## 4 Conclusions  
XCO\({}_{2}\) and XCH\({}_{4}\) were first measured at a Gobi Desert site in western China in the summer of 2021. The diurnal XCO\({}_{2}\) showed a sinusoidal model, while XCH\({}_{4}\) appeared to have a unimodal distribution. Most of the satellite-retrieved XCO\({}_{2}\) and XCH\({}_{4}\) were close to the ground-observed values, but more differences appeared in the spatial distribution of satellite retrievals than the temporal change of ground observations. Ground-based XCO\({}_{2}\) values were close to the surface CO\({}_{2}\) mole fractions, while XCH\({}_{4}\) had a large gap with CH\({}_{4}\) mole fractions. Many factors could affect the temporal variation and discrepancy of column and surface CO\({}_{2}\) and CH\({}_{4}\) mole fractions, such as differences in sources and sinks, changes in PBL height, plant photosynthesis and respiration rate, chemical removal of CH\({}_{4}\), valley wind, and dust storm. Wind can dilute and accumulate atmospheric CO\({}_{2}\) and CH\({}_{4}\) mole fractions from different wind directions, but its effect on XCO\({}_{2}\) and XCH\({}_{4}\) needs more investigation in the future because the wind also varies at different altitudes. The observation period in this study was short and some conclusions are not sufficient enough. A longer observation of column mole fractions, along with other atmospheric components, should be done in the future to obtain more valuable results and conclusions. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/atmos13040571/s1](https://www.mdpi.com/article/10.3390/atmos13040571/s1)]([https://www.mdpi.com/article/10.3390/atmos13040571/s1](https://www.mdpi.com/article/10.3390/atmos13040571/s1)), Figure S1: Diurnal variation of temperature (A), relative humidity (B), pressure (C), wind speed (D), and wind direction (E) at Gobi desert site in Dunhuang, west China during the observation period (26 June to 19 July 2021), respectively; Figure S2: Variation of hourly CO2 (A) and CH4 (B) mole fractions (both surface and column) at Dunhuang from 26 June to 20 July, 2021; Figure S3: Variation of CO2 and CH4 mole fractions at the observation site before and after the dust storm in 2 h (A, data in 5 s average) and 1 day (B, hourly average data); Figure S4: Diurnal variations of XCO2, XCH4, and XCO and their variation with SZA (solar zenith angle) on 11 (A,B), 12 (C,D), 14 (E,F), and 16 (G,H) July 2021; Figure S5: Footprint of XCH4 mole fractions from S5-P over CRCS (\(2^{\circ}\times 2^{\circ}\)) on 14 July and 15 July 2021; Figure S6: Footprints of XCO2 observations from GOSAT-2 near the EM27/SUN observation site from 26 June to 19 July; Table S1: The average mole fraction of XCO2, XCH4, and XCO as well as the observation hours and numbers during the observation period; Table S2: Comparison of the swath, footprint, spectrometer technologies, and data retrieved method of different satellites and the data version used in this study; Table S3: Comparison of satellite observed XCO2 and XCH4 with EM27/SUN observations. The coincidence criteria for OCO-2/OCO-3/GOSAT/GOSAT-2 was \(10^{\circ}\times 5^{\circ}\), while for S5-P was \(2^{\circ}\times 2^{\circ}\) with a center of CRCS. EM27/SUN observations were averaged for \(\pm 1\)h of the satellite transit time. Conceptualization, L.B. and J.L. ; methodology, C.W. ; formal analysis, C.W. ; investigation, C.W. ; resources, Z.L., L.B. and J.L. ; data curation, C.W. ; writing--original draft preparation, C.W. ; writing--review and editing, Z.L., L.B. and J.L. ; visualization, C.W. ; project administration, L.B. and J.L. All authors have read and agreed to the published version of the manuscript.