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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 23 | Copyright
Atmos. Chem. Phys., 17, 14485-14500, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Dec 2017

Research article | 06 Dec 2017

Online molecular characterisation of organic aerosols in an atmospheric chamber using extractive electrospray ionisation mass spectrometry

Peter J. Gallimore1, Chiara Giorio1,a, Brendan M. Mahon1, and Markus Kalberer1 Peter J. Gallimore et al.
  • 1Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
  • anow at: Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 13 35131 Padua, Italy

Abstract. The oxidation of biogenic volatile organic compounds (VOCs) represents a substantial source of secondary organic aerosol (SOA) in the atmosphere. In this study, we present online measurements of the molecular constituents formed in the gas and aerosol phases during α-pinene oxidation in the Cambridge Atmospheric Simulation Chamber (CASC). We focus on characterising the performance of extractive electrospray ionisation (EESI) mass spectrometry (MS) for particle analysis. A number of new aspects of EESI-MS performance are considered here. We show that relative quantification of organic analytes can be achieved in mixed organic–inorganic particles. A comprehensive assignment of mass spectra for α-pinene derived SOA in both positive and negative ion modes is obtained using an ultra-high-resolution mass spectrometer. We compare these online spectra to conventional offline ESI-MS spectra and find good agreement in terms of the compounds identified, without the need for complex sample work-up procedures. Under our experimental conditions, EESI-MS signals arise only from particle-phase analytes. High-time-resolution (7min) EESI-MS spectra are compared with simulations from the near-explicit Master Chemical Mechanism (MCM) for a range of reaction conditions. We show that MS peak abundances scale with modelled concentrations for condensable products (pinonic acid, pinic acid, OH-pinonic acid). Relative quantification is achieved throughout SOA formation as the composition, size and mass (5–2400µgm−3) of particles is evolving. This work provides a robust demonstration of the advantages of EESI-MS for chamber studies over offline ESI-MS (time resolution, relative quantification) and over hard online techniques (molecular information).

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This work helps to better understand the potential climate and health impacts of airborne aerosol particles. We applied a new technique to provide a diagnostic fingerprint of the organic compounds present in aerosols. We followed changes in this fingerprint over time in lab experiments which mimic the conversion of plant emissions into aerosols. Our results compare well with computer simulations of the reactions and we conclude that the technique merits continuing use and development in future.
This work helps to better understand the potential climate and health impacts of airborne...