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

Abstract

Abstract. Monitoring atmospheric anthropogenic halocarbons plays an important role in tracking their atmospheric concentrations in accordance with international agreements on emissions of ozone-depleting substances and, thus, in estimating the ozone layer recovery. Within the Network for the Detection of Atmospheric Composition Change (NDACC), regular Fourier transform infrared (FTIR) measurements can provide information on the abundancies of halocarbons on a global scale. We improved retrieval strategies for deriving the CFC-11 (CCl3F), CFC-12 (CCl2F2), and HCFC-22 (CHClF2) atmospheric columns from IR solar radiation spectra measured by the Bruker IFS125HR spectrometer at the St. Petersburg site (Russia). We used the Tikhonov–Phillips regularization approach for solving the inverse problem with optimized values of regularization parameters. We tested the strategies developed by comparison of the FTIR measurements with independent data. The analysis of the time series of column-averaged dry air mole fractions (Xgas) measured in 2009–2019 gives mean values of 225 pptv (parts per trillion by volume; CFC-11), 493 pptv (CFC-12), and 238 pptv (HCFC-22). Trend values total −0.40 % yr−1 (CFC-11), −0.49 % yr−1 (CFC-12), and 2.12 % yr−1 (HCFC-22). We compared the means, trends, and seasonal variability in XCFC-11, XCFC-12, and XHCFC-22 to that of (1) near-ground volume mixing ratios (VMRs), measured at the observational site Mace Head, Ireland (GVMR), (2) the mean in the 8–12 km layer VMRs, measured by ACE-FTS and averaged over 55–65∘ N latitudes (SVMR), and (3) Xgas values of the Whole Atmosphere Community Climate Model (WACCM) for the St. Petersburg site (WXgas). In general, the comparison of Xgas with the independent data showed a good agreement of their means within the systematic errors of the measurements considered. The trends observed over the St. Petersburg site demonstrate the smaller decrease rates for XCFC-11 and XCFC-12 than that of the independent data and the same increase rate for XHCFC-22. As a whole, Xgas, SVMR, and WXgas showed qualitatively similar seasonal variations, while the GVMR variability is significantly less, and only the WXHCFC-22 variations are essentially smaller than that of XHCFC-22 and SVMRHCFC-22.

Retrieval of Atmospheric CFC-11 and CFC-12 from High-resolution FTIR Observations at Hefei and Comparisons with Satellite Data

“…For CFC-12, the systematic error and random error are 1.32% and 1.21%, respectively, while the dominating errors are temperature, H 2 O spectroscopy and zshift. The systematic error for CFC-11 is 7.61% and the random error is 3.08%, and for CFC-12, the systematic error is 2.24% and the random error is 2.40% at the St. Petersburg site (Polyakov et al, 2021). Our error estimates are reasonable.…”

“…The annual decline of CFC-11 and CFC-12 is due to the prohibition of emissions from industrial production. For CFC-11, the annual decreasing rate of total column is (−0.47 ± 0.16) %/y -1 , which is close to the value of −0.40 %/y -1 at St Petersburg observed from 2009 to 2019, but lower than the value of (−0.86 ± 0.12) %/y -1 reported at St Denis and Maïdo station observed from 2004 to 2016, and (−0.79 ± 0.06) %/y -1 derived from ACE-FTS during from 2012 to 2018 covering the region between 30°S and 30°N (Steffen et al, 2019;Polyakov et al, 2021;Zhou et al, 2016). For CFC-12, the annual decreasing rate of the total column is (−0.79 ± 0.31) %/y -1 at the Hefei site, and close to the value of (−0.76 ± 0.05) %/y -1 derived from St Denis and Maïdo measurements, and (−0.79 ± 0.06) % /y -1 from ACE-FTS observations between 30°S and 30°N latitude, but larger than the value of −0.49%/y -1 from St. Petersburg measurements (De Maziere et al, 2018;Polyakov et al, 2021;Steffen et al, 2019).…”

“…The mean difference of total columns 360 of CFC-11 between the two data sets is 3.63×10 12 molec•cm -2 , while the mean difference of total columns of CFC-12 is 1.69×10 14 molec•cm -2 . In the study of Polyakov et al (2021), the annual decreasing rate of CFC-11 and CFC-12 is −0.40% yr −1 and −0.49% yr −1 from 2009 to 2019 at the St. Petersburg site, respectively (Polyakov et al, 2021). The annual decreasing rate of CFC-11 and CFC-12 at Hefei is greater than that the corresponding value at St. Petersburg.…”

“…Table 1 lists the parameters used for CFC-11 and CFC-12 retrievals. The retrieval window of CFC-11 are 830-860 cm -1 , and the spectral window centered at 1161 cm -1 were chosen to retrieve atmospheric CFC-12 (Zhou et al, 2016;Polyakov et al, 2021). Atmospheric parameters, such as H 2 O, temperature and pressure profiles are adopted from National Centers for Environment Protection (NCEP) reanalysis data (Kalnay et al, 1996).…”

“…The spectroscopic line parameters for CFC-11, CFC-12 and COCl 2 are calculated based on empirical pseudo-line-lists (PLL), and the line parameters of other interfering gases are provided by HITRAN 2012 (Rothman et al, 2013). According to the study of Polyakov et al (2021), because the CFC-11 retrieval window is wide, it is necessary to consider the influence of the increase in the thickness of amorphous water ice in the instrument caused by water vapor in the atmosphere (Polyakov et al, 2021).…”