Methane flux measurements with low-cost solid state sensors in Kobbefjord, West Greenland

Sammanfattning: Methane is one of the most important greenhouse gases, and the Arctic region plays an important role in its dynamics. Due to limited observations in this remote and often harsh environments, large uncertainties surround the role of the Arctic region in a warming climate. In this thesis, I examine the performance of the three low-cost solid state sensors, Figaro sensors TGS2600-B00, TGS2611-C00 and TGS2611-E00. These sensors could present a significant contribution in developing and expanding methane monitoring networks in the Arctic region, and furthermore improve the understanding of underlying processes controlling methane emissions. The sensors were added to the existing automatic chamber setup in Kobbefjord, close to Nuuk, West Greenland. Methane fluxes were calculated based on the change in methane concentration when chambers were closed. A reliable fast methane analyzer (RMT-200, Los Gatos Research Inc., USA) served as a proxy for methane fluxes, and the sensors’ data was compared to this. The resolution from the three sensors was limited by an analog-to-digital converter, which is expected to contribute to the larger spread in the sensors’ data compared to the LGR. Occasional changes of relative humidity inside the chambers, resulted in overestimated fluxes. The experimental setup caused low relative humidity inside the syringe containing the senors. Low relative humidity is known to be problematic, which could be why no clear relationships between the sensors’ signal and relative humidity and temperature were found. By filtering data with a relative humidity change ≥27%, most of the overestimated fluxes are most likely removed. The sensors were able to capture the seasonal trend in the methane fluxes, and the magnitude of the seasonal mean fluxes from different chambers. The results could not be statistically supported due to seasonal trends in the data and the lack of replicas. The sensors differ in sensitivity to other deoxidizing gases. At this site, no indications of such gases were found, but this could be a problem at other sites, meaning that one of the more methane specific sensors may be suitable. Although, the TGS2600-B00 sensor showed better results in this study, further tests are required to determine which of the sensors is the best. In conclusion, the results indicate that, these sensors with further refinements may well be used for expanding monitoring networks of methane fluxes in the Arctic.