Year: 2024
Type: dissertation
Abstract: This thesis has investigated the potential of combining Raman spectroscopy with Sheimpflug Light Detection and Ranging (lidar) for simultaneous characterization and ranging of aerosolized soot. The first part of the project involved the implementation of conventional non-ranging Raman spectroscopy for both deposited and aerosolized soot. The second part constituted the design, modelling, and evaluation of a hyperspectral Scheimpflug Raman lidar using a Prism-Grating-Prism (PGP) design method developed by M. Aikio [1]. From the first part it was concluded that there is a clear difference between Raman spectra of deposited and aerosolized soot, motivating the use of on-line spectroscopy. This is supported by previous experiments [2]. More specifically deposited soot showed signs of increased maturation, structural order and occurrence of graphitic regions, and decreased organic content compared to aerosolized soot. Simulations in the second part showed that the design has potential to be used for simultaneous ranging and rough characterization of soot particles up to at least 50 m, albeit with lower spectral resolution than the conventional methods. The design is tailored to the short distances of a laboratory environment (<10 m), but can easily be modified to suit longer ranges. The signal strength has moreover been identified as a bottle neck for maximum detection range, both because of light distribution and atmospheric interactions. Several potential improvements have additionally been pinpointed, such as using custom prisms, choosing a detector pixel arrangement that is appropriate for the specific area of use, and adding polarizers to decrease atmospheric contributions [3]. If successfully implemented the design has potential to be used where the soot concentrations are high, such as in proximity to highways or wildfires, or in industrial exhaust flows.
Author: Öjstedt, Oskar
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
Funder: Vetenskapsrådet
OpenAlex ID: W7027540198