A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item ATMOSPHERIC ORGANIC AEROSOLS: THE EFFECT OF PHYSIOCHEMICAL PROPERTIES ON HYGROSCOPICITY(2023) Malek, Kotiba; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols, tiny solid or liquid particles, are ubiquitous in the atmosphere yet their impact on climate remains poorly understood. One prominent way aerosols are able to impact the climate is through their ability to uptake water and form clouds. The chemical diversity and aerosol interactions in the atmosphere can greatly complicate the investigation of aerosol-cloud interactions. This complexity is expressed with a large uncertainty associated with aerosols’ role on climate change. This dissertation investigates the aerosol-cloud interaction by measuring the water uptake of atmospherically relevant aerosols. Our results highlight the importance of accounting for various physiochemical properties when exploring the water uptake of atmospheric aerosols. One such property is liquid-liquid phase separation (LLPS) in ternary mixtures. Our work offers new evidence, insight, and a paradigm shift to the contribution of LLPS to supersaturated droplet activation. We complemented this finding with a theoretical model, that incorporates solubility, O:C ratio, and LLPS, for predicting κ-hygroscopicity of ternary mixtures. Another physiochemical property that was shown to play a key role in droplet activation of polymeric aerosols is chemical structure. Our study shows that polycatechol is more hygroscopic than polyguaiacol and the difference in hygroscopicity is attributed to the density of hydroxyl groups in both structures. Polycatechol has a higher density of hydroxyl groups than polyguaiacol, resulting in polycatechol having stronger water uptake affinity than polyguaiacol. When maintaining the same structural makeup by investigating the water uptake of two isomeric compounds, we discovered that solubility was the driving force in water uptake. The more soluble isomer o-aminophenol was more hygroscopic than p-aminophenol. Hence, a small change in the position of functional groups can impact solubility which in turn influence hygroscopicity. Lastly, we explored the presence of gas-phase organics on the water uptake of isomers with a wide range of solubilities. Our work highlights that gas-phase organics, specifically ethanol, can influence the water uptake of aerosols. Ethanol was shown to increase water uptake efficiencies based on solubility, with the least soluble compound showing stronger affinity to water uptake. Overall, this thesis advances our knowledge and understanding of aerosol-cloud interactions and its implications on climate change.Item THE HYGROSCOPICITY OF PLASTIC AEROSOLS(2023) Mao, Chun-Ning; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymeric nanoparticles affect many aspects of human life. They directly absorb or scatter sunlight, or indirectly act as cloud condensation nuclei (CCN) to change the Earth’s climate. Additionally, micro-plastics released into the environment have the potential to degrade into nano-size particles. Plastic nanoparticles' sizes, number concentration, and hygroscopicity are important properties to understanding nano-plastics’ fates. In this work, I explored aerosol measurement techniques, aerosol hygroscopicity, and polymer nanoparticles to understand subsequent effects in the environment and on human health. The project was divided into three objectives:For the first objective, I developed the single-parameter hygroscopicity model for polymeric aerosols with Flory-Huggins Köhler theory. Traditional hygroscopicity, derived from Raoult’s law, depends on the molecular volume of the solute. For polymers with a high molecular volume, the predicted hygroscopicity from traditional Köhler theory is zero. However, the experimental results showed that polymers could take up water and readily act as CCN. I developed the expression of the hygroscopicity for polymers and showed the relation between the polymer-water interaction parameter and the water-uptake ability. I also considered water-insoluble polymers and the water-adsorption model combined with Köhler theory to define water-uptake. Thus the CCN activity of polystyrene and surface modified polystyrene particles were also measured. For the second objective, I predicted the fraction of the multiply charged particles, showing that the extinction cross section measured by Cavity Ring Down Spectroscopy (CRD) was influenced by a small amount of multiply charged particles using a Differential Mobility Analyzer (DMA). The initial results indicated that ~4% to ~6% of the total number concentration are triply and quadruply charged particles at 200 nm electrical mobility. This small percentage if neglected could induce errors greater than 5% in subsequent extinction cross section measurements. Thus, the errors induced with commercially available DMAs in the extinction cross section measurement were evaluated. For the third objective, I studied the fate of the nano-plastics in the environment. Results showed that low density polyethylene (LDPE) powders generated particles less than 100 nm at temperatures above 40 oC. I quantified the number concentration of 5 materials in water via traditional atmospheric aerosol measurement techniques. The five materials are cellulose, SiO2, LDPE, polyethylene terephthalate (PET), and polyvinyl chloride (PVC). They were all common materials used for food packaging. Furthermore, the hygroscopicities of the nano-plastics were measured. I demonstrated that the nano-plastics could act as CCN under a supersaturated environment and hence affect the climate. The results showed that the plastic materials (LDPE, PVC, PET) were more hygroscopic than cellulose. The nano-plastics could travel further and be found in remote and cold areas like Antarctica, the Arctic, and high mountains. The work in this objective provided evidence of wet deposition being a possible route for nano-plastics to come to the ground. Plastics are relatively new materials compared to papers, clays, and glasses, but have already been massively produced. The work in this thesis contributed to our understanding of the impact on nano-plastics to the environment. The interaction of the water and nano-plastics in the environment was studied. The measurements of size distribution and hygroscopicity of nano-plastics can be applied in the climate model to reduce the uncertainties in the indirect effect of the aerosols in future studies.Item AEROSOL-CLOUD-CLIMATE INTERACTIONS DUE TO CARBONACEOUS AEROSOLS(2022) Gohil, Kanishk; Asa-Awuku, Akua A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols can affect the net radiation budget and global climate of the Earth either “directly” – through their radiative properties, or “indirectly” – through their cloud-forming abilities by acting as Cloud Condensation Nuclei (CCN). The interactions between aerosols and clouds are the most significant sources of uncertainty in the overall radiative forcing from due to a lack of understanding related to the droplet formation mechanism of aerosols. These uncertainties are majorly associated with the carbonaceous aerosols present in the atmosphere, notably due to their compositional diversity, vastly variable physicochemical properties, and unique water uptake characteristics. In this dissertation, new lab-based measurement techniques and computational methods have been developed to resolve the CCN activity and water uptake behavior of pure and mixed carbonaceous aerosol particles.The first part of this dissertation accomplishes two goals: 1. The development and application of a new CCN measurement method, and 2. The formulation of a new computational framework for CCN activity analysis of aerosols. The results in this dissertation demonstrate the significance of size-resolved morphology and dissolution properties of aerosol particles in improving their CCN activity analysis under varying ambient conditions. Furthermore, these results suggest that in the future, more comprehensive CCN analysis frameworks can be developed by explicitly treating other physical and chemical properties of the aerosols to further improve their CCN activity analysis. The second part of this dissertation focuses on large-scale analysis. The CCN analysis framework is implemented into a climate model to quantify the water uptake behavior of carbonaceous aerosols, and then study the subsequent variabilities associated with the physical and radiative properties of ambient aerosols and clouds. Statistical techniques are also developed in this work for chemical characterization of ambient aerosols. The characterization results show large regional compositional variations in ambient aerosol populations. These results also suggest that the knowledge of chemical species is necessary to quantify the water uptake properties of the aerosol population.Item Controlling ammonia emissions from concentrated feeding operations(2011) Satam, Chinmay Charuhas; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ammonia is an essential component in the formation of particulate matter which has been a growing concern for areas along the Mid-Atlantic region. Also, animal husbandry operations have been isolated as the single largest sources of ammonia. Hale III (2005) suggests a strategy to reduce ammonia emissions from chicken manure using a dietary gypsum-zeolite infusion and slight crude protein reductions. A follow up study conducted by Wu-Haan et al. (2007) places the ammonia reduction values at 39 %. Simulations of this strategy for the MANEVU region find PM2.5 reductions of up to 37.5% for the Delmarva Peninsula. Additionally, 6 hours of improved compliance (15 μg/m3 standard) is seen in this region, during moderate PM2.5 episodes. It was also observed that regions near the source, and down wind, with high available nitric to sulfuric acid ratios are benefited by this strategy which primarily targets ammonium nitrates.