Influence of tropopause height on inversion of greenhouse gas column concentration in Lhasa, China

Abstract

The tropopause, as a transition layer between the troposphere and the stratosphere, has a significant influence on the inversion of trace gas concentration. Theoretical analysis of the influence of tropopause on the vertical distribution of atmospheric molecular content, combined with Lhasa observation data, is presented, and the quantitative analysis of the influence of tropopause on the inversion of column-averaged dry air mole fractions (DMFs) is given as well. The comparison results show that the tropopause height has a great influence on the inversion results. First, its height variation has a little effect on XH<sub>2</sub>O, but it has a great influence on XCO<sub>2</sub>, XCH<sub>4</sub> and XCO. The XCO<sub>2</sub> and XCH<sub>4</sub> have positive correlation with tropopause height variation, but for XCO, negative correlation with the tropopause height variation is observed. The correlation coefficient of XCO<sub>2</sub>, XCH<sub>4</sub> and XCO are 0.998, 0.78 and 0.994, respectively. When the tropopause height is varied by 3 km, XCO<sub>2</sub>, XCH<sub>4</sub> and XCO are varied by 8.64%、0.0354% and 0.0488%, respectively. The column-averaged dry air mole water vapor, carbon dioxide, carbon monoxide and methane in Lhasa are observed based on ground-based Fourier transform infrared spectrometer EM27/SUN. The time series of XH<sub>2</sub>O, XCO<sub>2</sub>, XCH<sub>4</sub> and XCO in a period from August 6 to August 16, 2018 in Lhasa were obtained. The main achievements are as follows. In the observation period, the daily average value of XH<sub>2</sub>O, XCO<sub>2</sub>, XCH<sub>4</sub> and XCO vary between 3432 and 4287 ppmv, 406.1 and 408.2 ppmv, 1.673 and 1.720 ppmv, and 0.082 and 0.095 ppmv, respectively. The average value of XH<sub>2</sub>O, XCO<sub>2</sub>, XCH<sub>4</sub> and XCO are 3919.70, 406.887, 1.689, and 0.091 ppmv, res[ectively. Comparison between XCO<sub>2</sub> and XCH<sub>4</sub> time series shows that XCO<sub>2</sub> and XCH<sub>4</sub> time series have similar daily trends, the correlation coefficient between XCO<sub>2</sub> and XCH<sub>4</sub> time serires is higher than 0.5. In particular, the correlation coefficient reached about 0.86 on August 7, 8, 13, 2018. High correlation coefficient indicates that CO<sub>2</sub> and CH<sub>4</sub> molecules come from the same source. Compared with the WACCM simulation values, the XCO<sub>2</sub> and XCH<sub>4</sub> of the ground-based observations are small. The observation results can provide reference and first-hand direct observation data for the study of the temporal and spatial distribution of greenhouse gases in the temperate zone of the plateau in China.