Abstract View
Enhanced Optical- and Atomic Force Microscopy- Photothermal Infrared and Raman Spectroscopy Enables Observation of Individual Ultrafine Aerosol Particles
YAO XIAO, Ziying Lei, Andrew Ault, University of Michigan
Abstract Number: 380
Working Group: Instrumentation and Methods
Abstract
Atmospheric aerosol particles participate in multiphase reactions that impact their climate-relevant properties (i.e. absorbing or scattering solar radiation, and nucleating ice particle and cloud droplet formation). Measuring the chemical composition of individual aerosol particles is challenging, particularly for particles with aerodynamic sizes <1 μm. In previous studies, our group was the first to apply Optical Photothermal Infrared Spectroscopy (O-PTIR) and Atomic Force Microscope - Photothermal Infrared Spectroscopy (AFM-PTIR) to aerosol particle characterization, which has the advantage of analyzing particles at ambient temperature and pressure. However, the signal is still limited for the smallest individual due to insufficient sensitivity for key vibrational modes, which limits our ability to detect key species present in particles. In this study, we show the first use of gold substrates to improve the signal of trace organic and/or inorganic species in both laboratory and atmospheric particles compared to traditional silicon or quartz substrates. Organic and inorganic functional groups were characterized for lab-generated and ambient particles with the smallest sizes (500 nm to 1 μm and 50 nm to 500 nm for O-PTIR and AFM-PTIR, respectively). IR mapping was collected to further strengthen our understanding of the enhance mechanism and hyperspectral mapping shows the distribution of different groups in the multi-component particles like core-shell morphology. This novel approach method leads to enhanced detection limits and spatial resolution, allowing us to detect trace organic and inorganic species in aerosol particles in a smaller particle size range than previously possible.