Multi-phase processes of atmospheric aqueous droplets
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
University of Oulu, hall L2
Topic of the dissertation
Multi-phase processes of atmospheric aqueous droplets
Doctoral candidate
Master of Science Sampo Vepsäläinen
Faculty and unit
University of Oulu Graduate School, Faculty of Science, Nano and Molecular Systems Research Unit
Subject of study
Physics
Opponent
Professor Markus Petters, University of California, Riverside
Custos
Professor Nønne Prisle, University of Oulu
Surfactants contribute significantly to uncertainty in cloud droplet growth and activation
Atmospheric aerosols, small particles suspended in the air, offer surfaces for water to condense upon to form cloud droplets. The aerosols often contain surface active compounds (surfactants) that adsorb at the surface of water droplets and can affect their properties as they grow. Inside the droplet, surfactants can also self-assemble to form a variety of aggregate structures.
The thesis investigates the effects of 1) surface adsorption and 2) surfactant self-assembly on the growth and activation of cloud droplets through thermodynamic modeling.
The first part shows that different surface activity models currently in use can predict significantly different cloud droplet formation, and that the comparison between the models changes with the studied system. These results highlight that the effects of surface adsorption should be established for a wider range of conditions and aerosol types relevant to the atmosphere than is currently the case. This will avoid over-generalizing results from a single type of surface active aerosol or surface activity model.
The second part shows that self-assembly causes only minor effects on cloud droplet activation but significantly impacts earlier stages of droplet growth. These mainly manifest as differences in water uptake at a given air humidity (RH < 100 %). The droplet water content affects the growth rates and optical properties. Self-assembly could therefore impact atmospheric visibility and climate-relevant interactions between the droplets and radiation.
The thesis investigates the effects of 1) surface adsorption and 2) surfactant self-assembly on the growth and activation of cloud droplets through thermodynamic modeling.
The first part shows that different surface activity models currently in use can predict significantly different cloud droplet formation, and that the comparison between the models changes with the studied system. These results highlight that the effects of surface adsorption should be established for a wider range of conditions and aerosol types relevant to the atmosphere than is currently the case. This will avoid over-generalizing results from a single type of surface active aerosol or surface activity model.
The second part shows that self-assembly causes only minor effects on cloud droplet activation but significantly impacts earlier stages of droplet growth. These mainly manifest as differences in water uptake at a given air humidity (RH < 100 %). The droplet water content affects the growth rates and optical properties. Self-assembly could therefore impact atmospheric visibility and climate-relevant interactions between the droplets and radiation.
Last updated: 3.4.2025