Assessing the success of the Montreal Protocol: trends of halogenated gases from ground-based, satellite, and model data

Our atmosphere protects life on Earth, but its current state and changes over the past century are major concerns, especially regarding ozone layer depletion and global warming. The Montreal Protocol (1987) successfully reduced ozone-depleting substances like CFCs, which are synthetic compounds mainly used as refrigerants. To address this, substitutes such as HCFCs and HFCs were introduced, with HFCs not contributing to ozone depletion. However, HFCs are potent greenhouse gases, leading to the Kigali Amendment (2016) to control their use.
Monitoring gases regulated by the Montreal Protocol requires long-term, high-quality data. This research analysed halogenated gases using FTIR spectroscopy, 3-D model simulations, in situ measurements, and satellite observations, as well as advanced statistical tools for trend analysis. We found that the decline of atmospheric CFC-11 had slowed since 2011 in the Northern Hemisphere and since 2014 in the Southern Hemisphere, likely due to undeclared emissions. Additionally, this thesis studies, for the first time using ground-based FTIR spectra, HFC-134a, the most abundant HFC, revealing a continuous rise of about 7% per year since the early 2000s.
These findings highlight the importance of continuous and global atmospheric monitoring to better understand changes in atmospheric composition and detect potential undeclared emissions of harmful substances, as a support to international regulations.