Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

1
Environmental Impact
The ozone layer
As the sun’s radiation approaches the planet’s surface it can be
scattered, reflected, or absorbed, intercepted and re-emitted. This
is where the ozone layer comes into its own by scattering and
reflecting harmful high energy ultraviolet radiation. Variations in
temperature and pressure divide the Earth’s atmosphere into layers
and the mixing of gases between the layers happens very slowly.
That is why this 90% of the ozone stays in the upper atmosphere.
This stratospheric ozone contains 90% of all ozone gas on the
Earth but it is spread thinly and unevenly.
Life on earth has been safeguarded because of a protective layer
in the atmosphere. This layer, composed of ozone, acts as a shield
to protect the earth against the harmful ultraviolet radiation from
the sun. Ozone is a form of oxygen with three atoms (O3) instead of
two (O2). Through natural atmospheric processes, ozone molecules
are created and destroyed continuously. Ultraviolet radiation
from the sun breaks up oxygen molecules into atoms which then
combine with other oxygen molecules to form ozone. Ozone is not
a stable gas and is particularly vulnerable to destruction by natural
compounds containing hydrogen, nitrogen and chlorine.
Near the earth’s surface (the troposphere) ozone is an increasingly
troublesome pollutant, a constituent of photochemical smog and
acid rain. But safely up in the stratosphere, 11 to 48 km above the
earth’s surface, the blue, pungent-smelling gas is as important
to life as oxygen itself. Ozone forms a fragile shield, curiously
insubstantial but remarkably effective.
The distribution of ozone in the atmosphere is illustrated in Figure 1.1.
ALTITUDE (KILOMETERS)
35
30
25
20
15
10
5
0
OZONE LAYER
OZONE
INCREASES
FROM POLLUTION
OZONE CONCENTRATION
Distribution of ozone in atmosphere.
STRATOSPHERIC
OZONE
TROPOSPHERIC
OZONE
17
20
15
10
05
ALTITUDE (MILES)