Improved FTIR retrieval strategy for HCFC-22 (CHClF<sub>2</sub>), comparisons with in situ and satellite datasets with the support of models, and determination of its long-term trend above Jungfraujoch

Abstract

Abstract. Hydrochlorofluorocarbons (HCFCs) are the first, but temporary, substitution products for the strong ozone-depleting chlorofluorocarbons (CFCs). HCFC consumption and production are currently regulated under the Montreal Protocol on Substances that Deplete the Ozone Layer and their emissions have started to stabilize or even decrease. As HCFC-22 (CHClF2) is by far the most abundant HCFC in today's atmosphere, it is crucial to continue to monitor the evolution of its atmospheric concentration. In this study, we describe an improved HCFC-22 retrieval strategy from ground-based high-resolution Fourier transform infrared (FTIR) solar spectra recorded at the high-altitude scientific station of Jungfraujoch, the Swiss Alps, 3580 m a.m.s.l. (above mean sea level). This new strategy distinguishes tropospheric and lower-stratospheric partial columns. Comparisons with independent datasets, such as the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), supported by models, such as the Belgian Assimilation System for Chemical ObErvation (BASCOE) and the Whole Atmosphere Community Climate Model (WACCM), demonstrate the validity of our tropospheric and lower-stratospheric long-term time series. A trend analysis on the datasets used here, now spanning 30 years, confirms the last decade's decline in the HCFC-22 growth rate. This updated retrieval strategy can be adapted for other ozone-depleting substances (ODSs), such as CFC-12. Measuring or retrieving ODS atmospheric concentrations is essential for scrutinizing the fulfilment of the globally ratified Montreal Protocol.

Climatological impact of the Brewer–Dobson circulation on the N<sub>2</sub>O budget in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses

“…In WACCM-CCMI, the parameterization of gravity waves was adjusted in order to reduce this issue while not significantly changing the dynamics in the NH, which results in an enhanced polar downwelling above the southern polar region (Garcia et al, 2017). Above the Antarctic, the forcing from resolved waves peaks in October in the reanalyses as a result of the vortex breakup that allows enhanced wave activity compared with austral winter (Randel and Newman, 1998). The WACCM simulations miss this strong springtime peak, and they are in good agreement with the reanalyses during the rest of the year (Fig.…”

“…6d). The Arctic is characterized by a very variable polar vortex with a shorter life span than the Antarctic vortex (Randel and Newman, 1998;Waugh and Randel, 1999), resulting in an enhanced contribution of the horizontal mixing to the N 2 O budget during winter compared with the Antarctic (Fig. 6f).…”

Measurements of CFC-11, CFC-12, and HCFC-22 total columns in the atmosphere at the St. Petersburg site in 2009–2019

“…Later, with the appearance of highresolution instruments, halocarbons started to be derived with ground-based FTIR spectrometers. In the last few A. atmospheric content 5351 decades, TCs of halocarbons are more actively measured by ground-based FTIR methods (e.g., Notholt, 1994;Rinsland et al, 2005Rinsland et al, , 2010Zander et al, 2005;Mahieu et al, 2010Mahieu et al, , 2013Mahieu et al, , 2017Zhou et al, 2016;Prignon et al, 2019). Time series of TCs above the Jungfraujoch station, Switzerland, are presented in World Meteorological Organization (WMO) reports on the scientific assessment of ozone depletion (e.g., WMO, 2018).…”

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

“…), thus the station is most of the time in free troposphere conditions. 15 The Institute of Astrophysics of the University of Liège has collected infrared (IR) solar spectra at that site since the early 1950s. Firstly, grating spectrometers were used and then two instruments, with a HgCdTe detector, under clear-sky conditions.…”