The Lifetimes and Time-Series of Chlorine and Fluorine Containing Gases from the Atmospheric Chemistry Experiment

The research presented in this thesis is focused around environmentally important chlorine- and fluorine-containing species. The work in this thesis was carried out using data from the ACE-FTS. This work is divided into four principle areas of research. The changes in the volume mixing ratio (VMR) of CCl4, CF4, CFC-11, CFC-12, CFC-113, CH3Cl, ClONO2, COF2, COCl2, COClF, HCFC-22, HCFC-141b, HCFC-142b, HCl, HF and SF6 between 2004 and 2010 in the tropics are presented. In addition to calculating the changes in the VMR of these species during this time, this work allowed a quick comparison between profiles from the new Version 3 ACE-FTS retrieval and from the 3D chemical transport model SLIMCAT. This work acted as a rough validation of these new retrieval schemes. The trends calculated from SLIMCAT and ACE-FTS are in generally in good agreement. They show decreases in CCl4, CFC-11, CFC-12, CFC-113 and CH3Cl and increases in CF4, HCFC-22, HCFC-141b and HCFC-142b. ACE-FTS shows no statistically significant change in COCl2 and COClF, whilst showing an increase in COF2. The total VMRs of stratospheric fluorine and chlorine have been calculated, allowing changes in the VMRs of total stratospheric fluorine and chlorine between 2004 and 2010 to be calculated. In addition to this, the changes in the global warming potential-weighted chlorine and fluorine are also presented. This value allows the radiative forcing effects of changes in the VMR of these species to be evaluated. In a similar manner the changes in the ozone depleting potential-weighted total chlorine are also presented. Total fluorine is increasing in all latitudes. Global Warming Potential-weighted fluorine is increasing at a mean rate of 3.85 ± 0.07 % per year in the Northern Hemisphere and 3.58 ± 0.07 % per year in the Southern Hemisphere. Radiative efficiency-weighted total fluorine show smaller increases of between 0.23 ± 0.11 % per year and 0.45 ± 0.11 % per year. In the short term the changes in fluorine-containing species is having a small climatological effect whilst in the long term these changes will have a more significant climatological effect. Total chlorine is decreasing in all latitude bands. Both the global warming potential- and radiative forcing-weighted chlorine is decreasing. Global warming potential-weighted chlorine is decreasing by 0.31 ± 0.08 % per year in the northern hemisphere and 0.23 ± 0.08 % per year in the southern hemisphere. The changes in radiative efficiency-weighted chlorine are smaller with decreases of 0.11 ± 0.04 % per year in the northern hemisphere and 0.06 ± 0.12 % per year in the southern hemisphere. When considered together these results suggest that in the short term there has been very little, if any, change in climatologically effective chlorine. However, in the long term the reduction in the emissions of long lived CFCs and halons will produce a small reduction in the climatological effect of chlorine containing species. Finally, the stratospheric lifetimes of CFC-12 (113 +(-) 26 (18) years), CCl4 (35 +(-) 11 (7) years), CH4 (195 +(-) 75 (42) years), CH3Cl (69 +(-) 65 (23) years) and N2O (123 +(-) 53 (28) years) have been calculated, by correlating the stratospheric VMR of the species of interest against the VMR of CFC-11 at the same altitude.