AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A Single Particle Approach for Exploring Aerosol Photochemistry and Optical Properties
JAMES F. DAVIES, Chelsea Price, Alison Bain, Thomas Preston, University of California, Riverside
Abstract Number: 286 Working Group: Instrumentation and Methods
Abstract A coupled understanding of the evolving chemical composition and related physical and optical characteristics of aerosol in the atmosphere is required to accurately predict their role in the environment. Aerosol become chemically transformed by several processes, such as evaporation and condensation of vapors, heterogeneous reactions with gas phase oxidants, and photochemical reactions initiated by direct solar illumination. These transformations lead to changes in physical and optical properties, impacting the effects of aerosol in the atmosphere. Aerosol containing light-absorbing compounds will have a warming effect on the atmosphere and may undergo additional photochemical transformations.
Using a newly developed particle levitation chamber (1) coupled with optical spectroscopy and mass spectrometry methods, the physical and chemical characteristics of light absorbing aerosol samples will be explored. Initial measurements focus on classifying the absorption properties of humic acid using Mie resonance spectroscopy, a broadband scattering technique capable of resolving both size to nanometer precision and complex refractive index. A sample droplet of radius on the order of 4 µm will be prepared from a dilute solution using a microdroplet dispenser and confined in the electric fields of a linear quadrupole EDB. The sample will be illuminated with focused light from an LED and the 180˚ back-scattered light will be collected by a fiber optic coupled to a spectrometer (Princeton Instruments FERGIE). Over a wide range of illumination wavelengths, both the scattering and absorbing properties as a function of wavelength may be determined by comparing the spectra with predictions from Mie theory (2).
These measurements will provide crucial data describing the optical scattering of aerosol particles, and will pave the way for future measurements to explore the evolution of optical properties as samples evolve by heterogeneous or photochemical reactions. Using this experimental framework, the influence of these transformations on the physical properties of the sample will also be explored, providing a comprehensive understanding of the coupling between composition and physical and optical properties.
[1] Davies, J. F. Mass, charge, and radius of droplets in a linear quadrupole electrodynamic balance. Aerosol Sci Tech 1–29 (2019). [2] Bain, A. & Preston, T. C. Mie scattering from strongly absorbing airborne particles in a photophoretic trap. J Appl Phys 125, 093101 (2019).