Atmospheric aerosols are very important in the Earth climate system due to their role in cloud formation and the global radiation budget. However, there are still many unanswered questions about how the composition of the aerosol varies and how this composition affects the climate system. While aerosols contain a mix of organic and inorganic material, a sub-fraction of the organic material in atmospheric aerosols is surface active, arranging itself into organic films at the gas-aerosol interface. These films can inhibit trace gas uptake, affecting atmospheric chemistry and composition, and they can also impact water uptake, influencing cloud formation properties. Additionally, these films can depress surface tension of atmospheric aerosols, leading to enhanced cloud nuclei. Organic film behavior strongly depends on aerosol pH as well as ionic content, and given the complexity of atmospheric chemistry, hundreds of possible surfactants could exist at a given time in atmospheric aerosols. Therefore, it is imperative to study and understand the formation of organic films and their behavior at atmospherically relevant conditions. In this work, we focus on three main questions about surfactant systems: 1. Do organic films form at all atmospherically relevant conditions? 2. How can complex reactive systems be modeled in terms of surface tension and light absorbing reaction products? and 3. What are the different effects that oxidation of organic films can have on cloud condensation nuclei activity? We studied systems of long chain fatty acids and α-dicarbonyls in aqueous aerosol mimics by using pendant drop tensiometry to measure surface tension, UV-VIS to measure the formation of light-absorbing products, Aerosol chemical ionization mass spectrometry (Aerosol-CIMS) to characterize the reaction products, and a continuous flow streamwise thermal gradient cloud condensation nuclei counter (CFSTGC) to measure the CCN activity. We found that organic films of oleic acid and stearic acid formed at all atmospherically relevant conditions (high ionic content and pH 0-8), though the efficacy of the surface film at depressing surface tension changed as the ionization state of the organic changed. Reactive systems of methylglyoxal and glyoxal showed the formation of some cross-reaction products that added to the total product mass formed; however, most of the products formed were from self-reaction. The formation of light absorbing products as well as the surface tension could be described solely by the effects of the isolated organics combined in parallel, rather than including any terms about cross-reaction species. The oxidation of mixed inorganic-organic aerosols with a sodium oleate film showed little change in CCN activity as compared to pure inorganic aerosols, but the same oxidation with an oleic acid film showed depressed CCN activity. This led to the idea that oxidative aging in the atmosphere might not always increase the hygroscopicity of aerosols. Overall, the results of this thesis demonstrate how variable aerosol properties are due to the organics present within complex aerosol compositions. This work will help direct future laboratory studies on atmospherically relevant systems in order to help elucidate an understanding of surfactant behavior in atmospheric aerosols.

The phase of atmospheric particles can influence heterogeneous chemistry, cloud formation, and radiative forcing. Sulfate particles ranging from sulfuric acid to ammonium sulfate are the largest contributor arising from anthropogenic activities to the global fine aerosol burden. Multi-component inorganic particles of neutralized or partially neutralized crystalline components and acidic solutions can form via uptake of gaseous ammonia. Under some atmospheric conditions, secondary organic material can combine with sulfate species to form internally mixed organic-sulfate particles. The way in which interactions between the constituents in ambient multi-component particles affect the phase of the overall particle are not well understood, especially for complex mixtures containing secondary organic material. This thesis presents measurements of relative humidity-dependent phase transitions of atmospherically relevant multicomponent particles, measured using tandem differential mobility analyzer (TDMA) setups. Particle morphologies implied by these measurements and their impact on other atmospheric processes are discussed. The connection between particle morphology and hygroscopic phase transitions is first discussed in the context of internally mixed ammonium bisulfate and letovicite particles. Unexpected differences in the deliquescence behavior of individual particles of identical diameter and overall composition were observed. From the deliquescence data, we hypothesized composition- and diameter-dependent morphologies based on heterogeneous crystallization of the particles that explained the variable water uptake and deviations from thermodynamic predictions of deliquescence. In multi-component particles containing both organic and inorganic material, phase separation can occur in addition to the deliquescence and efflorescence transitions. The phase transitions and hygroscopic growth of particles composed of ammonium sulfate mixed with secondary organic material are presented and interpreted in a morphological context. Secondary organic material was generated in the Harvard Environmental Chamber via the photo-oxidation of isoprene, the ozonolysis of \(\alpha\)-pinene, and the photo-oxidation of \(\alpha\)-pinene. The occurrence of liquid-liquid phase separation between aqueous ammonium sulfate and \(\alpha\)-pinene-derived organic material, not directly observable from hygroscopic growth measurements, was inferred from the minimal influence of the organic material on the ammonium sulfate phase transitions (less than 4% RH deviation from pure ammonium sulfate values). In contrast, the influence of isoprene photo-oxidation products on the phase transitions of ammonium sulfate was substantial: Both the deliquescence relative humidity and the efflorescence relative humidity of the mixed particles were decreased by over 30% RH from pure ammonium sulfate values for high organic volume fraction. These results implied that dissolved ammonium sulfate, organic molecules, and water were mixed in a uniphasic solution. The dependence of secondary organic material phase on relative humidity and growth factor was investigated via concurrent measurements of particle bounce and hygroscopic growth. Particles were composed of ammonium sulfate mixed with the products of isoprene photo-oxidation, \(\alpha\)-pinene ozonolysis, or \(\alpha\)-pinene photo-oxidation. Particle bounce gradually decreased as RH was increased. The bounce behavior of all three types of particles were closely correlated with growth factor. These results implied that the uptake of particle-phase water caused gradual softening of the particles. / Engineering and Applied Sciences

Copies of author's previously published articles inserted. / Supplement entitled: Addressing referee concerns, stapled to back end paper (5 leaves). / Bibliography: leaves 199-212. / xii, 212 leaaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Presents methodologies for the synthesis of charged analogues of a number of molecular species residing in the large gas clouds which are present in regions of interstellar and circumstellar space. Quantum chemical calculations have been used to provide further insight into the structure and energetics of these molecules. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 1999

Thesis (Ph.D.)-- University of Adelaide, Dept. of Chemistry, 1999. / Copies of author's previously published articles inserted. Supplement entitled: Addressing referee concerns, stapled to back end paper (5 leaves). Bibliography: leaves 199-212.

<p>Tropospheric fine particulate matter (PM) poses serious health risks and has a significant impact on global climate change. The measurement of various aspects of PM is challenging due to its complex chemical nature. This dissertation addresses various aspects of PM, including composition, measurement, and visibility. The U.S. Environmental Protection Agency (EPA) proposed a new secondary standard based on visibility in urban areas using 24-h averaged measurements of either light scatter or PM concentration. However shorter averaging times may better represent human perception of visibility. Data from two studies conducted in Lindon, UT, 2012, and Rubidoux, CA, 2003, were used to compare different techniques to estimate visibility, particularly the effect of relative humidity on visibility estimations. Particle composition was measured in Salt Lake City during January-February of 2009. One-hour averaged concentrations of several gas phase and particle phase inorganic species were measured. The results indicate ammonium nitrate averages 40% of the total PM2.5 mass in the absence of inversions and up to 69% during strong inversions. Also, the formation of ammonium nitrate is nitric acid limited, while the formation of ozone appears to be oxidant and volatile organic carbon (VOC) limited. Reduction of NOx will reduce ammonium nitrate secondary particle formation, however, a decrease in NOx may increase ozone concentration. </p><p> Due to the complexity of PM it is poorly characterized. A large fraction of PM is composed of organic compounds, but these compounds are not regularly monitored due to limitations in current sampling techniques. The GC-MS Organic Aerosol Monitor (OAM) combines a collection device with thermal desorption, gas chromatography and mass spectrometry to quantitatively measure the carbonaceous components of PM on an hourly averaged basis. A compact GC and simple pre-concentrator were developed for the system to decouple separation from manual injection and enhance separation of environmentally-relevant polar organic compounds, such as levoglucosan. The GC-MS OAM is fully automated and has been successfully deployed in the field. It uses a chemically deactivated filter for collection followed by thermal desorption and GC-MS analysis. Laboratory tests show that detection limits range from 0.2 to 3 ng for many atmospherically relevant compounds. The GC-MS OAM was deployed in the field for semi-continuous measurement of the organic markers, levoglucosan, dehydroabietic acid, and several polycyclic aromatic hydrocarbons (PAHs) during winter (January to March), 2015 and 2016. Results illustrate the significance of this monitoring technique to more fully characterize the organic components of PM and identify sources of pollution. </p><p> Keywords: air pollution, fine particulate matter, PM_2.5, secondary organic aerosol, organic markers, levoglucosan, PMF. </p>

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