Day 011 - 12 Jul 94 - Page 34
1 paragraph 5,
2 "While ozone loss is expected to increase with increasing
chlorine abundance in the atmosphere, the relationship
3 between stratospheric chlorine and ozone is not simple, as
indicated by the rapid deepening of the ozone 'hole' over
4 Antarctica during the 1980s. Stratospheric chlorine is
expected to continue to increase to levels higher than
5 previously experienced. There is a risk that these might
trigger disproportionately larger ozone losses.
6
"6. There is a time lag of several years before
7 tropospheric chlorine reaches the stratosphere, and takes
part in ozone destruction. The concentration of chlorine
8 in the troposphere (3.6 parts per billion by volume) ----
Is that what that stands for?
9 A. Yes.
10 Q. " .... At present exceeds that in the stratosphere (about 3
ppbv); ozone depletion can therefore be expected to
11 increase in the short term, even with a cessation of
emissions of halocarbons.
12
"7. The Review Group has used chlorine loading ....." And
13 I want to come back to that .,.. "(the total concentration
of chlorine held in halocarbons in the troposphere) rather
14 than ozone depletion potential (ODP) to compare the impact
of releases of different halocarbons on the atmosphere.
15 The use of ODP is limited by the failure of models to
predict ozone depletion correctly and by the fact that it
16 refers to steady state conditions which precludes
predictions of changes over the next few decades."
17
MR. JUSTICE BELL: That is a change in attitude really, is it
18 not?
A. Yes.
19
Q. Which is the most helpful measurement.
20
MR. RAMPTON: I will pause there, my Lord, because this might
21 be the appropriate moment for Professor Duxbury to explain
the difference between the two standards (or whatever you
22 call them)- chlorine loading and ozone depletion. Can I
ask you to do that? Remember that we are all laymen,
23 Professor Duxbury.
A. Chlorine loading of the stratosphere would be
24 basically the total number of substances in the
stratosphere which can liberate chlorine, and we are not
25 making any assumption about the rate of reaction. The
idea is that once substances get to the stratosphere,
26 sooner or later the chlorine in them will be liberated.
27 Q. Is that a markedly different approach from the use of ODP
as the measure?
28 A. It is different in that the ODP effectively was based
upon the idea of destruction of the substances which can
29 occur in the lower atmosphere, the troposphere, whereas
the chlorine loading more or less says that once things
30 have got to the stratosphere they effectively all have the
potential to damage the stratosphere. The current model
