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Thermally induced evaporation of organic aerosol from alpha-pinene ozonolysis

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Title: Thermally induced evaporation of organic aerosol from alpha-pinene ozonolysis
Author(s): Häkkinen, Ella
Contributor: University of Helsinki, Faculty of Science, none
Discipline: none
Degree program: Master's Programme in Atmospheric Sciences
Specialisation: Aerosol Physics
Language: English
Acceptance year: 2020
Abstract:
Atmospheric aerosol particles affect Earth’s radiation balance, human health and visibility. Secondary organic aerosol (SOA) contributes a significant fraction to the total atmospheric organic aerosol, and thus plays an important role in climate change. SOA is formed through oxidation of volatile organic compounds (VOCs) and it consists of many individual organic compounds with varying properties. The oxidation products of VOCs include highly oxygenated organic molecules (HOM) that are estimated to explain a large fraction of SOA formation. To estimate the climate impacts of SOA it is essential to understand its properties in the atmosphere. In this thesis, a method to investigate thermally induced evaporation of organic aerosol was developed. SOA particles were generated in a flow tube from alpha-pinene ozonolysis and then directed into a heated tube to initiate particle evaporation. The size distribution of the particles was measured with parallel identification of the evaporated HOM. This method was capable of providing information of SOA evaporation behaviour and the particle-phase composition at different temperatures. Mass spectra of the evaporated HOM and particle size distribution data were analyzed. The obtained results suggest that SOA contains compounds with a wide range of volatilities, including HOM monomers, dimers and trimers. The volatility behaviour of the particulate HOM and their contribution to SOA particle mass was studied. Furthermore, indications of particle-phase reactions occurring in SOA were found.
Keyword(s): SOA evaporation volatility VOC ozonolysis HOM


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