Description du sujet de thèse

Volatile organic compounds (VOCs) are emitted into the atmosphere from a variety of anthropogenic and biogenic sources, including industrial combustion and transportation, oil and natural gas, biomass burning, vegetation, and volatile chemical use (VCPs). Once emitted, VOCs can undergo chemical reactions that alter the oxidative capacity of the atmosphere via the formation of tropospheric ozone and secondary organic aerosols (SOA). Characterizing the composition of VOCs in changing environments such as urban areas is therefore imperative to implement effective measures to reduce both ozone and SOA, which have negative impacts on air quality, human health, and climate forcing. Urban areas have experienced a paradigm shift in the relative importance of VOC emissions from so-called “traditional” sources such as transportation versus non-combustion sources such as VCPs. These non-traditional urban emissions cover a wide range of volatilities and molecular structures that impact their reactivity in the atmosphere and their final fate. However, very little is known about these urban VOCs, including source distribution, magnitude, temporal behavior, and importance in ozone and SOA formation. There is therefore an urgent need to carefully assess VOC sources, including emerging volatile chemicals such as VCPs, and predict their impacts on O3 and SOA production. This project addresses this need, with the philosophy of obtaining new information on sources and their impacts on air quality. To this end, as part of this thesis, a measurement campaign will be carried out in the heart of one of the largest European metropolises (Paris, Les Halles site). These measurements will be based on the instrumentation present at the Halles site but also on the deployment of online mass spectrometers in order to obtain a molecular characterization of gas emissions. For this, a coupling, unprecedented in France, between gas chromatography and an online chemical ionization mass spectrometer will be carried out. Thanks to the unmatched sensitivity of this coupling, an exhaustive molecular quantitative mapping of VOCs will be established. The particulate phase will also be characterized using a new interface to determine the chemical composition in real time by very high resolution mass spectrometry to link VOC emissions and SOA formation.
Thanks to this campaign, a selection of VOCs based on representativeness (i.e., concentration), reactivity (with the hydroxyl radical) and the potential to form SOA will be carried out. Different mixtures representing the different major sources (e.g., traffic, VCP, cooking, ...) will be studied independently (all substances of the same group simultaneously) and in mixture to assess the impact of each source in the formation of SOA and O3. These innovative experiments will be carried out in a simulation chamber under controlled environment to simulate diurnal and nocturnal oxidation processes. The selected atmospheric simulation chamber is SAPHIR (Julich, Germany) and will allow to reproduce urban conditions with the greatest precision while benefiting from the many analytical techniques available on SAPHIR. This step will allow to better understand the mechanisms of SOA and O3 formation from VOC groups specific to the urban environment while taking into account the evolution of emissions (e.g., traffic reduction) but also the reduction of NOx.

Contexte de travail

IRCELYON, a joint research unit between the CNRS and the University of Lyon, brings together the skills in heterogeneous catalysis of the Lyon region to constitute the largest catalysis laboratory in France and Europe. The laboratory includes 115 permanent researchers from the CNRS and the University of Lyon, as well as a similar number of doctoral students and post-doctoral fellows. IRCELYON, an academic research laboratory entirely dedicated to heterogeneous processes, focuses its research activities on the challenges of sustainable development. More specifically, the CARE team is positioned at the crossroads of many major societal problems related to water resources, waste recovery, air quality and climate change. Its fundamental and applied research is based on the pooling of strong specificities associated with an innovative and efficient analytical park to characterize, eliminate and recover pollutants. By being at the interface between environmental sciences, heterogeneous catalysis, analytical chemistry and electrochemistry, the CARE team proposes developments of innovative methods of remediation (photocatalysis, electrochemical promotion of catalysis, etc.), process coupling (catalysis-photocatalysis, catalysis-electrochemistry, etc.), chemical analysis (high-resolution mass spectrometry) for the study of atmospheric processes.

The mission of INERIS (National Institute for Industrial Environment and Risks) is to contribute to the prevention of risks that economic activities pose to health, the safety of people and property, and the environment. Its scientific and technical skills are made available to public authorities, businesses and local authorities in order to help them make the most appropriate decisions to improve environmental safety. Within INERIS, the ANAE unit (Methods and development in environmental analyses) has all the laboratory testing resources required for extensive physicochemical characterization of atmospheric matrices and has already carried out numerous studies related to the characterization of secondary particles for the Ministry of Ecological Transition and ADEME. The MOCA unit (atmospheric modeling and environmental mapping) has been co-developing the CHIMERE chemistry-transport model with the CNRS/IPSL for over 15 years and is in charge of piloting the PREV'AIR air quality forecasting system (www.prevair.org).

Contraintes et risques

The interdisciplinary work will take place at the interface between two research institutes (INERIS and IRCELYON) and will promote collaboration and interaction within the project. The candidate will acquire expertise in analytical chemistry (mass spectrometry) and statistical analysis (clustering analysis).