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 ( nm), UV-B ( nm) UV-C ( nm). Visible: 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 3.5 O F (2 O C) per 1000 ft. Atmospheric conditions constantly changing –Weather About 80% of atmosphere At the top - Temperature about O C 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 (O 3 ) –Formed by reactions of oxygen –O 2 + energy → O + O –O + O 2 → O 3 Dissociation energy comes from the Sun. –Ultraviolet radiation Optimum conditions about 40 km (25 mi) O 3 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 O 2 + energy  O + O; then O + O 2  O 3 –Energy for temp increase comes from ozone absorbing UV radiation! Causes O 3 → O 2 + O; and O 3 + O → 2O 2 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: –N 2 + energy → N 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.mpgAurB2.mpg – m/watch?v=qIXs6Sh0 DKshttp:// m/watch?v=qIXs6Sh0 DKs