Novel mass spectrometric techniques for stable isotope measurements in atmospheric halocarbons and nitrous oxide

Ridley, Anna (2017) Novel mass spectrometric techniques for stable isotope measurements in atmospheric halocarbons and nitrous oxide. Doctoral thesis, University of East Anglia.

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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.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Jackie Webb
Date Deposited: 03 May 2018 14:20
Last Modified: 03 May 2018 14:20


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