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Molecular Structure Characterization of Nanoparticles Formed from the Ozonolysis of Alpha-Pinene
ADAM THOMAS, Véronique Perraud, Michelia Dam, James Smith, University of California, Irvine
Abstract Number: 33
Working Group: Instrumentation and Methods
Abstract
It is known that a major source of atmospheric aerosol originates from the oxidation of volatile organic compounds, of which monoterpenes represent an important class. In particular, the α-pinene + O3 system has been widely studied, in large part due to its role in new particle formation. However, there remains much to be learned about the distribution and structural identities of the products of this reaction, particularly as they are observed in the early stages of particle growth. It has been shown in recent years that ultra-high resolution mass spectrometry (HRMS) using an orbitrap mass analyzer features several key advantages over other more widely used approaches applied in the analysis of organic aerosol, including a superior mass resolving power (up to 140,000) and tandem mass spectrometry (MS2) capabilities. Here, nanoparticles were generated from reactions of ozone (1-1.5 ppm) with α-pinene (300-400 ppb) in an 8.5 L flow reactor and collected using a sequential spot sampler before being analyzed offline with an UHPLC-HRMS system consisting of a Vanquish Horizon UHPLC and a Q Exactive Plus orbitrap mass analyzer (ThermoScientific). Collectively, over 100 products with unique retention times were resolved in sub-100 nm diameter nanoparticles sampled during these experiments, with structural insight gathered from the detailed analysis of the MS2 fragmentation patterns collected from some of the most abundant species. We used data collected from these experiments to create and populate an MS2 spectral database which can be used to assist in future laboratory and field studies. Overall, our findings demonstrate the ability of orbitrap MS to highly resolve and structurally characterize compounds found in secondary organic nanoparticles.