Worksheet
No.____a
Lower atmosphere (troposphere)
class
Ozone & photosmog
name
date
A model experiment on photosmog
Mention: Some chemicals and the UV-light used in the experiment are harmful. Experiment
carefully and protect yourselves!
E1
Irradiation: (demonstration experiment, Work
in a fume hood! Use aluminium foil as UVprotection!)
A 450-mL-water-cooled immersion-lamp reactor
is filled with 2mL tetrachloroethene [Xn, N; R:
40-51/53; S: 2-23-36/37-61], ca. 1 cm high with
glass beads or glass rings and with fresh leaves.
Turn on the water-cooling and irradiate for 25
minutes with a 150 W -UV- immersion-lamp
(high-pressure mercury vapour lamp).
E2
Extraction, filtration: (group experiment)
Give cut leaves and quartz sand into a mortar
and grind it with methanol [T,F;
R: 11-23/24/25-39/23/24/25; S: 1/2-7-16-36/3745]. Filter the green solution afterwards.
Make extracts from irradiated and non-irradiated
leaves of the same kind.
E3
Thin layer chromatography: (group
experiment)
Divide a TLC-aluminium foil coated with silica gel
into two sections and add two points of
application from the two extracts from E2. For
the development of the thin layer chromatogram
use as solvent a mixture containing petroleum
ether (with a boiling-point range of 30-50°C)
[F+, Xn, N; R: 12-51/53-65-66-67; S: 9-16-2933-61-62], benzine (with a boiling-point range of
100-140°C) [F, Xn, N; R: 11-38-51/53-65-67; S:
9-16-23-24-33-61-62] and 2-propanol [F, Xi; R:
11-36-67; S: 2-7-16-24/25-26] in a ratio of
25:25:5.
Figure 1: Model experiment on photosmog.
In this model experiment you obtain different results according to
the kind of leaves used and the time of irradiation. Nevertheless
these results will be very similar to those depicted in Figure 2.
T1
Which pigments have been hurt or destroyed?
How can you recognise that?
Mostly ß-carotene and also chlorophylls b and
then a are damaged. You can see this from the
decrease of the DC bands if you compare parts A
and B with each other. Whereas in part A the
bands are easily visible, they are much thinner or
even almost invisible in part B.
Figure 2: Thin layer chromatogram
of extracts from non-irradiated (A)
and irradiated (B) leaves. [1: point of
application; 2,3,4: xanthophylls; 5:
chlorophyll a ; 6: chlorophyll b; 7 ßcarotene]
© 2004 ESPERE-ENC / Seesing, Tausch, Universität-Duisburg-Essen; Duisburg
Worksheet
No.____b
Lower atmosphere (troposphere)
class
Ozone & photosmog
name
date
A model experiment on photosmog
T2
The experiment on the damage of leaves (E1) is a model experiment for processes that can also
occur in nature. The reaction conditions inside the reactor are not quite the same as in nature
though. Partially they are stronly exaggerated concerning processes in the troposphere and in the
stratosphere.
Add suitable keywords in the table below (e.g. higher, lower, shorter, longer, different, almost the
same, etc.) comparing the processes in the troposphere and stratosphere with the experiment:
troposphere
the same
stratosphere
lower
different (lower
concentration of CHC)
longer (but less intense)
different (lower
concentration of CHC)
longer (but less intense)
periodicity of the irradiation
(day/night rhythm)
wavelength of the light ( )
different (with rhythm)
different (with rhythm)
longer wavelengths
longer wavelengths
open / closed system
dynamics of the gas masses
different (open)
more dynamic
different (open)
more dynamic
temperature of the gas mixture
the same or lower
lower
gas pressure
composition of the gas mixture
time of irradiation
Figure 3: Prognoses on the change of the total ozone
column referring to geographic latitude (left) and to the
change in the vertical ozone distribution (right). [Lit.: G.
Mégie, Ozon, Springer, Berlin 1989]
T3
Interpret the ozone prognoses from Figure 3. What is more alarming, the change in the total ozone
column or the vertical distribution? Give reasons for your answer.
The change in the vertical ozone column is more alarming. Ozone is harmful in
the troposphere and useful in the stratosphere. Therefore an increase of the
tropospheric and a decrease of the stratospheric ozone is especially bad, even
if the total ozone column remained constant.
© 2004 ESPERE-ENC / Seesing, Tausch, Universität-Duisburg-Essen; Duisburg
Worksheet
No.____c
Lower atmosphere (troposphere)
class
Ozone & photosmog
name
date
A model experiment on photosmog
T4
Look at the vertical distribution of ozone in Fig. 3 (right) in “60” years. Which phenomenon is
represented by the model experiment?
1. ozone hole
2. photosmog
3. ozone hole and photosmog
Give reasons for your answer.
No. 3 the ozone hole and photosmog. The model experiment demonstrates the
effect of photosmog together with the effect of strong UV radiation on the
vegetation. If the experiment were to demonstrate only the effect of
photosmog the leaves shouldn´t be irradiated by UV light.
Because of the existence of the ozone hole more UV light reaches regions
close to the ground and irradiated plants. In these regions it also contributes
to the production of photosmog.
T5
ß-carotene has a weak point
that can be attacked very
easily.
Which of the possible
reactions from Fig. 4 may
take place in experiment E1?
Give reasons for your answer.
Except for the bromination all
reactions from Fig. 4 could take
place. For a bromination there is
no bromine source .
Decomposition
products
of
.
tetrachloroethylene (e.g. Cl ) or
Figure 4: possible reactions of ß-carotene
oxygen atoms can serve as
radicals. There is also enough UV
radiation and ozone could be
formed under the given reaction conditions from oxygen from the air.
© 2004 ESPERE-ENC / Seesing, Tausch, Universität-Duisburg-Essen; Duisburg