Day 011 - 12 Jul 94 - Page 49


     
     1        As the measuring techniques have improved, so as the
              accuracy of the modelling because the computers have got
     2        better.  Perhaps I could say, my Lord, that the main model
              used is actually based on the standard model used by the
     3        meteorological office for weather forecasting which has
              chemistry added to.
     4
         Q.   I am not trying to attack you; I am just trying to clarify
     5        things.
              A.  No, I am just trying to clarify the point which is
     6        that the reason why it looks different from year to year
              is that the measurements in the atmosphere have improved,
     7        the laboratory measurements have improved and our ability
              to do the calculations have improved.
     8
         Q.   Right.  But to say it is clear cut that CFCs have a long
     9        life-span and HCFCs a short life-span, that is really
              relative, is it not, and it could be potentially
    10        misleading?  Perhaps that is too strong, but what really
              matters is the length of time, is their life-span?
    11        A.  What really matters is actually whether the thing
              lives long enough to be transported to the upper
    12        atmosphere, and the point about the HCFCs is that because
              they will react with hydroxyl in the lower atmosphere,
    13        their potential to be taken out of the system before they
              every transported into the upper atmosphere where the
    14        ozone is, is very much less than it is for the fully
              halogenated fluorocarbons, whether they be carbon
    15        tetrachloride or, in fact, CFC-12, CFC-11.
 
    16   Q.   Could we go back to your statement?
              A.  Yes.
    17
         Q.   On page 5, where you are talking about short term
    18        releases, where you say:  "Short term releases of a more
              highly reactive compound such as HCFC-22 can put a large
    19        transient burden on the atmosphere", what do you mean by
              that?
    20        A.  I mean basically (and this is actually paraphrasing
              what the SORG report says), that if you have even a more
    21        reactive compound which gets into the atmosphere, it can
              actually increase the chlorine loading.  If it is
    22        transient because the average lifetime is much shorter
              than the fully halogenated species, then the chlorine
    23        loading will be of a shorter duration.
 
    24   Q.   But?
              A.  The point I was trying to make is that the ozone
    25        depleting potential does make an estimate of how certain
              reactions occur.  The chlorine loading is just based on 
    26        the fact you are actually adding a compound to the 
              atmosphere containing chlorine. 
    27
         Q.   In the short term then could this actually have a more
    28        severe effect?
              A.  If you read the SORG report, you will see that the
    29        only reason this came in was that it was actually a group
              of scientists pointing out that, in fact, the HCFCs could
    30        increase the amount of chlorine in the atmosphere.
              Therefore, although at present they were classed not as,

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