Characteristics of greenhouse gas concentrations derived from ground-based FTS spectra at Anmyeondo, South Korea

Abstract. Since the late 1990s, the meteorological observatory established in Anmyeondo (36.5382° N, 126.3311° E, and 30 m above mean sea level) has been monitoring several greenhouse gases such as CO₂, CH₄, N₂O, CFCs, and SF₆ as a part of the Global Atmosphere Watch (GAW) Program. A high resolution ground-based (g-b) Fourier transform spectrometer (FTS) was installed at this observation site in 2013 and has been operated within the frame work of the Total Carbon Column Observing Network (TCCON) since August 2014. The solar spectra recorded by the g-b FTS cover the spectral range 3800 to 16 000 cm⁻¹ at a resolution of 0.02 cm⁻¹. In this work, the GGG2014 version of the TCCON standard retrieval algorithm was used to retrieve total column average CO₂ and CH₄ dry mole fractions (XCO₂, XCH₄) and from the FTS spectra. Spectral bands of CO₂ (at 6220.0 and 6339.5 cm⁻¹ center wavenumbers, CH₄ at 6002 cm⁻¹ wavenumber, and O₂ near 7880 cm⁻¹ ) were used to derive the XCO₂ and XCH₄. In this paper, we provide comparisons of XCO₂ and XCH₄ between the aircraft observations and g-b FTS over Anmyeondo station. A comparison of 13 coincident observations of XCO₂ between g-b FTS and OCO-2 (Orbiting Carbon Observatory) satellite measurements are also presented for the measurement period between February 2014 and November 2017. OCO-2 observations are highly correlated with the g-b FTS measurements (r² = 0.884) and exhibited a small positive bias (0.189 ppm). Both data set capture seasonal variations of the target species with maximum and minimum values in spring and late summer, respectively. In the future, it is planned to further utilize the FTS measurements for the evaluation of satellite observations such as Greenhouse Gases Observing Satellite (GOSAT, GOSAT-2). This is the first report of the g-b FTS observations of XCO₂ species over the Anmyeondo station.