Day 011 - 12 Jul 94 - Page 48
1 A. Yes, the hard CFCs were the ones which are not
degraded in the lower atmosphere and the soft CFCs are
2 those which are partially degraded in the low atmosphere.
3 Q. Just to reiterate, someone who was a chemist, or whatever,
would be able to distinguish in any event?
4 A. Somebody who was a chemist and who knew something
about the chemistry of the atmosphere would be able to
5 distinguish the differences between the two, yes.
6 Q. Just one small point -- I do not know whether it is a
small point or not -- if could you turn to, is it appendix
7 C -- tab C, page 12?
A. Can you tell me which of these?
8
Q. I think it is the orange file actually.
9 A. I am getting there slowly. OK.
10 Q. On page 12, just this small point about the lifetime:
These are estimates, are they not, would that be right?
11 A. Yes.
12 Q. Do you know what the margin of error is, for example, on
CFC-11?
13 A. The margin of error is actually roughly given by the
variety of estimates we had this morning which was in the
14 order of 10 to 15 per cent. If you look at the life times
which are quoted this morning, they range from about 110
15 years to 140 years. So you are talking about an error of
maybe up to 30 per cent, but you are talking about
16 something which is of the order of 100 years.
17 Q. It has 60 years for CFC?
A. Oh, for CFC-11, well, again it is the same percentage
18 error.
19 Q. So that would be from?
A. In other words, it could be something like 40 years
20 and it could be something like 60 years, but it is of the
order of 50 years.
21
Q. What about CFC-22?
22 A. Well, again if you have an estimate which is the order
of -- we have actually seen things today which vary
23 between just over 20 to 25 and 15, so we are talking about
something which is the order of, let us say, 15 to 18
24 years.
25 The reason why there are variations is that, as I tried to
explain this morning, many experiments have been done,
26 both in the laboratory and in the atmosphere, to try to
measure the transient concentrations of the species
27 involved in this, and the method of deciding whether the
modelling is accurate or not is to predict the amount of a
28 particular chemical that you would find in the atmosphere,
given a particular model and then measure experimentally
29 how much of that chemical exists in the atmosphere, and
see whether it is or it is not predicted correctly by the
30 model that you are using.
