Browsing by Subject "atmospheric Science"

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  • Garmash, Olga (Helsingin yliopisto, 2020)
    Aerosol particles present in the atmosphere can affect climate, visibility and human health. Low-volatility vapours form a large fraction of aerosol particles through gas-to-particle conversion. Our knowledge of chemical composition of low-volatility vapours has greatly improved in recent years with the development of more sensitive analytical tools. It is now widely accepted that in addition to sulphuric acid (SA), bases (e.g., ammonia and amines) and ions, which have been identified already a decade ago, highly oxygenated organic molecules (HOM) are crucial for the first steps of particle formation and growth. The main goal of this thesis was to identify which organic and inorganic vapours contribute to atmospheric particle formation in different environments. In this thesis, I aimed to 1) determine the role of HOM and SA in forming clusters and particles in the boreal forest; 2) identify the aerosol precursor vapours in a megacity; and 3) determine HOM composition and yield in laboratory oxidation of selected compounds emitted from these two environments. The primary tool that I used for investigating the vapours and clusters was an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF). It was applied to detect either natural ions or, when equipped with a nitrate chemical ionisation, electrically neutral vapours. To achieve the aims of the thesis, we conducted measurements at a boreal forest station in Finland and in Shanghai, China. In addition, we performed laboratory experiments in a flow reactor and an atmospheric simulation chamber. In the boreal forest, we observed that neutral HOM and SA concentrations influenced the composition of natural negatively charged clusters. Specifically, the ratio between HOM and SA controlled which chemical pathway initiated charged particle formation at this site. In contrast, by comparing our Shanghai observations to laboratory studies, we could conclude that SA-dimethylamine clustering initiated the formation of particles and their initial growth. In the laboratory experiments, we studied HOM formation in oxidation of sesquiterpenes and aromatics, which are emitted from the boreal forest and human activity, respectively. Both experiments showed that HOM formed at high yields. In aromatic oxidation, multi-step oxidation reactions were very important in HOM formation. The results of this thesis increased our understanding of vapours that participate in secondary aerosol formation in the atmosphere. Finally, the results underlined the utmost importance of combining ambient investigations with laboratory experiments in atmospheric science.