Description of the thesis topic

Over the past 150 years, hydrogen (H2) levels in the atmosphere have increased by 70%, from 330 ppbv to 550 ppbv (Patterson et al. 2020), mainly due to human activity and leaks associated with fossil fuel extraction. The establishment of a global hydrogen economy could therefore accelerate this trend. Forest fires are also a significant source of hydrogen emissions, contributing 20% of global emissions, on par with anthropogenic emissions. Thus, the increase in mega-fires will increase hydrogen injections at high altitudes. These emissions will cool the stratosphere, increasing water vapor concentration and slowing the recovery of the ozone layer (Ocko et al., 2022).
Observing extreme events such as mega-fires requires a high degree of responsiveness in organizing measurement campaigns. Furthermore, balloons are the only way of obtaining observations in these plumes between 10 and 30 kilometers. The development of lightweight instruments under small balloons is currently the only technical solution capable of taking up this scientific challenge. Balloons are also the only solution for assessing the impact of the new hydrogen energy transition on stratospheric chemistry. Hydrogen cannot currently be measured from satellites. Only in-situ measurements or sampling systems can provide hydrogen concentrations in the stratosphere.
As part of the CNES ARCHE project, LPC2E, in collaboration with the ICARE and CEMHTI laboratories (Orléans), is currently developing an instrument capable of measuring H2 in real time using a stratospheric balloon. This instrument will use innovative porous MOF (Metal Organic Framework) materials with electrical properties sensitive to the presence of H2 (Karuppasamy et al., 2023). These materials can analyze H2 concentrations of 100 ppbv, which is five times lower than the values expected in the stratosphere. The thesis will therefore begin with a strong instrumental heritage. The instrument will be made and tested at LPC2E via balloon flights organized at the Orleans site. Such flights are already routinely carried out as part of the validation of the European EarthCare satellite (ESA).
MOFs can be used to quantify other gases in the atmosphere. CO sensors containing MOFs have already been tested with a detection threshold around ppm (Montoro et al., 2024, Xie et al., 2024). Unfortunately, these studies were conducted at high temperatures (350°C) and the selectivity of the measurements needs to be reevaluated under atmospheric conditions. Similarly, the detection threshold of these sensors is still too high by an order of magnitude to be used in stratospheric conditions.
The aim of this thesis is therefore to develop a new instrument for use in a light stratospheric balloon, capable of measuring trace amounts of hydrogen using new materials under extreme pressure and temperature conditions for this type of sensor. To achieve this scientific challenge, collaboration with the technical teams at CEMHTI is essential to this project. Particular effort will be focused on optimizing the parameters that can influence the efficiency of MOFs, such as composition, particle morphology, material porosity, and the addition of dopants, with a view to significantly reducing the sensitivity of these materials.
In the longer term, measurements could be planned in the intertropical convergence zone, where the largest injections of hydrogen into the stratosphere are expected and where intense forest fires are a regular occurrence. One prospect is to participate in future CNES-AEB balloon campaigns from the Franco-Brazilian base (Las Palmas, Tocantins), which will be made available to the scientific community at the end of 2026. The new MOF-based sensors could also contribute to the validation of products from future European space missions Sentinel-4 and 5, IASI-NG, FORUM, and MERLIN by exploring new possibilities such as the measurement of volatile organic compounds (François et al., 2022).
References
François M., Sigot L., Vallières C., Impact of humidity on HKUST-1 performance for the removal of acetaldehyde in air: an experimental study. Adsorption 28, 275–291, 2022.
Karuppasamy K. et al., Room-temperature response of MOF-derived Pd@PdO core shell/γ-Fe2O3 microcubes decorated graphitic carbon based ultrasensitive and highly selective H2 gas sensor, Journal of Colloid and Interface Science 652, 2023.
Montoro C. et al., MOF-derived metal oxide (Cu, Ni, Zn) gas sensors with excellent selectivity towards H2S, CO and H2 gases, Composites Part B 283, 2024.
Ocko I. and P. Hamburg, Climate consequences of hydrogen emissions, Atmospheric Chemistry and Physics 22(14):9349-9368, 2022.
Patterson J. D. et al., Atmospheric History of H2 Over the Past Century Reconstructed From South Pole FirnAir, Geophysical Research Letter, 2020.
Xie R., Lu J., Liu Y., Carbon monoxide gas sensing properties of SnO2 modified metal-organic skeleton derived NiO. Sensors and Actuators A: Physical, 2024.

Work Context

The PhD student will be integrated into the “Atmospheric Environment” group of the SAMPLE team at LPC2E, based at the CNRS Campus in Orléans. This group's activities cover a wide range of fields, including the study of stratospheric chemistry and aerosols. These studies have required the development of innovative instruments that can be used in balloons and/or aircraft and deployed on the ground. These instruments are currently used to study volcanic and fire plumes on the one hand, and biogenic emissions from forests and wetlands on the other. The PhD student will work in collaboration with the technical teams of the three laboratories LPC2E, CEMHTI, and ICARE. The thesis will be co-supervised by Gwenaël BERTHET (LPC2E, CR HDR CNRS) and Lavinia BALAN (CEMHTI, DR CNRS). Fabrice JEGOU (LPC2E, CDI CNRS researcher) will be the main supervisor for the thesis. The doctoral work will be carried out as part of several related projects, including the CNES ARCHE and IIT CNRS MIMAG projects.