Investigation of the hygroscopic properties of Ca(NOsub3/sub)sub2/sub and internally mixed Ca(NOsub3/sub)sub2/sub/CaCOsub3/sub particles by micro-Raman spectrometry

摘要

To understand and predict the role of mineral aerosol particles processed byreactive nitrogen species in the atmosphere, the hygroscopic properties ofboth Ca(NO₃)₂ and Ca(NO₃)₂-containing mineral particlesmust be well understood. Using a micro-Raman system, the hygroscopicbehaviors of micro-sized individual Ca(NO₃)₂ and internally mixedCa(NO₃)₂/CaCO₃ particles in both dehumidifying andhumidifying processes were investigated systematically. In addition toaccurate quantification of the dependence of water content on relativehumidity (RH), significant new spectroscopic evidence related to chemicalstructure was also obtained to confirm the occurrence of amorphous solidstate and to better understand the phase transition process. TheCa(NO₃)₂ particles exhibit reversible behavior in thedehumidifying and humidifying processes; they are in the state of solutiondroplets above 10% RH and amorphous hydrates below 7% RH, and phasetransition occurs at 7–10% RH. The hygroscopic behavior ofCa(NO₃)₂/CaCO₃ particles is identical to that of pureCa(NO₃)₂ particles, suggesting a negligible effect of the slightly soluble CaCO₃inclusion on the hygroscopic behavior of a(NO₃)₂/CaCO₃ particles.