Abstract. Chemical composition, size, and mixing state of atmospheric particles are critical in determining their effects on the environment. There is growing evidence that soot aerosols play a particularly important role in both climate and human health, but still relatively little is known of their physical and chemical nature. In addition, the atmospheric residence times and removal mechanisms for soot are neither well understood nor adequately represented in regional and global climate models. To investigate the effect of locality and residence time on properties of soot and mixing state in a polluted urban environment, particles of diameter 0.2-2.0 µm were collected in the Mexico City Metropolitan Area (MCMA) during the MCMA-2003 Field Campaign from various sites within the city. Individual particle analysis by different electron microscopy methods coupled with energy dispersed x-ray spectroscopy, and secondary ionization mass spectrometry show that freshly-emitted soot particles become rapidly processed in the MCMA. Whereas fresh particulate emissions from mixed-traffic are almost entirely carbonaceous, consisting of soot aggregates with liquid coatings suggestive of unburned lubricating oil and water, ambient soot particles which have been processed for less than a few hours are heavily internally mixed, primarily with ammonium sulfate. Single particle analysis suggests that this mixing occurs through several mechanisms that require further investigation. In light of previously published results, the internally-mixed nature of processed soot particles is expected to affect heterogeneous chemistry on the soot surface, including interaction with water during wet-removal.

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Inelastic helium atom scattering has been used to measure the phonons on a stepped metallic crystalline surface, Ni(977). When the scattering plane is oriented parallel to the step edges and perpendicular to the terraces, two branches of step-induced phonons are observed. These branches are identified as transversely polarized, step-localized modes that propagate along the step edge. Analysis reveals significant anisotropy in the force field near the step edge, with all forces near the step edge being substantially smaller than in the bulk. Such measurements provide valuable information on metallic bonding and interface stability near extended surface defects.

Inelastic helium atom scattering has been used to measure the surface and step localized phonons on a stepped metallic surface, Ni͑977͒. These time-of-flight measurements were carried out both perpendicular and parallel to the step direction. Surface phonon dispersion data collected across the steps show backfolding of the surface Rayleigh mode, and, most importantly, dramatic softening as compared to the forces present at the smooth Ni͑111͒ surface. This softening suggests significant relaxation perpendicular to the step edge. Single-phonon scattering data collected along the step direction reveals the presence of two new step-edge localized modes, as well as the Rayleigh mode for this direction of the crystal. The Rayleigh mode here does not exhibit the notable softening that was found for the other direction. Novel in-and out-of-phase scattering measurements, with respect to the terraces, lead us to assign the new step induced modes as the two transversely polarized vibrations which propagate along the direction of the step edge. An analytic one-dimensional lattice model is proposed which well represents the dispersion data for these two step modes; its use allows us to determine the effective local force field in the two transverse directions with respect to the step edge. The findings reported herein shed new light on such topics as interface stability, crystal growth, and charge redistribution in the vicinity of well-characterized extended surface defects.

Economic and environmental favorability are vital considerations for the large-scale development and deployment of sustainable fuels. Here, we have conducted economic and sustainability analyses of pathways for producing bioblendstocks optimized for improved combustion for mixing-controlled compression ignition (MCCI) engines. We assessed 25 pathways for the production of target fuels from renewable feedstocks and conducted technoeconomic analysis (TEA) and life cycle analysis (LCA) to determine which bioblendstock candidates are likely to be viable given a slate of 19 metrics evaluating technology readiness, economic viability, and environmental impacts ranking each metric as either favorable, neutral, unfavorable, or unknown across a range of screening criteria. Among the results, we found that the economic metrics were largely favorable for most of the bioblendstocks. Of the near-term baseline cases, eight pathways offered the potential of a minimum fuel selling price (MFSP) of less than $5/gallon of gasoline equivalent (GGE). In comparison, under future target case scenarios, there is potential for seven pathways to reduce their fuel selling price to less than $4/GGE. Biochemically-based pathways struggled to achieve favorable target case MFSP under the processing approach taken here, but further economic improvements could be achieved when lignin valorization is included. Most of the conversion technologies were determined to be robust in that they would be minimally affected by the feedstock specifications and variations. However, given the early stage of development for most of the pathways, blending behavior and testing for regulatory limits are key data gaps as knowledge of how many of these bioblendstocks will perform when blended with existing fuels and how much can be added while still meeting fuel property specifications is still being assessed. Twelve pathways showed significant reductions in life cycle greenhouse gas (GHG) emissions greater than 60%, and 15 showed favorable fossil energy use reductions compared to conventional diesel fuel. Energy-intensive processes and the use of GHG-intensive chemicals such as sodium hydroxide contribute significantly to GHG emissions. Results from these analyses enable researchers and industry to assess the potential viability of MCCI bioblendstocks.

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The combination of transfer hydrogenation reaction with the 5 advantages of γ-valerolactone-based ionic liquids could result in an environmentally benign method for the reduction of organic substrates. Ionic liquids containing 4-hydroxyvalerate anion were applied as alternative solvents for the reduction of acetophenone and its substituted forms, and different alkenes 10 using transition metal based catalysts. The optimal conditions (e.g. type of catalyst precursor and hydrogen donor) for the transformation were also specified.

We have studied the effect of an extended array of defects on the two-dimensional phase behavior of adsorbed hydrogen on a Ni surface using helium atom scattering. Specifically, the interaction of hydrogen with the stepped Ni͑977͒ surface was examined and compared with similar interactions with the flat Ni͑111͒ surface. The phase behavior of hydrogen on Ni͑977͒ is qualitatively the same as that of hydrogen on Ni͑111͒; however, the temperature at which the order-disorder transition occurs is elevated. On the stepped surface, the ordered (2ϫ2)-2H phase exists at a temperature 40 K higher than on the flat surface. This reversible phase transition is second order and is best fit with T c ϭ310 K and ␤ϭ0.12, indicative of two-dimensional Ising behavior. Stabilization of the ordered phase is attributed to pinning from the step edges. The cross section for diffuse elastic He scattering by adsorbed hydrogen and the temperature-dependent domain size of ordered hydrogen along the step edges are also discussed.