Page 168 - Basic physical chemistry for the atmospheric sciences

1 5 4 Basic physical chemistry

UV radiation at the Earth' s surface, which accompany depletion in
the total column ozone, have led to international agreements to reduce
the manufacture of chlorofluorocarbons, and to eliminate them com­
pletely by the year 2000. Even so, due to the long lifetimes of Freons ,
the concentrations of chlorine in the stratosphere are expected to rise
substantially . Even if the release into the atmosphere of all Freons
were to stop right now , it would be well into the twenty-second cen­
tury before atmospheric concentrations returned to the pre-l 930s val­
ues . Thus, further decreases in total column ozone, and over increas­
ingly larger regions of the globe, are to be expected.

Exercises
7 . 6 . Answer, interpret, o r explain the following in light o f the
i
pr n ciples presented in this chapter.
(a) Photochemical reactions in the atmosphere generally
involve UV and visible radiation.
(b) Photochemical processes are sometimes extremely ef­
ficient in converting light into chemical energy. Give
an example.
(c) Ionization potentials are generally greater than corres­
ponding binding energies.
(d) Astronauts see a faint envelope of light in the upper
n
atmosphere on the i ght side of the Earth.
(e) If the primary photochemical quantum yields for a reac­
tion are all small ( < < I ) , the photophysical processes

must be important .
(f) Assuming that the photostationary state given by Eq.
(7. 2 3) is strictly applicable in the atmosphere and that k3
and [0 (g)] are approximately constant, how would you
3
expect the ratio [NOi(g)]/[NO(g)] to vary diurnally in
the atmosphere?
(g) In the troposphere air temperatures generally decrease
with height, but in the stratosphere they start to in­
crease with height near the level where ozone concen­
trations are a maximum.
(h) The use of nitrate fertilizers, which release nitrous ox­
ide (N20) into the troposphere , could affect strato­
sphere ozone concentrations. (Hint: N 2 0 photodissoci­
N
ates for A < 0 .25 µ,m yielding O . )