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=qIXs6Sh0
DKs