Multi-modal chemical characterization of highly viscous submicrometer organic particles

Abstract

Distinguishing highly viscous organic particles within complex mixtures of atmospheric aerosol and accurate descriptions of their composition, size distributions, and mixing states are challenges at the forefront of aerosol measurement science and technology. Here, we present results obtained from complementary single-particle measurement techniques employed for the in-depth characterization of highly viscous particles. We demonstrate advantages and synergy of this multi-modal particle characterization approach based on the analysis of individual viscous particles formed in the air-discharged waste produced by a common sewer pipe rehabilitation technology. Using oil immersion flow microscopy, we investigate particle size distributions and morphology of colloidal components present in field-collected aqueous waste condensates. We compare these results with corresponding measurements of viscous particles formed in drying droplets of the aerosolized discharged waste. The colloidal components and viscous particles were found to be approximately 10 µm and 0.5 µm, respectively. The aerosolized viscous particles exhibited a spherical morphology, while the colloidal particles appeared noticeably fractal, resembling fragments of a cured composite material. Chemical imaging of the viscous particles collected on substrates was performed using scanning electron microscopy and soft X-ray spectro-microscopy techniques. Through these methods, comprehensive description of these particles emerged, confirming their high solid-like viscosity, wide-ranging sizes, diverse carbon speciation with high degrees of oxygenation, and high organic volume fractions. The aerosolized viscous particles were further characterized using high-throughput single particle mass spectrometry. This technique provides real-time measurements of composition, size, and morphological metrics for large numbers of individual particles, enabling the identification of their distinct mass spectrometric signatures.

Copyright © 2023 American Association for Aerosol Research

Graphical Abstract

Editor:

• Jingkun Jiang

Acknowledgments

We acknowledge S.M.T. Sendesi, B. E. Boor, J.A. Howarter, Y. Noh, and A. J. Whelton for collection of waste condensate samples used in this study. The authors would like to acknowledge beamline 5.3.2.2 at the Advanced Light Source at Lawrence Berkeley National Laboratory and beamline scientist Matthew Marcus for his support. This work utilized the CCSEM/EDX at the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the U.S. National Science Foundation, Grant No. CBET-2107946.