1. The factors affecting the O3
layer
 There are two
major factors that
has tremendous
negative effects on
the O3 layer
 I. CFCs
 II. NOx

2. I. CFC’s and ozone depletion
 Chlorofluorocarbons are
created and used in
refrigerators and air
conditioners. These
chlorofluorocarbons are not
harmful to humans and have
been a benefit to us. Once
released into the atmosphere,
chlorofluorocarbons are
bombarded and destroyed by
ultraviolet rays. In the process
chlorine is released to destroy
the ozone molecules

3. Destruction of ozone by chlorine
Molecular oxygen is broken down in the stratosphere by solar
radiation to yield atomic oxygen, which then combines with
molecular oxygen to produce ozone. The ozone is then
destroyed by chlorine atoms.

4. Ozone destruction by UV rays
 UV radiation from the sun
releases the radicals Cl and
ClO.
 Ozone is a highly unstable
molecule so it readily donates
its extra oxygen molecule to
free radical species such as
hydrogen, bromine, and
chlorine.
 These compound species act
as catalysts in the breakdown
of ozone molecules.

5. I. Nitric oxide
NO is produced
abundantly in the
troposphere, but all of it
is converted into NO2 
HNO3 (removed through
precipitation)
Removal processes:
NO2 + .OH  HNO3
ClO. + NO2  ClONO2
NO in the stratosphere
produced from nitrous
oxide (N2O), which is
much less reactive than
NO.
N2O + hv  N2 + O
(90%)
N2O + O  2 NO
(~10%)

6. The two-sided effect of NOx
NOx provides a
catalytic chain
mechanism for O3
destruction.
NOx inhibit the NOx
and ClOx cycles for
O3 destruction by
removing radical
species in the two
cycles.
The relative magnitude of
the two effects is altitude
dependent.
–>25 km, the net effect
is to destruct O3.
–(NOx accounts for
>50% of total ozone
destruction in the
middle and upper
troposphere.)
–In the lower
stratosphere, the net
effect is to protect O3
from destruction.

7. The formation of the ozone layer
The formation of the ozone in the stratosphere region begins with the photodissociation of oxygen molecules by the solar
radiation at wavelengths below 240 nm.
O2 O + O
The highly reactive O atoms combine with oxygen molecules to form ozone as follows :
O3 + MO + O2 + M
M : Some inert substance.
The role of M in this exothermic reaction is to absorb some of the excess energy released and prevent the spontaneous
decomposition of the O3.molecule
O3 O + O2
UV < 240nm
UV