Application of data mining techniques to indoor and outdoor air studies

Humans emit a wide range of volatile organic compounds (VOCs). These molecules can be emitted via breath and skin and can be from endogenous or exogenous sources. The main breath gases besides N2 and O2 include CO2, acetone and isoprene and are mainly endogenously produced via metabolic pathways. Exogenously emitted molecules comprise methanol from the digestion of fruits and molecules such as monoterpenes and siloxanes used in hygiene products. The study of these human-made emissions is important for the detection of biomarkers for illnesses as well as for the estimation of the contribution of human emission to indoor and outdoor environments. The measurement of volatile organic compounds in indoor and outdoor studies was performed with a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). Closed spaces with controlled ventilation such as the showroom of a cinema allows the estimation of emission rates from a large group of people averaging over individual behaviour and habits. Factors such at diet or use of hygiene products depict the largest source for uncertainty in estimating the emission rates. On a much smaller scale the emission of human-emitted molecules varies with the emotional state. In the cinema showroom the screening of a film induces the same stimuli on a large amount of people and reproducible patterns in the time series of VOCs were found. The combination of the measured time series of VOCs and film scene annotations and the application of data mining techniques allows the discovery of relationships between the emission of VOC and specific scenes displayed in the film. Most of the world population now lives in urban areas and humans spend most of their time in indoor environments. In closed spaces people are exposed to volatile organic compounds which can occur in much higher abundances than outside. Since some of the VOCs can have adverse health impacts on humans it is important to estimate sources of VOCs in indoor environments such as emissions from furniture, human emissions and VOCs being transported from outside into these closed spaces. These outside sources are strongly dependent on biogenic sources such as emission of plants and vegetation and anthropogenic sources for example through combustion processes. Human emission can significantly impact the air chemistry in urban areas but on a global scale they only contribute a small amount to the total emission of VOCs. The behaviour and fate of a VOC is affected by many factors such as temperature, relative humidity and the origin of the air mass. To study the atmospheric chemistry of these VOCs, measurement campaigns were conducted in different locations lasting over 4 weeks. Typically, different meteorological conditions are faced during this measurement period. In order understand the atmospheric behaviour of a VOC it is useful to partition these time series in periods of similar meteorological conditions. To do this objectively a pattern identification method was applied. The data-driven investigation of the time series provided useful insights in the chemistry behind the VOCs. The proton transfer reaction time-of-flight mass spectrometer is able to capture hundreds of VOCs in real time and therefore the combination of this instrument with data mining techniques has huge potential for future research projects