Characterization of the physico-chemical properties of aerosols and their impact on atmospheric ice particles nucleation

Doctorant: Raouf Ikhenazene

For the Earth’s weather and climate system, clouds are of major importance. On the one hand they cool by reflecting parts of the solar radiation and on the other, they heat by absorbing solar radiation and by trapping the outgoing infrared radiation. However, the latest report of the international panel of climate change (IPCC) continue to present clouds and aerosols as the largest non-anthropogenic uncertainties of earth’s radiation balance (IPCC 2013). It is known that aerosols affect climate indirectly via their interaction with clouds and thus significantly influence the life cycle of clouds. For example, a change in aerosols can shift the formation of ice clouds to lower water supersaturations and warmer temperatures. The influence of aerosols on the formation of ice clouds is a complex phenomenon. It can proceed via different pathways commonly termed deposition, condensation, immersion and contact nucleation. Aerosols that are of natural origin (pollens) or anthropogenic (soot from aircraft engine) can act as condensation nuclei of atmospheric ice crystals.

One of the current research themes of the team ANATRAC at PhLAM is to try to better understand the mechanisms of nucleation of the ice crystals from aerosols. For this purpose, a physical (structure, surface) and chemical (elemental and functional composition) characterizations  are required. The plan of the project is then 1) to analyze the surface and the composition of soot particles collected on a burner (CAST or equivalent) in collaboration with local laboratory PC2A (Univ. Lille1) or external lab. (ex: Coria, Rouen), 2) analyze the surface and composition of bio-aerosols or their extracts that proves recently to act as ice nucleator as well. These samples will be used to model the behavior of aerosol particles in the atmosphere. Concerning the anthropogenic aerosols, soot proxies of size and composition comparable to soot aerosols collected at the outlet of turbine aircraft engine will be generated (work in collaboration with SNECMA within the MERMOSE project). The student will benefit from analytical techniques available at PhLAM and on the campus (Lille 1 and the regional platform for surface analysis) to perform the analysis. Bioanalytical techniques like Desorption / Ionization Laser + TOF -MS (mass spectrometry time of flight ) and possibly MALDI (Matrix Assisted Laser Desorption Ionization ), Raman spectroscopy, XRD and ESEM will be applied to determine the specific sites responsible for the ice nucleation process. Once the nature and the specific structure of glaciogenic agents of aerosol particles will be identified, certain sites on the surface of aerosols will be degenerated or processed to better understand their particular role in the nucleation activity (INA , " Ice nucleation Activity"). The impact of their physico-chemical properties on the nucleation and growth of ice will then be deduced in the relevant thermodynamic conditions occuring in the atmosphere.

Nucleation experiments will be carried using a new dedicated environmental cell working from -196°C to 120°C, which spans over the entire atmospheric temperature range and allow for real-time monitoring of Relative Humidity during experimentation.

Depositional nucleation experiments will be monitored with Laser Raman spectroscopy by following the molecular spectra of condensed water vapor and aerosols signals. The thermodynamic and  kinetic conditions of nucleation will be studied and special attention will be given to chemical aging effect of aerosols. The immersion mode of nucleation will also be studied by using a specific protocole of micro-droplet generations.  These approaches will allow determining the ice nucleation properties of the aerosols to better understand their impact on the formation of clouds that affect radiative properties and global climate.

This research project is part of a broader framework of LabEx CaPPA and the MERMOSE project (DGAC). 

Director: B. Chazallon (PhLAM)
Co-responsible: C. Focsa (PhLAM)

Laboratory: PhLAM

Financing: Université Lille 1 / Labex CaPPA