PROTON-TRANSFER-REACTION MASS SPECTROMETER MEASUREMENTS OF VOLATILE ORGANIC COMPOUND MIXTURES, AND SECONDARY ORGANIC AEROSOL FORMATION FROM THE PHOTOCHEMISTRY OF THESE COMPOUNDS

Volatile organic compounds (VOCs) are emitted from biogenic and anthropogenic sources into the atmosphere, thus they are truly ubiquitous. VOCs play a major role in atmospheric chemistry, and their oxidation processes can lead to the formation of a secondary organic aerosol (SOA). SOA, a major component of atmospheric aerosols, is not only detrimental to human health, but it also affects the climate and air quality. When VOCs are oxidized in the atmosphere, this leads to the formation of oxidation products with lower vapor pressure and higher polarity than the original reactants. Eventually, oxidation processes result in the formation of reaction products that have a low enough vapor pressure to condense on existing aerosol particles, i.e. the formation of SOA occurs. The chemical and physical processes linked to SOA formation are complex and diverse; they depend on which VOCs are forming the SOA and on the conditions under which SOA formation takes place. It is vital to understand the mechanisms underpinning the formation of SOA under specific conditions, as this will make it possible to conduct more realistic climate modelling, when future aerosol loadings in different environments are predicted. The main objective of this thesis was to provide new information about the photochemical SOA formation from different mixtures of VOCs. In order to achieve this aim, laboratory experiments were conducted with VOC mixtures that were exposed to OH-radicals and the formation of the SOA was examined. VOCs were measured using a proton-transfer-reaction mass spectrometer with a time-of-flight mass analyzer (PTR-ToF-MS) that can continuously measure atmospheric trace VOCs with high time and mass resolution. However, PTR-ToF-MS suffers from some limitations, including the fragmentation of the measured VOCs. Hence, before SOA formation from VOC mixtures was explored, the PTRToF-MS product ion distributions of several terpenoid compounds were studied to reduce the uncertainty related to the PTR-ToF-MS quantification of VOCs. In this thesis studied VOC mixtures were emitted by real emission sources i.e. Scots pines, pellet boiler, and gasoline vehicle. Furthermore, controlled laboratory experiments were conducted with real anthropogenic emissions sources to clarify the interactions between biogenic and anthropogenic emissions. Examining the interactions between these emissions and assessing their implications for aerosol production require the use of real anthropogenic emission sources since this is the only way to adequately obtain a relevant level of chemical diversity in laboratory studies. The studies with real anthropogenic emission sources made it possible to more precisely explore the complex real-life interactions between the biogenic and anthropogenic emissions occurring in the atmosphere. This thesis adds important information about the PTR-ToF-MS product ion distributions of several terpenoid compounds. These results will improve analytical quantification of terpenoid measurements. Furthermore, the results of this thesis clarify SOA formation from different VOC mixtures under controlled laboratory conditions. This thesis demonstrates that the damage caused by bark feeding herbivores change VOC emissions from Scots pines, and thus they alter Scots pine SOA mass yields. In addition, the results presented in this thesis show that the two studied anthropogenic emission sources, pellet boiler and gasoline vehicle, both generate an organic aerosol into the atmosphere, but the form of this aerosol is different between these two sources, i.e. with gasoline vehicles, the SOA dominates the organic aerosol loading, while with pellet boilers, the primary OA (POA) is the main contributor to the total organic aerosol loading emitted into the atmosphere. Finally, this thesis demonstrates that biogenic SOA formation is suppressed in the presence of anthropogenic emissions, and there is more than one factor affecting this suppression. Overall, the results of this thesis increase our knowledge about VOC emissions from different sources and SOA formation from the photochemistry of these compounds under different conditions.