Developing new laser-based instruments to characterise optical properties of aerosol particles

This thesis describes the development and testing of a novel Multi-angle Particle Sizer (MPS) consisting of multiple high sensitivity sensors collecting scattered 445 nm laser light within different large angle ranges, enabling more information to be collected from each aerosol particle, compared to standard optical particle sizer (OPS) instruments. The MPS has been designed to support multiple detectors without sacrificing a low detection limit, along with maintaining a robust, compact and modular design. This report details the full design and testing processes of the instrument, from the earliest conceptual stages to laboratory-based particle analysis. To test the capabilities of the MPS, nebulised polystyrene latex (PSL) spheres of different diameters (200-3000 nm) and colours were analysed and their scattering data compared to instrument output simulations. These simulations used Mie theory to calculate the relative scattering expected to be intercepted by each PMT, and thus predict the instrument’s output based on particle parameters. This is a common operating principle of OPS but leaves them vulnerable to misinterpretations caused by unexpected particle properties (e.g. non-spherical), but the more nuanced data collected by the MPS reduces this vulnerability by giving more information to compare with theoretical simulations. Using three scattering intensities results in signal pattern fingerprints for each particle class, allowing for verification versus theoretical data and superior differentiation of the components of mixed particle samples. The MPS was determined to have high dynamic signal range and to be capable of real-time data collection for fast-flowing aerosols, although its minimum resolution could not be definitively verified. Integration with an optical tweezers instrument was also performed, by modifying central structural components without changing the optical array formation (laser, lenses and PMTs). This demonstrates the versatility of the instrument to be altered for use in different contexts to explore different avenues of aerosol analysis.