1,093 research outputs found
INVESTIGATION OF TRACER GAS VARIABILITY FROM OBSERVATIONS AND MODELS
No full textThe variability of the tracer gases CO2 and ozone was investigated utilizing in-situ measurements, satellite retrievals, and model simulations.
In the tropical region, using Atmospheric Infrared Sounder (AIRS) mid-tropospheric CO2 retrievals led to the discovery of a signal with a periodicity of around two years, which was found to be related to the Tropospheric Biennial Oscillation (TBO). During strong (weak) monsoon years, the Western Walker Circulation was strong (weak), resulting in more (less) CO2 in the mid-troposphere. The MOZART-2 model results were consistent with observations with a smaller amplitude.
In the North Hemisphere polar region, the influence of sudden stratospheric warming (SSW) on AIRS CO2 was investigated. The Eliassen-Palm flux divergence was negative before the SSW; as a result, the westerly wind in the stratosphere decreased. During the SSW, the polar zonal mean wind switched to easterly and the temperature increased. Mid-latitude CO2 was transported to the high latitudes, leading to an increase of mid-tropospheric CO2 concentrations in the polar region.
Over the Central Pacific Ocean, the influence of El Niño on the mid-tropospheric CO2 was investigated using the MOZART-2 model. Model simulation results were consistent with the observations. There was more (less) mid-tropospheric model CO2 in the central Pacific and less (more) mid-tropospheric model CO2 in the western Pacific during El Niño (La Niña) events.
In addition to exploring these CO2 variations, the impacts of ENSO on the tropical total column ozone, the tropical tropopause pressure, and the 3.5-yr ozone signal in the mid-latitude were also investigated. Both the observations and Goddard Earth Observing System Chemistry-Climate Model (GEOS CCM) show tropical tropopause pressure to be related to the ENSO signal in the total column ozone. The GEOS CCM was also used to investigate a possible mechanism for the 3.5-yr signal observed in the mid-latitude total column ozone. Results suggested that a model with realistic ENSO could reproduce the 3.5-yr signal. Hence, it is likely that the 3.5-yr signal was caused by ENSO.Earth and Atmospheric Sciences, Department o
The construction of Karen Karnak: The multi-author-function
No full textThis thesis is situated within the comparatively recent developments of Web 2.0 and the emergence of interactive WikiMedia, and explores the mode of authorship within a Read/Write culture compared to that of a Read/Only tradition. The hypothesis of this study is that the role of the audience has become merged with the author, and as such, represents new functions and attributes, distinct from a more conventional concept of authorship, in which the roles of audience and author are more separate. Read/Write and participatory culture, as defined by this study, is focused on collaboration, and includes the influences of D.I.Y. culture, Open-Source practices and the production of text by multiple authors. Multi-authorship presents a re-thinking of several concepts which support the notion of the individual author, since the focus of multi-authorship is not on attribution and ownership of a finished text, but on the continued malleability of a text. Modes of multi-authorship, demonstrated in the use of the pseudonyms Alan Smithee and Karen Eliot, represent declarative authors whose names signify multiple origins, whilst concurrently indicating a distinct body of work. The function of these names form an important context to this study, since primary research involves the construction of an experimental mode of multi-authorship utilising WikiMedia technology and the interaction of thirty nine participants, who are invited to create a body of work under the collective pseudonym Karen Karnak. The data generated by this experiment is analysed using aspects of Michel Foucault's author-function to identify and determine power structures inherent in the WikiMedia context. The interplay of power structures, including concepts such as identity, ownership and the body of work, affect the resulting mode of authorship and contribute to the construction of Karen Karnak, suggesting further areas of research into the emerging multi-author
Teaching and Learning from the Mediations in Barry Werth\u27s \u3cem\u3eDamages\u3c/em\u3e
No full textThis essay is based primarily on materials the author developed for courses taught at the University of Missouri-Columbia, School of Law, in the winter 2002 and 2003 semesters, based on Barry Werth\u27s book, Damages
Atmospheric Mercury and Methane in the South-Central U.S.
No full textThis study characterized temporal and spatial variations of atmospheric mercury and methane (CH4), and investigated their emission sources. Speciated atmospheric mercury observations collected over the period from 2008 to 2010 at the U.S. Atmospheric Mercury Network sites (AMNet) were analyzed. We found similar median levels of gaseous elemental mercury (GEM) as well as its seasonality at 11 sites. Seasonal and diurnal variations were also observed for gaseous oxidized mercury (GOM) and particulate bound mercury (PBM).
This study also reports continuous measurements of total gaseous mercury (THg = GEM + GOM) for the first time in urban Houston area. We found that the median level of THg was consistent with the current global background level. A predominant feature of THg was the frequent occurrence of large THg spikes. Our measurements revealed that the variability of THg was primarily controlled by nearby mercury sources.
Atmospheric mercury emissions in the Barnett Shale area were studied by employing both stationary measurements and mobile laboratory surveys. The influence of oil and natural gas (ONG) emissions was substantial in this area, as inferred from the i-pentane/n-pentane ratio (= 1.17). However, few THg plumes were captured in our extensive mobile laboratory surveys. Only one compressor station and one natural gas condensate processing facility were found to have significant THg emissions. Our results suggest that the majority of ONG facilities are not significant sources of THg; however, it is highly likely that a small number of these facilities contribute a relatively large amount of the emissions in the ONG sector.
Atmospheric CH4 was also investigated to quantify emissions from ONG operations and landfills in the Barnett Shale area. The background CH4 level (10th percentile) was 1.89 ppmv, which was higher than the northern hemisphere background level. Emission rates were estimated using Inversed Dispersion Models. Model results show that well pad emissions were linearly correlated with gas production, yielding a total well pad emission rate of 1.44×105 kg CH4/hr in the Barnett Shale area. It was found that CH4 emissions from compressor stations and gas processing plants were substantial; several of them have similar emission rates as a major landfill.Earth and Atmospheric Sciences, Department o
Machine Learning Estimation of Daily Surface Concentrations of PM2.5, NO2, and MDA8 Ozone at High Spatiotemporal Resolutions
No full textHigh concentrations of pollutants in the atmosphere endanger public health and negatively impact other domains. Although surface measurements of pollutants at ground stations are quite reliable, they still suffer from the low spatial coverage due to the limited number of ground stations. Such limitations call for the development of accurate approaches to estimating surface concentrations of pollutants, particularly in regions with no monitoring stations. This thesis proposes machine learning (ML) and deep learning (DL) techniques to estimate daily surface concentrations of PM2.5, NO2, and daily maximum 8-h average (MDA8) ozone.
The first task focuses on using random forest (RF) to estimate daily surface concentrations of PM2.5 at 1-km spatial resolution in the 2014-2018 period over Texas to obtain a correlation coefficient (R) of 0.83-0.90 and a mean absolute bias (MAB) of 1.47-1.77 µg/m3. Our results also show the high capability of RF compared to the commonly used models for estimating PM2.5 concentrations. The second task focuses on developing the PCNN-DNN , a novel two-step DL model, to estimate daily surface NO2 concentrations over the contiguous United States (CONUS) from 2005 to 2019. To the best of our knowledge, the PCNN-DNN is the most accurate model in the globe to estimate surface NO2 levels, with an R of 0.975 to 0.978 and an MAB of 0.99 ppb to 1.38 ppb. Moreover, the PCNN-DNN model generates estimated NO2 grids without any missing values, improving the quality of various applications such as public health studies.
The third task is to develop a DL approach to accurately estimate surface MDA8 ozone and examines the spatial contribution of several factors on ozone levels over the CONUS in 2019. The model obtains an R of 0.95 and an MAB of 2.79 ppb, highlighting the promising performance of the Deep-CNN at estimating surface MDA8 ozone. We also use Shapley additive explanations (SHAP) to generate, for the first time, a spatial feature contribution map (SFCM) for ozone, the results of which confirm an advanced ability of Deep-CNN to accurately capture the relationships between ozone and most predictor variables.Earth and Atmospheric Sciences, Department o
A model comparison of basic and surface energy variables in the development of the PBL in a southeast Texas coastal region
No full textAir quality forecasting requires atmospheric weather models to generate reliable and accurate meteorological conditions. Some variables are well-simulated, but others, like the planetary boundary layer (PBL) height, are not as accurately reproduced. This study compares rarely observed energy balance and turbulence variables to modeled results, and seeks to determine if and to what extent these variables contribute to the development of the PBL. Similarly configured MM5 and WRF model outputs were compared to observations of temperature, wind fields, radiation, heat fluxes, and PBL heights during an intensive field campaign on the Gulf Coast in the summer of 2006. The r2 and bias values were calculated as a measure of model performance. The results showed that in general, WRF performed comparably or better than MM5 for all variables except wind speed and directions, sensible heat flux, ground flux, and PBL height. Nighttime simulations for both models are not well-parameterized except for water vapor mixing ratio. PBL height timing was good for both models, but the morning development was not well-simulated. A frontal passage occurred during the study period that led to two mostly cloud-free days; on these days the relationship between incoming solar radiation and the energy variables suggests that there may be an energy sink in the models that could lead to underestimations of PBL height. The dry bias or disparate land-surface initialization datasets might contribute to deviations of the models from the observations and may explain the models' PBL height performance. Further examination of the energy budget and turbulent dataset under extended cloud-free days could provide a better understanding of these variables to PBL height development and lead to better air quality predictions.Earth and Atmospheric Sciences, Department o
Spatial and Temporal Distribution of Speciated Atmospheric Mercury in Southeastern Texas
No full textThe purpose of this study was to investigate and compare the contribution of anthropogenic emissions to the levels of atmospheric mercury in both urban and coastal settings of southeastern Texas. Speciated atmospheric mercury measurements were obtained from the ideally located University of Houston Moody Tower and University of Houston Coastal Center from March 22, 2012- June 6, 2013 and July 26, 2013-June 6, 2013, respectively. The use of key tracer gases from various data sources as well as meteorological data from ground-based stationary monitoring facilities was used in the evaluation of high-mercury pollution plumes, the general direction of the source origin as well as seasonal and diurnal mixing ratios of the three atmospheric mercury species. At the costal site measurements showed consistently lower mixing ratios for all mercury species and had no significant mercury events recorded. The urban University of Houston Moody Tower had much higher and more dramatic fluctuations in mixing ratios for all three mercury species with two major mercury events recorded. Both events were associated with periods of low wind conditions and Houston Ship Channel origins. While the measurements collected at the urban location show consistencies with past studies conducted at the same location, the complexity of atmospheric mercury interactions prevent any indepth interpretations of the results.Earth and Atmospheric Sciences, Department o
Measurements and analysis of ozone production in Houston and Los Angeles
No full textOzone is a respiratory irritant that affects all groups of people, but can be of significant concern to young children, those with respiratory illnesses such as asthma, and the elderly. Repeated exposure can cause permanent lung damage. An estimated 123 million people in the Unites States live in regions designated as non-attainment for the 2008 8-hour ozone standard of 75 ppbv. Nearly 5.9 million people live in the Houston-Galveston-Brazoria non-attainment area, and over 15.7 million live in the Los Angeles-South Coast Air Basin non-attainment area.
The work presents the results and analysis of measurements collected during several field campaigns in Houston, TX between 2006 and 2012, as well as in Pasadena, CA (CalNex) in the summer of 2010. Part one focuses on the comparison of O3, CO, NO, and NO2 measured continuously at two heights on the UH main campus in the fall of 2011 and 2012 and finds that the titration of O3 to NO2 accounts for ~50% of the observed nighttime differences on average, while it accounts for nearly 100% of the differences during some mornings. The second part presents the results of photochemical box modeling of O3 production rates during three campaigns in Houston and during CalNex, which shows the effects of VOC reductions on O3 production and the differences between the spring and fall O3 seasons in Houston. Finally, an examination of the NOy budget during CalNex and the impacts that the choice of classification of days has on the analysis will be discussed reports that the overall agreement between measured NOy and the sum of individual NOy species is good, and that distinctly different results for calculated O3 production efficiencies are found depending on which classification method is applied to the measurements.Earth and Atmospheric Sciences, Department o
Investigation of the Source, Fate, and Transport of Mercury in Hunza River, Northern Areas, Pakistan
No full textMercury is one of the most hazardous and toxic elements with a high degree of mobility. Although it occurs naturally, anthropogenic activity can also release mercury to the environment. Globally, the use of mercury in gold mining has caused significant environmental pollution since Ancient Roman times. Small-scale gold mining activities along Hunza and Gilgit rivers are long known to be discharging mercury in the amalgamation and roasting processes. Previous studies reported high mercury concentrations in soils close to mining operations as well as serious health problems for miners. However, none of the studies have focused on the level of contamination in aqueous environments. This is the first study on the investigation on fluvial fate and transport of mercury in Hunza River. This research study aimed to investigate the source, fate and transport of river-borne mercury. Eleven (11) out of thirty-seven (37) river water samples showed higher dissolved mercury concentration than critical levels suggested by Environmental Protection Agency. These sites corresponded to the observed gold panning sites. Particulate mercury concentration was roughly three orders of magnitude higher than that of dissolved mercury per liter of water for all sampled rivers. Thus, suspended sediments represented the major pathway of mercury transport. A mass balance was performed to calculate annual mercury discharge to Hunza River basin. A conservative estimation resulted in 0.63 tonnes of annual mercury flux. This amount of mercury is difficult to result from anthropogenic discharge alone. An index based physical model was created to estimate mercury yield at sub-basin level. It was found that the dominant source of mercury is the mercury-rich soils upstream of Attabad Lake rather than the direct mercury release from mining activities. This result is supported by previous soil geochemistry data. Significant decrease in both dissolved and particulate-bound mercury concentration downstream of Attabad Lake suggested that mercury is being accumulated or consumed in the lake. Although minimization or elimination of mercury loses from mining process seems important for the well-being of the miners, preventing further accumulation of mercury in Attabad Lake would be a much more effective mean of mercury control in the region.Earth and Atmospheric Sciences, Department o
Comparison of MODIS Snow Albedo To Field Measurements In Central Greenland
No full textSpectral snow albedo, physical snow properties, and snow chemistry were measured daily during May, June, and July 2011 at Summit, Greenland to investigate the variability in snow albedo and its impact on aerosol direct radiative forcing. In this study we compare our spectral albedo measurements to the Moderate Resolution Imaging Spectrometer (MODIS) daily albedo product. We additionally compare to albedo measurements from the Baseline Surface Radiation Network station at Summit (BSRN), and to modeled albedo using measured snow physical and chemical properties as input to the DISORT code. The spectral albedo measurements were made with an Analytical Spectral Devices (ASD) spectroradiometer at 350 – 2200 nm. We calculate weighted integrals of the spectral data to compare to seven MODIS narrow bandwidths ranging the UV through Infrared, as well as a broadband product that represents the full solar spectrum.
Root mean square error (RMSE) for MODIS and field-measured albedo is 0.033 (mean difference of 0.023) for the broadband integration using MODIS high-quality only retrievals, and the narrow bandwidths range 0.022 – 0.077 RMSE (0.009 – 0.063 mean difference). The broadband values show an improvement in error from previous MODIS field validation studies, particularly in the UV and visible wavelengths. MODIS is consistently lower in magnitude than the field measured albedo, and shows poor correlation. The daily and multiday range of variability of the field measurements is much greater than MODIS albedo, and evidence is presented in support of the field-measured daily variability. Spatial variability is also constrained with data from multiple spatial surveys, and it is shown that surface roughness and error due to apparent albedo likely has a dominating effect on spatial variability, whereas the greater range of daily variability is dominated by changes in snow surface properties.Earth and Atmospheric Sciences, Department o
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