Tropospheric ozone, an air pollutant and greenhouse gas, is a hazard to both human health and ecosystems. Health-based ozone standards are regularly exceeded in many regions of the world. Controlling ozone formation is a challenge for scientists and policy makers due to the non-linear dependence of ozone on its precursors, namely nitrogen oxides (NO_x) and volatile organic compounds (VOC). Photochemical air quality modeling is one the primary tools used to assess the effectiveness of strategies intended to control ozone formation. Air quality model predictions are sensitive to meteorological and emission inputs, as well as the description of atmospheric chemistry embodied in the chemical mechanism. Typical chemical mechanisms describe the reactants, reaction rates, and product yields for each of hundreds of individual chemical reactions that take place in the atmosphere.

The Statewide Air Pollution Research Center (SAPRC) mechanism developed by Dr. William Carter at UC Riverside is a chemically accurate, but also computationally intensive, example of a chemical mechanism used to describe the dynamics of photochemically-formed air pollutants. This mechanism is widely used for air quality research and planning at urban and regional scales. The first step in my research was to assess the effects of using a new version (SAPRC07) of this mechanism in place of an outdated earlier version (SAPRC99). This assessment was done using an Eulerian photochemical air quality known as the Community Multiscale Air Quality model or CMAQ, applied to the prediction of air quality in Central California under polluted summertime conditions. Domain-wide reductions in predicted ozone were found using the newer mechanism as compared with SAPRC99, with larger ozone reductions colocated spatially and temporally with higher ozone concentrations. Underprediction of peak ozone was already evident using the older (SAPRC99) mechanism, and this bias increased with the new mechanism.

In order to understand the reasons for the changes in predicted ozone, first-order sensitivity coefficients using both mechanisms were calculated with respect to important rate coefficients. Among the more important revisions to the mechanism is a ~20% increase in the rate of the chain-terminating reaction OH^. + NO₂ → HNO₃. This revision in SAPRC07 was a dominant contributor to overall decreases (relative to SAPRC99) of up to 25 ppb in peak predicted ozone concentrations in the San Joaquin Valley. Other significant revisions include the rate coefficient for the reaction O₃ + NO → NO₂ + O₂ and the photolysis rate for the reaction NO₂ + hv → NO + O3P, but these changes were found to exert offsetting effects with ozone responses of similar magnitude acting in opposite directions.

A reassessment of ozone sensitivity to changes in precusor emissions shows that the updated mechanism has a response to VOC emissions that is stronger than that of SAPRC99, indicating more ozone reduction potential associated with VOC emission controls. With the exception of the Bay Area, the newer mechanism drives the model predictions more toward a NO_x disbenefit regime, where moderate NO_x emission reductions (by 20%) lead to local increases in ozone in the near field. An unexpected finding was that use of a condensed and computationally efficient version of SAPRC07 known as CS07A contributed substantially to the decreases in predicted ozone levels mentioned above. For this reason, a less condensed mechanism (SAPRC07A) is used in further research presented in this dissertation, with a resulting increase in computational demand necessary for model simulations. Additionally a recent study (Mollner et al., 2010) recommends a lower value for the reaction rate coefficient for OH^. + NO₂ → HNO₃ that I have implemented as a revision to SAPRC07A.

The many hundreds of individual anthropogenic VOC emitted into the atmosphere are primarily represented in the SAPRC mechanism using lumped species groups. Species are separated into groups based on their reaction mechanism and rate coefficient, and surrogate species are used to represent the reactions of all VOC assigned to each lumped group. The existing surrogate species mixtures defining the chemistry of the lumped groups were developed by Carter based on speciated measurements of ambient hydrocarbon concentrations, but these data were collected in the mid-1980s. Reformulation of fuels and consumer products, and control measures that have altered the total amounts of VOC emitted by various source categories, have substantially changed the concentrations and relative abundances of many individual VOC present in the atmosphere. The next step in my research was to develop updated lumped species definitions using emission inventories and source category-related VOC speciation profiles. The resulting lumped species definitions created in this dissertation are up-to-date and simpler, but still represent 95% of the total moles of species assigned to each lumped group. Most of the inventory-based lumped VOC definitions now align better with ambient VOC measurements compared to the existing lumped species definitions in SAPRC99 and SAPRC07. The updated definitions result in lower rate coefficients for most lumped VOC + OH^. reactions, that reflect the effects of emission control measures that have required reformulation to reduce the reactivity of VOC mixtures used in fuels and consumer products. In the air quality model, the new surrogate species definitions result in slightly lower peak ozone concentrations, as much as a 1.8 ppb reduction in houly maximum ozone concentration in some cases.

Consistent with current practice in other mechanisms, the SAPRC mechanism describes the atmospheric oxidation of VOC using temperature-independent parameters that specify branching in peroxy radical + NO reactions between NO to NO₂ conversion and organic nitrate-forming channels. Additional temperature-independent parameters are used to describe the fate of alkoxy radicals: reaction with O₂, isomerization, and decomposition. In reality, the branching ratios for these pathways depend on temperature. The final major element of my research, needed to reproduce more accurately the spatial, diurnal, and day-to-day differences in air quality that are driven in part by differences in temperature, is development of a new version of the mechanism that captures the missing temperature dependencies of alkoxy and peroxy radical reactions. Organic nitrate formation, which decreases with temperature, competes with NO to NO₂ conversion and hence inhibits production of ozone locally. Alkoxy radical decomposition competes with isomerization, resulting in increased aldehyde yields and decreased ketone yields with increasing temperature. This drives the resulting VOC oxidation products toward a more reactive mix at higher temperatures. The VOC oxidation product yields for the existing SAPRC mechanism are all specified for T = 300 K, and do not vary with temperature. Changes in predicted organic nitrate, aldehyde, and ketone concentrations follow as expected with inclusion of these missing temperature dependencies in the mechanism, as do subsequent changes in predicted ozone. Variations in predicted ozone linked to temperature differences are further enhanced with the additional inclusion of temperature-dependent evaporative VOC emissions. However, predicted ozone is not very sensitive to these mechanism changes, the largest changes were in the maximum hourly ozone (up to ~±1.5 pbb).

Temperatures in California are predicted to rise by 1 to 4^oC throughout the state of California by 2050 relative to year 2000. In studying the effects of climate change on air quality, it is important to describe correctly the temperature dependence of relevant atmospheric chemistry. The effect of using the temperature-dependent VOC reaction mechanism developed as part of this research is assessed for a future climate change scenario. Compared to previous assessments, use of the revised chemical mechanism indicates a slightly increased potential penalty from climate change with respect to ozone air quality in central California.

In this dissertation, I study two fundamental topics in seismology, tidal triggering of earthquakes and attenuation and scattering structure. Studies of tidal triggering help constrain earthquake nucleation models and relate to earthquake predicability and forecasting. Resolving

attenuation and scattering behavior can provide more physically realistic models for strong ground motion prediction equations (GMPEs) and improve our understanding of the physical properties of rocks in the lithosphere. Chapter 1 is an introduction, providing background and motivation for each of the following chapters. Chapters 2 & 3 focus on the topic of tidal triggering of earthquakes. Chapter 2 studies tidal triggering in the central Japan region using M>3 earthquakes and finds no clear evidence for tidal triggering. Chapter 3 analyzes seismicity in the Coso region of California and finds strong tidal triggering but an absence of remote triggering at the Coso geothermal field, constraining earthquake triggering sensitivities at different time scales of stress perturbations. Chapters 4-6 study the inelastic properties of the crust and upper mantle in southern California using both coda and direct-wave observations. Chapter 4 stacks coda envelope functions across southern California and synthesizes them using a two-layer model, composed of a shallow crustal

layer with strong wide-angle scattering and high P and S intrinsic attenuation and a deeper layer with weaker scattering and lower intrinsic attenuation. Chapter 5 describes improvements to the conventional coda-Q method to solve for coda attenuation, site amplification and source radiated energy simultaneously. Chapter 6 models focal-sphere-dependent S/P amplitudes assuming a

whole-space intrinsic and scattering attenuation model around the San Bernardino region.

Earthquakes are the primary source of seismic waves in seismology and understanding the earthquake source is essential for predicting ground motions and detailing the physics of rupture. Earthquake kinematic source imaging describes the whole rupture process during an earthquake. It does not directly require the resolved source model to be physically or dynamically plausible, but can help in understanding the conditions of rupture dynamics. Therefore, accurate earthquake source models are highly desirable.

In Chapter 2, we develop a frequency-based approach to earthquake slip inversion that requires no prior information on the rupture velocity or slip-rate functions.

In Chapter 3, we characterize the rupture process of the 25 April 2015 Nepal earthquake with globally recorded teleseismic P waves.

In Chapter 4, we investigate the 10 January 2012 Mw 7.2 Sumatra earthquake in the Wharton basin and detect dynamically-triggered large early aftershocks occurring on or near the subduction interface.

In Chapter 5, we constrain the spatiotemporal evolution of the 2009 Tonga-Samoa earthquake with global P-wave back-projection and a multiple moment-tensor inversion. Our results show that the rupture branches east of the trench axis were controlled by the geometry of bending-related faults on the Pacific plate, and that the rupture branch west of the trench axis may correlate with along-strike fore-arc segmentation.

In Chapter 6, we detect and locate 48 previously unidentified large early aftershocks triggered by 7 < M < 8 earthquakes within a few fault lengths, during times that high-amplitude surface waves arrive from the mainshock. The observations indicate that near-to-intermediate-field dynamic triggering commonly exists and fundamentally promotes aftershock occurrence.

In Chapter 7, we analyze the 2006 Mw 7.8 Java tsunami earthquake with global P-wave back-projection, tsunami tide-gauge back-propagation, and P-wave source spectra modeling. The results suggest that the splay faults may have been reactivated during the Java earthquake.

In Chapter 8, we explore back-projection resolution by imaging M6 earthquakes within the Japan subduction zone. The quantitative analysis of uncertainties can provide guidelines for interpreting back-projection results in the region.

Finally, in Chapter 9, we discuss future research prospects of kinematic earthquake source imaging.

We place constraints on the amounts and length scales of seismic velocity variations throughout the mantle that are beyond the resolving capabilities of seismic tomography. We model global stacks of various seismic phases that are thought to have a scattering origin, using a Monte Carlo phonon method.

In Chapter 2, we forward model stacks of over 10,000 high-frequency (~1 Hz) PKP precursor waveforms with velocity perturbations of ~0.1% distributed throughout the lowermost mantle, resolving a debate between older studies. We confirm that models where scattering is distributed uniformly throughout the lowermost mantle better match the observations than those where scattering is restricted to a thin region just above the core--mantle boundary.

In Chapter 3, we characterize the frequency dependence of PKP precursors at central frequencies ranging from 0.5 to 4 Hz. At greater frequencies, we observe more scattered energy, particularly at shorter ranges. We model this observation by invoking heterogeneity at length scales from 2 to 30 km. Amplitudes at 0.5 Hz, in particular, suggest the presence of more heterogeneity at scales >8 km than present in previously published models.

In Chapter 4, we constrain the heterogeneity spectrum of Earth's upper mantle at scales from a few kilometers to tens-of-thousands of kilometers using observations from high-frequency scattering, long-period scattering, and tomography. We explore geodynamically plausible scenarios that might be responsible for the rms and fall-off rate of the proposed spectrum, including a self-similar mixture of basalt and harzburgite.

In Chapter 5, we stack a large global dataset of 1-Hz PKKP waveforms to constrain globally-averaged properties of PKKP precursors. We propose a new 1-D reference model that fits both our PKKP precursor amplitudes and constraints on absolute PKPbc travel times. Our globally averaged PKKP precursor observations are consistent with random CMB topography with rms variations of ~440 m and a horizontal correlation length of ~7 km.

Finally, in Chapter 6, we discuss outstanding challenges and future prospects for deep Earth scattering research.

The properties of interfacial electronic states in device-relevant materials are investigated

using time- and angle-resolved two photon photoemission (TPPE) spectroscopy.

Angle- and time-resolved TPPE is used to investigate electronic states in the buffer layer

of 4H-SiC(0001). An image potential state (IPS) series is observed on this strongly surface-bound buffer layer, and dispersion measurements indicated free-electron-like behavior for all states in this series. These results are compared with TPPE taken on bilayer graphene, which also shows the existence of a free-electron-like IPS series. Lifetimes for the n = 2, and n = 3 states are obtained from time-resolved TPPE; slightly increased lifetimes are observed in the bilayer graphene sample for the n = 2 the n = 3 states. Despite the large band gap of graphene at the center of the Brillouin zone, the lifetime results demonstrate that the graphene layers do not behave as a simple tunneling barrier, suggesting that the buffer layer and graphene overlayers play a direct role in the decay of IPS electrons. Ultrafast response of the room temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpyr][NTf2]) to a photoinjected electron is investigated in few-monolayer films using time- and angle-resolved two-photon photoemission spectroscopy. A delocalized precursor state and a localized solvated state are resolved at early times, but after 200 fs only a single solvated state is observed. The dynamics of film response to this solvated state are shown to depend significantly on film temperature and thickness. Population lifetime measurements demonstrate that the RTIL film can significantly affect the coupling between solvated state and metal substrate, as the solvated state’s average lifetime increases from 90 ± 20 fs in 1 ML films to 195 ± 83 ps in 3 ML films. Additionally, a temperature dependence of the time-dependent binding energy shift of the solvated state after c.a. 500 fs is attributed to a phase change occurring between the two temperature regimes that were investigated. Results from xenon overlayer experiments suggest that the solvation process occurs near the surface of the RTIL film. Finally, film degradation is found to be present, suggesting that the observed solvation response could involve a radical species. Valuable information about two very different interfacial materials is collected using TPPE, proving the power and versatility of the technique. The results presented here show that interfacial states can be used to monitor a variety of physical phenomena, from corrugation in graphitic materials to solvation and degradation in RTILs.