Secondary organic aerosol (SOA) generated through the partitioning of gas phase volatile organic carbon compounds (VOCs) into the condensed phase has both epidemiological and climatic impacts through the growth of particulate matter into relevant sizes for respiratory interactions and cloud condensation nuclei activity. Considering the complex chemistry involved with VOC oxidation and subsequent formation of SOA, bulk properties like oxidation state, often represented by O:C ratio, and volatility are used to simplify the representation of SOA in chemical transport models (CTMs) and the like [e.g. Tsimpidi et al. 2010]. This preference for bulk properties is supported by the availability of ambient measurement techniques to constrain model parameters and scenarios. The volatility of SOA is often described by treating it as a mixture of components with differing partitioning coefficients through the volatility basis set (VBS) approach rather than explicitly resolving the complex chemistry [Donahue et al., 2006]. This study presents a method of determining the volatility of an aerosol sample through the use of an optimizing thermodenuder (TD) instrument model that is used to fit laboratory data. Data collected using a volatility tandem differential mobility analyzer (VTDMA) setup consist of inlet and outlet particle size and number concentrations for select dicarboxylic acids - compounds known to contribute to atmospheric SOA. These are interpreted by the model through an iterative optimization routine to obtain estimates of volatility parameters (e.g. saturation concentrations) which are compared to available literature data. The instrument model is currently divided into two decoupled modules. The first resolves the flow field characteristics, obtaining the temperature profile, pressure variations, and radial velocity distribution of the TD, and the second resolves the gas to particle partitioning of aerosol with a given condensed-phase volatility distribution in the TD using the VBS approach as described in the literature. Solving the full hydrodynamic equations for the flow characteristics provides a better numeric representation of entry length and radial velocity variations and is an improvement over similar TD modeling studies in the literature. However, results indicate that coupling the two modules is necessary to more accurately resolve the suppression of evaporation due to buildup of organic vapors in the TD, even at the low mass concentrations involved with the presented experiments.

Atmospheric aerosols are known to exert a significant influence on the Earth's climate system; however, the magnitude of this influence is highly uncertain because of the complex interaction between aerosols and water vapor to form clouds. Toward reducing this uncertainty, this dissertation outlines a series of laboratory and in-situ field measurements, instrument technique development, and model simulations designed to characterize the ability of aerosols to act as cloud condensation nuclei (CCN) and form cloud droplets. Specifically, we empirically quantify the mixing state and thermodynamic properties of organic aerosols (e.g., hygroscopicity and droplet condensational uptake coefficient) measured in polluted and non-polluted environments including Alaska, California, and Georgia. It is shown that organic aerosols comprise a substantial portion of the aerosol mass and are often water soluble. CCN measurements are compared to predictions from theory in order to determine the error associated with simplified composition and mixing state assumptions employed by current large-scale models, and these errors are used to constrain the uncertainty of global and regional cloud droplet number and albedo using a recently-developed cloud droplet parameterization adjoint coupled with the GMI chemical transport model. These sensitivities are important because they describe the main determinants of climate forcing. We also present two novel techniques for fast measurements of CCN concentrations with high size, supersaturation, and temporal resolution that substantially improve the state of the art by several orders of magnitude. Ultimately, this work represents a step toward better understanding how atmospheric aerosols influence cloud properties and Earth's climate.

Regional patterns in tropospheric and sea surface temperature (SST) trends are examined for the period 1979 ??01 using MSU, NCEP-NCAR, ECMWF ERA-40 reanalyses, NOAA OI SST, and the CARDS radiosonde data set. Trends are estimated using a nonparametric Mann-Kendall approach. Substantial regional variability in temperature trends is seen in all of these data sets, with the magnitude of the variability (including substantial regions with cooling trends) far exceeding the average warming trend. The global analyses from MSU and the NCAR/NCEP and ECMWF reanalyses are used to identify sampling problems in using the radiosonde network to infer global trends. Analysis of the trends in tropospheric temperature concurrent with trends in SST shows regions where the signs disagree for both surface cooling and warming. Interpretation of these differing trends using the reanalyses suggest that the models used for the reanalyses are simulating the necessary dynamics/thermodynamics thatcould lead to a tropospheric cooling in contrast to a surface warming (and vice versa).

A framework is developed for the assessment of climate change impacts on water resources systems. The applied techniques include: quantifying global climate model (GCM) skill over a range of time scales; developing future climate scenarios based on GCM data that are found to skillfully represent the observed climate over an historical baseline period; and using the climate scenarios together with hydrologic and water resources models to make assessments of the potential impacts and implications of climate change on water resources systems. A statistical analysis of GCM skill in East Africa shows that temperature is well represented in the GCMs at monthly to annual time scales. Precipitation is found to be much less reliable in the models and shows skill in fewer seasons and nodes than temperature. Eight climate scenarios, stemming from three global climate models and two atmospheric emissions scenarios, project temperature increases between 2 and 5 ° Celsius by the year 2080. Precipitation projections vary widely across models as well as regionally. The scenarios project changes in precipitation from -38% to +42%. The climate change impact methodology is applied to the Nile River Basin. It is shown that, in spite of widely varying precipitation projections, the major sub-basins of the Nile River will experience decreases in watershed runoff under all eight climate scenarios. Detailed water resources models are employed to assess the system wide response to the climate-induced hydrologic changes. The assessments indicate that water supply deficits will emerge by 2030 and continue to grow in frequency and magnitude by 2080. Additional impacts include reservoir depletion and reduced hydropower generation. An assessment of the river system response to basin development projects, including additional water storage and wetlands water conservation, indicates that adverse climate impacts may be mitigated for 30 to 40 years. The assessments demonstrate the relevance of climate change considerations to water resources management and the development of water policy.

Using ERA40 and independent observations, I assess how well Amazon surface water budget is estimated. ERA40 basin wide annual precipitation (P) agrees with observations showing an underestimation of 10%, whereas runoff (R) is underestimated by a larger margin (~25%). Observed residual of precipitation and runoff (P-R) is better estimated by ERA40 P-R than actual ET which includes soil moisture nudging. Nudging is necessary during the dry season to produce realistic ET and compensate for low soil moisture recharge during the wet season. Insufficient recharge may be caused by: underestimation of rainfall amount and intensity; a shallow root layer in the model that does not represent the deep soil water reservoir of the Amazonian forest. The physical links between changes in wet season onset and synoptic scale systems are investigated in the second part of my work. A delayed wet season onset is consistent with a decreasing number of cold air incursion (CAI) days in southern Amazon during 1979-2001. CAI variability in southern Amazon is related to SST in the tropical Pacific and Indian Oceans. The first mode of co-variability shows that during El Nio (La Nia) a strong (weak) subtropical jet stream over South America is related to decreased (increased) CAI days during SON. The second mode shows warm western Indian Ocean also related to strong subtropical jet stream. The absence a well defined subpolar jet stream, favors the northward displacement of transient waves into central South America, but shows little response in southern Amazon. CAI days reconstructed from the first and second modes do not present any significant trend in southern Amazon. CAI days reconstructed from the third mode of co-variability reproduces SON observed trend. This mode describes negative (positive) anomalies in CAI days associated with cold (warm) SST anomalies, anomalous wavetrain in the tropical Pacific and Walker Cell displacement that are unfavorable (favorable) to the incursion of CAI into southern Amazon. This mode's temporal evolution correlates with the Pacific Decadal Oscillation (PDO), suggesting that its recent gradual signal shift reflected on the interannual response of southern Pacific atmospheric patterns, hence on the behavior of transients propagation.

Tez (Doktora) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, İnşaat Mühendisliği Anabilim Dalı, 2008. / Kaynakça var.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Daniel J. Leathers, Dept. of Geography. Includes bibliographical references.

Thesis (M.E.S.)--Evergreen State College, 2009. / "June, 2009." Title from title screen (viewed 3/16/2010). Includes bibliographical references (p. 150-171).

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 16, 2010). Includes bibliographical references. Also issued in print.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on December 18, 2009). Thesis advisor: Dr. Corinne Valdivia. Includes bibliographical references.