Follow-up measurement of methane over the area of the Nord Stream leaks yields another important data set
December 5, 2022
Follow-up measurement of methane over the area of the Nord Stream leaks yields another important data set
After the first successful methane measurements over the southern Baltic Sea only one week after the Nord Stream leaks occurred at the beginning of October, IPA scientists together with the Institute of Flight Guidance (IFF) of the Technical University of Braunschweig have now carried out follow-up measurement flights in the region. Starting once again from the Polish coast near Kołobrzeg, a total of two helicopter flights with the towed probe HELiPOD could be carried out on November 15 and 16, 2022. The HELiPOD, operated by the IFF and equipped with an extensive payload for atmospheric measurements, is flown as a sling load on an approximately 25-meter-long rope under the helicopter. For the new flights over the Baltic Sea, the helicopter was additionally equipped at short notice with a special methane instrument from the DLR Institute of Atmospheric Physics. This instrument can be used to determine the origin of methane from its isotopic signature, for example to distinguish between biogenic and fossil sources.
Fig. 1: Monitoring of methane concentrations during flight over the Baltic Sea by mission scientist (Photo: IFF / F. Pätzold, CC BY-ND-NC 3.0).
The first measurements had indicated that the atmospheric distribution of methane is not only determined by bubbles rising directly from the leaks, but also from methane dissolved in water, which is transported with currents, and only released later. The flight planning was therefore now supported by initial model calculations by DLR, which simulated the dispersion of the methane escaping from the leaks in the surface water of the Baltic Sea. However, it was unclear whether and how much of the methane dissolved in the water still escapes into the atmosphere. To investigate this process, an attempt was made to probe an area as large as possible with the HELiPOD at low altitudes of about 50 meters above sea level.
Fig. 2: The HELiPOD helicopter probe during preparation for a measurement flight at Bagicz airfield, east of Kołobrzeg, Poland (Photo: DLR / E. Förster, CC BY-ND-NC 3.0).
However, due to unfavourable weather conditions at this time of year, there was some risk that the helicopter flights would have to be cancelled due to fog or high wind speed. Fortunately, a time window of two days with optimal conditions could be used for the measurements. During the first flight, the IFF and DLR scientists were already able to detect slightly elevated methane concentrations over different areas of the southern Baltic Sea online in the cockpit with the HELiPOD mission monitor, so that the helicopter could be successfully guided through the optically invisible methane clouds. A second flight the following day confirmed methane increases, but interestingly over a different area than the previous day.
Whether the elevations originate actually from the methane released by the pipeline leaks and still dissolved in seawater, or if another source is responsible for the elevated methane will now be part of the intensive data evaluation. Taken air samples, which will be analysed with high-precision measurements in the laboratory, will provide additional information on the origin of the methane. Further model calculations considering the collected data will help to better understand the dispersion of methane from such leaks.
Methane is the second most important anthropogenic greenhouse gas after carbon dioxide with an approximately 80 times stronger radiative forcing than CO2, in respect to the first 20 years after its emission. Large deposits of methane in the ocean are stored primarily in the form of methane hydrate. At low depths, rising temperatures lead to its decay, which in turn could strengthen climate warming. Methane release is influenced by degradation processes in the water, but more research is needed on this. Hence, the measurements taken at the Nord Stream leaks can also contribute to a better understanding of the processes at other submarine methane sources.
