Sabrekov A.F.
Lomonosov Moscow state university
Methane plays an important role in the atmospheric chemistry and radiative budget of the Earth. For this reason, continuous monitoring of the methane mixing ratio is carried out throughout the world. The studies involve wetland landscapes because those are the largest natural source of methane.
In our opinion, the previous studies have paid an insufficient attention to dynamics of the methane mixing ratio at smaller scale in space and time. Therefore, in the article we attempt to analyze diurnal pattern of the methane mixing ratio in the surface boundary layer and to study relationship between the mixing ratio and the coefficient of turbulent diffusion. This information can be used for estimation of methane emission if we know the diffusion coefficient. It can also help in separating point sources (e. g., leeks from pipelines) from weaker, per square unit, but extensive sources (e. g., wetlands). On the base of the conservation law and the absence of chemical sources and sinks of methane in the atmosphere (the reaction of methane with hydroxyl radical is very slow), the dynamics of the methane mixing ratio in the surface boundary layer is determined by two factors: the surface methane emission and the circulation processes in the surface boundary layer.
Methane emission did not follow an easily describable pattern, although the possibility of an increase of emission in night-time is pointed out in some articles. The intensity of the circulation processes in the surface boundary layer clearly differed between day and night and strongly varied depending on stability of the atmosphere. In the study, the maximum night-time rise of the methane mixing ratio was significantly more pronounced than the night-time increase of methane emission, which had been described in some studies. These maximal night-time peaks are associated with temperature inversions in the surface boundary layer. The coefficient of determination for the relationship between the coefficient of turbulent diffusion and the methane mixing ratio on the same height is quite high, 0.80. Thus, we can make a conclusion that the diurnal pattern of the methane mixing ratio in the surface boundary layer is mainly determined by the turbulence in the surface boundary layer.
Key words: diurnal pattern of the methane mixing ratio in the surface boundary layer, coefficient of turbulent diffusion, methane emission at wetlands.