Water adsorption and dynamics on kerosene soot under atmospheric conditions

Abstract

Morphology, microstructure and surface chemistry of laboratory made kerosene soot used as an aircraft soot surrogate have been studied to establish the correlation between the porosity and the mechanism of water adsorption on the soot surface. The quasielastic neutron scattering (QENS) technique has been used to characterize the dynamics of water confined in the soot pores network. Spectra above and below the water triple point Tm describe the translational and rotational diffusion of water molecules adsorbed in 0.5 nm micropores, 2 nm supermicropores and ≥2 nm mesopores. Below Tm an appreciable amount of liquid water exists in the soot micropores down to the lowest tropospheric temperatures. The depression in freezing temperature is related to the pore dimension. Water confined in the micropores appears to freeze completely only at T below 200 K showing that the nucleation process depends on the specific microporosity. At the saturation plume conditions ≅30% of adsorbed water has been transformed into ice. These results show that, in the upper troposphere, soot particles presenting the above‐mentioned properties will contain stable water/ice components inside the pores with 25% of unfrozen water.