Investigation of the hygroscopic properties of Ca(NO₃)₂ and internally mixed Ca(NO₃)₂/CaCO₃ particles by micro-Raman spectrometry

Y. J. Liu (1) , T. Zhu (1) , D. F. Zhao (1) , Z. F. Zhang (1)

1 State Key Joint Laboratory of Environmental Simulation and Pollution Control

To understand and predict the role of mineral aerosol particles processed by reactive nitrogen species in the atmosphere, the hygroscopic properties of both Ca(NO₃)₂ and Ca(NO₃)₂-containing mineral particles must be well understood. Using a micro-Raman system, the dehydration and hydration processes of micro-sized individual Ca(NO₃)₂ and internally mixed Ca(NO₃)₂/CaCO₃ particles were investigated systematically. In addition to accurate quantification of the dependence of water content on relative humidity (RH), significant new spectroscopic evidence related to chemical structure was also obtained to confirm the occurrence of amorphous solid state and to better understand the phase transition process. The Ca(NO₃)₂ particles exhibit reversible behavior in the dehydration and hydration processes; they are in the state of solution droplets above 10% RH and amorphous hydrates below 7% RH, and phase transition occurs at 7?10% RH. The hygroscopic behavior of Ca(NO₃)₂/CaCO₃ particles is identical to that of pure Ca(NO₃)₂ particles, suggesting a negligible effect of the inclusion of slightly soluble CaCO₃.

Domaines: Océan, Atmosphère

Y. J. Liu, T. Zhu, D. F. Zhao, Z. F. Zhang. Investigation of the hygroscopic properties of Ca(NO₃)₂ and internally mixed Ca(NO₃)₂/CaCO₃ particles by micro-Raman spectrometry. Atmospheric Chemistry and Physics Discussions, 2008, 8 (3), pp.10597-10625. ⟨hal-00304227⟩