American Association for Aerosol Research - Abstract Submission

AAAR 38th Annual Conference
October 5 - October 9, 2020

Virtual Conference

Abstract View


Atmospheric Nanoparticles: Optical Photothermal Infrared Spectroscopy of Determining Particle Sizes

Nicole Olson, YAO XIAO, Ziying Lei, Andrew Ault, University of Michigan

     Abstract Number: 95
     Working Group: Aerosol Chemistry

Abstract
Atmospheric aerosol particles have a huge impact on climate by triggering multiple chemical reactions which are pH dependent, scattering solar radiation and nucleating clouds and ice crystals. Although the importance of aerosol particles has been addressed, determining particle sizes at the most abundant size level (<1μm) is still an analytical change due to their ultrafine size. Moreover, the traditionally used microspectroscopy techniques like scanning electron microscopy will perform under the vacuum which will distort the physicochemcial property of ambient samples. Therefore, in this study, we introduced the first application of Optical Photothermal Infrared Spectroscopy (O-PTIR) to determine properties of both lab-generated and ambient aerosol particles. A visible and a tunable IR lasers are aligned together to introduce the change of scatter Raman signal caused by the thermal expansion of the particles when the IR frequency matches the vibrational absorption of samples. Due to the change of signals, both Raman and IR spectra can be extracted from the samples under submicron resolution spontaneously. Microscopy substrates were tested and used to minimize the background interference and maximize the sample signals. Organic and inorganic functional groups were characterized for lab-generated and ambient aerosol particles. Mapping was also introduced to study the distribution of different groups in the multi-component particles. The results presented the strong capability of O-PTIR to study the atmospheric aerosols at submicron levels which is far beyond the traditional vibration spectroscopy like Fourier-transformed IR. Therefore, this study provides an important method to further understand the impact of aerosols on the climate and human health at a critical size range.