Probing Heterogeneous Efflorescence in an Optical Levitator for Earth and Mars Systems by Shuichi Ushijima B.S., Colorado School of Mines, 2013 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of Philosophy Chemistry 2020 Committee Members: Margaret Tolbert Raina Gough Joost de Gouw Eleanor Brown Ryan Davis Ushijima, Shuichi (Ph. D., Chemistry) Probing Heterogeneous Efflorescence in an Optical Levitator for Earth and Mars Systems Thesis directed by Distinguished Professor Margaret A. Tolbert ABSTRACT The phase transition of soluble inorganic salts has great importance to both Earth’s atmosphere and the Martian surface. On Earth, the phase state of an aerosol will affect their impact on the climate. On Mars, the formation and stability of liquid brines could be key in understanding present day geological features and potentially life on Mars. While the homogeneous phase transitions have been studied in detail, heterogeneous efflorescence has not. Heterogeneous efflorescence occurs when a heterogeneous nucleus induces efflorescence, or crystallization, of an aqueous salt droplet at the surface upon a collision, or from within the droplet after it has become immersed inside the droplet. Heterogeneous efflorescence can change our current understanding of how many aerosols in Earth’s atmosphere are solid particles, and the time that a brine is stable for on the Martian surface. In this study, heterogeneous efflorescence of salt aerosols in Earth’s atmosphere by mineral dust particles were probed. Specifically, the effect of three mineral particles, illite, Na- montmorillonite, and NX Illite on the efflorescence of ammonium sulfate and sodium chloride was studied. The study showed that mixing of salt and mineral aerosols can occur quite often and some salt and mineral dust pairing caused efflorescence to occur under significantly more humid conditions than without the mineral dust. The effect that organic molecules, such as secondary organic aerosols, have on the efflorescence behavior of atmospheric aerosols was also investigated. Two organics, polyethylene glycol 400 and raffinose were mixed with ammonium sulfate for the study. Polyethylene glycol 400 phase separates from ammonium sulfate and coats the aqueous ii droplet whereas raffinose stays homogenously mixed. The study showed that the effect of organics on efflorescence seems to be strongly linked to how the organic affects the mixed aerosols viscosity. Finally, heterogeneous efflorescence of brines believed to be on Mars were investigated. While some brines were completely unaffected by the presence of Martian dust analogues, the stability of other brines were drastically reduced when exposed to mineral particles. iii To Mom, Dad, Miki, Aya, and Shiho. Thank you for always supporting me. iv ACKNOWLEDGEMENTS I would like to first thank my advisor Maggie Tolbert for giving me the opportunity to work with such a unique instrument. When I first met with Maggie, I had no clue what optical levitation was nor did I have any idea what heterogeneous efflorescence was. But Maggie gave me a chance to work with the optical levitator and through it I have worked on projects that span our solar system. I truly appreciate all the guidance that you have given me during my time in your lab. I would also like to Ryan Davis who taught me everything about the optical levitator. With Ryan’s help I learned how optical levitation works, how to run experiments and maintain the optical levitator. Also, to all the past and current members of the Tolbert Research Group I thank you for all the times you helped me out in lab, the times you listened to my practice talks, and for just being a great group of people. Finally, I would like to thank my family. Thank you, mom, for always supporting me. Without your support I would not have made it here. For my three amazing sisters who have and always will inspire me to be better and work harder. And to my dad who I know would be proud of me if he were here today. This work was supported by a National Science Foundation grant, a NASA Earth and Space Science Fellowship, and a Cooperative Institute for Research in Environmental Sciences Fellowship. v TABLE OF CONTENTS Chapter 1. Introduction ...............................................................................................................1 1.1. Research Overview ..............................................................................................................1 1.2. Homogeneous Efflorescence and Deliquescence ...............................................................1 1.3. Heterogeneous Nucleation: Contact and Immersion Mode ................................................3 1.4. Relevance to Earth ...............................................................................................................5 1.5. Relevance to Mars................................................................................................................9 1.6. Thesis Focus.......................................................................................................................12 Chapter 2: Immersion and Contact Efflorescence Induced by Mineral Dust Particles.......14 2.1. Introduction ........................................................................................................................14 2.2. Experimentation ................................................................................................................16 2.2.1. Preparation of Aqueous Solution Droplets ................................................................16 2.2.2. Preparation of Mineral Dust Particles ........................................................................16 2.2.3. Experimental Arrangement .........................................................................................17 2.2.4. Imaging Efflorescence and Collisions ........................................................................20 2.2.5. Determining Heterogeneous ERH ..............................................................................22 2.3. Results ...............................................................................................................................23 2.3.1. Heterogeneous Efflorescence by Mineral Dust ..........................................................23 2.3.2. Immersion ERH as a Function of Surface Area of Immersed Illite .............................28 2.4. Discussion ..........................................................................................................................30 vi 2.4.1. Crystal Lattice Match .................................................................................................30 2.4.2. Active Site ...................................................................................................................33 2.4.3. Ion-Specific Effects .....................................................................................................33 2.4.4. Collisions Lifetimes of Salt Aerosol in a Dust Plume .................................................36 2.5. Conclusion .........................................................................................................................39 Chapter 3: Contact Efflorescence of Internally Mixed Organic – Ammonium Sulfate Aerosols: A Glassy Organic vs An Organic Coating ................................................................41 3.1. Introduction ........................................................................................................................41 3.2. Experimentation ................................................................................................................44 3.2.1. Preparation of Droplets for Trapping ........................................................................44 3.2.2. Experimental Setup ......................................................................................................44 3.2.3. Observing Efflorescence .............................................................................................47 3.2.4. Conducting Contact Efflorescence Experiments ........................................................48 3.2.5. Measuring Viscosity and Immersion Times .................................................................48 3.3. Results ...............................................................................................................................51 3.3.1. Raman Signal for the Components .............................................................................51 3.3.2. Dehumidification of Mixed (NH4)2SO4:Organic Droplets .........................................51 3.3.3. Contact Efflorescence of Mixed (NH4)2SO4:Organic Droplets ..................................56 3.4. Discussion ..........................................................................................................................60 3.4.1. PEG-400: Coating Thickness and Diffusion Times ...................................................60 vii 3.4.2. Raffinose: Viscosity and Diffusion .............................................................................68 3.5. Conclusion ..........................................................................................................................72 Chapter 4: Probing Heterogeneous Efflorescence of Mars Relevant Salts with an Optical Levitator........................................................................................................................................74