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.
 

Prev Next Index