Environmental Chemistry Commons^™

Unraveling Sources Of Cyanate In The Marine Environment: Insights From Cyanate Distributions And Production During The Photochemical Degradation Of Dissolved Organic Matter, Rui Wang, Jihua Liu, Yongle Xu, Li Liu, Kenneth Mopper

Chemistry & Biochemistry Faculty Publications

Cyanate is a nitrogen and energy source for diverse marine microorganisms, playing important roles in the nitrogen cycle. Despite the extensive research on cyanate utilization, the sources of this nitrogen compound remain largely enigmatic. To unravel the sources of cyanate, distributions and production of cyanate during photochemical degradation of natural dissolved organic matter (DOM) were investigated across various environments, including freshwater, estuarine, coastal areas in Florida, and the continental and slope regions of the North American mid-Atlantic Ocean (NATL). Cyanate production was also examined during the photochemical degradation of exudates from a typical strain of Synechococcus, an important phytoplankton …

Potentially Massive And Global Non-Pyrogenic Production Of Condensed "Black" Carbon Through Biomass Oxidation, Aleksandar I. Goranov, Hongmei Chen, Jianshu Duan, Satish C. B. Myneni, Patrick G. Hatcher

Chemistry & Biochemistry Faculty Publications

With the increased occurrences of wildfires worldwide, there has been an increase in scientific interest surrounding the chemistry of fire-derived "black" carbon (BC). Traditionally, wildfire research has assumed that condensed aromatic carbon (ConAC) is exclusively produced via combustion, and thus, ConAC is equated to BC. However, the lack of correlations between ConAC in soils or rivers and wildfire history suggests that ConAC may be produced non-pyrogenically. Here, we show quantitative evidence that this occurs during the oxidation of biomass with environmentally ubiquitous hydroxyl radicals. Pine wood boards exposed to iron nails and natural weather conditions for 12 years yielded a …

Investigation Of Emissions And Chemistry Of Formic Acid And Acetic Acid In Wildfire Smoke, Catherine Elizabeth Wielgasz

Graduate Student Theses, Dissertations, & Professional Papers

Formic acid (HCOOH) and acetic acid (CH₃COOH) are two of the most ubiquitous organic acids in the atmosphere. Chemical transport models consistently underestimate HCOOH and CH₃COOH concentrations in environments including fire smoke, implying our incomplete understanding of their global budget. Emissions and secondary production of HCOOH and CH₃COOH within complex mixtures in fire smoke is uncertain.

I used measurements from the NSF/NCAR C-130 aircraft during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) campaign to investigate emissions and photochemical production of HCOOH and CH₃COOH from smoke plumes. First, …

Iron Speciation In Pm2.5 From Urban, Agriculture, And Mixed Environments In Colorado, Usa, Joseph R. Salazar, David J. Pfotenhauer, Frank Leresche, Fernando L. Rosario-Ortiz, Michael P. Hannigan, Sirine C. Fakra, Brian Majestic

Chemistry and Biochemistry: Faculty Scholarship

Atmospheric iron solubility varies depending on whether the particles are collected in rural or urban areas, with urban areas showing increased iron solubility. In this study, we investigate if the iron species present in different environments affects its ultimate solubility. Field data are presented from the Platte River Air Pollution and Photochemistry Experiment (PRAPPE), aimed at understanding the interactions between organic carbon and trace elements in atmospheric particulate matter (PM). 24-hr PM2.5 samples were collected during the summer and winter (2016–2017), at three different sites on the Eastern Colorado plains: an urban, agricultural, and a mixed site. Downtown Denver had …

Production Of Singlet Oxygen (1O2) During The Photochemistry Of Aqueous Pyruvic Acid: The Effects Of Ph And Photon Flux Under Steady-State O2(Aq) Concentration, Alexis J. Eugene, Marcelo I. Guzman

Chemistry Faculty Publications

The photochemistry of pyruvic acid (PA) in aqueous atmospheric particles contributes to the production of secondary organic aerosols. This work investigates the fate of ketyl and acetyl radicals produced during the photolysis (λ ≥ 305 nm) of 5-100 mM PA under steady state [O₂(aq)] = 260 μM (1.0 ≤ pH ≤ 4.5) for photon fluxes between 1 and 10 suns. The radicals diffuse quickly into the water/air interface of microbubbles and react with dissolved O₂ to produce singlet oxygen (¹O₂^*). Furfuryl alcohol is used to trap and bracket the steady-state production of …

The Effects Of Reactant Concentration And Air Flow Rate In The Consumption Of Dissolved O2 During The Photochemistry Of Aqueous Pyruvic Acid, Alexis J. Eugene, Marcelo I. Guzman

Chemistry Faculty Publications

The sunlight photochemistry of the organic chromophore pyruvic acid (PA) in water generates ketyl and acetyl radicals that contribute to the production and processing of atmospheric aerosols. The photochemical mechanism is highly sensitive to dissolved oxygen content, [O₂(aq)], among other environmental conditions. Thus, herein we investigate the photolysis (λ ≥ 305 nm) of 10–200 mM PA at pH 1.0 in water covering the relevant range 0 ≤ [O₂(aq)] ≤ 1.3 mM. The rapid consumption of dissolved oxygen by the intermediate photolytic radicals is monitored in real time with a dissolved oxygen electrode. …

Cross Photoreaction Of Glyoxylic And Pyruvic Acids In Model Aqueous Aerosol, Sha-Sha Xia, Alexis J. Eugene, Marcelo I. Guzman

Chemistry Faculty Publications

Aerosols of variable composition, size, and shape are associated with public health concerns as well as with light-particle interactions that play a role in the energy balance of the atmosphere. Photochemical reactions of 2-oxocarboxylic acids in the aqueous phase are now known to contribute to the total secondary organic aerosol (SOA) budget. This work explores the cross reaction of glyoxylic acid (GA) and pyruvic acid (PA) in water, the two most abundant 2-oxocarboxylic acids in the atmosphere, under solar irradiation and dark thermal aging steps. During irradiation, PA and GA are excited and initiate proton-coupled electron transfer or hydrogen abstraction …

Organic Photochemistry: Remote Delivery Of Reactive Oxygen Intermediates Via A Heterogeneous Approach, Niluksha Walalawela Abeykoon

Dissertations, Theses, and Capstone Projects

Photosensitized oxidation reactions produce a number of intermediates species, which are generated in varying amounts over time. This complexity presents major challenges in the study of oxidation processes. Mechanistic efforts to separate and deliver reactive oxygen intermediates enable their controlled use in processes such as bacterial inactivation. This thesis describes a heterogeneous reaction approach taken to control the generation and delivery of reactive oxygen intermediates. The mechanistic details of photosensitized reactions were elucidated via synthetic, materials, and physical organic techniques to optimize the delivery of reactive oxygen intermediates. This thesis contains six chapters as described below.

Chapter 1 gives a …

Photochemistry Of Polycyclic Aromatic Hydrocarbons With Environmentally Relevant Metals, John P. Haynes

Electronic Theses and Dissertations

The details of the work presented in this dissertation focus on simulated reactions in the atmosphere and water systems between persistent aromatic compounds and varying species of metals with an emphasis on iron. Bulk water suspensions of a standard soil and polycyclic aromatic hydrocarbons (PAH) were analyzed for soluble iron by inductively-coupled plasma mass spectroscopy (ICP-MS) following a 16 hour reaction period using simulated sunlight. Significant increases in soluble iron were only seen with 2-3 ring linear PAH and carboxylic acids.

A two-stage study was conducted to investigate the potential for and possible mechanisms involving the photo-oxidation of PAH into …

Reactivity Of Ketyl And Acetyl Radicals From Direct Solar Actinic Photolysis Of Aqueous Pyruvic Acid, Alexis J. Eugene, Marcelo I. Guzman

Chemistry Faculty Publications

The variable composition of secondary organic aerosols (SOA) contributes to the large uncertainty for predicting radiative forcing. A better understanding of the reaction mechanisms leading to aerosol formation such as for the photochemical reaction of aqueous pyruvic acid (PA) at λ ≥ 305 nm can contribute to constrain these uncertainties. Herein, the photochemistry of aqueous PA (5-300 mM) continuously sparged with air is re-examined in the laboratory under comparable irradiance at 38° N at noon on a summer day. Several analytical methods are employed to monitor the time series of the reaction, including (1) the derivatization of carbonyl (C═O) functional …

Aqueous Photochemistry Of Glyoxylic Acid, Alexis J. Eugene, Sha-Sha Xia, Marcelo I. Guzman

Chemistry Faculty Publications

Aerosols affect climate change, the energy balance of the atmosphere, and public health due to their variable chemical composition, size, and shape. While the formation of secondary organic aerosols (SOA) from gas phase precursors is relatively well understood, studying aqueous chemical reactions contributing to the total SOA budget is the current focus of major attention. Field measurements have revealed that mono-, di-, and oxo-carboxylic acids are abundant species present in SOA and atmospheric waters. This work explores the fate of one of these 2-oxocarboxylic acids, glyoxylic acid, which can photogenerate reactive species under solar irradiation. Additionally, the dark thermal aging …

Studies On Hydroxyl Radical Formation And Correlated Photoflocculation Process Using Degraded Wood Leachate As A Cdom Source, Luni Sun, Kenneth Mopper

Chemistry & Biochemistry Faculty Publications

In this study, we examined hydroxyl radical (•OH) formation with respect to photoreactivity of colored dissolved organic matter (CDOM), the Fenton reaction, and photoflocculation using leachate from decaying wood. The relationship between •OH photoproduction rate and leachate optical properties (UV-visible absorption and fluorescence excitation-emission matrices (EEMS)) was studied during irradiation using a UV solar simulator. The results showed that the •OH photochemical formation rate is strongly related to humic-like fluorescence as characterized by parallel factor analysis (PARAFAC), and that these fluorescence components are more photolabile than most of the other CDOM components. Fourier transform infrared spectroscopy (FT-IR) indicated the photodegradation …

Advances In Understanding The Molecular Composition Of Dissolved Organic Matter And Its Reactivity In The Environment, Rajaa Mesfioui

Chemistry & Biochemistry Theses & Dissertations

Dissolved organic matter (DOM) is the ultimate product of Earth's systems dynamics. DOM chemical signature is strongly shaped by the interaction among Earth's spheres, such as the atmosphere, the geosphere, the biosphere, and the hydrosphere, but also life and human activity. DOM source, composition, photochemical alteration and availability affect freshwater ecosystems, their carbon and nitrogen fluxes and, thus, the global carbon and nitrogen cycles. The aim of this thesis was to gain an understanding of the molecular composition of DOM and its photochemical and biological reactivity in an environment impacted by anthropogenic disturbance. The York and James River systems within …

Open-Ocean Carbon Monoxide Photoproduction, Aron Stubbins, Günther Uher, Cliff S. Law, Kenneth Mopper, Carol Robinson, Robert C. Upstill-Goddard

Chemistry & Biochemistry Faculty Publications

Sunlight-initiated photolysis of chromophoric dissolved organic matter (CDOM) is the dominant source of carbon monoxide (CO) in the open-ocean. A modelling study was conducted to constrain this source. Spectral solar irradiance was obtained from two models (GCSOLAR and SMARTS2). Water-column CDOM and total light absorption were modelled using spectra collected along a Meridional transect of the Atlantic ocean using a 200-cm pathlength liquid waveguide UV-visible spectrophotometer. Apparent quantum yields for the production of CO (AQY_CO) from CDOM were obtained from a parameterisation describing the relationship between CDOM light absorption coefficient and AQY_CO and the CDOM spectra collected. …