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

摘要

The oxidation of biogenic volatile organic compounds(VOCs) represents a substantial source of secondary organic aerosol (SOA) inthe atmosphere. In this study, we present online measurements of themolecular constituents formed in the gas and aerosol phases during oxidation in the Cambridge Atmospheric Simulation Chamber (CASC). Wefocus on characterising the performance of extractive electrospray ionisation(EESI) mass spectrometry (MS) for particle analysis. A number of new aspectsof EESI-MS performance are considered here. We show that relativequantification of organic analytes can be achieved in mixed organic–inorganicparticles. A comprehensive assignment of mass spectra for -pinenederived SOA in both positive and negative ion modes is obtained using anultra-high-resolution mass spectrometer. We compare these online spectra toconventional offline ESI-MS spectra and find good agreement in terms of the compoundsidentified, without the need for complex sample work-up procedures. Under ourexperimental conditions, EESI-MS signals arise only from particle-phaseanalytes. High-time-resolution (7 min) EESI-MS spectra are compared withsimulations from the near-explicit Master Chemical Mechanism (MCM) for arange of reaction conditions. We show that MS peak abundances scale withmodelled concentrations for condensable products (pinonic acid, pinic acid,OH-pinonic acid). Relative quantification is achieved throughout SOAformation as the composition, size and mass (5–2400 µg m)of particles is evolving. This work provides a robust demonstration of theadvantages of EESI-MS for chamber studies over offline ESI-MS (timeresolution, relative quantification) and over online techniques(molecular information).