Determination and analysis of time series of CFC-11 (CCl3F) from FTIR solar spectra, in situ observations, and model data in the past 20 years above Jungfraujoch (46◦N), Lauder (45◦S), and Cape Grim (40◦S) stations

Trichlorofluoromethane (CFC-11) is the second most important chlorofluorocarbons (CFCs) in the Earth’s atmosphere. CFCs are long-lived chemicals which were exclusively produced by the industry and broadly used as aerosol spray propellants, refrigerants, inflating and insulating agents in the production of foam materials, as well as solvents. CFCs are transported into the stratosphere where they are photodissociated by UV radiation, releasing chlorine atoms that catalytically destroy stratospheric ozone.
The atmospheric concentration of CFC-11 has declined in response to the phase-out of its production by the Montreal Protocol. Nevertheless, this atmospheric concentration decline suffered a slowdown around 2012 due to emissions from non-reported production. Since CFC-11 remains one of the most important ozone-depleting halocarbons, its continuous monitoring is essential.
We present the CFC-11 total column time series (2000 – 2020) retrieved in a consistent way from ground-based high-resolution solar absorption Fourier transform infrared (FTIR) spectra. These observations were recorded at two mid-latitude stations of the Network for the Detection of Atmospheric Composition Change (NDACC.org): the Jungfraujoch station (Northern Hemisphere; 46.5⁰N) and the Lauder station (Southern Hemisphere; 45⁰S). These time series were compared with Cape Grim station (40.7⁰S) in situ surface observations conducted within the Advanced Global Atmospheric Gases Experiment (AGAGE) network and with total column datasets calculated by the TOMCAT/SLIMCAT 3-D chemical transport model implementing the unreported emissions. Trend analyses were performed in order to identify and characterise the timing and magnitude of the trend change in both hemispheres. The observations are consistent with the model results and confirm the slowdown in the CFC-11 atmospheric concentration decay, since ≈ 2011 in the Northern Hemisphere, and since ≈ 2014 in the Southern Hemisphere.