Probing the chemical composition of atmospheric aerosols by observation of their physico-chemical properties

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http://urn.fi/URN:ISBN:978-952-7091-64-7
Title: Probing the chemical composition of atmospheric aerosols by observation of their physico-chemical properties
Author: Hong, Juan
Contributor: University of Helsinki, Faculty of Science, Department of Physics
Thesis level: Doctoral dissertation (article-based)
Abstract: Atmospheric aerosol particles affect the global climate as well as human health and air quality. To better understand the climate effect of these aerosols, detailed information on their number size distribution, particle phase chemical composition as well as on their other physicochemical properties in the atmosphere is needed. In this thesis, a Volatili-ty-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) system was ap-plied in both field and laboratory environments to measure the physico-chemical proper-ties, i.e. hygroscopicity and volatility, of atmospheric particles directly. This helped us to get indirect information on the aerosol chemical composition and made it possible to in-vestigate the chemistry of some specific constituents (i.e. organosulfates).The hygroscopicity of boreal forest particles increased from the morning until afternoon. In case of accumulation and Aitken mode particles, this is probably connected with the diurnal variation of the ratio of sulfate to organic matter and the oxidation level of the or-ganic matter in the particle phase. For nucleation mode particles, it was found that the more sulfuric acid in the gas phase, the more hygroscopic these particles were. Using the kinetic evaporation model to interpret the evaporation of boreal forest aerosols measured by the VH-TDMA system, the model was found to be sensitive to the vaporiza-tion enthalpies of the organic compounds (ΔHVAP). To best approximate the measurement data, considerably low ΔHVAP values of around 80 kJ mol-1 were applied in the model. In addition, semi-volatile and low-volatile organic mass fractions were independently deter-mined by applying Positive Matrix Factorization (PMF) to High-Resolution Aerosol Mass Spectrometer (HR-AMS) data. The agreement between the model- and PMF-derived re-sults was reasonable when ΔHVAP of 80 kJ mol-1 was used for all organic groups in the model. The thesis also showed that there was always hygroscopic material remaining in the particles at different heating temperatures, even at 280 °C, indicating that the non-volatile residual might consist of some highly-oxidized organic compounds. This thesis suggests that interactions between inorganic and organic compounds in the particle phase might alter the effective physico-chemical properties (e.g. hygroscopicity and volatility) of each compound from their intrinsic values in their pure form. These in-teractions between the organic and inorganic compounds, which were important for the studied mixtures, in both laboratory-generated and ambient aerosols, might be non-linear and species/system dependent.Atmospheric aerosol particles affect the global climate as well as human health and air quality. To better understand the climate effect of these aerosols, detailed information on their number size distribution, particle phase chemical composition as well as on their other physicochemical properties in the atmosphere is needed. In this thesis, a Volatili-ty-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) system was ap-plied in both field and laboratory environments to measure the physico-chemical proper-ties, i.e. hygroscopicity and volatility, of atmospheric particles directly. This helped us to get indirect information on the aerosol chemical composition and made it possible to in-vestigate the chemistry of some specific constituents (i.e. organosulfates). The hygroscopicity of boreal forest particles increased from the morning until afternoon. In case of accumulation and Aitken mode particles, this is probably connected with the diurnal variation of the ratio of sulfate to organic matter and the oxidation level of the or-ganic matter in the particle phase. For nucleation mode particles, it was found that the more sulfuric acid in the gas phase, the more hygroscopic these particles were. Using the kinetic evaporation model to interpret the evaporation of boreal forest aerosols measured by the VH-TDMA system, the model was found to be sensitive to the vaporiza-tion enthalpies of the organic compounds (ΔHVAP). To best approximate the measurement data, considerably low ΔHVAP values of around 80 kJ mol-1 were applied in the model. In addition, semi-volatile and low-volatile organic mass fractions were independently deter-mined by applying Positive Matrix Factorization (PMF) to High-Resolution Aerosol Mass Spectrometer (HR-AMS) data. The agreement between the model- and PMF-derived re-sults was reasonable when ΔHVAP of 80 kJ mol-1 was used for all organic groups in the model. The thesis also showed that there was always hygroscopic material remaining in the particles at different heating temperatures, even at 280 °C, indicating that the non-volatile residual might consist of some highly-oxidized organic compounds. This thesis suggests that interactions between inorganic and organic compounds in the particle phase might alter the effective physico-chemical properties (e.g. hygroscopicity and volatility) of each compound from their intrinsic values in their pure form. These in-teractions between the organic and inorganic compounds, which were important for the studied mixtures, in both laboratory-generated and ambient aerosols, might be non-linear and species/system dependent.
URI: URN:ISBN:978-952-7091-64-7
http://hdl.handle.net/10138/168501
Date: 2016-11-24
Subject: atmospheric sciences
Rights: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.


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