Observations of volatile organic compound concentrations and fluxes from different ecosystems

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Title: Observations of volatile organic compound concentrations and fluxes from different ecosystems
Author: Schallhart, Simon
Contributor: University of Helsinki, Faculty of Science, Department of Physics, Division of Atmospheric Sciences
Publisher: Helsingin yliopisto
Date: 2017-11-17
Language: en
URI: http://urn.fi/URN:ISBN:978-952-7091-93-7
Thesis level: Doctoral dissertation (article-based)
Abstract: Volatile organic compounds (VOCs) are emitted in vast amounts from biogenic and anthropogenic sources. They influence air quality and thereby human health. In the atmosphere VOCs can be oxidized to form compounds with lower volatility and form aerosol particles, which can affect the climate. The basis of this thesis are VOC measurements with a proton transfer reaction time of flight (PTR-TOF) mass spectrometer. Its suitability for measuring the volatile organic compound spectra with 10 Hz resolution made it possible to calculate VOC exchange from different ecosystems with the eddy covariance method. The reliability of this method was determined by comparisons with other well-established ecosystem scale flux methods and upscaled emissions from leaf cuvettes. The measurements in this work resulted in the quantification of the total exchange in a broadleaf forest in Bosco Fontana, Italy and a conifer forest in Hyytiälä, Finland. By using a new automated method, 29 VOCs with exchange were measured in Bosco Fontana and 25 VOCs in Hyytiälä. These two ecosystems differ as the major terpene emissions are isoprene for the oak forest and monoterpenes for the Scots pine forest. Additional to isoprene and the monoterpenes, methanol, acetonitrile, acetaldehyde, acetone and acetic acid fluxes were measured at both sites. To identify the measured signals and determine error sources, fragmentation, possible losses and sources of different compounds were investigated. In a research stable in Switzerland, amine measurements and calibrations were performed to identify the source of trimethylamine. During measurements in Hyytiälä, the anthropogenic source of the measured butene was determined and a memory effect of acetic acid in our measurement setup was discovered. Overall, this thesis addresses the potential of concentration and ecosystem exchange measurements using a PTR-TOF and challenges which arise during the measurements and data analysis. The obtained results are useful insights into the precursors and amplifiers (amines) of new particle formation and aerosol growth. Furthermore, the recorded direct total ecosystem exchange measurements expand the limited data available and can be used to improve and validate emission models.N/A
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