Fig. 1. Laboratory instrument. (a) FTS; (b) solar tracker

Fig. 2. Individual measurements and daily averages of CH₄ column concentration

Fig. 3. Time series of atmospheric column concentration ($X_{\mathrm{C}{\mathrm{H}}_{\mathrm{4}}}$) on July 11, 2022

Fig. 4. Monthly average column concentration of CH₄

Fig. 5. Comparison of daily average data observed by ground-based FTS with satellite data

Fig. 6. Correlation between ground-based FTS data and satellite observation data

Fig. 7. Correlation of ${\Delta }_{\mathrm{C}{\mathrm{H}}_{\mathrm{4}}}$ and ${\Delta }_{\mathrm{C}\mathrm{O}}$ measured by ground-based FTS at Hefei site in four seasons. (a) Spring; (b) summer; (c) autumn; (d) winter