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

Peter J Gallimore,Markus Kalberer,Brendan M Mahon,Chiara Giorio

doi:10.5194/acp-17-14485-2017

Peter J Gallimore, Markus Kalberer + Show 2 more

Open Access

https://doi.org/10.5194/acp-17-14485-2017

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Abstract

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 (7 min) 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 (5–2400 µg m−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).

Highlights

Airborne particulate matter has significant impacts on global climate (Hallquist et al, 2009), human health (Dominici et al, 2006) and visibility (Husar et al, 1981)
To enable presentation of data as measured, including “raw” electrospray ionisation (EESI)-mass spectrometry (MS) time series, wall-loss correction was not attempted and we focus primarily on the initial time following ozone introduction, where aerosol production will dominate over loss to the chamber walls
We investigate the possible impact of inorganic salts on the EESI-MS peak abundance of organic ions in mixed aerosol particles

Summary

Introduction

Airborne particulate matter has significant impacts on global climate (Hallquist et al, 2009), human health (Dominici et al, 2006) and visibility (Husar et al, 1981). Organic compounds typically comprise around 50 % of submicron aerosol mass (Jimenez et al, 2009). Most of this is secondary and biogenic in origin (Hallquist et al, 2009); the oxidation of biogenic volatile organic compounds (VOCs) such as monoterpenes and isoprene represents a major source of atmospheric secondary organic aerosol (SOA) (Kroll and Seinfeld, 2008; Ziemann and Atkinson, 2012). SOA formation processes remain highly uncertain and this is regarded as a major weakness in the current understanding and model representation of atmospheric aerosols (Boucher et al, 2013). The chemistry involved is complex, and the range of organic compounds present in the atmosphere is extremely diverse (Goldstein and Galbally, 2007). Understanding how SOA components form and react is a conceptual and analytical challenge (Noziere et al, 2015)

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