions
• Making of O3 Molecule
• UV Light (lt240nm) splits O2
• into highly reactive Oxygen
• atoms
• Oxygen atoms then combine
• with other O2 creating O3

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Ozone Layer

• Making of O2 Oxygen Atom
• UV light (lt290nm) splits O3 into O2 and an Oxygen
  atom
• Energy absorbed
• The ozone layer absorbs 97-99 of the UV light in
  the 150 300 nm range
• The energy is given off in an exothermal reaction

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Sunscreen

• Active sunscreen ingredients
• UVB (sunburn)
• PABA
• Salicylates
• Cinnamates
• Octocrylene (new)
• UVA (premature aging)
• Benzophenones
• Dibenzoylmethanes

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Sunscreen

• Physical Blockers (broad spectrum)
• Zinc Oxide and Titanium Oxide (absorbs, reflects
  scatters)
• Micronized
• How absorption is done
• Organic chemicals degrade
• How much energy is absorbed
• Depends upon the SPF and the individuals skin
  type

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Sunglasses

• Glass
• Passes only visible light
• Polycarbonates
• Add chemicals to polycarbonate to perform
  absorption
• Tinting
• Coating outside of lens performs the absorption
• Photochromic
• Bi-directional chemical process changes size of
  molecule that absorbs visible light
• Introduction of UV light starts chemical process
• Splits silver halide into silver and halide

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Questions?