First ground-based Fourier transform infrared (FTIR) spectrometer observations of HFC-23 at Rikubetsu, Japan, and Syowa Station, Antarctica

• Published in: Atmospheric Measurement Techniques
• Main Authors: M. Takeda, H. Nakajima, I. Murata, T. Nagahama, I. Morino, G. C. Toon, R. F. Weiss, J. Mühle, P. B. Krummel, P. J. Fraser, H.-J. Wang
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Environmental engineering; TA170-171; Earthwork. Foundations; TA715-787; Syowa Station; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/amt-14-5955-2021; https://doaj.org/article/a15e89d2ed9d4d71bdfc3f8506c9409b

We have developed a procedure for retrieving atmospheric abundances of HFC-23 ( CHF 3 ) with a ground-based Fourier transform infrared (FTIR) spectrometer and analyzed the spectra observed at Rikubetsu, Japan (43.5 ∘ N, 143.8 ∘ E), and at Syowa Station, Antarctica (69.0 ∘ S, 39.6 ∘ E). The FTIR retrievals were carried out with the SFIT4 retrieval program, and the two spectral windows of 1138.5–1148.0 cm −1 and 1154.0–1160.0 cm −1 in the overlapping ν 2 and ν 5 vibrational–rotational transition bands of HFC-23 were used to avoid strong H 2 O absorption features. We considered O 3 , N 2 O , CH 4 , H 2 O , HDO, CFC-12 ( CCl 2 F 2 ), HCFC-22 ( CHClF 2 ), peroxyacetyl nitrate (PAN) ( CH 3 C(O)OONO 2 ), HCFC-141b ( CH 3 CCl 2 F ), and HCFC-142b ( CH 3 CClF 2 ) to be interfering species. Vertical profiles of H 2 O , HDO, and CH 4 are preliminarily retrieved with other independent spectral windows because these profiles may induce large uncertainties in the HFC-23 retrieval. Each HFC-23 retrieval has only one piece of vertical information with sensitivity to HFC-23 in the troposphere and the lower stratosphere. Retrieval errors mainly arise from the systematic uncertainties of the spectroscopic parameters used to obtain HFC-23 , H 2 O , HDO, and CH 4 abundances. For comparison between FTIR-retrieved HFC-23 total columns and surface dry-air mole fractions provided by AGAGE (Advanced Global Atmospheric Gases Experiment), FTIR-retrieved HFC-23 dry-air column-averaged mole fractions ( X HFC-23 ) were calculated. The FTIR-retrieved X HFC-23 values at Rikubetsu and Syowa Station have negative biases of − 15 % to − 20 % and − 25 % compared to the AGAGE datasets, respectively. These negative biases might mainly come from systematic uncertainties of HFC-23 spectroscopic parameters. The trend of the FTIR-retrieved X HFC-23 data at Rikubetsu was derived for December to February (DJF) observations, which are considered to represent the background values when an air mass reaching Rikubetsu has the least influence by transport of ...