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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Feb 2019

Research article | 04 Feb 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometry (EESI-TOF): Part II, biomass burning influences in winter

Lu Qi1,2, Mindong Chen2, Giulia Stefenelli1, Veronika Pospisilova1, Yandong Tong1, Amelie Bertrand1, Christoph Hueglin3, Xinlei Ge2, Urs Baltensperger1, André S. H. Prévôt1, and Jay G. Slowik1 Lu Qi et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), Switzerland
  • 2Nanjing University of Information Science & Technology, 21000 Nanjing, China
  • 3EMPA, Dübendorf 8600, Switzerland

Abstract. Real-time, in situ molecular composition measurements of the organic fraction of fine particulate matter (PM2.5) remain challenging, hindering a full understanding of the climate impacts and health effects of PM2.5. In particular, the thermal decomposition and ionization-induced fragmentation affecting current techniques has limited a detailed investigation of secondary organic aerosol (SOA), which typically dominates OA. Here we deploy a novel extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) during winter 2017 in downtown Zurich, Switzerland, which overcomes these limitations, together with an Aerodyne high resolution time of flight aerosol mass spectrometer (HR-TOF-AMS) and supporting instrumentation. Positive matrix factorization (PMF) implemented within the Multilinear Engine (ME-2) was applied to the EESI-TOF data to quantify the primary and secondary contributions to OA. An 11-factor solution was selected as the best representation of the data, including 5 primary and 6 secondary factors. Primary factors showed influence from cooking, cigarette smoke, biomass burning (2 factors) and a special local unknown event occurred only during two nights. Secondary factors were affected by biomass burning (3 factors, distinguished by temperature and/or wind direction), organonitrates, monoterpene oxidation, and undetermined regional processing, in particular the contributions of wood combustion. While the AMS attributed slightly over half the OA mass to SOA but did not identify its source, the EESI-TOF showed that most (> 70 %) of the SOA derived from biomass burning. Together with significant contributions from less aged biomass burning factors identified by both AMS and EESI-TOF, this firmly establishes biomass burning as the single most important contributor to OA mass at this site during winter. High correlation was obtained between EESI-TOF and AMS PMF factors where specific analogues existed, as well as between total signal and POA/SOA apportionment. This suggests the EESI-TOF apportionment can be approximately taken at face value, despite ion-by-ion differences in relative sensitivity. The apportionment of specific ions measured by the EESI-TOF (e.g. levoglucosan, nitrocatechol, and selected organic acids), and utilize a cluster analysis-based approach to identify key marker ions for the EESI-TOF factors are investigated. The interpretability of the EESI-TOF results and improved source separation relative to the AMS within this pilot campaign validate the EESI-TOF as a promising approach to source apportionment and atmospheric composition research.

Lu Qi et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Lu Qi et al.
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Publications Copernicus
Short summary
Current understanding of OA sources is limited by the chemical resolution of existing real-time measurement technology. We describe the first wintertime deployment of a novel extractive electrospray ionization time-of-flight mass spectrometer, which provides near-molecular OA measurements with high time resolution. We show that biomass combustion strongly influences winter OA. Via factor analysis, aging-dependent signatures and time contributions of biomass combustion-derived OA are resolved.
Current understanding of OA sources is limited by the chemical resolution of existing real-time...