AN EXAMINATION OF HYDROXYL RADICAL: OUR CURRENT UNDERSTANDING OF THE OXIDATIVE CAPACITY OF THE TROPOSPHERE THROUGH EMPIRICAL, BOX, AND GLOBAL MODELING APPROACHES

Hydroxyl radical (OH) is the primary oxidant in the troposphere, initiating the removal of numerous atmospheric species including greenhouse gases, pollutants that are detrimental to human health, and ozone-depleting substances. Because of the complexity of OH chemistry, models vary widely in their OH chemistry schemes and resulting methane (CH4) lifetimes. The current state of knowledge concerning global OH abundances is often contradictory. This body of work encompasses three projects that investigate tropospheric OH from a modeling perspective, with the goal of improving the tropospheric community’s knowledge of the atmospheric lifetime of CH4. First, measurements taken during the airborne CONvective TRansport of Active Species in the Tropics (CONTRAST) field campaign are used to evaluate OH in global models. A box model constrained to measured variables is utilized to infer concentrations of OH along the flight track. Results are used to evaluate global model performance, suggest against the existence of a proposed “OH Hole” in the tropical Western Pacific, and investigate implications of high O3/low H2O filaments on chemical transport to the stratosphere. While methyl chloroform-based estimates of global mean OH suggest that models are overestimating OH, we report evidence that these models are actually underestimating OH in the tropical Western Pacific. The second project examines OH within global models to diagnose differences in CH4 lifetime. I developed an approach to quantify the roles of OH precursor field differences (O3, H2O, CO, NOx, etc.) using a neural network method. This technique enables us to approximate the change in CH4 lifetime resulting from variations in individual precursor fields. The dominant factors driving CH4 lifetime differences between models are O3, CO, and J(O3-O1D). My third project evaluates the effect of climate change on global fields of OH using an empirical model. Observations of H2O and O3 from satellite instruments are combined with a simulation of tropical expansion to derive changes in global mean OH over the past 25 years. We find that increasing H2O and increasing width of the tropics tend to increase global mean OH, countering the increasing CH4 sink and resulting in well-buffered global tropospheric OH concentrations.

The Educational Imaginary in Radical Reconstruction: Congressional Public Policy Rhetoric and American Federalism, 1862-1872

Facing the exigencies of Emancipation, a South in ruins, and ongoing violence, between 1862 and 1872 the United States Congress debated the role education would play in the postbellum polity. Positing schooling as a panacea for the nation’s problems, a determiner of individual worth, and a way of ameliorating state and federal tensions, congressional leaders envisioned education as a way of reshaping American political life. In pursuit of this vision, many policymakers advocated national school agencies and assertive interventions into state educational systems. Interrogating the meaning of “education” for congressional leaders, this study examines the role of this ambiguous concept in negotiating the contradictions of federal and state identity, projecting visions of social change, evaluating civic preparedness, and enabling broader debates over the nation’s future. Examining legislative debates over the Reconstruction Acts, Freedmen’s Bureau, Bureau of Education, and two bills for national education reform in the early 1870s, this project examines how disparate educational visions of Republicans and Democrats collided and mutated amid the vicissitudes of public policy argument. Engaging rhetorical concepts of temporality, disposition, and political judgment, it examines the allure and limitations of education policy rhetoric, and how this rhetoric shifted amid the difficult process of coming to policy agreements in a tumultuous era. In a broader historical sense, this project considers the role of Reconstruction Era congressional rhetoric in shaping the long-term development of contemporary Americans’ “educational imaginary,” the tacit, often unarticulated assumptions about schooling that inflect how contemporary Americans engage in political life, civic judgment, and social reform. Treating the analysis of public policy debate as a way to gain insights into transitions in American political life, the study considers how Reconstruction Era debate converged upon certain common agreements, and obfuscated significant fault lines, that persist in contemporary arguments.