The molecular characterization of secondary organic aerosol (SOA) has been a topic of interest in atmospheric chemistry for several decades due to its importance in air quality, human health, and global climate. Analysis of the composition is often carried out by collecting the particles offline and then applying mass spectrometry using various ionization methods such as electrospray (ESI). Online methods without prior collection have also been widely used, where vaporization and ionization are accomplished using the input of energy using heat, lasers, and voltage.<br/>We report here for the first-time spontaneous ionization of SOA particles with the assistance of a matrix compound, but without the addition of energy via heat, light or electron impact. SOA particles were generated from ozonolysis of α-pinene in a flow tube. The SOA by itself produces only small signals without a traditional ionization source. However, products were detected with a high signal-to-noise level in the presence of an added matrix compound.<br/>Experiments were performed with varying α-pinene concentrations. The signal intensities of matrix compounds and SOA change systematically with a change in the α-pinene concentration and SOA concentration. Spectra generated with the assistance of a matrix are compared to those from well-known mass spectrometric techniques, such as direct analysis in real time (DART) mass spectrometry and ESI-MS. The matrix compound does not change the masses that are observed in the SOA and show evidence of products commonly observed in this reaction such as pinonaldehyde, pinic acid, pinonic acid, norpinonic acid, and pinalic acid. In addition, high molecular weight compounds, which can be subject to decomposition by heat or high voltage are detected with relatively high signal intensities. The mechanism of this spontaneous ionization of SOA with matrix assistance is currently under investigation, but it potentially provides an approach that minimizes alteration of the SOA during analysis.

On-the-fly analysis of the chemical composition of secondary organic aerosol particles using a novel ionization method

ACS Spring 2022

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