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