It is now established that the strong amplification of global warming accelerates the thawing of permafrost in the Arctic. Permafrost contains approximately 50% of the global soil carbon, and when it thaws, a subsequent quantity of carbon is available for microbial degradation, which releases into the atmosphere large quantities of methane (CH4) and carbon dioxide (CO2). This process is expected to yield positive feedback on global warming by releasing into the atmosphere greenhouse gases (GHGs), including CH4 and CO2. According to the Intergovernmental Panel on Climate Change (IPCC), the Arctic air temperature is anticipated to increase by up to 10◦C by 2100 compared with the temperature levels in 1986–2005. While the processes leading to the release of GHGs from permafrost thaw, driven by microbial processes, have been identified, the impact of permafrost thaw on emissions of reactive gaseous species such as volatile organic compounds (VOCs) and particle formation remains unknown and must be assessed. Notably, the pivotal role of microbial functional groups involved in gas emissions, including (nitrifiers, denitrifiers), methanogens, and methanotrophs under changing environmental conditions must be evaluated to elucidate the impact of microbial degradation on the atmospheric composition in present and future climate scenarios.

VOCs play a pivotal role in climate change and air pollution by modulating tropospheric oxidation capacity and providing precursors for ozone and atmospheric particles. Of specific importance to both air quality and climate are ultrafine particles (< 100 nm), which contribute to a major fraction of the total aerosol load. Such particles result from the gas-to-particle conversion of (highly) oxygenated VOCs (OVOCs) formed from the gas-phase oxidation of VOC emitted from both natural and anthropogenic sources. The quantitative assessment of the impact of aerosols on climate remains poorly understood due to several factors, including an incomplete understanding of the sources of OVOC. These uncertainties lead to large errors between modeled and ambient observations of aerosol loading.

In this context, we hypothesize that microbial degradation of organic-rich soil driven by permafrost thaw and accelerated by global warming is an overlooked source of reactive gaseous species that produce particles and mitigate the oxidation capacity and particle formation in the Arctic. 

Work description 

The Ph.D. work will be carried out at the Institut de Recherches sur la Catalyse et l'Environnement de Lyon (IRCELYON, http://www.ircelyon.univ-lyon1.fr/) and the Microbial Ecology Laboratory (LEM, https://www.ecologiemicrobiennelyon.fr/).

The temperature-dependency of VOC emissions will be examined by sequentially increasing the temperature inside a climate-controlled chamber. Emissions will be characterized by current state-of-the-art mass spectrometers (i.e., chemical ionization (CI) and proton transfer). CI is a highly selective and sensitive technique able to characterize organic and inorganic species. To constrain the evolution of gaseous species from permafrost thaw, the activity, abundance, and   composition of microbial groups involved in gas emissions will be characterized by a highly complementary approach to retrieve the taxonomy and the functions of the permafrost samples. VOCs and other reactive species emitted from the permafrost will be further oxidized using an aerosol oxidation flow reactor to evaluate the potential of the emissions to form new particles. The outcome of this work is a better description of future global warming that can greatly enhance microbial degradation and result in larger VOC emissions from the Arctic permafrost, which may significantly impact the Arctic atmospheric chemistry and climate change.

Funding category: Contrat doctoral



PHD Country: France