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SUMMARY:Isotope fractionation in nitrous oxide and CFC-12 reflects stratos
 pheric chemistry and transport rates - Dr Jan Kaiser\, University of East 
 Anglia
DTSTART:20120309T141500Z
DTEND:20120309T153000Z
UID:TALK36309@talks.cam.ac.uk
CONTACT:Dr Alex Archibald
DESCRIPTION:Nitrous oxide (N<sub>2</sub>O) and dichlorodifluoromethane (CF
 C-12) are the third- and fourth-most important anthropogenic greenhouse ga
 ses. Both have long atmospheric lifetimes of about 100 years and are only 
 destroyed in the stratosphere. There\, they are the most important ozone-d
 epleting gases in terms of abundance (CFC-12) and emissions (N<sub>2</sub>
 O).\n\nNovel mass-spectrometric techniques have been developed over the la
 st decade\, which allow the detailed study of individual isotopologues and
  isotopomers of these gases. Strong enrichments in the heavier isotopic va
 riants were found in stratospheric balloon and aircraft\, tightly related 
 to the degree of photochemical decomposition and the age of air. Kinetic m
 easurements in the laboratory have provided a good understanding of the wa
 velength- and temperature-dependent isotopic fractionation.\n\nThe compari
 son between field observations and laboratory measurements provides insigh
 ts into the rates of stratospheric transport and chemistry as well as the 
 relative contributions of individual sink reactions (photolysis and photo-
 oxidation). The increase of the apparent isotopic fractionation with altit
 ude and its decrease towards the poles reflects the interplay between chem
 istry\, mixing and transport in different regions of the stratosphere.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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