Green Chemistry and the Ten Commandments

10-16 km, -56 ̊C

O 2         +       hν → O      +       O

O 2         +       O → O 3

O 3         +       hν → O 2        +       O

(filtration of  ultra-

        violet  radiation)

Stratosphere

~ 50 km, -2 ̊C

Ultraviolet between 200-330

nanometers  penetrating to

around  50  km  altitude

High-energy ultraviolet,    wave-

length  less    than    100 nanometers,

penetrating to  around  200 km

altitude Ultraviolet    above   330 nano-

meters, visible light,  infrared,

penetrating through the strat-

osphere and to  Earth’s surface

Figure 8.2. The upper atmosphere including the stratosphere and regions beyond is particularly important
in the absorption of radiation that would make life impossible if it reached Earth’s surface. The layer
of ozone, O 3 , in the stratosphere is of the utmost importance and one that is subject to damage from
anthropogenic species released into the atmosphere.

8.2. Atmospheric Chemistry and Photochemical Reactions

Atmospheric chemistry describes chemical processes that occur in the atmosphere.
One notable aspect of atmospheric chemistry is that it occurs in the gas phase where
molecules are relatively far apart, so a molecule or a fragment of a molecule may travel
some distance before bumping into another species with which it reacts. This is especially
true in the highly rarefied regions of the stratosphere and above.
A second major aspect of atmospheric chemistry is the occurrence of photochemical

reactions that are initiated when a photon (see Section 6.2) of ultraviolet radiation is
absorbed by a molecule. The energy of a photon, E, is given by

E = h ν (8.2.1)

Chap. 8. Air and the Atmosphere 199