Fig. 1. (a) Observing site (Lhasa meteorological bureau); (b) FTIR spectrometer (EM27/SUN).

Fig. 2. The profiles of H₂O (a), HDO (b), CO₂ (c), CH₄ (d), CO (e), N₂O (f), HF (g) and O₂ (h) at different heights of top troposphere

Fig. 3. The diurnal variation of XH₂O (a), (e), XCO₂ (b), (f), XCH₄ (c), (g) and XCO (d), (h) with tropopause height.

Fig. 4. Linear fit of the average mole fraction of CO₂ (a), CH₄ (b) and CO (c) to the top of the troposphere.

Fig. 5. Time series of XH₂O (a), XCO₂ (b), XCH₄ (c)and XCO (d).

Fig. 6. Time series of XCO₂ (a), (b)and XCH₄ (c), (d)at August 7, 8, 2018.

Fig. 7. The correlation between XCO₂ and XCH₄:　(a) August 6, 2018; (b) August 7, 2018; (c) August 8, 2018; (d) August 10, 2018

Fig. 8. 72-hour back trajectories of Lhasa during August 6—16, 2018:　(a) August 4-6, 2018; (b) August 7-9, 2018; (c) August 10-12, 2018; (d) August 14-16, 2018

Fig. 9. Comparison of XCO₂ (a) and XCH₄ (b) based on ground-based observations and WACCM data.