10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Investigation of Seasonal Sources of Secondary Organic Aerosol in Switzerland Using Extractive Electrospray Ionization Time-Of-Flight Mass Spectrometry (EESI-TOF)
GIULIA STEFENELLI, Veronika Pospisilova, Felipe Lopez-Hilfiker, Kaspar Rudolf Dällenbach, Martin Rigler, Christoph Hueglin, Yandong Tong, Urs Baltensperger, Andre S.H. Prévôt, Jay G. Slowik, Paul Scherrer Institut
Abstract Number: 1147 Working Group: Source Apportionment
Abstract Anthropogenic and biogenic emissions contain large amounts of volatile organic compounds (VOCs) which may undergo photochemical aging to yield secondary organic aerosol (SOA). The magnitude of SOA production from different sources remains highly uncertain, hindering the estimation of the contribution of these sources to the total ambient organic aerosol. Measurement techniques with high time resolution and chemical specificity are thus urgently needed. PSI has recently developed a novel extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF), which enables real-time chemical analysis of atmospheric particles without thermal decomposition or ionization-induced fragmentation. We present results from the first field deployments of the EESI-TOF. Measurements were performed during summer 2016 at a well-characterized urban site in Zurich and subsequently in the Swiss alpine valley (Magadino) during winter 2017. Positive matrix factorization (PMF) analysis of EESI-TOF data yielded several organic aerosol factors related to primary and secondary emissions. Factors were separated according to different mass spectral fingerprints and aging processes. Some of the retrieved factors correlated strongly with reasonable counterparts from AMS PMF analysis while others provided previously inaccessible insight into sources and ambient processing. Primary factors related to cooking processes, traffic and cigarette smoke emissions were obtained. The retrieved secondary factors during summer in Zurich were strongly influenced by biogenic emissions, and exhibited significant day/night differences. Factors dominating during daytime showed predominantly ions characteristic of monoterpene and sesquiterpene oxidation while the night-time factor included less oxygenated and more volatile terpene oxidation products, as well as organonitrates which were likely derived from NO3 radical oxidation of monoterpenes. These results contrast with measurements in a Swiss alpine valley during winter, where wood burning emissions were dominant and the retrieved factor mass spectra are compared to spectra generated from smog chamber aging of emissions from residential wood burning appliances.