Modification of aerosol properties due to relative humidity

PhD student: Danielle ELHAJJ

The Earth radiative budget is largely modified by aerosol particles within the atmosphere due to absorption and scattering of solar radiation. In-situ observations rely on measurements performed at humidities lower than the ambient humidity (RH ≤50%). The condensation of water vapour on aerosol’s surfaces can modify their optical properties and thus the Aerosol Optical depth. Although well known aerosol hygroscopic properties are essential to better characterise aerosol radiative effect, the hygroscopic effect on aerosol optical properties is not well quantified in theoretical (Mie) and atmospheric models. Only few closure studies were performed to compare in-situ physical and optical properties at different relative humidities.

Modifications of the aerosol properties (physical and optical) at different humidity will be studied during this PhD. Laboratory measurements at controlled humidities with state-of art instruments (Atomic force microscope, nephelometer and aethalometer) of different types of aerosols will be performed. Marine aerosols (highly hygroscopic), biomass burning aerosols and dust particles (low to high hygroscopicity) will be submitted to different relative humidities and the modification of their properties will be observed during one and multiple humidity cycles (from 30% to 90%). These observations will then be compared to classical model results (Mie). The possible errors made in the model will be highlighted, estimated and corrected. A similar comparison will be done with results from atmospheric models (RAMS, WRF …) in order to better quantify the condensed water vapour on aerosols. The aerosol activation processes (in-cloud processes) will also be studied through successive humidities cycles (Liu et al., 2008).

Director: Isabelle Chiapello (LOA)
PhD advisors: Marie Choël (LASIR), Suzanne Crumeyrolle (LOA)

Laboratories: LOA-LASIR

Financing: Region / Labex CaPPA