Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.743313
Title: Novel mass spectrometric techniques for stable isotope measurements in atmospheric halocarbons and nitrous oxide
Author: Ridley, Anna
ISNI:       0000 0004 7227 393X
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2017
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Abstract:
Understanding source and sink process of atmospheric species can help to constrain budgets of gases which contribute towards ozone destruction and warming of the Earth’s atmosphere. The use of isotope ratio analysis is a key tool in budget quantification. GC-MS techniques allowed quantification of δ(37Cl) of CFC-11, CFC-12 and CFC-113 deeper in the stratosphere than previously recorded. Isotope enrichment increased with decreasing mixing ratios for all CFCs. A maximum 37Cl enrichment in CFC-12 significantly exceeded that published to date. Apparent isotope fractionation (εApp ) varied with respect to latitude for 37Cl analysis. The first measurements of δ(13C) of CFC-11, CFC-12 and CFC-113 at stratospheric altitudes displayed increasing enrichment with altitude. Minimal correlation was observed between latitude and apparent isotope fractionation. Values of εApp are significantly lower than that given by fractionation observed in laboratory photolysis experiments. Reanalysis of samples which had undergone photolysis allowed measurements to be linked to an internationally recognised 13C scale (VPDB) allowing direct comparison between photolysis rates of CFC-12 analysed using different analytical systems. Based on the mass difference, the isotope fractionation of 17O should be approximately half as much as that of 18O, with respect to 16O. The proportion of 17O in tropospheric air is in fact higher. Identifying the source of the 17O excess would identify possible non-mass dependent fractionation in sources or sinks. The development of an IR-MS measurement system allowed for the first measurements of Δ17O in stratospheric N2O above 12 km altitude. The data suggest that photolysis and reaction with O(1D) are not the source of the 17O anomaly. The newly developed system allowed participation in an interlaboratory compatibility study. Development of a measurement system capable of analysis of 37Cl in CH3Cl allowed analysis of test gas preparations of CH3Cl in preparation for air concentrate analysis. The first steps towards the synthesis of a calibration gas of characterised isotopic composition were carried out.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.743313  DOI: Not available
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