RADIATIVE FORCING; MIE RESONANCE SPECTROSCOPY; EFFLORESCENCE/DELIQUESCENCE; THERMODYNAMICS; ORGANIC AEROSOLS; MISCIBILITY GAPS
Bastelberger S., Krieger U. K., Luo B. P., Peter Th. (2018), Time evolution of steep diffusion fronts in highly viscous aerosol particles measured with Mie resonance spectroscopy, in The Journal of Chemical Physics
, 149(24), 244506-244506.
Fard Mehrnoush M., Krieger Ulrich K., Peter Thomas (2018), Shortwave radiative impact of liquid–liquid phase separation in brown carbon aerosols, in Atmospheric Chemistry and Physics
, 18(18), 13511-13530.
Fard Mehrnoush M., Krieger Ulrich K., Peter Thomas (2017), Kinetic Limitation to Inorganic Ion Diffusivity and to Coalescence of Inorganic Inclusions in Viscous Liquid–Liquid Phase-Separated Particles, in The Journal of Physical Chemistry A
, 121(48), 9284-9296.
Bastelberger Sandra, Krieger Ulrich K., Peter Thomas, Luo Beiping (2017), Diffusivity measurements of volatile organics in levitated viscous aerosol particles, in Atmospheric Chemistry and Physics
, 17, 8453-8471.
Zieger Paul, Bastelberger Sandra, Mousavi-Fard Mehrnoush, Krieger Ulrich K., et al. (2017), Revising the hygroscopicity of inorganic sea salt particles, in Nature Communications
, 8, 15883.
Aerosols are an integral part of the atmospheric hydrological cycle and radiation budget, with many possible feedback mechanisms that are far from being fully understood. To reduce the uncertainties connected with aerosol forcings, a better physical understanding of the aerosols, their mixing states and properties, and a better representation in regional and global models is needed. Recently, experiments and modeling studies have shown that deliquesced aerosols can be present not only as one-phase systems containing organics, inorganic salts and water, but often as two-phase systems consisting of a predominantly organic and a predominantly inorganic aqueous phase. Also, there is growing evidence that aerosol particles containing a large fraction of organic molecules with medium to high molecular weight tend to become highly viscous or even glassy at low humidities and/or low temperatures. An important consequence of phase separation or glass formation is that the aerosol particles are no longer homogeneous, but may exhibit strong internal concentration gradients. Within SNF projects 200020-103651 and 200020-125151 (Physical states of mixed organic / inorganic aerosols) we were able to demonstrate the occurrence of liquid-liquid phase separation (LLPS) for a wide range of organics as function of O:C ratios and functional group compositions. However, in these studies we always used fully neutralized aqueous ammonium sulfate as inorganic component. In contrast, in the atmosphere the aerosol is often not fully neutralized or contains in addition ammonium nitrate. Hardly any data on the physical state of such acidic or nitrate-containing organic/inorganic mixed particles are available. It has been shown that forcing a liquid one-phase aerosol bears the potential for vastly incorrect gas/particle partitioning predictions with repercussions for the aerosol radiative properties. Moreover, the morphologies of phase separated particles and the diffusion impedance in highly viscous or glassy particles are open issues. Conversely, regional and global models are approaching a stage enabling incorporation of aerosol phase state information. In this continuation project for two PhD students we intend to investigate the phases and morphologies of aerosol particles depending on atmospherically relevant particle composi-tions, relative humidity and temperature. In PhD work I, we intend to investigate the phases and morphologies of aerosol particles in relation to the O:C ratio of the organic fraction for different atmospherically relevant inorganic particle compositions. Inorganic aerosol compositions will comprise partially neutralized sulfates and mixtures of ammonium sulfate and nitrate. Most experiments will be carried out on single particles deposited on a hydrophobically coated substrate observed with light and Raman microscopy. In PhD work II, we propose to investigate the internal heterogeneity of aerosol particles. Mie resonance spectra of single particles levitated in our electrodynamic balance will be used to characterize the phase volumes and concentration gradients quantitatively and to validate the liquid diffusion model that we developed recently. The diffusion model can be applied to aerosol particles of atmospheric sizes to study the impact of water uptake impedance on e.g. lifetime of particles and the direct effect of aerosol on radiation.Both PhD students will work closely together, partially investigate the same model systems with complementary methods and merge their results to obtain a comprehensive understanding of the morphology of aerosol particles. They will have the opportunity to also become involved in other ongoing projects of our group and collaborations with other ETH groups, with the aim to implement their results into regional and global models.