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

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    An evaluation of a severe smog episode in the Eastern U.S. using regional modeling and satellite measurements
    (2011) Yegorova, Elena Andreyevna; Dickerson, Russell R; Allen, Dale J; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    An ensemble of regional chemical modeling (WRF/Chem with RADM2) simulations, satellite, ozonesonde, and surface observations during July 7-11, 2007 was used to examine the horizontal and vertical signature of one of the worst smog events in the eastern U.S. in the past decade. The general features of this event -- a broad area of high pressure, weak winds and heavy pollution, terminated by the passage of a cold front -- were well simulated by the model. Average 8-hr maximum O3 has a mean (±Σ) bias of 0.59 (±11.0) ppbv and a root mean square error of 11.0 ppbv. WRF/Chem performed the best on poor air quality days, simulating correctly the spatial pattern of surface O3. Yet the model underpredicted O3 maxima by 5-7 ppbv in the Northeast and overpredicted by 8-11 ppbv in the Southeast. High O3 biases in the Southeast are explained by overpredicted temperatures in the model (>1.5°C). Sensitivity simulations with 1) accelerated O3 dry deposition velocity and 2) suppressed multiphase nitric acid formation pushed the model closer to observations. Simulated O3 vertical profiles over Beltsville, MD showed good agreement with ozonesonde measurements, but the modeled boundary layer depth was overpredicted on July 9, contributing to the low bias over this region. During this severe smog episode, space-borne TES detected high total tropospheric column ozone (TCO) over the Western Atlantic Ocean off the coast near North and South Carolina. The standard product (OMI/MLS) missed the magnitude of these local maxima, but the level-2 ozone profile (OMI) confirmed the TES observations. HYSPLIT back trajectories from these O3 maxima intersected regions of strong convection over the Southeast and Great Lakes regions. When lightning NO emissions were implemented in WRF/Chem, the high concentrations of NOx and O3 off the coast were well reproduced, showing that the exported O3 was produced by a combination of natural NO and pollutants lofted from the lower atmosphere. Lastly, WINTER MONEX O3 data from 1978 are presented for the first time here in discussion of open cell convection over Indonesia.
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    OMI Tropospheric Sulfur Dioxide Retreival: Validation and Analysis
    (2007-08-28) McClure, Brittany; Dickerson, Russell R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    SO2 impacts the radiative balance of the Earth and is the precursor to the major acid and much of the particulate matter in the atmosphere. Improved spectrometer resolution of the Ozone Monitoring Instrument (OMI) enables SO2 retrieval in the planetary boundary layer. OMI has a small spatial resolution of 13 km x 24 km and daily near-global coverage. I have evaluated the accuracy of the OMI by comparing aircraft measurements in Northeast China to the OMI retrieval of three different algorithms: the Band Residual Difference (BRD), the Spectral Fit (SF), and a combination of the two (SF & BRD). The SF algorithm shows the best agreement with a less than 15% difference for high SO2 loading (greater than 1 DU). The SF & BRD has a ~ -0.25 DU bias, the BRD and SF a ~ -0.1 DU bias. The noise of the OMI is reduced to ~0.2 DU by averaging over 100 days and is not improved by increasing the averaging time. The OMI is also able to track SO2 as it moves away from its source region in the PBL and once it is lofted above this layer.