## 3 Results and Discussion
### Influences of Meteorological Conditions  
Wind could dilute a high concentration of atmospheric compositions from their source region and transport them to relatively clean areas. CO\({}_{2}\) and CH\({}_{4}\) mole fractions were 412.62 \(\pm\) 2.94 ppm and 1960 \(\pm\) 22 ppb at the wind speed at \(<\)1 m s\({}^{-1}\), and increased to their highest values at wind speeds between 1 and 2 m s\({}^{-1}\). Their mole fractions generally decreased with increasing wind speed (Figure 7A,B). The patterns were different from those observed in an urban site in Shanghai, where their mole fractions continuously decreased from the wind speed at \(<\)1 m s\({}^{-1}\) to 3-4 m s\({}^{-1}\) but reversed after that [31]. There are few emission sources around the observation site, so the mole fractions reflect the local background level near the CRCS under the lowest wind speed (\(<\)2 m s\({}^{-1}\)), and emissions from Dunhuang city were transported to the CRCS at higher wind speeds (2-4 m s\({}^{-1}\)), while clean airmasses from surrounding mountains were carried at the highest wind speed (\(>\)4 m s\({}^{-1}\)). Although XCO\({}_{2}\) and XCH\({}_{4}\) were column mole fractions, they also varied along with wind speed (Figure 7C,D). The XCO\({}_{2}\) was highest (413.47 ppm) at 1-2 m s\({}^{-1}\), and decreased to the lowest value (411.53 ppm) at 4-5 m s\({}^{-1}\), but reversed at wind speeds \(>\)5 m s\({}^{-1}\) (Figure 7C). However, the XCH\({}_{4}\) increased continuously with increasing wind speed until 5 m s\({}^{-1}\) (Figure 7D). GHG mole fractions and wind varied at different altitudes [16; 58; 59], which was probably the main reason for the discrepancy among surface and column mole fractions.  
Figure 6: Diurnal variation in hourly XCO\({}_{2}\) (**A**) and XCH\({}_{4}\) (**B**) mole fractions and their ratio (**C**), as well as the comparison with the corresponding greenhouse gas mole fractions and the ratio in the Gobi Desert in Dunhuang, China. The data were averaged from the hourly data on 11, 12, 14, and 16 July 2021.  
The bivariate polar plots provide a graphic method to show the impact of wind speed and wind direction on the concentrations of atmospheric compositions [31; 60]. CO\({}_{2}\) enhancements mainly occurred under the wind direction (WD) from the northeast and northwest, while its mole fractions can be diluted under the WD from the southwest (Figure 8A). Higher CH\({}_{4}\) mole fraction mainly occurred under the WD from the northwest, similar to one of the CO\({}_{2}\) source regions (Figure 8B), suggesting there was a point source from the northwest emitting both CO\({}_{2}\) and CH\({}_{4}\). The nearby solar thermal power plants (\(\sim\)2 km south of CRCS, Figure 1D) or other sources probably emitted some anthropogenic emissions and transport them to the CRCS. Wind from the southwest direction could bring the airmass with a lower CH\({}_{4}\) mole fraction. The bivariate plot for XCO\({}_{2}\) and XCH\({}_{4}\) would be a useful tool to investigate the influences of wind in the future, although these plots cannot be drawn in this study due to the limited volume of hourly data.  
Figure 8: Bivariate polar plots for hourly CO\({}_{2}\) and CH\({}_{4}\) mole fraction and their ratio between 26 June and 19 July 2021 in Dunhuang, west China.  
Figure 7: Boxplots of hourly average CO\({}_{2}\) (**A**), CH\({}_{4}\) (**B**), XCO\({}_{2}\) (**C**), and XCH\({}_{4}\) (**D**) mole fractions against wind speed. GHG mole fractions were binned by wind speed with an interval of 1 m s\({}^{-1}\).