10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Real Time Source Quantification of Secondary Organic Aerosol in Zurich Using Extractive Electrospray Ionization Time-Of-Flight Mass Spectrometry (EESI-TOF)
LU QI, Giulia Stefenelli, Veronika Pospisilova, Yandong Tong, Christoph Hueglin, Martin Rigler, Xinlei Ge, Mindong Chen, Urs Baltensperger, Andre S.H. Prévôt, Jay G. Slowik, Paul Scherrer Institute
Abstract Number: 999 Working Group: Source Apportionment
Abstract Real-time, in situ molecular composition measurements of the organic fraction of fine particulate matter (PM2.5) remains challenging, hindering a full understanding of the climate impacts and health effects of PM2.5. Unlike primary organic aerosol (POA), which has been studied extensively and relatively well characterized, the source contributions and mechanistic studies of secondary organic aerosol (SOA), which typically dominates OA, remains unclear due in large part to the limitations of existing measurement systems. In this study, a new extractive electrospray ionization time-Of-flight mass spectrometer (EESI-TOF), which OA composition on a near-molecular level without fragmentation or thermal decomposition, was deployed to measure OA in downtown Zurich, Switzerland, during winter 2017. Positive matrix factorization (PMF) and the Multilinear Engine (ME-2) were applied to separate the detected SOA species into several factors, relating these factors to POA and SOA sources. Moreover, some of the factors agreed well with factors retrieved from PMF analysis of the mass spectra of a co-located Aerodyne AMS.
Eleven factors were selected to explain the EESI-TOF data, including six SOA factors (two aged emissions, one aged pollution event, two photo chemistry factors, one nitrogen containing factor), four POA factors (cooking, two special events, one local wooding burning emission) and one factor dominated by nicotine. The two local aged emission factors had a negative correlation with temperature, the temporal variation of one factor is distinct at low temperature and another one factor varied at high temperature. The factor enhanced at lower temperatures contains compounds with lower carbon and oxygen numbers, and correlates with phthalic acid (C8H6O4) and glutaconic acid (C5H6O4). The photo-chemistry factors are similar to laboratory spectra generated from oxidation of -pinene by ozone and hydroxyl radicals. The local wooding burning emission factor was related to domestic wood burning for heat and peaks from 18:00 to 6:00 o’clock, correlating with levoglucosan (C6H10O5) and the hydroperoxide (C8H12O6). Also, nitrocatechol (C7H7NO4), suggested to be another tracer of secondary biomass burning, exhibited a similar diurnal pattern as local wood burning emission factor with a nocturnal peak. The nicotine factor correlates well with a cigarette smoke factor retrieved from the AMS PMF, as well the C5H10N+ ion identified as a cigarette smoke tracer. These findings improve our understanding of SOA sources and production, highlighting in particular the complexities of biomass burning evolution in the atmosphere.