Dissertation
Analytical methods to classify maturation of model and native environmental films
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2022
DOI: 10.17077/etd.006367
Abstract
Atmospheric particles and molecules arise from anthropogenic, industrial, mechanical, and naturally occurring sources. The amount of time that these particles and molecules stay suspended in air is referred to as the atmospheric lifetime. This time comes to an end when molecular species react or when the molecular species or particles deposit on surfaces. Deposition of molecular compounds of interest, such as polychlorinated biphenyls (PCB) or polyaromatic hydrocarbons (PAH), can result in film bound hotspots. Over time, this deposition on impervious outdoor surfaces results in what is known as an environmental film. These accumulations grows to reach the order of tens to hundreds of microns from the host surface. As the film builds, the chemical composition and physical morphology it changes the underlying surface. These changes impact the environmental impact on pollutant (PCBs or PAHs) fate and transport. While changing the surface function, the film also undergoes physical and chemical transformations. This process is known as maturation. The environmental films mature chemically and physically. Chemical maturation includes changes to surface bound molecular and elemental species. Physical maturation involves changes in phase state, roughness, or mobility of particulate and molecular species. These changes are not uniform and depends both on the composition of starting materials and the environment surrounding the film. Understanding the atmospheric conditions and film components that undergo these processes can help define how dynamic the film’s impact on the environment is. Quantifying the observed changes contributes to developing models revealing how environmental films impact air and water quality. In this work, I present analysis of model (laboratory) and collected (naturally occurring) environmental films. The goal is to further understand how reactive species, relative humidity, and occurring processes impact the physical form and chemical composition of the films. We found that an increase in relative humidity can cause both physical and chemical maturation, resulting in farther lateral reach (increase of size) of particulate on the surface and molecular mobility. This finding has implications for acid base chemistry that changes secondary organic aerosol production. Exposure of films to ozone changes both the chemical and physical composition of mono-unsaturated films, causing aggregation with a roughened surface made of polymerized saturated hydrocarbons. Increased roughness increases the capacity of films to adsorb and change persistent organic pollutants. We can also start to understand how the films change with seasonally by collecting a series of samples on various timescales at separate locations. Furthermore, we have found that two sample sites separated by one kilometer produce drastically different films. One observed difference in elemental markers of fireworks, surface roughness, and chloride content. The chemical differences reflect changes in environmental film composition with respect to anthropogenic sources. The resulting independent physical form changes the future environmental impact of the films. Samples with two different orientations accumulate films with different roughness and pH. The implication of these results are that rooftops and walls have different impacts environmental processes including adsorption and transformation of molecular species in the atmosphere. Surfaces with different hydrophilicities accumulate different films with individual surface roughness and molecular adsorption and transformation Throughout these studies we have found fundamental concepts that affect modeling atmospheric transport in cities. Specifically, work in this study can help define fate and transport of persistent organic pollutants such as PCBs and PAHs in the environment.
Details
- Title: Subtitle
- Analytical methods to classify maturation of model and native environmental films
- Creators
- Jessica Lauren DeYoung
- Contributors
- Scott Shaw (Advisor)Renée Cole (Committee Member)Christopher Cheatum (Committee Member)Elizabeth Stone (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 2022
- DOI
- 10.17077/etd.006367
- Publisher
- University of Iowa
- Number of pages
- xxxv, 398 pages
- Copyright
- Copyright 2022 Jessica Lauren DeYoung
- Grants
- W911-NF-1-71600-CH, DEVCOM Army Research Laboratory (United States, Adelphi) - ARL
- Language
- English
- Description illustrations
- illustrations (chiefly color), tables, graphs, map
- Description bibliographic
- Includes bibliographical references (pages 355-362).
- Public Abstract (ETD)
- If you have ever put off cleaning your windows for a little too long, you have probably noticed a buildup of grime. While a potential mild nuisance visually, window grime has much more of an impact on the environment than you might realize. One aspect of this impact is the ability of the grime to concentrate pollutants on the surface of windows. While some airborne pollutants may not have “relevant” or harmful concentrations in the air, the concentrated version on the film form can bring new risk to ecosystems. This grime and other materials that similarly build up on outdoor surfaces are known as environmental films. This material originates from a combination of various environmental contributors such as dust, road salts, plant waxes, soil, and soot as well as other lesser contributions. There is also evidence of tiny organisms like fungi and bacteria living on these surfaces. The growth of films depends on the weather, nature, human activity, as well as what the film is made of and what the film looks like. Growth like this is known as “maturation”. The work presented here is focused on identifying various methods of maturation of environmental films. We have studied the following influencers on maturation: humidity, ozone, underlying surface identity and orientation, distance away from cities, and season. Results show that the composition of the film impacts maturation pathways. When exposed to high humidity, film materials that attract more water spreads out across the surface, causing an increase in surface coverage and roughness. This change is important, because it increases the capacity of the film to capture pollutants and other particulates from the air creating potentially harmful concentrations in ecosystems. Additionally, by exposing oily films to ozone, the optical properties change reflecting more light which causes a hazy effect on the surface. While this does not seem to be important, it could change the kind of light that transmits through windows or to solar panels. We have collected films to study how location and season change the x composition. We found that films one kilometer outside of the city have less impact on the environment than those within the city. Films within the city have a chemical composition that changes seasonally, and that exterior-walls collects different films than those on rooftops of the same building. This means our current environmental models of pollutant transport in cities are not correct and we need to consider the orientation of building walls and rooftops. Additionally, we observed more water-soluble species if the films were formed in cities; these films have a higher impact on wastewater contamination when it rains. In terms of the effects of environmental films on ecosystems, we can say buildings in cities have bigger impacts than more rural areas. This work has contributed to our fundamental understanding of how environmental films form in different spaces. Moving forward, we can start to create better models for understanding how these materials impact air quality, water quality, and pollutant transport.
- Academic Unit
- Chemistry
- Record Identifier
- 9984271354102771
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