Infrared Spectral Modeling for Detection of Aerosols using the Complex Refractive Indices

Jessica Salcido, Schuyler Lockwood, Tracy Baker, Alla Zelenyuk, Tanya Myers, TIMOTHY JOHNSON, Pacific Northwest National Laboratory

     Abstract Number: 522
     Working Group: Aerosol Physics

Abstract
Detection of aerosolized chemicals using traditional spectroscopic methods and (absorption) reference libraries is challenging because such methods do not take into account the particles’ ability to scatter and refract light. Due to an infinite number of aerosol sizes, shapes and compositions, constructing a database of such laboratory-measured scattering/absorption reference spectra is not feasible. As an alternative approach, the measured n(λ)/k(λ) optical vectors, i.e. the complex refractive indices, can be used in combination with particle absorption / Mie scattering theory and the Beer-Lambert law to generate a series of synthetic infrared transmission / scattered light spectra. These synthetic spectra manifest the unique aerosol spectral signatures, for either scattering or transmission measurements: Relative to simple “slab” transmission measurements, the aerosol spectra peak display significant spectral peak shifts and peak profile changes depending on the n/k values, the aerosols particle size(s) and particle shape(s). The modeled spectra are validated vs. laboratory transmission spectra of liquid and solid aerosols.