Determination and analysis of time series of CFC-11 from Lauder and Jungfraujoch

The monitoring of the chlorofluorocarbons (CFCs) and their successive substitutes - the
hydrochlorofluorocarbons (HCFCs) and the hydrofluorocarbons (HFCs) - is essential to track
the evolution of their atmospheric concentrations and emissions in accordance with the
Montreal Protocol on Substances that Deplete the Ozone Layer. In this study, we used the
retrievals of ground-based high-resolution Fourier transform infrared (FTIR) solar spectra and
model data (TOMCAT/SLIMCAT developed by Martyn Chipperfield) in order to analyse the CFC-
11 total columns above the Jungfraujoch (46.5°N, 3580 m a.s.l.) and Lauder (45°S, 370 m a.s.l)
stations. The Jungfraujoch time series has been scaled allowing the creation of a significant
time series from June 1986 to December 2020. We analysed and compared ground-based FTIR
and model data for both stations to obtain the trends for the last 20 years. A deceleration in the
CFC-11 total column decrease has been observed from 2013 in both stations as reported by
Montzka et al., 2018 and Rigby et al., 2019. Lauder time series however shows an acceleration
in the decrease over the period between 2008 and 2012. Currently, we are (in collaboration with Dan Smale) therefore studying the possible causes of this behaviour since the drop is
mainly observed on the tropospheric column.