Multiangle light scattering techniques for measuring shape and refractive index of submicron atmospheric particles

This thesis embodies a study of the application of multiangle light scattering (MALS) detection to the measurement of submicron particle shape and refractive index. The role of this research has been to assist in characterizing atmospheric aerosols in a federally-mandated Class I area so that visibility impairment may be unambiguously apportioned to aerosol chemical species and their emission sources.; Variability in azimuthal light scattering was measured with eight detectors and found to be highly distinguishable between spheres and nonspheres illuminated by a circularly polarized laser beam (488 nm wavelength) for particle size as low as 0.2 microns. Quantification of spherical and nonspherical particle fractions was demonstrated with measurements of coal dust and liquid droplet mixtures.; Nonspherical fractions of submicron atmospheric aerosols were measured during the 1995 Southeastern Aerosol and Visibility Study (SEAVS) conducted in the Great Smoky Mountains National Park. They were generally correlated with fractions of soil dust particles and with fractions of "less hygroscopic" particles, confirming that soil dust particles of local origin were nonspherical and nonhygroscopic. Soil particles attributed to North African origin appeared to be more spherical and hygroscopic.; Measured water content was observed to be in excess of thermodynamic predictions of water associated with deliquescent sulfate compounds measured during SEAVS. A clear association between excess water and organic carbon mass fraction was observed, from which an empirical model of organic carbon hydration was developed.; Size- and humidity-dependent values of real refractive index were determined for spherical particles measured during SEAVS by fitting Lorenz-Mie theory to calibrated light scattering signatures. Detector calibrations were derived as functions of particle size (0.2 to 0.8 microns) for seven polar angles (40 to 140 degrees) based on measurements of a variety of aerosol materials with known values of real refractive index. Measured indices were compared to values modeled using composition data and three estimates of water content. The best agreement was achieved for the sum of water content estimates for organic carbon and supersaturated sulfate, in support of the model derived for organic carbon hydration.