Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (p. 334-344). / by M. Burc Oral. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Includes bibliographical references (p. 289-310). / by Mark Hunter Murray. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references (p. 203-212). / Mobile emissions represent a significant fraction of the total anthropogenic emissions burden in megacities and have a deleterious effect on air quality at local and regional scales. Due to the significant sources of uncertainties involved during the estimation of mobile emissions, an adequate treatment of emission uncertainties is critical during the design of air quality control strategies using AQMs. This thesis focuses on quantifying the effects of parametric uncertainties of input emission fields on model uncertainties of ozone predictions. We obtained direct measurements of mobile emission sources in the Mexico City Metropolitan Area (MCMA) using a novel measurement technique and quantified the magnitude and variability of key pollutant species. This analysis allowed a direct evaluation of the emissions inventory used in AQMs for the MCMA. Measured selected VOCs and NOy showed a strong dependence on traffic mode and indicated a larger than expected burden of emitted NOx and aldehydes. Our measurements of benzene, toluene, formaldehyde, and acetaldehyde in the MCMA indicate that the emissions of these toxic pollutants are similar or higher than for some US cities. We derived approximate historical trends of the VOC/NOx emission ratio and quantified the impact of changes of mobile emission sources on the photochemical levels using the Brute Force Method and Direct Decoupled Method sensitivity techniques with the CAMx model. The model reasonably reproduces concentrations of ozone and VOCs and accurately those of CO and NOx but over predicts OH by about 25% and severely under-predicts HO2 by a factor of 2 to 3 suggesting that the radical formation pathways in current state of the art AQMs should be revised. / (cont.) The model successfully reproduces the corresponding relative changes in historical observations of ozone peak and diurnal average concentrations and suggests a current moderate VOC-sensitive regime. The analysis of the model's sensitivity coefficients to individual perturbations of VOC group species as described by the SAPRC99 chemical mechanism showed that the model is particularly sensitive to aromatics, higher alkenes, and formaldehyde emissions. We found, however, that NOx, olefins and aromatic species can potentially contribute significantly to uncertainties in ozone predictions. / by Miguel Angel Zavala-Perez. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (leaves 129-138). / by George P. Panteleyev. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990. / Vita. Accompanied by 8 folded maps in back pocket. / Includes bibliographical references. / by Lawrence William McKenna III. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references (leaves 40-42). / This work presents the DeMeo taxonomy, an asteroid taxonomy with 24 classes based on Principal Component Analysis of spectral data over the visible and near-infrared wavelengths, specifically the 0.45 to 2.45 micron range. Principal Component Analysis was used by both Tholen (1984) and Bus (1999) to create taxonomies on visible data. There is no pre-existing taxonomic system for the entire suite of asteroid characteristics because only in the current decade has spectral data collection become available in the near-infrared for asteroids down to relatively faint (V= 17) limiting magnitudes. (Rayner et al. 2003) With a larger data range, which includes important absorption features at one and two microns suggesting the presence of minerals, there is a need for an extended system to encompass this range of information. In this work we explain the process of creating the taxonomy, the method for finding an object's taxonomic class under this system, and present spectral types for the 365 objects that were used to create the system. / by Francesca E. DeMeo. / S.M.

Thesis: S.B. in Geosciences, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2004. / Cataloged from PDF version of thesis. Some pages in original thesis contain text that run off the edge of the page. / Includes bibliographical references (pages 61-64). / Desertification, the spread of desert-like conditions in arid or semiarid areas due to human influence or to climatic change, affects most arable land in arid and semi-arid China. This project provides an analysis of desertification in northeastern arid and semi-arid China to determine its spatial distribution, severity, and causes. It locates areas of desertification and identifies and ranks in order of importance their anthropogenic and climatological causes. It especially focuses on the savanna transition zone west of Beijing to see if climate factors or increasing population density can be correlated to land cover change. GIS (Geographic Information Systems) software is used to recognize locations of rapid land cover change. Statistical tests, such as unbalanced multi-way ANOVA, determine if climatic or anthropogenic factors can predict if an area is undergoing rapid land cover change. The climate and population data is resampled to an uniform 0.5' scale and converted into qualitative, data before statistical testing. This project tests if land cover change, a more difficult indicator to measure, can be predicted by analyzing trends in vegetation, precipitation, temperature, wind and population. Desertification is more likely and more severe in climates with low precipitation. Areas with low population density tend to have less severe land degradation than areas with medium or high density; this may be due to more intense land use in high population areas. / by Leah Hutchison. / S.B. in Geosciences

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: p. 125-126. / by Carl B. Godkin. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references. / The eastern margin of the Tibetan plateau is characterized by large rivers dissecting regional topography that has been uplifted in association with the continued convergence of the Indian subcontinent and Eurasia. In this thesis, I utilize field observations, digital topographic data, cosmogenic isotope data, low-temperature thermochronology and numerical simulations to better understand the evolution of these rivers and tectonics of the region. The goals of this work are: 1) to characterize the rates and processes of river incision and erosion associated with major rivers dissecting the eastern margin; 2) to better understand and constrain the transient landscape evolution that defines regional topography; and 3) to move closer to understanding the relationships among tectonics, topography and erosion that apply directly to the eastern margin, and may be applied to other landscapes around the world. To accomplish these goals, I study the rates and processes of river incision and erosion on the eastern margin on a variety of spatial and temporal scales. I discuss local incision processes and related landforms by exploring the influence of large landslides and discussing epigenetic gorges, which are secondary bedrock-walled channels that form in relation to episodes of river blockage or afgradation. I quantify short-term (102-105 yr) erosion rates using cosmogenic isotopes ( Be) from river sand for 65 small river basins (typically <100 km2) throughout the eastern margin, and long-term (106-107 yr) incision rates using low-temperature thermochronology from elevation transects collected within the Dadu, Yalong, and Yangtze river gorges. / (cont) Each short-term, basin-averaged erosion rate represents erosion for a unique subset of eastern margin topography, lying within the context of the large-scale transient morphology of the region; while the long-term incision rates quantify the onset and rates of rapid incision associated with regional scale river response to plateau uplift. All of these datasets combine to provide a valuable example of a large, actively evolving transient river with spatially variable erosion and incision, from which can be drawn implications for regional tectonics and models of river incision and landscape evolution, in general. / by William Burke Ouimet. / Ph.D.

Thesis: S.M. in Atmospheric Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 81-82). / Through the analysis of the high-resolution radiosonde measurements over the U.S., we identified a decreasing trend near the surface and an increasing trend at the upper levels, which is consistent with previous studies. The decreasing trend of near-surface wind speed is statistically significant (p<0.01). However, the statistical significance of the decreasing trend drops with increases in altitude. We identified a largest negative trend in wind speed close to the surface. The magnitude of this largest negative trend is up to 15 times of the values reported in the previous studies. This might be due to the higher resolution in the vertical than data used in the previous studies, but it could also be a short-term phenomenon due to the shorter record considered as compared with the previous work. We also found a relationship between the elevation of the sites and the trend of near-surface wind and wind aloft. We identified a statistically negative relation between the magnitude of the decreasing trend and the elevation of the stations. The height of the planetary boundary layer (PBL) is estimated using three different methods. For non-elevated sites, a decreasing trend is seldom found for wind above the PBL, suggesting an important role for the land surface in determining the trend of wind speed. For elevated sites such as those in the mountainous west of the US, a decreasing trend is found for both the near-surface wind and the wind aloft, indicating that the changes in free-tropospheric circulation may also exert influence on changes in surface wind speeds for these sites. / by Tao Feng. / S.M. in Atmospheric Science