Molecularly Revealing 3D Structure of Organic Aerosol Particles Using Mass Spectrometry Imaging

ZIHUA ZHU, Fan Mei, Jeffrey Dhas, Zezhen Cheng, Pacific Northwest National Laboratory

     Abstract Number: 246
     Working Group: Aerosol Chemistry

Abstract
Organic aerosol particles are of great importance because they are highly prevalent in atmosphere, significantly affect our planet’s radiation budget, and actively influence human health. Understanding 3-demensional (3D) structure of aerosol particles is critical, because heterogeneous mixing states lead to different activities of light diffraction and water condensation/ice nucleation. However, it has been challenging to reveal 3D structure of organic aerosols at a molecular level. For example, aerosol mass spectrometry can provide molecular information, but it is majorly a bulk analysis tool without any useful spatial resolution. Scanning electron microscope and transmission electron microscopy can provide delicate nanoscale resolution images, while no molecular information is available. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful surface analysis tool, providing both nanoscale spatial resolution and molecular recognition capability. We have recently used it to examine PM2.5 particles collected from a typical pollution case in Beijing wintertime.[1] In this presentation, we show ToF-SIMS 3D molecular imaging data of aerosol particles collected on October 14, 2021, at ARM SGP site in Oklahoma. A large amount of solid shell-liquid vegetable oil core organic aerosol particles are observed. As far as we know, such structure was never reported before. Our results not only provide interesting information to understand organic aerosol formation and aging mechanism, but also open a new door for investigation of 3D structure of organic aerosol particles at a molecular level.

References:
[1] Li, Y., Zhou, Y., Guo, W., Zhang, X., Huang, Y., He, E., Li, R., Yan, B., Wang, H., Mei, F., Liu, M., Zhu, Z. “Molecular Imaging Reveals Two Distinct Mixing States of PM2.5 Particles Sampled in a Typical Beijing Winter Pollution Case” Environ. Sci. Technol. 2023, 57, 6273−6283.