Open Collections

Zeleny, Anna T.

University of British Columbia

Mixed-phase clouds are important climate regulators, providing significant annual precipitation and global cloud coverage. An increase in wildfires in the past decade is changing cloud cover and cloud composition which are currently difficult to predict due to a lack of mechanistic understanding. Although there is evidence of the ability of organic aerosols to nucleate ice under mixed-phase cloud conditions, the underlying physicochemical mechanism through which organic materials promote ice nucleation is an active area of research. The goal of this thesis is to study the mechanism through which lignin, and, by extension, biomass burning organic aerosols, nucleate ice in the atmosphere. To determine ice activity of lignin, we employ a bottom-up approach by synthesizing lignin nanoparticles (LNPs). LNPs have controllable, measurable, characteristics; valuable for elucidating the mechanism of ice nucleation of lignin. To determine the role of size and surface properties, we synthesized lignin nanoparticles (LNPs) from commercially available Kraft lignin and tested their freezing ability in our home-built Freezing Ice Nuclei Counter (FINC). LNPs were characterized for their size and dispersity with dynamic light scattering (DLS). Transmission Electron Microscopy (TEM) provided additional confirmation of shape and dispersity. We then prepared LNP solutions of different sizes at equal concentration via thermogravimetric analysis (TGA) to isolate the role of size on ice nucleation. Our FINC and DFA results confirmed that lignin nanoparticles, ranging in size from 80 – 500 d.nm, at the same concentration (0.2 mg/mL) are ice active with T\textsubscript{50} values ranging from -14.96 to -15.91 ºC. We found that few large LNPs nucleate ice with the same ability as many small LNPs. Normalizing the freezing data to mass and number suggests that aggregation facilitates ice nucleation of LNPs in the 10s and 100s of nanometers in size. From this research, we further contribute to the growing literature suggesting the key role of aggregation, and therefore likely of chemical composition on organic aerosols' ability to nucleate ice. These findings help understand how lignin within wildfire organic aerosols are able to nucleate ice and hence impact the ice crystal concentration in mixed-phase clouds.

Text

2024-02-13

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87426

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/