Characterization of aerosol particles at low temperatures in a bath gas cooling cell and Bessel beam optical trap

by Merrill Isenor

Institution: University of British Columbia
Department: Chemistry
Degree: PhD
Year: 2015
Record ID: 2061235
Full text PDF: http://hdl.handle.net/2429/52299


This thesis focuses on low temperature studies of ensembles of aerosol particles formed in a bath gas cooling cell (78 K) and of single aerosol particles trapped in a counter-propagating Bessel beam optical trap (228-260 K). Ensemble particle measurements provide average data for all particles within the ensemble. These measurements are directly applicable to the study of clouds and aerosols in the atmospheres of a variety of planets and moons. Conversely, single particle measurements offer insight into behaviours which may be dependent on a particular particle property, such as particle size. Single particle data complement that obtained from ensemble measurements. The ensemble particle studies are performed with rapid-scan Fourier-transform infrared (FTIR) spectroscopy to determine intrinsic particle properties (size, shape, composition, and architecture) and the temporal evolution of these properties. The assignments based on infrared spectra are supported by calculations using the vibrational exciton model. In this work, several mixed water aerosol ensembles are considered: carbon dioxide-water, ammonia-water, and acetylene-water aerosols. Each of these aerosol systems have relevance to the atmospheres of planets and moons (e.g. Mars, Saturn, Jupiter, Enceladus ). All three mixtures are studied under similar pressure and temperature conditions. While ammonia-water and acetylene-water are found to form molecularly mixed particles, there is no evidence of molecular mixing in carbon dioxide-water aerosol particles. Measurements are performed at low temperatures to study the freezing and evaporation of single aerosol particles. Our new experimental setup consists of a counter-propagating Bessel beam optical trap for trapping of micron and submicron sized particles down to temperatures of 223 K. The measurements in this thesis present the first freezing studies of single particles into the submicron size range. A series of freezing studies for supercooled liquid hexadecane, dodecane, and water particles are presented here, along with preliminary evaporation experiments for supercooled hexadecane droplets. These measurements show that the low temperature trap is an attractive device to study freezing and evaporation of single particles.