Abstract View
Dual Cavity Spectrometer for Monitoring Broadband Light Extinction by Atmospheric Aerosols
AISWARYA SASEENDRAN, Susan Mathai, Shreya Joshi, Anoop Pakkattil, Tyler Capek, Gregory Kinney, Claudio Mazzoleni, Ravi Varma, Michigan Technological University
Abstract Number: 288
Working Group: Instrumentation and Methods
Abstract
Atmospheric aerosols directly influence Earth’s climate by scattering and absorbing solar radiation. To study the broadband optical properties of aerosols, we developed a dual cavity enhanced extinction spectrometer that uses a supercontinuum laser source and a compact spectrometer. The spectrometer measures the extinction coefficient over a broad wavelength region from 420 to 540 nm simultaneously. A dual cavity approach is employed to account for changes in background signal and for spectral and intensity fluctuations of the laser. Polystyrene latex spheres and aerosolized salt particles were used to test the system, and the measured extinction showed good agreement with Mie calculations. Furthermore, we favorably compared the scattering coefficient of non-absorbing aerosols measured using a nephelometer with the extinction coefficient measured using the dual cavity system. The spectrometer was also used to measure the extinction Ångström exponent of laboratory generated soot particles that was found to be equal to ~1.6, comparable to values previously reported in the literature. The broadband dual-cavity extinction spectrometer is simple and robust and should be particularly useful for laboratory measurements of the extinction coefficient of brown carbon aerosol. In the future, the instrument could be deployed in the field to study the optical properties of brown carbon such as smoke particles emitted from biomass burning.