Discrimination and geo-spatial mapping of atmospheric VOC sources using full scan direct mass spectral data collected from a moving vehicle†
Volatile and semi-volatile organic compounds (S/VOCs) are ubiquitous in the environment, come from a wide variety of anthropogenic and biogenic sources, and are important determinants of environmental and human health due to their impacts on air quality. They can be continuously measured by direct mass spectrometry techniques without chromatographic separation by membrane introduction mass spectrometry (MIMS) and proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). We report the operation of these instruments in a moving vehicle, producing full scan mass spectral data to fingerprint ambient S/VOC mixtures with high temporal and spatial resolution. We describe two field campaigns in which chemometric techniques are applied to the full scan MIMS and PTR-ToF-MS data collected with a mobile mass spectrometry lab. Principal Component Analysis (PCA) has been successfully employed in a supervised analysis to discriminate VOC samples collected near known VOC sources including internal combustion engines, sawmill operations, composting facilities, and pulp mills. A Gaussian mixture model and a density-based spatial clustering of application with noise (DBSCAN) algorithm have been used to identify sample clusters within the full time series dataset collected and we present geospatial maps to visualize the distribution of VOC sources measured by PTR-ToF-MS.