Abstract:

 Methane (CH₄) is one of the most important greenhouse gases in the atmosphere, making it worthwhile to study its temporal and vertical distributions in source areas, e.g., North China. For this purpose, a ground-based high-resolution Fourier transform infrared spectrometer (FTIR), the Bruker IFS 125HR, along with an in-situ instrument, the Picarro G2301, were deployed in Xianghe County (39.8°N,117.0°E), Hebei Province, China. Data have been recorded since June 2018. For the FTIR measurements, we used two observation modes to retrieve the mole fraction of CH₄: the Total Carbon Column Observing Network (TCCON) method (retrieval algorithm: GGG2014), and the Network for the Detection of Atmospheric Composition Change (NDACC) method (retrieval algorithm: SFIT4). Combining FTIR with in-situ measurements, we found the temporal and vertical distributions of atmospheric CH₄ within three vertical layers (near the ground, in the troposphere, and in the stratosphere), and throughout the whole atmosphere. Regarding the diurnal variation of CH₄ near the ground, the concentration at night was higher than during the daytime. Regarding the seasonal variation, CH₄ was low in spring and high in summer, for all three vertical layers. In addition, there was a peak of CH₄ in winter near the ground, both in the troposphere and the whole atmosphere. We found that variation of CH₄ in the tropospheric column was close to that of the in-situ measurements near the ground. Furthermore, the variations of CH₄ in the stratospheric column could be influenced by vertical motions, since it was higher in summer and lower in winter.