Reply on RC1

Abstract

Synthetic halogenated organic chlorofluorocarbons (CFCs) play an important role in stratospheric ozone depletion, and contribute significantly to the greenhouse effect. In this work, the mid-infrared solar spectra measured by ground-based high-resolution Fourier transform infrared spectroscopy (FTIR) were used to retrieve atmospheric CFC-11 (CCl3F) and CFC-12 (CCl2F2) at Hefei, China. We implemented a new retrieval strategy, and analyzed the retrieval errors. The CFC-11 columns observed from January 2017 to December 2020 and CFC-12 columns from September 2015 to December 2020 show a similar annual decreasing trend and seasonal cycle, with an annual rate of (−0.47 % ± 0.16) % yr−1 and (−0.79 ± 0.31) % yr−1, respectively. CFC-11 total columns were higher in summer, and CFC-12 total columns were higher in summer and autumn. Both of CFC-11 and CFC-12 total columns reached the lowest in spring. The annual decreasing rate of near-surface concentration is (−0.60 ± 0.26) % y−1 for CFC-11, and (−0.81 ± 0.25) % y−1 for CFC-12. So the decline rate of CFC-11 is significantly lower than that of CFC-12. Further, FTIR data were compared with the ACE-FTS satellite data, WACCM (Whole Atmosphere Community Climate Model) data and the data from other NDACC (Network for the Detection of Atmospheric Composition Change) station. The mean relative difference between the vertical profiles observed by FTIR and ACE-FTS is (−5.6 ± 3.3) % and (4.8 ± 0.9) % for CFC-11 and CFC-12 for altitude from 5.5 to 17.5 km, respectively. The results demonstrate our FTIR data agree relatively well with the ACE-FTS satellite data. The annual decreasing rate of CFC-11 measured from ACE-FTS and calculated by WACCM are (−1.15 ± 0.22) % and (−1.68 ± 0.18) %, respectively. The interannual decreasing rates of atmospheric CFC-11 obtained from ACE-FTS and WACCM data are higher than that from FTIR observations. Also, the annual decreasing rate of CFC-12 from ACE-FTS and WACCM is (–0.85 ± 0.15) % and (–0.81 ± 0.05) %, respectively, close to the corresponding values from the FTIR measurements. Further, the total columns of CFC-11 observed at the Hefei site are very close to those at St. Petersburg station, with a mean difference of 3.63 × 1012 molec·cm-2, while the total columns of CFC-12 are 1.69 × 1014 molec·cm-2, slightly higher than those at St. Petersburg station.