Solid State Light Source Based Analytical Measurement Systems For Atmospheric Particles

Abstract

Solid-state light sources such as light-emitting diodes, use a solid semiconductor block instead of a conventional heated filament or discharge source. Such light sources are preferred in analytical instrumentation because of various environmental benefits, cost benefits and most importantly performance benefits due to their characteristic features. This thesis deals with the fabrication of solid-state light source based analytical instrumentation for measuring size distribution and spectral absorption characteristics of ambient aerosol particles and provides insights into the behavior of aerosol organic carbon concentrations determined in a continuous and automated manner. Various analytical instruments are commercially available for either measuring the particle size or optical absorption of ambient aerosols, but not both. Also, the instruments available for determining the optical absorption of particles do so only at one or two wavelengths. This thesis describes a unique instrument that uses an array of eleven light- emitting diodes ranging in wavelength from ultraviolet to near-infrared that are alternately turned on as the light source and a 512-element photodiode array as the detector, the latter providing information on where spatially particles are deposited, This "particle spectrometer" provides semi-quantitative information about size and optical absorption of aerosol particles sampled by the device. Additionally I report on the efficiency of various particle collection systems for collecting fine and ultrafine particulate matter that can operate continuously. This will contribute to the development of analytical instrumentation capable of collecting atmospheric aerosol and analyzing its organic carbon content in a continuous and automated fashion.