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The UV range

The UV range. The UV range starts below 400 nm, i.e. deep violet. Usually UV radiation is divided into three main ranges. UV-A (320-395 nm), UV-B (280-320 nm) UV-C (200-280 nm). Visible: 400 - 700 nm. Book also includes UV-V (visible UV) from 395 to 445 nm.

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The UV range

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  1. The UV range • The UV range starts below 400 nm, i.e. deep violet. Usually UV radiation is divided into three main ranges. • UV-A (320-395 nm), • UV-B (280-320 nm) • UV-C (200-280 nm). • Visible: 400 - 700 nm.

  2. Book also includes UV-V (visible UV) from 395 to 445 nm. • Also have VUV (vacuum UV) from 100 to 200 nm. • Man-made • Readily absorbed by gases so created in vacuum. • Most small molecules have first transition in this region, so most gases are invisible.

  3. Temperature Variations • Regions based on change in temperature. • Troposphere • nearest the Earth • From surface up to about 15 km (10 mi) • Temperature decreases as altitude increases • About 3.5OF (2OC) per 1000 ft. • Atmospheric conditions constantly changing • Weather • About 80% of atmosphere • At the top - Temperature about 45 - 50OC below zero.

  4. Regions of the Atmosphere • Stratosphere – strato - layered • 15 to 50 km • Troposphere and stratosphere about 99.9% atmospheric mass. • Non-uniform increase to about 50 km (30 mi) • Mesosphere • Uniform decrease in temperatures again. • 50 km to 100 km (30 mi to 60 mi) • Thermosphere • Temp increases, dependent on Solar activity.

  5. Ozone and Ion concentrations • Ozone (O3) • Formed by reactions of oxygen • O2 + energy → O + O • O + O2→ O3 • Dissociation energy comes from the Sun. • Ultraviolet radiation • Optimum conditions about 40 km (25 mi) • O3 concentration decreases to about 70 km (45 mi)

  6. Vertical Structure of the Atmosphere

  7. Ozone • Region below 75 km known as ozonosphere • Roughly corresponds to stratosphere. • Formed by reaction of molecular oxygen • O2 + energy  O + O; then O + O2 O3 • Energy for temp increase comes from ozone absorbing UV radiation! • Causes O3→ O2 + O; and O3 + O → 2O2 • Creates balance of ozone / oxygen in atmosphere. • Pollutant at the Earth’s surface • Also relatively unstable at the surface.

  8. Ozone and Ion Concentrations • Serves as ‘umbrella’ for uv radiation. • Greatly decreases uv radiation that makes it to the surface of the Earth. • Upper atmosphere: • N2 + energy → N2+ + e- • Ionosphere • Made up of 3 layers

  9. Ionosphere • D layer • Absorbs some lower frequency radio waves • Allows higher (AM and FM) frequencies to pass. • E and F layer • Reflect AM • Allow FM to pass

  10. Ionosphere • Can use for long distance communication. • Not as reliable as satellite communication • Ionosphere layer will vary with solar activity.

  11. Ionospheric Effects • Auroura Borealis • Northern lights • Recombination of ions with electrons • Directed by Earth’s magnetic field • Auroura Australis • AurB2.mpg • http://www.youtube.com/watch?v=qIXs6Sh0DKs

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