CCN and IN Abilities of Metal Oxide Particles Measured with MRI Cloud Simulation Chamber and MRI Continuous Flow Diffusion Chamber-type IN Counter

Al₂O₃ and Fe₂O₃ particles have been observed not only in the surroundings of the industrial area but also in the natural atmospheric environment. These two kinds of aerosols can influence aerosol-cloud interaction. Physico-chemical properties of Al₂O₃ and Fe₂O₃ particles, such as size distribution, cloud condensation nuclei (CCN) and ice nuclei (IN) abilities, were investigated by using CCN counter, MRI dynamic cloud chamber, continuous flow diffusion chamber-type IN counter (CFDC-type INC) and several aerosol instruments in this study. The results indicated that their hygroscopicity (κ-value) were around 0.01-0.03, which are comparable to that of surrogates of mineral dust particles, and smaller than typical κ-values of atmospheric aerosols. On the other hand, based on ice nucleation active surface site (INAS) density, these materials may act as good ice nuclei via immersion freezing mode. Al₂O₃ and Fe₂O₃ particles continuously nucleated ice crystals at -14°C and colder temperatures and at -20°C and colder temperatures, respectively, in cloud simulation experiments. While in CFDC-type INC experiments, only Al₂O₃ seemed to act as good IN below -25 °C. Al₂O₃ seemed to have better IN ability than Fe₂O₃ and its INAS values as a function of temperature were relatively close to those of illite particles which are better surrogates of natural atmospheric dust and have been well investigated so far.