Chemical & Biomolecular Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2219
Formerly known as the Department of Chemical Engineering.
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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 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 REAL-TIME COMPARISON OF PHYSICAL AND CHEMICAL AEROSOL MEASUREMENT METHODS(2019) OYEBANJO, FRANCIS; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric aerosols are major contributors to air pollution. Overexposure to these particles can cause severe respiratory and cardiovascular impairments. Aerosols also affect the planet's climate through radiative forcing. Various techniques exist to monitor the physical and chemical characteristic of aerosols but few allow for real-time analysis. In this thesis, real-time field measurements of aerosol particles were compared with values reported by state regulatory agencies. These values were also compared to mass concentrations of PM2.5 in order to determine if a correlation exists between the two. Lastly, the relationship between particle mobility-size and chemical characterization using Raman spectroscopy is explored in an effort to obtain quantitative semi-continuous spectral data. This study found no variation between local and regional particulate matter measurements and no discernable correlation between PM2.5 mass and particle number concentration. The relationship between particle size and Raman intensity remains unknown due to the non-uniformity of mobility-size selected particles.Item OBSERVATIONS AND EMISSIONS OF ENERGY-ASSOCIATED OZONE PRECURSORS IN THE MID-ATLANTIC UNITED STATES(2016) Vinciguerra, Timothy P.; Ehrman, Sheryl H.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Surface ozone is formed in the presence of NOx (NO + NO2) and volatile organic compounds (VOCs) and is hazardous to human health. A better understanding of these precursors is needed for developing effective policies to improve air quality. To evaluate the year-to-year changes in source contributions to total VOCs, Positive Matrix Factorization (PMF) was used to perform source apportionment using available hourly observations from June through August at a Photochemical Assessment Monitoring Station (PAMS) in Essex, MD for each year from 2007-2015. Results suggest that while gasoline and vehicle exhaust emissions have fallen, the contribution of natural gas sources to total VOCs has risen. To investigate this increasing natural gas influence, ethane measurements from PAMS sites in Essex, MD and Washington, D.C. were examined. Following a period of decline, daytime ethane concentrations have increased significantly after 2009. This trend appears to be linked with the rapid shale gas production in upwind, neighboring states, especially Pennsylvania and West Virginia. Back-trajectory analyses similarly show that ethane concentrations at these monitors were significantly greater if air parcels had passed through counties containing a high density of unconventional natural gas wells. In addition to VOC emissions, the compressors and engines involved with hydraulic fracturing operations also emit NOx and particulate matter (PM). The Community Multi-scale Air Quality (CMAQ) Model was used to simulate air quality for the Eastern U.S. in 2020, including emissions from shale gas operations in the Appalachian Basin. Predicted concentrations of ozone and PM show the largest decreases when these natural gas resources are hypothetically used to convert coal-fired power plants, despite the increased emissions from hydraulic fracturing operations expanded into all possible shale regions in the Appalachian Basin. While not as clean as burning natural gas, emissions of NOx from coal-fired power plants can be reduced by utilizing post-combustion controls. However, even though capital investment has already been made, these controls are not always operated at optimal rates. CMAQ simulations for the Eastern U.S. in 2018 show ozone concentrations decrease by ~5 ppb when controls on coal-fired power plants limit NOx emissions to historically best rates.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.