Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> A combination of online and offline mass spectrometric techniques was used to characterize the chemical composition of secondary organic aerosol (SOA) generated from the photooxidation of <span class="inline-formula"><i>α</i></span>-pinene in an atmospheric simulation chamber. The filter inlet for gases and aerosols (FIGAERO) coupled with a high-resolution time-of-flight iodide chemical ionization mass spectrometer (I<span class="inline-formula"><sup>−</sup></span>-ToF-CIMS) was employed to track the evolution of gaseous and particulate components. Extracts of aerosol particles sampled onto a filter at the end of each experiment were analysed using ultra-performance liquid chromatography ultra-high-resolution tandem mass spectrometry (LC-Orbitrap MS). Each technique was used to investigate the major SOA elemental group contributions in each system. The online CIMS particle-phase measurements show that organic species containing exclusively carbon, hydrogen, and oxygen (CHO group) dominate the contribution to the ion signals from the SOA products, broadly consistent with the LC-Orbitrap MS negative mode analysis, which was better able to identify the sulfur-containing fraction. An increased abundance of high-carbon-number (<span class="inline-formula"><i>n</i><sub>C</sub>≥16</span>) compounds additionally containing nitrogen (CHON group) was detected in the LC-Orbitrap MS positive ionization mode, indicating a fraction missed by the negative-mode and CIMS measurements. Time series of gas-phase and particle-phase oxidation products provided by online measurements allowed investigation of the gas-phase chemistry of those products by hierarchical clustering analysis to assess the phase partitioning of individual molecular compositions. The particle-phase clustering was used to inform the selection of components for targeted structural analysis of the offline samples. Saturation concentrations derived from nearly simultaneous gaseous and particulate measurements of the same ions by FIGAERO-CIMS were compared with those estimated from the molecular structure based on the LC-Orbitrap MS measurements to interpret the component partitioning behaviour. This paper explores the insight brought to the interpretation of SOA chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical techniques.

Highlights

  • Secondary organic aerosol (SOA) makes a significant contribution to atmospheric aerosols, which have an important influence on climate and adverse impact on human health and air quality (Nel, 2005; Kroll and Seinfeld, 2008; Hallquist et al, 2009)

  • This paper explores the insight brought to the interpretation of secondary organic aerosol (SOA) chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical 45 techniques

  • The purpose of this paper is to explore the benefits of combinatorial LC-Orbitrap MS and 115 FIGAERO-CIMS analytical techniques to investigate SOA chemical composition, demonstrating the power of this combination from a technical perspective

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Summary

Introduction

Secondary organic aerosol (SOA) makes a significant contribution to atmospheric aerosols, which have an important influence on climate and adverse impact on human health and air quality (Nel, 2005; Kroll and Seinfeld, 2008; Hallquist et al, 2009). As a result of the various VOCs involved and the complexity of the oxidation 60 processes, oxidation products span a wide range of molecular composition and physiochemical properties (Ma et al, 2008; Laj et al, 2009; Mentel et al, 2015; Mutzel et al, 2015; Mohr et al, 2019). Such chemical complexity poses a major challenge in the molecular characterization of SOA

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