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Doctoral defence of Zijun Li, MSc, 29.6.2022: Factors controlling the evaporation of secondary organic aerosol particles 

The doctoral dissertation in the field of Applied Physics will be examined at the Faculty of Science and forestry, Kuopio Campus and online. 

What is the topic of your doctoral research? Why is it important to study the topic? 

Large amounts of aerosol particles are present in the air that we breath in every day. The aerosol particles have important effects on air quality, human health, and the global climate. The majority of aerosol particles is formed from the gas-phase oxidation of volatile organic compounds (VOCs), referred to as secondary organic aerosol (SOA) particles. Once formed, the SOA particles can be subjected to evaporation, if the air parcel is diluted with clean air or temperature increases. During evaporation, organic molecules evaporate from the particle into the gas phase, and this changes the composition and properties of the SOA particles. However, there is still very limited knowledge about the factors determining the evaporation processes of SOA particles.

What are the key findings or observations of your doctoral research?

This thesis consists of five studies focusing on the evaporation of SOA particles under different atmospheric-relevant conditions in the Aerosol Physics Lab. The SOA particles were generated by oxidizing representative VOCs in boreal forest and even real tree emissions. By state-of-art instruments, modelling, and statistical approaches, we find that the evaporation of SOA particles is jointly affected by physical and chemical factors. Particle viscosity and volatility are the two principal physical factors controlling the evaporation of SOA particles. Notably, these two physical factors are highly dependent on the particle constituents which keep evolving not only due to evaporation but also due to chemical interactions.

How can the results of your doctoral research be utilised in practice?

The investigated particle evaporation is not unique to certain laboratory conditions. It can commonly happen under the non-equilibrium conditions between the gas and particle phases in the outdoor and indoor settings. Therefore, evaporation should be taken into account when we consider the composition and properties of aerosol particles in the air.

What are the key research methods and materials used in your doctoral research?

The thesis work has been successfully carried out with the use of state-of-art instruments, modelling, and statistical approaches. It has produced a high yield of scientific publications on several impactful peer-review journals.

The doctoral dissertation of Zijun Li, MSc, entitled Factors controlling the evaporation of secondary organic aerosol particles, will be examined at the Faculty of Science and Forestry. The Opponent will be Group leader, Docent Thomas Mentel, Forschungszentrum Jülich, Germany, and the Custos will be Professor Annele Virtanen, University of Eastern Finland. Language of the public defence is English.

For more information, please contact:

Zijun Li, zijun.li@uef.fi, Twitter: rexzjli