Worksheet
No.____a
Higher atmosphere (stratosphere)
class
photoreactor atmosphere
name
date
Modell of the two-chamber photoreactor of the earth atmosphere
The absorption spectrum of ozone was elucidated between 1881 and 1890. As early as in 1878 Alfred
Cornu, a professor of physics, found out that the spectrum of the sun (as it reaches the earth) abruptly
ends at wavelengths below 300 nm as if it was cut along a sharp edge. This edge even moves towards
greater wavelengths when the sun is low (Fig. 1a).
Figure 1
a) radiation: absorption and
emission: γ, UV, Vis, IR,
radiowaves
T1
b) model of the two-chamber photoreactor of the atmosphere
Is this fact due to one of the properties of
the sun or to one of the properties of the
earth atmosphere?
a) How would Cornu have answered this
question?
b) What is the answer according to our
present knowledge almost 130 years after
Cornu ?
a) Alfred Cornu deduced from his observations
that in the atmosphere there must be some
species which absorbs light of short
wavelengths. The lower the sun the longer
the way through the atmosphere that has to
be passed by light seen by an observer.
At the same rate the filtering effect in the
area of short wavelengths increases.
b) Today we know that the ozone of the
atmosphere is responsible for this effect.
It absorbs especially well at wavelengths
Figure 2
Layers of the atmosphere and temperature profile
below 300 nm.
Nevertheless it is also able to absorb light
at slightly longer wavelengths. This property
declines with increasing wavelengths. Thus the thickness of the ozone layer has to
increase for a sufficient filtering effect. This is given due to the round shape of the
earth´s geometry: with decreasing angle of incidence the thickness of the ozone layer
which is passed by light increases.
© 2004 ESPERE-ENC / Seesing, Tausch, Universität-Duisburg-Essen; Duisburg
Worksheet
No.____b
Higher atmosphere (stratosphere)
class
photoreactor atmosphere
name
date
Modell of the two-chamber photoreactor of the earth atmosphere
T2
Why can we regard the earth atmosphere as a two-chamber photoreactor (Fig. 1b)? Use the
temperature profile from Fig. 2 for your answer.
The division into two chambers can be seen as a minimum in the temperature profile.
Because of this cold zone between two warmer layers there is hardly any exchange of
matter between the layers. (Convection is prevented.) The cold zone can be regarded as
a wall separating two separate chambers.
[In the upper chamber there is solar radiation of short wavelengths. Due to
photoreactions this light is filtered off and only light of longer wavelengths can reach the
lower chamber. This is another difference between the two chambers.]
T3
Why is the temperature in the upper atmosphere much higher than in the tropopause? Use the
reactions from the information on ozone ("wanted - ozone") for your answer!
In the upper stratosphere there is ozone. As you can see from the Chapman-cycle, heat
is produced at both, the formation and the decomposition of ozone. For both reactions
light of chort wavelengths is needed. In addition the reactions of the Chapman cycle give
a conversion of (UV) light energy into heat. This heat is responsible for the relatively high
temperature of the stratosphere.
T4
Explain why the wavelengths of light are quite different in the stratosphere and in the troposhere
(see Fig. 2). Use the absorption curve from the " wanted - ozone" for your answer.
Before the sunlight reaches the troposphere it has to pass through the stratosphere.
From the absorption curves you can see that the stratospheric gases oxygen and ozone
absorb light of shorter wavelengths very well. Thus this light is filtered off in the
stratosphere and cannot reach the troposphere.
© 2004 ESPERE-ENC / Seesing, Tausch, Universität-Duisburg-Essen; Duisburg
Information- Higher atmosphere (stratosphere)
sheet
Wanted poster ozone
class
date
name
© 2004 ESPERE-ENC / Seesing, Tausch, Universität-Duisburg-Essen; Duisburg