Long-term Variations of Atmospheric CH4 Concentration over Siberia Derived from Aircraft Observation.

Abstract:

We have been carrying out monthly flask sampling over 3 Siberian sites (Surgut, Novosibirsk, and Yakutsk) using aircraft and obtained the vertical profile of CH₄ concentration up to 7 km since 1993. Temporal variation at each altitude exhibited increasing trend as observed globally (Figure). Seasonal variation at Yakutsk in East Siberia showed expected summer minimum, as seen at remote sites in northern mid to high latitudes, although no clear seasonality was observed at West Siberian sites (Surgut and Novosibirsk). Large CH₄ emissions from West Siberian Lowlands (WSL) might compensate CH₄ loss by reaction with OH radical during summer. The vertical gradient in CH₄ concentration was larger in Surgut and Novosibirsk than in Yakutsk, which suggests a strong CH₄ emission from WSL as well. However, the vertical gradient at Surgut was obviously decreasing; the annual mean difference between 5.5 km and 1.0 km decreased from 62-76 ppb during 1994-1996 to 33-49 ppb during 2012-2014. Chemical transport model reproduced this decrease tendency and suggested that global CH₄ emissions have increased, but the contribution from WSL and Europe have decreased in this decade.

Figure. Temporal variations in CH₄ concentration observed at 1000 and 5500 km altitude over Surgut in West Siberia. Dot color and error bar indicates the number of samples in the same altitude and the range of measured concentration, respectively. The curved line shows fitting line.