Retrieval of atmospheric CH<sub>4</sub> vertical information from TCCON FTIR spectra

Abstract

Abstract. TCCON (Total Carbon Column Observing Network) column-averaged dry air mole fraction of CH4 (XCH4) measurements have been widely used to validate satellite observations and to estimate model simulations. The GGG2014 code is the standard TCCON retrieval software performing a profile scaling retrieval. In order to obtain several vertical information in addition to total column, in this study, the SFIT4 retrieval code is applied to retrieve CH4 mole fraction vertical profile using TCCON spectra (SFIT4TCCON) at six sites (Ny-Ålesund, Sodankylä, Bialystok, Bremen, Orléans and St Denis) during the time period of 2016−2017. The retrieval strategy of SFIT4TCCON is investigated. The degree of freedom for signal of the SFIT4TCCON retrieval is about 2.4, with two distinct species of information in the troposphere and in the stratosphere. The averaging kernel and error budget of the SFIT4TCCON retrieval are presented. The data accuracy and precision of the SFIT4TCCON retrievals, including the total column and two partial columns (in the troposphere and stratosphere), are estimated by TCCON standard retrievals, ground-based in situ measurements, ACE-FTS satellite observations, TCCON proxy data and AirCore measurements. By comparison against TCCON standard retrievals, it is found that the retrieval uncertainty of SFIT4TCCON XCH4 is similar to that of TCCON standard retrievals with the systematic uncertainty within 0.35 % and the random uncertainty about 0.5 %. The tropospheric and stratospheric XCH4 from SFIT4TCCON retrievals are assessed by comparing with AirCore measurements at Sodankylä, and there is a 1.2 % overestimation in the SFIT4TCCON tropospheric XCH4 and a 4.0 % underestimation in the SFIT4TCCON stratospheric XCH4, which are within the systematic uncertainties of SFIT4TCCON retrieved partial columns in the troposphere and stratosphere, respectively.

Emission Characteristics of Greenhouse Gases and Air Pollutants in Northern Hemisphere Cities: Comprehensive Assessment Using Ground‐Based Fourier Transform Spectrometers

“…The ground‐based FTS stations used in this study are listed in Table 1. These stations are located in Seoul, South Korea; Thessaloniki, Greece (https://doi.org/10.48477/coccon.pf10.thessaloniki.R01 accessed on 04 September 2023); Tsukuba, Japan (https://doi.org/10.48477/coccon.pf10.tsukuba.R02 accessed on 04 September 2023); Karlsruhe, Germany (https://doi.org/10.48477/coccon.pf10.karlsruhe.R02 accessed on 04 September 2023); Xianghe, China (Zhou et al., 2022); Pasadena, USA (Wennberg et al., 2022); and Paris, France (Té et al., 2022). Our analysis focused on data from 2021 because this was the only year that data were consistently available across all seven ground‐based FTS stations.…”

“…After calculating ∆XCO 2 , ∆XCH 4 , and ∆XCO, we performed a linear regression analysis to estimate the emission ratios of ∆XCO:∆XCO 2 and ∆XCH 4 :∆XCO 2 , represented by the slopes of the regression lines between the two species. (Zhou et al, 2022); Pasadena, USA (Wennberg et al, 2022); and Paris, France (Té et al, 2022). Our analysis focused on data from 2021 because this was the only year that data were consistently available across all seven ground-based FTS stations.…”

“…The TCCON data sets from Xianghe (Zhou et al., 2022), Pasadena (Wennberg et al., 2022), and Paris (Té et al., 2022) are obtained from the TCCON Data Archive hosted by CaltechData (https://tccondata.org). The COCCON data sets from Thessaloniki and Karlsruhe are available at the COCCON Data Repository.…”