PNNL

Abstract

While visible and ultraviolet techniques are common, infrared optical methods have not been extensively used for the detection and identification of aerosol particles. This is in part due to the more complex nature of the photon-particle interaction in the infrared, but also due to the necessity of recording large numbers of reference spectra to accommodate different particle sizes, morphologies, phases etc. In this work we use a different approach, namely employing the measured n/k (complex refractive index) optical vectors in combination with particle scattering theory and the Beer-Lambert law to generate a series of synthetic infrared transmission / scattered light spectra. To test such models, we record some of the first infrared transmission spectra of aerosol particles where both the size distribution and number density of the particles are quantified; the synthetic signatures of well-characterized aerosols are then generated based on the n(?)/k(?) values and these data. To validate the modeled spectra, experimental data were recorded using an FTIR coupled to a simple aerosol chamber filled with a quantified size distribution of dioctyl sebacate (DOS) particles. The synthetic spectra were generated using laboratory n/k measurements to simulate both the absorption and Mie scattering effects due to the aerosols, both of which were seen to have significant effect on band shapes. The agreement between the measured and model spectra is excellent.