Atmospheric aerosols are a major contributor to the total energy balance of the Earth's atmosphere. The exact effect of these aerosols on global climate is not well understood, due to poorly-characterized compositional variation that takes place over a given aerosol's lifetime. Organic aerosol (OA) species are of particular interest, forming through a myriad of gas- and aerosol-phase mechanisms and contributing to aerosol light absorbance, cloud formation properties, and overall particle lifetime. As different organic species will affect physical properties in different ways, proper prediction of these compounds forming in the aerosol phase is necessary to estimate the net physical properties of aerosols, and subsequently their effects on overall global climate. Several previous models exist that attempt to predict organic components of aqueous-phase mass in aerosols, with varying degrees of scope of chemistry and range of applicability. Many of such simulations emphasize OA formation via oxidation of gas-phase organic species that results in low-volatility compounds that subsequently partition into aerosols. Other models focus on aqueous-phase processing of semi-volatile and non-volatile water-soluble organic compounds (WSOC's) under cloud water conditions. However, aqueous reactions that occur in atmospheric, deliquesced salt aerosols have recently also been found to be potentially important additional pathway for the creation of additional aerosol-phase organic mass, contributing different products due to the significantly higher inorganic concentrations present under these conditions. It is desirable to incorporate these reactions into analogous predictive simulations, allowing for the chemistry taking place in small, deliquesced salt atmospheric aerosols to be more accurately represented. In this work, we discuss a new photochemical box model known as GAMMA, the Gas-Aerosol Model for Mechanism Analysis. GAMMA couples gas-phase organic chemistry with highly detailed aqueous-phase chemistry, yielding speciated predictions for dozens of secondary organic aqueous aerosol-phase compounds under various atmospheric and laboratory initial conditions. From these studies, we find that isoprene-derived epoxides (IEPOX) and their substitution products are predicted to dominate aqueous-phase organic aerosol mass in conditions with low NOx in the atmosphere, representative of rural environments. The contribution of these epoxide species is expected to be high under acidic conditions, though our findings still estimate significant contribution to aqueous-phase organic mass under higher pH or under cloudwater conditions, when acidity is expected to be lower. Under high-NOx conditions typical of urban environments, glyoxal is seen to form the majority of evolved aqueous organic species, with organic acids comprising the bulk of the difference. We then implement a series of physical property modules, designed to predict changes in aerosol absorbance and surface tension due to bulk concentrations of evolved OA species. Preliminary results from these modules indicate that bulk solution effects of aqueous-phase carbonyl-containing volatile organic compounds (CVOCs) and organic acids are insufficient to significantly affect net aerosol surface tension under any condition tested, implying that observed deviations from pure inorganic aerosol surface tension will arise from surface-aerosol partitioning rather than bulk compositional effects. Light absorption of aqueous aerosols is seen to be driven by dark glyoxal chemistry in deliquesced salt aerosols and organic acids in cloud droplets, though additional information about the absorbance properties of IEPOX and its derivatives is required to accurately predict the net absorbance of aerosols where these species dominate OA mass. The predictions as described by GAMMA are comparable to field observations, and give further credence to the significance of epoxide formation as a source of aqueous-phase organic aerosol mass. These results also suggest the relative importance of specific organic compounds in the aqueous phase of both deliquesced salt aerosols and cloud droplets in the atmosphere, which gives direction to the study of compounds whose impact on aerosol physical properties will matter the most. In turn, new kinetic and physical information can be directly applied into the groundwork laid here, allowing GAMMA to provide a continuously better understanding of the effect of organic material on aqueous aerosols and their implicit effect on the environment.

No description available.

Aerosol particles are ubiquitous in the atmosphere and their properties impact on the atmospheric energy balance. They scatter and absorb incoming sunlight and can perturb cloud microphysical properties, which affects cloud lifetimes and albedo. Africa is one of the world’s largest sources of aerosol due to both its large deserts and prolific biomass burning during the dry seasons. Nevertheless, the continent's atmosphere has, to date, been among the least studied in the world. The southern coast of West Africa is developing rapidly, with both population and anthropogenic emissions being predicted to increase substantially in coming years. It is therefore becoming ever more important to understand the characteristics of aerosols in this region, which will have consequences for issues as diverse as local health and global climate change. This project addresses this problem in two ways: first, laboratory experiments were carried out to characterise biomass burning aerosol at source. Biomass burning is one of the most poorly understood aerosol sources, but one of the most prevalent in tropical regions. Second, aircraft observations were made in southern West Africa during the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) field campaign in summer 2016, to observe the broad-scale distribution of chemical and physical aerosol properties. Results were collected in-situ with Aerodyne Aerosol Mass Spectrometers (AMS) and other online aerosol instrumentation; they were considered alongside observations from DACCIWA ground sites and model results. Distinguishable chemical signatures were reliably observed during three phases of combustion events in the laboratory study. This gave insight into the mechanisms linking combustion phases and emissions. Airborne observations in southern West Africa revealed a remarkably consistent background of aged, accumulation mode aerosol present across the region in the boundary layer, including in the region upwind of the cities on the south coast. It was demonstrated that this likely originated from large-scale biomass burning in central and southern Africa, which had become entrained into the boundary layer above the Atlantic and transported north. A second result from the DACCIWA campaign showed that the hygroscopic growth of these particles, due to the high humidity in the region during June and July, more than doubled the mean dry aerosol optical depth. Taken together, these findings shed light on the substantial impacts that biomass burning aerosol, in particular, has on the atmosphere above southern West Africa.

Introduction: Poultry workers have an increased risk of respiratory symptoms associated with various irritant and allergenic exposures causing airway inflammation. This study investigated the levels of (1-3)-β-D glucan exposure in several poultry farming processes. The objectives involved categorising the different tasks undertaken in the poultry industry. After which a method was established and validated to detect and quantify the levels of (1-3)-β-D glucan using the Glucatell assay. This assay was used to measure the amount of (1-3)-β-D glucan poultry farm workers were exposed to using personal sampling. Thereafter, general respiratory symptoms were described briefly via the administration of a respiratory questionnaire. Method: A total of 308 personal air samples were collected from several poultry farming processes (rearing, laying, hatchery, broilers, catching) of a large poultry farm in the North West Province. A walkthrough checklist was used to obtain information on various exposure determinants such as farm size, number of chickens, ventilation system, bedding material used and poultry feed used. The Glucatell assay (Associates of Cape Cod, East Falmouth, MA, USA) was used to quantify the concentration of (1-3)-β-D glucans in the air samples. Results: The geometric mean concentrations of (1-3)-β-D glucans ranged from 24.38 to 645.98 ng/m3 across the various poultry farming processes investigated. Workers in the broiler farms were exposed to two times higher levels of (1-3)-β-D glucans compared to those in the breeding farms. The sizes of the broiler farm houses as well as the age of the chickens were among the main determinants of exposure. The larger broiler farm houses (GM=5.2 ng/m3, GSD=3.74) had significantly (p<0.05) lower levels than the smaller broiler farm houses (GM=6.4 ng/m3, GSD=2.14) whilst houses with older chickens had higher (1-3)-β-D glucan levels (G=5.8 ng/m3,

Aerosols are ubiquitous throughout Earth's atmosphere and their size, chem- ical composition, and concentration cause varying degrees of impact on climate and human health. Atmospheric aerosols can affect climate by their varied interactions with incoming solar radiation and their role in cloud formation and microphysics. Nucleation of fresh particles plays a significant role in the number of boundary layer cloud condensation nuclei (CCN). Elevated sulfuric acid concentration from power production has long been shown to contribute to new particle formation, but is not present in all instances where nucleation is observed. A third component has long been hypothesized and different studies in different locations have shown evidence of either ammonia, amines, or organics acting in conjunction with sulfuric acid and water to initiate new particle formation under certain meteorological conditions. While atmospheric nucleation has been examined world-wide in many urban as well as remote forested locations, it has not been studied extensively in the non-forested Midwestern United States, where sulfuric acid from coal-fired power plants and ammonia from agricultural activity are prevalent. For this doctoral dissertation work, instruments were designed, built, and tested for the purpose of investigating the concentration, size distribution, and volatility of atmospheric aerosols in non-forested rural continental environments in the Midwestern United States. An impact assessment of the University of Iowa Power Plant on air quality in Johnson County, IA highlights the ability to field test the emission ratios of fine particulates emissions to other gaseous emissions. Analysis on 20 years of climatically relevant aerosol properties in the rural Midwestern location of Bondville, IL reveals enhancement of particle number in the Spring and Fall seasons. Bondville is also the location of a three-year aerosol vertical profiling field campaign, where ultra-fine particles were found to be enhanced in the planetary boundary layer. The long standing records are compared with current full aerosol size distribution particle measurements for a period of ∼ 10 months in Bondville, where the seasonality of high particle number concentrations are verified and attributed to nucleation. Nucleation is observed to varying degrees in all seasons at this location, but is most prevalent and intense in the Spring and Fall months under otherwise clean atmospheric conditions. This work paves the way for a more in depth examination of the volatility of fine particle matter during nucleation and the development of a Midwestern chemical nucleation model to investigate numerous nucleation conditions and mechanisms. This work will contribute important information to the atmospheric science community on the process controlling the particle number size distribution in the region.

An experimental study of solid-gas interactions was made for sodium chloride particles, using a specially fabricated environmental chamber in a transmission electron microscope. It was found that under suitable conditions the hydration and dehydration of these particles could be directly observed and quantitatively measured. Measurements of growth were obtained with a time resolution of one-thirtieth of a second for particles having diameters ranging from 0.02 μm to 1.0 μm.

The creation of new atmospheric particles via nucleation is an important source of particles, and may influence climate by altering the aerosol size distribution. The objectives of my dissertation research were to better understand the process by which new particles are created (homogeneous nucleation), and how these particles are modified throughout their lifetime in the atmosphere. The approach combined field-measurements and observations with advanced instrumentation development and extensive data analysis. In the laboratory, a Dry-Ambient Aerosol Size Spectrometer (DAASS) was constructed. The DAASS is an automated combination of aerosol sizing instruments and supporting equipment that measures aerosol size distributions from 10.9 nm to 10 µm at both ambient and dry relative humidities and was deployed during the MILAGRO field campaign. The design and construction of a Differential Mobility Analyzer from parts was also completed in order to provide the capability to perform Tandem DMA (or TDMA) measurements. New particle formation events, occurring in both rural (Midwest United States) and urban (Mexico City) locations were analyzed. In the Midwest, the temporal pattern, frequency, associated meteorology and contributing factors were quantified for the first time in this location. The urban observations were conducted in Mexico City, Mexico, as part of an international field campaign known as MILAGRO (Megacity Initiative: Local and Global Research Observations 2006). It was determined that new particle formation in Mexico City occurs following periods of decreased pre-existing aerosol surface area. These sharp decreases in pre-existing aerosol surface area are tied to the rapid ventilation of the Mexico City basin that occurs in the early afternoon as a result of its unique geographical setting in a mountain basin. Number-based emission factors representative of Mexico City were determined using a method of signal peak identification in collocated SMPS and CO2 measurements. The emission factor as a function of time of day, day of week, and wind direction were examined. The overall emission factor is size resolved, and comparisons to other size resolved emission factors determined in other locations (such as Los Angeles) were performed.

The necessity to explore nanoscopic systems is ever increasing in the world of science and technology. This evolving need to study such physically small systems demands new experimental techniques and methodologies. Atomic force microscopy (AFM) is a versatile technique that can overcome many nanoscopic size limitations. AFM has been utilized in the world of nanotechnology to study physiochemical properties of particles, materials, and biomolecules through characterization of morphology, electrical and mechanical properties, binding interactions, and surface tension, among others. The work discussed herein is largely a report of several novel AFM methodologies that were developed to allow new characterization techniques of individual submicrometer particles and single biomolecular interactions. The effects of atmospheric aerosols on the radiative budget of the earth and climate are largely unknown. For this reason, characterizing the physiochemical properties of aerosols is vital. Since the particles that have relatively long lifetimes in the atmosphere are smaller than one micrometer in size, high resolution microscopy techniques are required to study them. AFM is a suitable technique for single particle studies because it has nanometer spatial resolution, can perform experiments under ambient pressure and variable relative humidity and temperature. These advantages were utilized here and AFM was used to study morphology, organic volume fraction, water uptake, and surface tension of nascent sea spray aerosol (SSA) particles as well as laboratory generated aerosols composed of relevant chemical model systems. The morphology of SSA was found, often times, to be composed of core-shell structure. With complementary microscopy techniques, the composition of the core and the shell was found to be inorganic and organic in nature, respectively. Novel methodology to measure water uptake and surface tension of single substrate deposited particles with AFM was established using chemical model systems. Furthermore, these methodologies were employed on nascent chemically complex SSA particles collected from a biologically active oceanic waveflume experiment. Finally, phase imaging was used to measure organic volume fraction on a single particle basis and was correlated with biological activity. Overall, this suite of single (submicrometer) particle AFM analysis techniques have been established, allowing future systematic studies of increasing complexity aimed at bridging the gap between the simplicity of laboratory generated particles and the complexity of nature. Another nanotechnology topic of interest is studying single biomolecular interactions. Virtually every biological process involves some amount of minute forces that are required for the biomolecular system to function properly. For example, there are picoNewton forces associated with enzymatic motions that are important for enzyme catalysis. The AFM studies reported here use a model enzyme/drug system to measure the forces associated with single molecule adhesion events. Escherichia Dihydrofolate Reductase (DHFR) is a target of cancer therapeutic studies because it can be inhibited by drugs like methotrexate (MTX) that are structurally similar to the natural folate binder but have much higher binding affinity. One of the obstacles of single molecular recognition force spectroscopy (MRFS) studies is the contribution of non-specific forces that create a source of uncertainty. In this study, DHFR and MTX are bound to the surface and the AFM tip, respectively, using several different linking molecules. These linking molecules included polyethylene glycol (PEG) and double stranded DNA (dsDNA) and the distribution of forces was compared to scenarios were a linker was not employed. We discovered that dsDNA and PEG both allow identification and removal of non-specific interaction forces from specific forces of interest, which increases the accuracy of the measurement compared to directly bound constructs. Traditionally, the linker of choice in the MRFS community is PEG. Here, we introduce dsDNA as a viable linker that offers more rigidity than PEG, which may be desirable in future molecular constructs. The majority of the work and data presented in this dissertation supports the establishment of new AFM methodologies that can be used to better explore single biomolecular interactions and individual submicrometer particles on the nanoscale.

Typescript (photocopy) / ix, 171 leaves, 2 leaves of plates : ill. ; 30cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1980

Thesis (Ph.D.)--University of Nevada, Reno, 2005. / "May 2005." Includes bibliographical references. Online version available on the World Wide Web.