Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item EXAMINATION OF THE PHOTOCHEMISTRY AND MESOSCALE METEOROLOGY ASSOCIATED WITH POOR AIR QUALITY IN THE U.S.(2018) Mazzuca, Gina; Dickerson, Russell R; Pickering, Kenneth E; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mesoscale meteorological processes including advection, vertical mixing, thermally-direct circulations (sea/bay breezes) combined with chemical processes and deposition dominate boundary-layer ozone (O3). While bay breezes (BBs) transport higher O3 over land on polluted days, they also advect humid air and induce low-level convergence, which can lead to haze and deep convection. Thunderstorms can vent pollution out of the boundary layer and entrain cleaner, mid-tropospheric air into it, reducing surface pollutant concentrations. Here, the net local effect of these two mesoscale forcings (BBs and thunderstorms) on O3 concentrations are quantified. First, case studies using vertical profiles and surface observations during the 2011 MD and the 2013 TX deployments of DISCOVER-AQ show the severity of bay/gulf breeze exacerbation of pollution. Next is a BB and thunderstorm climatology for a Chesapeake Bay coastal site (summer 2011-2016). BBs are identified by a data-driven automated detection algorithm customized for the complex coastline. Thunderstorm vs. non-thunderstorm days are analyzed using gridded lightning data within an influential radius of the site. These meteorological classifications are compared with O3 exceedance days. While the highest conditional mean O3 was on BB days and the lowest on thunderstorm only days, thunderstorms do not always terminate an O3 event, especially in combination with a BB. To further understand the dynamical mechanisms responsible for changes in O3 from BBs and thunderstorms, the Weather Research and Forecasting (WRF) model is run at fine resolution with water vapor nudging to capture air-mass thunderstorms forced by the BB in MD. The model compared well with DISCOVER-AQ observations and radar reflectivity. Finally, an observation-constrained box model was used to study photochemical processes along the flight track during the 2013 TX DISCOVER-AQ deployment. O3 production and its sensitivity to NOx and VOCs were calculated at different locations and times of day. Results indicate controlling NOx emissions will benefit the Houston area overall, but select areas will also benefit from controlling VOC emissions. These studies, which can also be applied to particulate matter, uncover how meteorology and photochemistry come together to generate smog events at coastal cities, and can help develop efficient, high resolution policies for cleaner air.Item RELATIONSHIP BETWEEN COLUMN DENSITY AND SURFACE MIXING RATIO FOR O3 AND NO2: IMPLICATIONS FOR SATELLITE OBSERVATIONS AND THE IMPACTS OF VERTICAL MIXING(2016) Flynn, Clare Marie; Pickering, Kenneth E; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Satellites have great potential for diagnosis of surface air quality conditions, though reduced sensitivity of satellite instrumentation to the lower troposphere currently impedes their applicability. One objective of the NASA DISCOVER-AQ project is to provide information relevant to improving our ability to relate satellite-observed columns to surface conditions for key trace gases and aerosols. In support of DISCOVER-AQ, this dissertation investigates the degree of correlation between O3 and NO2 column abundance and surface mixing ratio during the four DISCOVER-AQ deployments; characterize the variability of the aircraft in situ and model-simulated O3 and NO2 profiles; and use the WRF-Chem model to further investigate the role of boundary layer mixing in the column-surface connection for the Maryland 2011 deployment, and determine which of the available boundary layer schemes best captures the observations. Simple linear regression analyses suggest that O3 partial column observations from future satellite instruments with sufficient sensitivity to the lower troposphere may be most meaningful for surface air quality under the conditions associated with the Maryland 2011 campaign, which included generally deep, convective boundary layers, the least wind shear of all four deployments, and few geographical influences on local meteorology, with exception of bay breezes. Hierarchical clustering analysis of the in situ O3 and NO2 profiles indicate that the degree of vertical mixing (defined by temperature lapse rate) associated with each cluster exerted an important influence on the shapes of the median cluster profiles for O3, as well as impacted the column vs. surface correlations for many clusters for both O3 and NO2. However, comparisons to the CMAQ model suggest that, among other errors, vertical mixing is overestimated, causing too great a column-surface connection within the model. Finally, the WRF-Chem model, a meteorology model with coupled chemistry, is used to further investigate the impact of vertical mixing on the O3 and NO2 column-surface connection, for an ozone pollution event that occurred on July 26-29, 2011. Five PBL schemes were tested, with no one scheme producing a clear, consistent “best” comparison with the observations for PBLH and pollutant profiles; however, despite improvements, the ACM2 scheme continues to overestimate vertical mixing.