The present perturbation of the atmospheric radiative balance on Earth, and hence the global climate, is mainly due to anthropogenic emissions of carbon dioxide (CO₂) and methane (CH₄), both important contributors to the greenhouse effect (IPCC, 2001). Although CH₄ is a trace gas, it contributes up to 20% of the greenhouse effect due to its high global warming potential (25 times more influential than CO₂ over a 100 year timescale) that have resulted in atmospheric CH₄ concentration doubling within the last 300 years (IPCC, 2007). Methane, which has a short residence time (~20 years) is rapidly oxidized to CO₂ and H₂O, implying that to sustain climate warming due to increasing CH₄ requires a continuous supply (Legget, 1990). Sustained supplies must be provided by the potential sources including oceans, continental wetlands and permafrost (Haq, 1995). There are significant uncertainties on the amount of methane emitted and absorbed by the oceans.

To overcome the limitation in spatial and temporal resolution of methane oceanic measurements, sensors are needed that can autonomously detect CH₄-concentrations over longer periods of time. The proposed project is aimed at:

• Designing molecular receptors for methane recognition (cryptophane-A and –111) and synthesizing new compounds allowing their introduction in polymeric structure (Task 1; LC, France);
• Adapting, calibrating and validating the 2 available optical technologies, one of which serves as the reference sensor, for the in-situ detection and measurements of CH₄ in the marine environments (Task 2 and 3; GET, LAAS-OSE, IOW). Boulart et al. (2008) showed that a polymeric film changes its bulk refractive index when methane docks on to cryptophane-A supra-molecules that are mixed in to the polymeric film. It is the occurrence of methane in solution, which changes either the refractive index measured with high resolution Surface Plasmon Resonance (SPR; Chinowsky et al., 2003; Boulart et al, 2012b) or the transmitted power measured with differential fiber-optic refractometer (Boulart et al., 2012a; Aouba et al., 2012).
• Using the developed sensors for the study of the CH₄ cycle in relevant oceanic environment (the GODESS station in the Baltic Sea, Task 4 and 5; IOW, GET); GODESS registers a number of parameters with high temporal and vertical resolution by conducting up to 200 vertical profiles over 3 months deployment with a profiling platform hosting the sensor suite.
• Quantifying methane fluxes to the atmosphere (Task 6); Monitoring of greenhouse-gas emissions such as CO₂ and CH₄ (GHG), is a world-wide concern, where UNESCO has a strong influence through the implementation of observatories. The conclusions of the workshop on anthropogenic GHG emissions organized by the UNESCO in 2006 clearly identified in-situ monitoring as an immediate action to better quantify GHG emissions. Clearly, the current project, which aims at developing in-situ aqueous gas sensors, provides the technological tool to achieve this.

The aim is to bring the fiber-optic methane sensor on the TRL (Technology Readiness Level) from their current Level 3 – i.e. Analytical and laboratory studies to validate analytical predictions - to the Levels 5 and 6 - i.e. Component and/or basic sub-system technology validation in relevant sensing environments-, in comparison to the SPR methane sensor, taken as the reference sensor (TRL 4-5). This would lead to potential patent applications before further tests and commercialization. This will be achieved by the ensemble competences and contributions from the proposed consortium in this project.