Executive summary\n● Target audience: AmeriFlux community, AmeriFlux Science Steering Committee & Department of Energy (DOE) program managers [ARM/ASR (atmosphere), TES (surface), and SBR (subsurface)]\n● Problem statement: The atmospheric boundary layer mediates the exchange of energy and matter between the land surface and the free troposphere integrating a range of physical, chemical, and biological processes. However, continuous atmospheric boundary layer observations at AmeriFlux sites are still scarce. How can adding measurements of the atmospheric boundary layer enhance the scientific value of the AmeriFlux network?\n● Research opportunities: We highlight four key opportunities to integrate tower-based flux measurements with continuous, long-term atmospheric boundary layer measurements: (1) to interpret surface flux and atmospheric boundary layer exchange dynamics at flux tower sites, (2) to support regionalscale modeling and upscaling of surface fluxes to continental scales, (3) to validate land-atmosphere coupling in Earth system models, and (4) to support flux footprint modelling, the interpretation of surface fluxes in heterogeneous terrain, and quality control of eddy covariance flux measurements.\n● Recommended actions: Adding a suite of atmospheric boundary layer measurements to eddy covariance flux tower sites would allow the Earth science community to address new emerging research questions, to better interpret ongoing flux tower measurements, and would present novel opportunities for collaboration between AmeriFlux scientists and atmospheric and remote sensing scientists. We therefore recommend that (1) a set of instrumentation for continuous atmospheric boundary layer observations be added to a subset of AmeriFlux sites spanning a range of ecosystem types and climate zones, that (2) funding agencies (e.g., Department of Energy, NASA) solicit research on land-atmosphere processes where the benefits of fully integrated atmospheric boundary layer observations can add value to key scientific questions, and that (3) the AmeriFlux Management Project acquires loaner instrumentation for atmospheric boundary layer observations for use in experiments and short-term duration campaigns.
This is the FLUXNET-CH4 version of the carbon flux data for the site US-Bi2 Bouldin Island corn.
The interactions of CO and H/sub 2/ with Pd/SiO/sub 2/ promoted with Li, Na, K, Rb, and Cs have been investigated using temperature-programmed desorption and temperature-programmed surface reaction. Introduction of the promoter following the preparation of the Pd/SiO/sub 2/ catalyst causes a small increase (similarly ordered 7%) in the dispersion of the Pd particles. Reduction of the promoted catalysts removes a significant quantity of oxygen from the promoter, but only a small portion of the promoter appears to cover the Pd particles. Alkali promotion of Pd/SiO/sub 2/ does not significantly influence the amounts of H/sub 2/ and CO that can be adsorbed on the metal. The alkali promoters have a slight influence on the distribution of H/sub 2/ adstates but cause a significant change in the distribution of CO adstates. For low reduction temperatures, alkali promotion of Pd/SiO/sub 2/ decreases the activity of Pd for the dissociation of CO. However, increasing the reduction temperature increases the CO dissociation activity of the promoted samples due to the increased degree of reduction of the promoter. This enhanced dissociation activity is reversed by the reoxidation of the promoter by the H/sub 2/O or CO/sub 2/ formed under reaction conditions. The nascent carbon formedmore » by CO dissociation on alkali-promoted Pd/SiO/sub 2/ is less reactive than that on unpromoted Pd/SiO/sub 2/, and the promoted catalysts have a lower activity for CH/sub 4/ synthesis relative to that for unpromoted Pd/SiO/sub 2/ decreasing in the order: unpromoted > Li > Na > K > Rb > Cs. 49 references.« less
This is the FLUXNET-CH4 version of the carbon flux data for the site US-Bi1 Bouldin Island Alfalfa.
Read moreThis is the FLUXNET-CH4 version of the carbon flux data for the site US-Tw5 East Pond Wetland.
Read moreAbstract Ein neuartiges, auf funktionalisiertem, nanoporösen Graphen basierendes Verfahren zur Abtrennung chiraler Moleküle wird vorgestellt. Auf Dichtefunktionaltheorie basierende Computersimulationen zeigen, dass durch Anhaften eines chiralen “Türsteher”‐Moleküls an den Porenrand einer Form des Enantiomers der Eintritt verweigert wird, während sein Spiegelbild passieren kann.
Read moreThe CO + H/sub 2/ reaction was studied. Infrared spectra indicate that under reaction conditions, the catalyst surface is saturated with CO. Conversion of CO to CH/sub 4/ depends on the H/sub 2//CO ratio. The Ru surface is covered by CO, and in order for CH/sub 4/ to form, H/sub 2/ must compete for the remaining unoccupied sites. CH/sub 4/ and C/sub 2/H/sub 6/ probably arises through a common precursor, e.g., an Ru-CH groups, and C/sub 2/H/sub 6/ might occur through dimerization of Ru-CH groups. 6 figs. (DLC)
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Read moreThe energy delivered to the land surface via insolation is a primary driver of evapotranspiration (ET)—the exchange of water vapor between the land and atmosphere. Spatially distributed ET products are in great demand in the water resource management community for real-time operations and sustainable water use planning. The accuracy and deliverability of these products are determined in part by the characteristics and quality of the insolation data sources used as input to the ET models. This paper investigates the practical utility of three different insolation datasets within the context of a satellite-based remote sensing framework for mapping ET at high spatiotemporal resolution, in an application over the Sacramento–San Joaquin Delta region in California. The datasets tested included one reanalysis product: The Climate System Forecast Reanalysis (CFSR) at 0.25° spatial resolution, and two remote sensing insolation products generated with geostationary satellite imagery: a product for the continental United States at 0.2°, developed by the University of Wisconsin Space Sciences and Engineering Center (SSEC) and a coarser resolution (1°) global Clouds and the Earth’s Radiant Energy System (CERES) product. The three insolation data sources were compared to pyranometer data collected at flux towers within the Delta region to establish relative accuracy. The satellite products significantly outperformed CFSR, with root-mean square errors (RMSE) of 2.7, 1.5, and 1.4 MJ·m−2·d−1 for CFSR, CERES, and SSEC, respectively, at daily timesteps. The satellite-based products provided more accurate estimates of cloud occurrence and radiation transmission, while the reanalysis tended to underestimate solar radiation under cloudy-sky conditions. However, this difference in insolation performance did not translate into comparable improvement in the ET retrieval accuracy, where the RMSE in daily ET was 0.98 and 0.94 mm d−1 using the CFSR and SSEC insolation data sources, respectively, for all the flux sites combined. The lack of a notable impact on the aggregate ET performance may be due in part to the predominantly clear-sky conditions prevalent in central California, under which the reanalysis and satellite-based insolation data sources have comparable accuracy. While satellite-based insolation data could improve ET retrieval in more humid regions with greater cloud-cover frequency, over the California Delta and climatologically similar regions in the western U.S., the CFSR data may suffice for real-time ET modeling efforts.
Read moreGlucose–fructose isomerization mediated by Sn-BEA is investigated using an extended QM/MM model containing 208 tetrahedral atoms. The isomerization mechanism consists of a sequence of ring-opening, isomerization, and ring-closing processes, consistent with the previously reported experimental observations. In agreement with the experimentally observed kinetic isotope effect, the rate-determining step is found to involve a hydride shift from the C2 carbon to the C1 carbon. The apparent activation energy for the rate-limiting step is 22.3 kcal/mol at 343 K. The difference in the reaction barriers for the partially hydrolyzed and the fully coordinated Sn sites was investigated using energy decomposition analysis. It is found that the higher activity of the partially hydrolyzed site comes from the extra flexibility provided by the defect in the lattice. The effect of substituting Sn in the active site by Ti, Zr, V, Nb, Si, and Ge was examined, and it was found that Sn and Zr are metals that result in the lowest reaction barrier for glucose isomerization. By using energy decomposition analysis, two physical properties are shown to contribute to the magnitude of the reaction barrier: the polarizability of the metal atom in the active site and the Brønsted basicity of the oxygen atom bound to the metal atom.
Read moreThis is the FLUXNET-CH4 version of the carbon flux data for the site US-Tw3 Twitchell Alfalfa.
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