On the Surface Interaction of Aerosol Particles

Aerosol particles interact with surfaces in different environments and applications. The knowledge of fundamental surface interaction phenomena can be used to investigate the structural properties of particles, describe the performance of different instruments, and develop new applications. In this thesis, particle rebound from a surface as well as the transfer of the electric charge during rebound and resuspension were studied. The research was based on the experimental and numerical characterization of these surface interaction phenomena. Along with the fundamental understanding obtained for the interaction between aerosol particles and surfaces, new methods were developed and applied for specific aerosols, such as fungal spores.The critical velocity of rebound, which is the smallest incident velocity for a particle to rebound, was determined in a wide particle size range combining the separate groups of previous results. The main instrument developed during the research of this thesis, a variable nozzle area impactor (VNAI), was used throughout the wide size range for different particle and surface materials. The particle material was found to have a significant effect on the critical velocity of rebound. On the contrary, the effect of the surface material was observed to be much smaller, at least for the hard surface materials studied in the experiments. Also the critical velocity for oblique impacts in the impactor was characterized. It was found that the critical velocity of rebound significantly decreased with the increasing obliquity of the impact. Based on the results of this thesis, the effect of materials and obliquity on the critical velocity can be estimated quantitatively and exploited in the development of new applications, such as impactors and collectors.The triboelectric charge transfer during rebound was characterized for nanoparticles with a new simplified method developed for an electrical low pressure impactor (ELPI). In addition, the charge transfer was measured for fungal spores and standard test dusts during rebound and resuspension. The results of this thesis showed that the triboelectric charging of particles during resuspension correlated with the triboelectric charging during rebound. Spores of different fungal species were found to obtain both positive and negative charges from substrates of different materials. The information on the triboelectric charging and rebound behavior can be used for predicting the particle dynamics in different environments and designing new applications, for instance, in ventilation and filtration systems