Investigation of aerosol chemistry and growth under atmospheric conditions in a novel rotating aerosol suspension chamber with cavity ring-down spectroscopy provided key insight into the effect of pollutants and other vapors on the overall atmospheric lifetime of particulate matter. The Atmospheric Cloud Simulation Instrument (ACSI) creates a well-defined and controllable atmosphere of suspended particles, analyte gases, and background gas molecules, which remains stable up to several days. Preliminary studies have shown that monodisperse polystyrene latex (dp = 0.994 µm) and polydisperse ammonium sulfate (CMD dp = 100 nm) particles remain suspended for at least 22 hours while the chamber rotates at 2 RPM. Further investigation into the aerosol dynamics showed the coagulation efficiency of high concentration particle suspensions (>10^6 particles/cm3) depends on particle phase state and composition. The coagulation efficiency decreased with increased humidity in the model atmosphere and with increased ion concentrations in the aerosols. The decrease in efficiency is attributed to repulsive forces from like-charges on the particle surfaces. In addition to humidity, the spectroscopy integrated into the main chamber monitors the real-time response to a perturbation in the model atmosphere, such as the introduction of a gas-phase reactant. Cavity ring-down spectroscopy, performed in situ along the center axis, records mid-infrared spectra (1010 cm-1 to 860 cm-1) to identify gas species evolved from gas-particle heterogeneous chemistry. In accord with previous studies, my results show that a known reaction between monomethyl amine and ammonia occurs readily on suspended ammonium sulfate particles in >50% RH and the extent of the reaction depends on the humidity of the model atmosphere. Acidic ammonium bisulfate aerosols also produced a detectable amount of ammonia upon exposure to monomethyl amine in a model atmosphere with >50% RH. Overall, the new ACSI approach to atmospheric science provides the opportunity to study the influence of interfacial chemistry on particle growth, aging, and re-admission of gas-phase compounds. / Doctor of Philosophy / "Molecules don't have a passport." - Carl Sagan. Gas molecules and particles emitted into the atmosphere in one area can travel thousands of kilometers over the course of hours to days, even weeks for some compounds. The gas-solid interactions that occur over the lifetime of particulate matter are largely unknown. I focused my doctorate on bridging the knowledge gap between traditional environmental monitoring research and highly controlled laboratory experiments. To do so, I designed a new instrument capable of creating stable model atmospheres that more accurately simulate the gas-particle interactions in Earth's atmosphere than previous environmental chambers. The Atmospheric Cloud Simulation Instrument design included a rotating chamber to increase the duration of stable particle suspensions in a laboratory and a multi-pass infrared spectrometer to monitor gas-phase reactions in situ. I explored the effect of humidity and particle composition on particle-particle coagulation and gas-particle reactions. For example, liquid aerosols at humidities higher than 35% RH do no coagulate as fast as a solid particle with the same composition in <35% RH. Similarly, the same liquid aerosols produced more gaseous product during a heterogeneous reaction with a 'pollutant' gas than solid particles. Overall, the ACSI will be an important tool for future experiments exploring individual aspects of complex atmospheric processes.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/103541 |
| Date | 04 December 2019 |
| Creators | Amick, Cecilia Lynn |
| Contributors | Chemistry, Morris, John R., Tissue, Brian M., Isaacman-VanWertz, Gabriel, Marr, Linsey C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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