A Novel Approach to Calibrate a Photoacoustic Absorption Spectrometer using Monodispersed Gold Nanoshell

YINGJIE SHEN, Shane Murphy, Matthew Burkhart, Gavin McMeeking, Bryan Rainwater, University of Wyoming

     Abstract Number: 571
     Working Group: Instrumentation and Methods

Abstract
A new technique for calibrating multi-pass photoacoustic aerosol absorption spectrometers (multi-pass PAS) has been developed using monodisperse absorbing gold coated silica nanoshells. This is the first time a monodisperse particle is found and utilized in the calibration for multi-pass PAS. In this new approach, gold coated silica nanoshells are atomized and measured simultaneously with a multi-pass PAS and a Single-Particle Soot Photometer – Extended Range (SP2-XR) instrument. Gold nanoshells absorb from near-UV to near-IR wavelength and the incandescence channel from SP2-XR can distinguish and count gold nanoshells from other pure scattering aerosols from solution, therefore it is an ideal calibration substance for multi-pass PAS operated at multiple wavelengths. Gold nanoshells are commercially synthesized at well-defined sizes, together with the know refractive index, we are able to calculate the theoretical absorption coefficient via Mie theory and then further calibrate multi-pass PAS. This approach may be utilized in a system with both Differential Mobility Analyzer (DMA) and Condensation Particle Counter (CPC) as a replacement for the SP2-XR, but it will increase 27% error due to the miscounting for non-gold containing particles. Other Optical Particle Counter may replace the SP2-XR and only increase 5% error once the correct bins are selected. The advantage of this new calibration substance includes known size and refractive index, stability over a long period and with different capping agent, and absorption at a broad range of wavelength, which is convenient to calibrate at multiple wavelengths.