Date of Completion

2020

Thesis Type

College of Arts and Science Honors

Department

Chemistry

First Advisor

Giuseppe A. Petrucci

Keywords

squalane, dioctyl sebacate, aerosol mass spectrometry, artificial growth, aerosol particles

Abstract

Secondary organic aerosol (SOA) makes up a large proportion of organic, fine particulate matter in the atmosphere and has an impact on climate and human health. Various sources of SOA precursors have been identified, but of particular interest to the Petrucci research group is a subset of biogenic volatile organic compounds (BVOCs), green leaf volatiles (GLVs). Upon oxidation of these precursors by ozone, SOA is formed and measurements for chemical analysis can be taken, however, current methods pose limitations to the analysis of ultrafine (particle diameter of 50 nm and smaller) and solid phase particles.

Aerosol mass spectrometry (AMS) is the standard method by which to perform chemical analyses on SOA particles. The Petrucci group has developed a mass spectrometer that uses near-infrared laser desorption/ionization (NIR-LDI) along with a time-of-flight mass spectrometer for chemical analyses of SOA particles. However, the particle lens, which aligns particles into a beam focused onto an aluminum wire probe for deposition, inefficiently collimates ultrafine particles. Additionally, solid particles directed at the probe can bounce off and are lost, preventing subsequent measurement. These limitations are surmounted by a method developed and described herein for coating particles with an organic matrix. This matrix artificially grows ultrafine particles to a size that can be sampled by the particle lens into our mass spectrometer and which coats solid particles in a liquid layer so that they may stick to the probe for measurement.

Dioctyl sebacate (DOS) and squalane (Squ) are proposed for use as the organic matrix to artificially grow and coat ultrafine and solid particles of interest for chemical analysis. Growth apparatuses were designed and optimized for coating SOA particles generated in an environmental chamber. The NIR-LDI-AMS spectrometer and scanning mobility particle sizers (SMPSs) were used to study these particles both with and without organic coating. Use of both DOS and Squ showed that particle growth and measurement was possible, but due to significant particle transmission efficiency inconsistencies through the growth apparatus and the appearance of matrix ions in mass spectra, DOS was deemed unsuitable for further use. Using Squ, optimization for maximum and consistent particle transmission efficiency (~80-90%) through the growth apparatus was achieved. Furthermore, few spurious ions were generated for squalane-coated SOA particles. Therefore, Squ was deemed suitable for artificial growth and coating of particles for mass spectrometry measurement, and the method described herein is validated.

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