Reference : UMR7376-ANNMON-001
Workplace : MARSEILLE 02
Date of publication : Thursday, June 23, 2022
Scientific Responsible name : Anne MONOD, (https://lce.univ-amu.fr/fr/users/monod-anne) and Fabien ROBERT-PEILLARD (https://lce.univ-amu.fr/fr/users/robert-peillard-fabien)
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
As clouds play a key role in the Earth's radiation budget, the complex but incompletely understood interactions between aerosol and clouds makes cloud effects the most uncertain component of current climate projections (Boucher et al., 2013; Sorooshian et al., 2019). While there is no doubt that clouds in the atmosphere form on ubiquitous aerosol particles, the ability to predict cloud droplet size and number concentration from aerosol properties is poor. The theoretical basis of cloud formation from aerosol particles, so-called cloud condensation nuclei (CCN), has been established by Köhler. 1 It combines the Kelvin effect and Raoult's law, which together determine the saturation water vapor pressure over a curved aqueous surface at varying relative humidity. Surface tension has long been neglected in these processes, and it is only recently that measurements have shown the relevance of this property.2 Surfactants (amphiphile organic molecules) are the only species to be significantly surface active in natural aerosol.3 However, the environmental content of surfactants has been scarcely investigated on aerosols and sea water, and to our knowledge, clouds or fogs have not yet been investigated in this way. The scarcity of information on aerosol and droplets surface tension, types of surfactants and their potential exchanges between sea water, aerosol and clouds limits our current ability to predict cloud formation.4 The objectives of the PhD work are to contribute to answer these questions, and more specifically: i) What are the characteristics of surfactants (quantities per class and related surface tension) in aerosols, cloud droplets, and sea water? Are they influenced by specific sources? ii) What are the relationships between aerosol/CCN and cloud droplet number concentrations in the marine boundary layer? Can these relationships afford insight on the role of surface tension? iii) Are sea-spray derived CCN aerosol also a source of surfactants? iv) How do different kinds of surfactants influence the CCN properties of aerosols under controlled conditions?
The PhD study proposes 2 approaches:
Two interactive approaches will help tackle these questions:
Approach A : Field characterization of aerosol, clouds over the Ocean and sea water: field measurements will serve to robustly characterize aerosol-cloud-meteorology interactions using extensive measurements of aerosols, fogs/clouds and sea water and the associated surfactants and surface tension. This will be done at various places over the world, influenced by specific marine sources: anthropogenic in Marseille-Gulf-of-Fos5, biogenic on Namibian Austral Atlantic coasts6, and over the Western Atlantic Ocean.7 The latter will be conducted through a close collaboration with the University of Arizona in a program led by Dr. Sorooshian (https://activate.larc.nasa.gov/). NASA's Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE)e.g. 8 is focused on: (i) gathering high volumes of data across multiple years and seasons; (ii) using a dual aircraft approach where both planes fly in synchrony to simultaneously characterize the same vertical column of the lower atmosphere to capture data relevant to droplet activation; and (iii) probing a region with a wide range of meteorology and aerosol types. While conducting real-time characterization of meteorology, aerosol, and cloud parameters, ACTIVATE is also collecting both aerosol and cloud water samples relevant to INSPIRE due to the off-line laboratory experiments in Approach B. These samples will be provided by the U-Arizona team to the CNRS team.
The U-Arizona team will further conduct analysis of the data collected simultaneous to the aerosol and cloud samples shipped to CNRS with a focus on the relationships between aerosol properties (size distribution, total concentration, composition, CCN concentrations, and volatility) immediately below cloud base to cloud droplet size distributions immediately above cloud base. An assessment of “closure” will be made to see how well aerosol size distribution data and updraft velocity can predict cloud droplet number concentrations, with discrepancies indicative of potential chemical effects including those of surfactants. A secondary closure test will be done using just aerosol size distribution data to see how well they can predict measured CCN concentrations at a fixed instrument supersaturation using the CCN counter on an ACTIVATE aircraft. The advantage of ACTIVATE is the high volume of flights and data in different seasons, which will allow a test of closure in a variety of conditions to see how influential surfactants can be in different ambient regimes.
In this approach, the PhD student will be responsible for surfactant chemical analysis and surface tension analysis, using off-line advanced techniques. Solid phase extraction (SPE) provide extraction of the different classes of surfactants (ionic and non-ionic) by specific elution procedures, 8 and specific extractions are required for sea water.9 For the quantification of surfactants, colorimetric and UV-vis absorbance methods will be used per class of surfactants.10 11 12 13 14 Identification of specific surfactants will be achieved using liquid chromatography coupled to mass spectrometry (LC-MS)15 and ultra-high resolution mass spectrometry (LC-MS-ORBITRAP)16 available at LCE through the national platform IMAGINE² (national EQUIPEX+ platform). For each sample, surface tension measurements, determination of adsorption isotherms and Critical Micelle Concentrations (CMC) values will be performed and intercomparisons with other methodologies will be done through national and international collaborations (C. Ferronato IRCELYON and B. Noziere KTH, Stockholm).13 14
Approach B: Laboratory experiments of the processes governing cloud droplet activation
Laboratory experiments of cloud droplet activation will be performed in a simulation chamber situated at ETH-Zurich (Switzerland) in the frame of the ORACLE (AerOsol-Cloud Interactions: the Role of orgAnic compounds in CLoud droplEt activation) project. These experiments will be deployed under controlled conditions initially using synthetic aerosols followed by more complex mixtures. The MASSALYA platform (Aix-Marseille University) will be used for on-line sub-micron particle characterization in terms of physical aspects (granulometry and size distribution - SMPS) and chemical aspects (inorganic and organic) with high resolution on-line mass spectrometers. Physical and chemical characteristics of gases, aerosols and their partitioning will be monitored by online state-of-the-art mass spectrometry (CHARON-PTR-MS). The effects due to organic matter and associated surface tension will be investigated. In the 1st step, a monodisperse particle population of pure chemical composition (e.g. deliquesced ammonium sulfate, or dry hydrophobic particles) will be coated by a synthetic surfactant bearing a known CMC. Investigation of the effect on CCN activity from coating by different synthetic surfactants bearing various CMC will be done. In a 2nd step, more realistic conditions will be investigated for the coating, with mixtures of components, and ultimately real mixtures, collected in Approach A, especially those containing various marine surfactants, to determine their specific role on CCN activity. The experiments will be accompanied by thermodynamic and kinetic modelling of surface tension, solution non-ideality, and co-condensation effects on CCN activation through collaborations with ETH-Zurich.
The results obtained on surfactants and their related surface tension will be uniquely complemented by up-to-date instrumentation for aerosol hygroscopicity, CCN activity through an international consortium collaboration with the University of Arizona, USA. The results are expected to lead to new aspects on the understanding on cloud droplet activation, in terms of processes, measurement techniques, and model parameterizations.
1. Köhler, H. The nucleus in and the growth of hygroscopic droplets. Trans. Faraday Soc. 32, 1152–1161 (1936).
2. Ovadnevaite, J. et al. Surface tension prevails over solute effect in organic-influenced cloud droplet activation. Nature 546, 637–641 (2017).
3. Frossard, A. A. et al. Properties of Seawater Surfactants Associated with Primary Marine Aerosol Particles Produced by Bursting Bubbles at a Model Air–Sea Interface. Environ. Sci. Technol. 53, 9407–9417 (2019).
4. Bzdek, B. R., Reid, J. P., Malila, J. & Prisle, N. L. The surface tension of surfactant-containing, finite volume droplets. Proc. Natl. Acad. Sci. U. S. A. 117, 8335–8343 (2020).
5. Dron, J. et al. Contaminant signatures and stable isotope values qualify European conger (Conger conger) as a pertinent bioindicator to identify marine contaminant sources and pathways. Ecol. Indic. 107, 105562 (2019).
6. Formenti, P. et al. The aerosols, radiation and clouds in southern Africa field campaign in Namibia overview, illustrative observations, and way forward. Bull. Am. Meteorol. Soc. 100, 1277–1298 (2019).
7. Sorooshian, A. et al. Aerosol–cloud–meteorology interaction airborne field investigations: Using lessons learned from the U.S. West coast in the design of activate off the U.S. East Coast. Bull. Am. Meteorol. Soc. 100, 1511–1528 (2019).
8. Robert-Peillard, F. et al. Occurrence and fate of selected surfactants in seawater at the outfall of the Marseille urban sewerage system. Int. J. Environ. Sci. Technol. 12, 1527–1538 (2015).
9. Fauvelle, V. et al. One-single extraction procedure for the simultaneous determination of a wide range of polar and nonpolar organic contaminants in seawater. Front. Mar. Sci. 5, 1–10 (2018).
10. Baduel, C., Nozière, B. & Jaffrezo, J. L. Summer/winter variability of the surfactants in aerosols from Grenoble, France. Atmos. Environ. 47, 413–420 (2012).
11. Nozière, B., Baduel, C. & Jaffrezo, J. L. The dynamic surface tension of atmospheric aerosol surfactants reveals new aspects of cloud activation. Nat. Commun. 5, 1–7 (2014).
12. Gérard, V. et al. Anionic, Cationic, and Nonionic Surfactants in Atmospheric Aerosols from the Baltic Coast at Askö, Sweden: Implications for Cloud Droplet Activation. Environ. Sci. Technol. 50, 2974–2982 (2016).
13. Gérard, V. et al. Concentrations and Adsorption Isotherms for Amphiphilic Surfactants in PM1 Aerosols from Different Regions of Europe. Environ. Sci. Technol. 53, 12379–12388 (2019).
14. Frossard, A. A. et al. Properties of Seawater Surfactants Associated with Primary Marine Aerosol Particles Produced by Bursting Bubbles at a Model Air-Sea Interface. Environ. Sci. Technol. 53, 9407–9417 (2019).
15. Renard, P., Tlili, S., Ravier, S., Quivet, E. & Monod, A. Aqueous phase oligomerization of α,β-unsaturated carbonyls and acids investigated using ion mobility spectrometry coupled to mass spectrometry (IMS-MS). Atmos. Environ. 130, (2016).
16. Dufour, A., Thiébaut, D., Ligiero, L., Loriau, M. & Vial, J. Chromatographic behavior and characterization of polydisperse surfactants using Ultra-High-Performance Liquid Chromatography hyphenated to High-Resolution Mass Spectrometry. J. Chromatogr. A 1614, (2020).
The Environmental chemistry laboratory (UMR7376) has an experience of more than 20 years in chemistry of the atmosphere and chemistry of surface waters, aerosol, clouds, VOC characterization, and processes. The laboratory is situated in down-town Marseille, at the St Charles campus, it comprises 60 people, of which 50% are PhD students and post-docs. It handles state-of-the art analytical devices, it holds the LC-MS-ORBITRAP instrument of the national IMAGINE² platform and it is the University principal investigator of the mobile MASSALYA platform. http://lce.univ-amu.fr/. The PhD thesis will be co-advised by A. Monod and F. Robert-Peillard, at the intersection between the IRA group and the TRAME group.
Constraints and risks
Research funding program: The research activities will be funded by 3 different national and international projects funded national programs (CNRS-INSU, CNRS-80PRIME and ANR). These projects are collaborative studies involving other French institutes (IRCE-LYON, IGE-Grenoble, LaMP-Clermont-Ferrand, LISA-Paris) and international institutes (University of Arizona, USA ).
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