Browsing by Subject "Aerosols"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item Atmospheric Measurements of Submicron Aerosols at the California-Mexico Border and in Houston, Texas(2013-04-29) Levy, Misti EUsing an innovative arrangement of instruments to obtain a comprehensive set of properties, we present a description of the submicron aerosol properties for two distinct regions. During the 2009 SHARP/SOOT campaign in Houston, TX, the average effective density was 1.54 ? 0.07 g cm^-3, consistent with a population comprised largely of sulfates and organics Even in low concentrations (0.31 ? 0.22 ?g m^-3), black carbon concentration has a significant impact on the overall density and optical properties. Under prevailing northerly winds, the average black carbon concentration increases from 0.26 ? 0.18 ?g m^-3 to 0.60 ? 0.21 ?g m^-3. Throughout the campaign, aerosols are often internally mixed, with one peak in the effective density distribution located at 1.55 ? 0.07 g cm^-3. In addition, we conclude that in this region the meteorology has a discernible impact on the concentration and properties of aerosols. After a frontal passage, there is a significant shift in the size distribution as the concentration of <100 nm particles increase and the average effective density decreases to 1.43 ? 0.08 g cm^-3. In Tijuana, Mexico, the submicron aerosols are heavily influenced by vehicle emissions. We observe an average single scattering albedo of 0.75. This average SSA is lower than observed in many US urban environments, and indicates a high concentration of black carbon. The average black carbon concentration is 2.71 ? 2.65 g cm^-3. The aerosol size distributions reveal a high concentration of small particles (< 100 nm) during the day, which are frequently associated with vehicle emissions. Overall, 46 and 81 nm particles are hydrophobic, have an average effective near 1.30 g cm^-3, a higher volatile growth factors than the larger particles, and exhibit a distinct diurnal cycle, which, on average, ranges between 0.80 during the afternoon and 1.70 g cm^-3 overnight. 46 and 81 nm distributions indicate a uniform aerosol composition. 151 and 240 nm aerosols are less cyclical, and the hygroscopicity, volatility, and effect density distributions all exhibit a bimodal distribution, which indicates an external mixture of aerosols. Black carbon and vehicle and industrial organic emissions appear to be the main components of the external mixture.Item Automated measurement of aerosol acidity(Texas Tech University, 1996-08) Chasteen, Coleman C.Acidic aerosols have been shown to contribute to diseases of the upper respiratory tract and are a source of environmental acidification. Though aerosols can be coUected by various means, though none of these collection methods have been particularly well suited for the measurement of rapidly changing aerosol concentrations and temporal events. The performance of an instrument designed to measure aerosol acidity is reported for both idealized and chaUenging conditions. The abiUty to measure changes in acidity in short periodic episodes has been documented in the measurement of acidity in a room during the operation of a kerosene fueled space heater.Item Development of nanofiber protective substrates(Texas Tech University, 2004-08) Subbiah, ThandavamoorthyElectrospinning uses high voltage electric field to produce high surface area fibers in the nanometer range. Polymeric nanofibers were prepared by the electrospinning process and were characterized using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). A study on the relationship between process parameters and fiber characteristics was undertaken. The dependence of fiber morphology on the solvent volatility and collector substrate characteristics was critically analyzed. Results on the self assembling nature of the charged fibers over different collector substrates were obtained and reported in the thesis. Defect free nanofiber webs with high specific surface area and low porosities suitable enough to be used as adsorptive filtration membranes were prepared. Polyurethane nanofibers were used as nano metal oxide catalyst carriers by successfully impregnating the catalyst in a single-step electrospinning process. Aerosol filtration abilities of nanofiber membranes were tested and the results are presented.Item Interaction between aerosols and the mesoscale convective systems over the tropical continents(2016-05) Chakraborty, Sudip, Ph. D.; Fu, Rong (Professor); Dickinson, Robert E; Yang, Zong-Liang; Allen, David T; Massie, Steven T; Marengo, JosePresence of aerosols in the upper troposphere can have significant impacts on the Earth’s radiative energy budget. However, the aerosol–cloud relationship represents the largest uncertainty in the radiative energy budget. Relationships between aerosols and the mesoscale convective systems (MCSs) are complicated and difficult to ascertain, due in large part to inadequate availability of satellite datasets until recent years. Variation of aerosol impacts with meteorological parameters and the relative influence of these parameters on the convective strength of the MSCs can also be attributed to limited detectability of aerosol invigoration effects. To address the interaction between aerosol and the MCSs, I first address the influence of MCS on the distribution of the aerosols, which is poorly known on a global scale. Then, I investigate the influence of aerosol on MCSs. This dissertation addresses these problems by collocating a suite of geostationary and polar orbital satellites at three different phases of their convective lifecycle. First, I estimate the extent of upper tropospheric aerosol layers (UT ALs) surrounding the MCSs and explore the relationships between UT AL extent and the morphology, location, and developmental stages of collocated MCSs in the tropics over equatorial Africa, South Asia, and the Amazon basin between June 2006 and June 2008. I identify that the most extensive UT ALs over equatorial Africa are associated with the mature MCSs, while the most extensive UT ALs over South Asia and the Amazon basin are associated with the growing MCSs. Convective aerosol transport over Amazonia is weaker than that observed over the other two regions despite similar transport frequencies, likely due to smaller sizes and shorter mean lifetimes of Amazonian MCSs. Variations in UT ALs in the vicinity of tropical MCSs are primarily explained by variations in the horizontal sizes of the associated MCSs and are not related to aerosol loading in the lower troposphere. Relationships between convective properties and aerosol transport are relatively weak during the decaying stage of convective development. Then I estimate the relative influence of aerosols and other meteorological parameters on MCS strength and longevity using collocated samples of MCSs from January 2003 to June 2008. The results show that relative humidity (RH) and convective available potential energy (CAPE) have the strongest impacts on MCS lifetime and enhance the lifetime of the MCSs by 6-36 hours when other parameters such as vertical wind shear (VWS) and aerosols are kept constant. Aerosols also enhance the convective lifetime of MCSs, however at a much weaker rate (6-24h) and only when RH and VWS are high. Moreover, aerosol influence on convective lifetime is detected during the mature and decaying phases only. At the continental scale, aerosols explain 20-27% of the total variance of MCSs’ lifetime over equatorial South America, but explain only 8% of the same over equatorial Africa. South Asian MCSs are more strongly influenced by meteorological parameters and MCS-associated aerosols when they are over the ocean than when over the land since most MCSs form and develop over the oceans. After that, I estimate the influence of aerosols and other meteorological parameters on MCSs’ rain rate (RR). Results show that an increase in aerosol concentration enhance IWC and suppress RR and LH during all three phases of convective lifetime. Increasing aerosol concentrations suppress RR at the rate of -0.38 mm/h and -0.47 mm/h during the growing, decaying phases when VWS is high and at a rate of -0.30 mm/h during the mature phase when RH is low. Meteorological parameters such as VWS and RH have significant effects on these aerosol influences. The suppression of RR is also associated with a decrease in latent heat released by large hydrometeors. Aerosols explain 16%, 23%, and 29% of RR’s variance during the growing, mature and decaying phases, respectively, as estimated by a multiple linear regression method. Consequently, aerosols enhance IWC of the MCSs inside the anvil up to 0.72, 1.41, 0.82 mg/m3 and enhance the total integrated reflectivity of the larger-sized ice particles up to 8, 11, and 18 dBZ in the convective core regions during the growing, mature and decaying phases, respectively. In contrast, changes (one standard deviation) in CAPE and RH enhance the RR up to 0.35 mm/h. This dissertation study provides the first satellite based global tropical assessment of the relative influences of aerosols and meteorological conditions on MCSs’ lifetime, rain rate, and IWC and the mutual dependence of these influences. It also shows how aerosols influence the rain rate, cloud ice and lifetime of the MCSs, varying within their lifecycle and between different tropical continents ranging from humid equatorial South America during wet season and big monsoonal systems over South Asia to relatively dry equatorial Africa with high aerosol loading. In doing so, this work has also advanced our capability to evaluate whether or not aerosols could increase convective lifetime by suppressing rain rate and invigorating the MCSs on climate scale and what are the favorable meteorological conditions for aerosol to affect the lifetime of the MCSs. Our results also provide an interpretive framework for devising and evaluating numerical model experiments that can examine relationships between convective properties and ALs transported in the upper troposphere. In the future, we would like to investigate the influence of different meteorological parameters and aerosols on extra tropical MCSs and on self-aggregation of convection.Item Intraseasonal modulation of Indian summer monsoon by Middle East dust : an observational and numerical modeling study(2015-08) Jin, Qinjian; Yang, Zong-liang; Dickinson, Robert E.; Fu, Rong; Jackson, Charles S.; Wang, ChienAs one of the world's strongest monsoon systems, the Indian summer monsoon affects one-third of the global population. The temporal and spatial variability of the ISM rainfall has great socio-economic impacts, particularly on agriculture and food supply in South Asia. Additionally, South Asia is an area with heavy atmospheric loading of aerosols from both wind-blown mineral dust and manmade pollutants. These aerosols can significantly influence the ISM rainfall through their radiative and microphysical effects. In our study, we focus on three questions. 1) How does the ISM rainfall respond to the Middle East dust in observations on intraseasonal timescales? 2) Can the regional climate model reproduce the observed relationship between Middle East dust and the ISM rainfall, and what are the model uncertainties and how do they influence our results? 3) How does the ISM system respond to different types of aerosols in different source regions on the intraseasonal timescales? I use multiple satellite retrievals, reanalysis datasets, and ensemble modeling experiments to study the dust-monsoon connection. Multivariate empirical orthogonal function is performed on aerosol optical depth and rainfall from satellite observations, and winds and geopotential height from reanalysis to identify the coupled spatial patterns among these variables. Cross-correlation analyses between satellite-retrieved AOD in the Middle East and the ISM rainfall are calculated to characterize the timescales of dust-monsoon connections. Furthermore, ensemble numerical experiments are conducted to examine the causal relationship and physical mechanisms between Middle East dust aerosols and the ISM monsoon. The ensemble experiments are created by perturbing physical and chemical model schemes to examine the uncertainties in parameterizing the shortwave radiation, dust diffusion in the boundary layer, and aerosol chemical mixing rules. The primary scientific findings are summarized here. (1) Middle East dust aerosols are positively correlated with the ISM rainfall in Pakistan, central and northern India, and Coastal South West India. (2) The timescale of the dust–monsoon connection is about 11 to 13 days. (3) Middle East dust aerosols can enhance the southwesterly monsoon flow over the Arabian Sea due to their direct radiative heating effect in the lower troposphere, which can increase the south–north ocean–land thermal contrast. The enhanced monsoon flow can transport more water vapor from the Arabian Sea to the Indian subcontinent, thereby resulting in more monsoon rainfall. (4) Middle East dust aerosols play a dominant role in modulating the ISM rainfall compared to dust aerosols from other regions; local anthropogenic aerosols in India, although with much lower concentrations than dust, can play a similar role to Middle East dust aerosols. Our findings demonstrate that a better representation of Middle East dust aerosols and their interactions with meteorological fields is important for understanding and modeling the variability of the ISM rainfall.Item Isolation of ambient aerosols of known critical supersaturation: the differential critical supersaturation separator (DSCS)(Texas A&M University, 2007-09-17) Osborn, Robert JohnA field-deployable instrument has been developed that isolates from an ambient aerosol population only those particles that have critical supersaturations, Sc, within a narrow, user-specified, range. This Differential Critical Supersaturation Separator (DScS) is designed to supply one or more particle size and/or composition analyzers to permit the direct examination of the factors that influence the activation properties of ambient aerosols. The DScS consists of two coupled parallel plate continuous flow thermal gradient diffusion cloud chambers housed within a single enclosure. Descriptions of instrument operation, construction and calibration data collected, when pure ammonium sulfate aerosols were injected into the DScS for operation at 0.15%< Sc<0.175%, 0.30%< Sc<0.35%, and 0.60% < Sc<0.70%, are included. Following instrument development, the DScS was deployed during March 2006 for the Megacities Impact on Regional And Global Environment (MIRAGE) field campaign in Mexico City, Mexico. Throughout the MIRAGE field campaign a Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system measured aerosol size distributions and size-resolved hygroscopicity of DScS separated aerosol. The dry diameter (Dp*) of particles sampled in the TDMA system as well as the known Sc prescribed in the DScS were combined in a modified version of K????hler Theory to make predictions of particle hygroscopicity. These predictions frequently overestimated the measurements. Further analysis of DScS separated aerosols compares the known particle Sc to a predicted particle Sc, providing insight into particle activation efficiency. Overall, the sampled aerosol exhibited properties that indicate they were more efficient at activation than K????hler Theory would predict.Item Measuring and modeling aerosols in carbon dioxide capture by aqueous amines(2016-08) Fulk, Steven Michael; Rochelle, Gary T.; Bonnecaze, Roger T; Chen, Eric; Hildebrandt Ruiz, Lea; McDonald-Buller, ElenaPilot scale CO2 capture plants have shown that amine condensation onto seed nuclei results in very high amine emissions which are very difficult to control using traditional aerosol removal techniques. Aerosol emissions can be suppressed by adjusting operating conditions such that drops evaporate, or, alternatively, grow to a size that can be efficiently captured by low cost methods. The effects of operating conditions on aerosol growth were investigated by experimental measurement and numerical modeling with sensitivity analyses. Total particle densities and particle size distributions (PSDs) were measured using a custom-built phase Doppler interferometer (PDI) on bench and pilot scale CO2 absorbers. Seed nuclei were generated using vaporized H2SO4, gaseous SO2, and flue gas from a coal-fired power plant. PSDs were used to calculate the aerosol amine concentration when compared to total phase (gas and aerosol) measurements collected by FTIR. The effects of operating conditions on aerosol growth were simulated in a combined heat and mass transfer model coded in MATLAB®. Aerosol transport equations included corrections for surface curvature and transport length scale regimes. Absorber and water wash models were simulated using Aspen Plus®. Inlet CO2 is crucial in creating supersaturation in the absorber; the loading difference between the aerosol and bulk solvent creates an amine driving force for condensation. Aerosols grow faster in non-intercooled columns due to differences in solvent composition (CO2 loading) and temperature. H2O condensation is the primary growth mechanism in the water wash. Reducing the water wash amine concentration and providing additional residence time leads to more aerosol growth. Doubling the water wash height results in a 13.7 % increase in the final aerosol diameter for a generic 8 m PZ absorber. Similar to some other volatile amines, PZ forms 1–5 μm aerosols because its amine volatility is a strong function of CO2 loading. The amine concentration in measured aerosol distributions, calculated by PDI/FTIR comparison, was one-to-two orders of magnitude lower than the bulk solvent. SO2 forms aerosol with PZ. 65 % of injected SO2 leaves in the aerosol phase. Therefore, SO2 polishing scrubbers are essential and systems should not be designed for simultaneous absorption of CO2 and SO2.Item Modeling the effects of aerosols on groundwater systems(1989-12) Brown, Theresa Jean; Sharp, John Malcolm, Jr., 1944-Just as children eventually learn that covering their eyes does not make them invisible, we as adults have realized that just because harmful substances are "out-of-site" it does not necessarily mean they are gone for good. As we expanded our ability to think abstractly we began to consider how our actions affect our future and the lives of future generations. For example, we established procedures for the handling and disposal of high level radioactive waste and other hazardous materials because of the threat such materials pose to the environment. To date, however, the effect of atmospheric pollutants on groundwater supplies has been virtually ignored. Atmospheric pollution sources include, but are not limited to, smoke stack emissions, releases from power plants, weapons testing and manufacturing, fires, explosions, and deflation from tailings, spills and playas. This study evaluates the potential for groundwater to be contaminated by a point-source atmospheric emission. Pollutant concentrations in groundwater are estimated using a Gaussian model of atmospheric transport, a transfer function model for transport through the unsaturated zone, and a two-dimensional groundwater flow model based on Darcy's law to simulate transport in the saturated groundwater system. A sensitivity analysis of the composite atmospheric-groundwater transport model suggests that the most important factors influencing the susceptibility of a groundwater system to contamination by an aerosol source are: the concentration of the source, the amount of recharge, the depth to the water-table, and the velocity distribution in the unsaturated zone. This study indicates a significant potential for pollution of groundwater systems by aerosols. Shallow aquifers are especially vulnerable; however, deeper aquifers where rapid travel times through the unsaturated zone exist are also susceptible to aerosol contamination.