Ship-borne measurements of XCO<sub>2</sub>, XCH<sub>4</sub>, and XCO above the Pacific Ocean and comparison to CAMS atmospheric analyses and S5P/TROPOMI

Abstract

Abstract. Measurements of atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2), methane (XCH4), and carbon monoxide (XCO) have been collected across the Pacific ocean during the Measuring Ocean REferences 2 (MORE-2) campaign in June 2019. We deployed a ship-borne variant of the EM27/SUN Fourier Transform Spectrometer (FTS) on board the German research vessel Sonne which, during MORE-2, crossed the Pacific ocean from Vancouver, Canada, to Singapore. Equipped with a specially manufactured fast solar tracker, the FTS operated in direct-sun viewing geometry during the ship cruise reliably delivering solar absorption spectra in the shortwave infrared spectral range (4000 to 11 000 1/cm). After filtering and bias correcting the dataset, we report on XCO2, XCH4, and XCO measurements for 22 days along a trajectory that largely aligns with 30° N of latitude between 140° W and 120° E of longitude. The dataset has been scaled to the Total Carbon Column Observing Network (TCCON) station in Karlsruhe, Germany, before and after the MORE-2 campaign through side-by-side measurements. The precision for hourly means of XCO2, XCH4, and XCO during the campaign is found 0.24 ppm, 1.1 ppb, and 0.75 ppb, respectively. Comparing concentration fields analysed by the Copernicus Atmosphere Monitoring Service (CAMS) to our data, we find excellent agreement of 0.52 ± 0.31 ppm for XCO2, 0.9 ± 4.1 ppb for XCH4, and 3.2 ± 3.4 ppb for XCO (mean difference ± standard deviation of differences for entire record). Likewise, we find excellent agreement to within 2.2 ± 6.6 ppb with the XCO observations of the TROPOspheric MOnitoring Instrument (TROPOMI) on the Sentinel-5 Precursor satellite (S5P). The ship-borne measurements are accessible at https://doi.org/10.1594/PANGAEA.917240 (Knapp et al., 2020).

Retrievals of XCO2, XCH4 and XCO from portable, near-infrared Fourier transform spectrometer solar observations in Antarctica

“…The comparatively low cost, portability and relative easeof-use of these instruments have meant that they can be utilised in greater numbers or to cover specific targets in locations where the more complex instruments cannot be deployed. For example, Velazco et al (2019) used an EM27/SUN in a semiarid region of Australia to validate retrievals from GOSAT, Knapp et al (2021) have conducted observations from a ship transiting the Pacific Ocean and Frey et al (2021) have established a COCCON site in Namibia while Hase et al (2015) and Dietrich et al (2021) have used dense networks of these instruments to estimate the carbon fluxes of Berlin and Munich, respectively. Tu et al (2022) have gone on to demonstrate the utility of these instruments to quantify fluxes at the facility level.…”