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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.• 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.
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.
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.
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)
Vertical Structure of the Atmosphere
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.
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
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
Ionosphere
• Can use for long distance communication.– Not as reliable as
satellite communication
– Ionosphere layer will vary with solar activity.
Ionospheric Effects
• Auroura Borealis– Northern lights– Recombination of ions
with electrons– Directed by Earth’s
magnetic field– Auroura Australis
– AurB2.mpg– http://www.youtube.co
m/watch?v=qIXs6Sh0DKs