The tropospheric abundances, emissions, and transport of halogenated substances on regional and global scales

The primary aim of this thesis was to use models to study the (a) regional emissions of very short-lived (i.e. chlorinated VSLS) and short-lived (i.e. methyl halides) halogenated gases, as well as (b) global emissions of long-lived halogenated gases (i.e. CFC-114 & CFC-114a). The 3-D dispersion model was employed to determine the impact of different source types and regions on the variability of halogenated gases measured during the campaigns in Taiwan and Bachok, Malaysia. On the other hand, the 2-D global model was used for estimating the emissions of CFC-114 and -114a in archived remote Southern Hemispheric tropospheric air and firn air data. Overall, this thesis has demonstrated that the measured chlorinated VSLS and methyl halides were observed at significantly high abundances. In addition, the quantitative analyses of the NAME backwards trajectories (i.e. using ArcGIS-generated shapefile and emissions data of carbon monoxide (CO) taken from Representative Concentration Pathway 8.5) and the usage of the cold surge index have further shed some light on the potential sources of emission & regions and transport of halogenated gases; these in turn could inform as well as guide future campaigns. Importantly, the studies highlighted the important roles of the (a) Northeast Monsoon’s cold surges and (b) East Asian and South East Asian emissions in the enhancements of halogenated substances levels in that regions. In addition, this thesis presented the first long-term trends and emissions of CFC-114 and-114a. The mixing ratios of both isomers were no longer increasing significantly but significant global atmospheric emissions have persisted until at least 2014, suggesting a need for continual efforts to ensure that these substances eventually disappear from the atmosphere. Evidently, complementary ground-based observations of the Taiwanese air samples in Taiwan suggested the presence of persistent emissions of CFC-114a in East Asia