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Dilini Kirindigoda Gamage_Thesis2.33 MB
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Dissertation
Molecular characterization of sea spray aerosol and traffic related air pollution
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2025
DOI: 10.25820/etd.007946
Abstract
Atmospheric aerosols are tiny solid or liquid particles suspended in the air, typically ranging in size from 10 nm to 100 μm. Aerosols play a significant role in climate by scattering and absorbing solar radiation, as well as influencing cloud and ice formation. Exposure to atmospheric aerosols also poses significant health risks. Understanding the size-resolved chemical composition of aerosols is essential for improving climate predictions and assessing their impact on human health. The first objective of this dissertation is to provide new insights into the size-resolved chemical composition of sea spray aerosol (SSA) and how factors such as wind speed, seawater temperature, and chemical aging in the atmosphere affect its composition. The second objective is to characterize PM2.5 in traffic-related air pollution (TRAP), investigate major organosulfate species and their formation pathways, and assess their contribution to PM2.5. Together, these objectives lead to a more chemically complete and robust characterization of these globallyimportant aerosol types.
Chapter 2 examines the variations in composition of supermicron (1.0-25 μm) and submicron SSA (0.25-1.0 μm) over varying wind speeds. As wind speed increased from 9.6 to 21.2 m s-1, the mass concentration of inorganic ions and metals in supermicron and submicron SSA rose exponentially, up to factors of 7.7 and 18 respectively. As wind speed increased the absolute concentration of organic carbon (OC) increased in both submicron and supermicron SSA by factors of 3.6 and 3.4, respectively. Meanwhile the ratio of OC to Na⁺ declined by factors of 4.5 and 1.7, indicating that organic enrichment relative to Na+ in SSA is more pronounced at lower wind speeds. Additionally, organosulfates, a class of compounds that can originate from primary emissions and reactions of VOCs with acidic sulfate, contributed to OC enrichment in submicron SSA at low wind speeds. These findings demonstrate size dependent chemical changes in SSA, in which SSA particles produced at high wind speeds are smaller and saltier with less OC and are expected to be more hygroscopic and cloud condensation nuclei active.
Chapter 3 describes an investigation of the impact of seawater temperature on the chemical composition of supermicron, submicron SSA, and particles <0.25 µm across temperatures ranging from 2.2 to 20.0 °C. Decreased seawater temperatures increased inorganic ion concentrations in SSA. Concentrations peaked between 6.2 and 9.5 °C across three particle sizes as seawater temperature decreased, with NaCl concentrations varying by factors of 1.5 for supermicron, 3.6 for submicron, and 6.5 for particles <0.25 µm across the temperature range. The OC relative to Na⁺ ratio in submicron SSA decreased sixfold with decreasing seawater temperatures, showing the lowest values between 5-10 °C and the highest at 20 °C. This understanding of seawater temperature dependent chemical changes, including higher inorganic ion concentrations and lower OC relative to Na⁺ at colder temperatures, provide insights into climate-relevant properties, such as enhanced CCN activity at colder temperatures.
Chapter 4 examines how the chemical composition of SSA varies after emission by chemical aging. Aging of SSA increased concentrations of sulfate, phosphate, nitrate, ammonium, and organic carbon relative to sodium. The most significant increases in sulfate and organic carbon to Na⁺ ratios by factors of 7 and 5 were found in particles <0.25 µm. The presence of organosulfates in aged SSA showed that acidic sulfate played a role in the formation of low-volatility secondary organic aerosols by reacting with biological molecules like unsaturated fatty acids, isoprene, and monoterpenes during aging. Isoprene derived organosulfates were greatly increased by a factor of 40 by aging marine volatile gases. The observed organosulfates also originated from primary emissions, with the strongest signals detected coming from anthropogenic surfactants. Organic species, such as alkyl amines, also increased with chemical aging. This study provides molecular insight into the composition of SSA and reveal likely primary and secondary sources of organosulfates and other functional groups and their formation pathways in the marine environment. Furthermore, this study contributes to understanding how the chemical composition of SSA alters upon aging.
In Chapter 5, the chemical characterization of PM2.5 in a highway tunnel revealed the major organosulfates associated with TRAP and their formation pathways. The strongest signals were from 2- methyltetrol sulfate, an isoprene-derived organosulfate, and C10H16NSO7 ̶ (m/z 294), a monoterpene-derived organosulfate. The isoprene-derived organosulfate was predominant in summer, while C10H16NSO7 ̶ (m/z 294) dominated the organosulfate concentrations during winter months. Understanding the composition of organosulfates in TRAP enables targeted laboratory experiments to investigate their potential health impacts.
Overall, this dissertation presents new insights to the chemical characterization of SSA and traffic-related PM2.5. By examining the size-resolved chemical changes in SSA and identifying key organosulfates in PM2.5, this work advances our understanding of aerosol composition across different sizes and the influence of environmental factors such as wind speed, seawater temperature, and chemical aging on their organic and inorganic composition. These advances contribute to the understanding of changes in climate-relevant properties of SSA and offer valuable insights for assessing and mitigating their health impacts.
Details
- Title: Subtitle
- Molecular characterization of sea spray aerosol and traffic related air pollution
- Creators
- Dilini Kirindigoda Gamage
- Contributors
- Elizabeth A. Stone (Advisor)James Gloer (Committee Member)Renee Cole (Committee Member)Edward Gillan (Committee Member)Alexei Tivanski (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2025
- DOI
- 10.25820/etd.007946
- Publisher
- University of Iowa
- Number of pages
- xv, 132 pages
- Copyright
- Copyright 2025 Dilini Kirindigoda Gamage
- Grant note
- This work was supported by the National Institutes of Health (NIH) under Grant No. 3P30ES005605-27S1. The contents of this work do not necessarily represent the views of the NIH, and the NIH does not endorse the purchase of any commercial products or services mentioned in this study.
- Language
- English
- Date submitted
- 03/18/2025
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 107-124).
- Public Abstract (ETD)
Particles in the atmosphere influence Earth's climate by absorbing and reflecting sunlight and influencing cloud and ice formation. Inhaling atmospheric particles also has adverse effects on human health. Understanding these effects requires studying their abundance, size, and chemical composition. This dissertation focuses on two particle sources: sea spray particles and traffic-related air pollution. Sea spray is influenced by wind speed, seawater temperature, and atmospheric oxidation, environmental factors that affect its concentration and chemical composition. Increasing wind speeds from 9.6 m s-1 to 21.2 m s-1 led to a significant increase in the mass concentrations of sea spray components by up to a factor of 18, while the ratio of organic carbon relative to sodium ion was enhanced at lower wind speeds. As seawater temperature decreased from 20.0 °C to 2.2 °C, inorganic ion concentrations in sea spray particles increased, peaking around 9.5-6.2 °C. In particles sized 0.25-1.0 μm, organic carbon relative to sodium ion increased sixfold with temperature, lowest at 5-10 °C and highest at 20 °C. After emission, atmospheric aging of sea spray increased organic carbon and inorganic ions relative to sodium ion due to reactions between marine gases, emitted sea spray, and atmospheric reactants. Regarding traffic-related air pollution, this dissertation characterized atmospheric particles in a highway tunnel. Sulfate-containing organic compounds formed from both anthropogenic and biogenic sources were identified and among them several compounds accounted for 0.04-0.06% of PM2.5. This dissertation highlights the most abundant sulfate-containing organic compounds, their sources and provides insight into their formation pathways. Overall, this thesis demonstrates changes in composition of sea spray and traffic-related air pollution due to different environmental factors. This knowledge will help improve our understanding of the chemical composition of particles in the atmosphere, which affects human health and climate.
- Academic Unit
- Chemistry
- Record Identifier
- 9984831125402771
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