Ice crystals in clouds frequently form upon a subset of aerosol particles called ice nuclei (IN). IN influence cloud ice crystal concentrations, consequently affecting cloud lifetime and reflectivity. The present understanding of these effects on climate is hindered by limited data on the global distribution of IN. This thesis presents measurements of deposition-mode IN concentrations under conditions relevant to mid-level clouds, 238 K and 138% RHi. at two Canadian sites: Toronto, a major city, and Whistler, a pristine coniferous rainforest. In Toronto, chemically-resolved surface areas were estimated by single-particle mass spectrometry and regressed against IN concentrations to identify a significant relationship between IN concentrations and both carbonaceous aerosols (EC and/or OC) and dust. In Whistler, IN concentrations during a biogenic secondary organic aerosol (SOA) event did not increase from background levels (0.1 /L), suggesting that biogenic SOA particles do not nucleate ice under these conditions.

The indirect aerosol effect contributes to major uncertainties in determining the radiation budget of the earth. A large uncertainty is due to the formation of ice clouds onto natural or anthropogenic aerosols. Field studies have shown that mineral type particles are often associated with ice crystals in the mid-upper troposphere and given the long residence time in the atmosphere of dust particles (~2 weeks in the absence of precipitation), their contribution to ice formation processes is not fully defined. In order to probe ice formation onto natural mineral dust in a setting where it could be suspended as aerosol, a new continuous flow diffusion chamber (CFDC) was built. This allowed investigations of the effects of total aerosol surface area and particle size. The CFDC was also used in an international inter-comparison of ice nucleation instrumentation to compare efficiencies of soot, biological aerosol (bacteria) and samples of natural desert dusts from different regions of the world. The laboratory observations were parameterized using nucleation rates (Jhet) and contact angles () as described by classical nucleation theory. For both this experimental technique and a static one developed during the candidate’s Masters degree, mineral dust particulate proved to be the most efficient ice nuclei (IN) activating at RH with respect to ice (RHi) as low as 105% at T = 233 K. The efficiency varied with particle size and aerosol surface area (SA). Large particles or higher SA activated at lower RHi than small particles or lower SA. The static chamber was sensitive to the first ice event out of a large SA and therefore gave true onset RHi, which was lower than the onset defined by the CFDC studies, which was not sensitive to a single ice event. In addition the static chamber used a broader size range of particulate matter, including super micron particles while the CFDC particles sizes were restricted to below 0.5 µm. Soot and organic coated dust particles were inefficient IN compared to pure dust. Soot aerosols showed some efficiency at T < 233K where deposition ice formation was apparent. The hygroscopic organics had intermediate ice activity between dusts and alkyl-organics and soot. Bacteria aerosols were active in the deposition mode for T as high as 247 K. Contact angles () computed for ice germs forming onto natural mineral dust were small, 7<  < 29, at 223 K for RH ranging from ice to water saturation. It was concluded that there is no single value for the onset of ice formation in the atmosphere via deposition freezing. The associated contact angles show that there is a distribution of active sites on IN and that not all active sites have the same affinity for initiation of ice formation even within the same aerosol type. This work provides evidence that deposition mode nucleation can be an alternate pathway to homogeneous nucleation when mineral aerosols are present in the troposphere since the high T - low RH conditions required for deposition mode nucleation are more easily encountered in the atmosphere than the low T - high RH required for homogeneous nucleation.

Ice crystals in clouds frequently form upon a subset of aerosol particles called ice nuclei (IN). IN influence cloud ice crystal concentrations, consequently affecting cloud lifetime and reflectivity. The present understanding of these effects on climate is hindered by limited data on the global distribution of IN. This thesis presents measurements of deposition-mode IN concentrations under conditions relevant to mid-level clouds, 238 K and 138% RHi. at two Canadian sites: Toronto, a major city, and Whistler, a pristine coniferous rainforest. In Toronto, chemically-resolved surface areas were estimated by single-particle mass spectrometry and regressed against IN concentrations to identify a significant relationship between IN concentrations and both carbonaceous aerosols (EC and/or OC) and dust. In Whistler, IN concentrations during a biogenic secondary organic aerosol (SOA) event did not increase from background levels (0.1 /L), suggesting that biogenic SOA particles do not nucleate ice under these conditions.

Microwave chemistry has expanded over the last two decades due to the enhanced reaction rates achieved for many processes, including organic synthesis, inorganic synthesis and polymerization. Significant time and energy saving can be realized using microwave chemistry, which is important both commercially and for the environment. One of the most exciting and commercially/technologically significant areas where microwave energy has been demonstrated to influence the kinetics and selectivity is in the synthesis of nanoporous materials, such as zeolites. New nanoporous materials can be created, and the times for their syntheses can be significantly reduced, involving using less energy. By reducing the times by up to over an order of magnitude, continuous production would be possible to replace batch synthesis. However, the mechanism and engineering for the enhanced rates of these syntheses are unknown. The results from different laboratories are not consistent, and experimental details are sparse. Therefore, more research is required to unlock the mystery behind this "gee-wiz" chemistry. Furthermore, understanding the fundamental processes leading to rate enhancement by microwaves will also enable the optimization of these microwave heated reactions. In this work, the formation of SAPO-11 (and AlPO-11), silicalite and NaY zeolites under microwave heating was investigated and the influence of various microwave reactor engineering parameters was studied. Microwaves enhanced the SAPO-11 synthesis by two orders of magnitude over the conventional synthesis. Both nucleation and growth steps were enhanced by the presence of microwaves. Fast microwave heating was not solely responsible for this enhancement. This indicates that non-thermal interactions of material with microwaves are present for this synthesis. Many microwave reactor engineering parameters were identified as possibly influencing the microwave synthesis of SAPO-11 (and AlPO-11). These factors are precursor volume, reaction temperature, reactor size, stirring, applicator type and microwave frequency. Among those, the reaction temperature had the greatest influence on this SAPO-11 (and AlPO-11) synthesis. Increasing the reaction temperature decreased the nucleation time and increased the growth rate. The crystallization growth rate in the microwave synthesis showed higher activation energy (1.5 times) compared to the conventional synthesis. However, the pre-exponential factor increased by 8 orders of magnitude in the microwave synthesis. Nucleation rate also showed an increase in the activation energy (3.6 times) and an increase in the pre-exponential factor (10 orders of magnitude) by using microwave heating. This substantial increase in the pre-exponential factor could be the reason behind this microwave synthesis enhancement. High temperature, stirred synthesis, large vessel and using multimode field distribution oven found to be the optimum reaction conditions for microwave synthesis of SAPO-11 (and AlPO-11). Thermal variations within SAPO-11, silicalite and NaY synthesis solutions were measured using a reaction vessel with multiple fiberoptic temperature probes. NaY synthesis solution has the shortest microwave penetration depth among these zeolite synthesis solutions which led to great thermal variations between the region near the wall (high temperature) and the center (low temperature) when placed in a vessel with diameter 20 times larger than its penetration depth. Increasing these thermal variations led to a decrease in the nucleation time and thus enhanced this NaY microwave synthesis. Microwave power delivery mode (pulsed vs. continuous) effect on the synthesis of the three zeolites mentioned above was investigated. Pulsing the microwave power required less average power to maintain the synthesis reaction temperature compared to continuous delivery mode. No effect of using pulsed compared to continuous microwave power delivery was found on the nucleation time and the crystal growth for these zeolite syntheses. However, pulsed microwave power delivery produced smaller particles in the case of SAPO-11. The effect of simultaneous cooling effect on the microwave synthesis of SAPO- 11 and silicalite was studied. Increasing the amount of power delivered to the SAPO-11 synthesis while maintaining the reaction temperature fixed using the simultaneous cooling, decreased the nucleation time and increased the growth rate. Smaller particles were formed at high power. Silicalite showed no change in the nucleation time, crystal growth and/or the morphology. This indicates that there is no universal pattern among the microwave synthesis of zeolites. What could be an important factor for one synthesis is not necessarily important for another, and is likely dependent on the dielectric properties and the reaction mechanism.

No description available.

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 1995" Wang-Chi Vincent Yeh. 12/12/2003. Report is also available in paper and microfiche from NTIS.

Thesis (Ph. D.)--Michigan State University. Chemical Engineering, 2008. / Title from PDF t.p. (viewed on Mar. 30, 2009). Includes bibliographical references. Also issued in print.

Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p.138-143 ). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 158-165). Also available via the World Wide Web.

Thesis (M.S.)--State University of New York at Binghamton, Program of Materials Science and Engineering, 2007. / Includes bibliographical references.