Investigation of titanium liquid/gas diffusion layers in proton exchange membrane electrolyzer cells

In a proton exchange membrane electrolyzer cell (PEMEC), liquid/gas diffusion layer (LGDL) is expected to transport electrons, heat, and reactants/products to and from the catalyst layer with minimum voltage, current, thermal, interfacial, and fluidic losses. In addition, carbon materials, which are typically used in PEM fuel cells (PEMFCs), are unsuitable in PEMECs due to the high ohmic potential and highly oxidative environment of the oxygen electrode. In this study, a set of titanium gas diffusion layers with different thicknesses and porosities are designed and examined coupled with the development of a robust titanium bipolar plate. It has been found that the performance of electrolyzer improves along with a decrease in thickness or porosity of the anode LGDL of titanium woven meshes. The ohmic resistance of anode LGDL and contact resistance between anode LGDL and the anode catalyst play dominant roles in electrolyzer performance, and better performance can be obtained by reducing ohmic resistance. Thin titanium LGDLs with straight-through pores and optimal pore morphologies are recommended for the future developments of low-cost LGDLs with minimum ohmic/transport losses.     

A comprehensive review of climate adaptation in the United States: more than before, but less than needed

We reviewed existing and planned adaptation activities of federal, tribal, state, and local governments and the private sector in the United States (U.S.) to understand what types of adaptation activities are underway across different sectors and scales throughout the country. Primary sources of review included material officially submitted for consideration in the upcoming 2013 U.S. National Climate Assessment and supplemental peer-reviewed and grey literature. Although substantial adaptation planning is occurring in various sectors, levels of government, and the private sector, few measures have been implemented and even fewer have been evaluated. Most adaptation actions to date appear to be incremental changes, not the transformational changes that may be needed in certain cases to adapt to significant changes in climate. While there appear to be no one-size-fits-all adaptations, there are similarities in approaches across scales and sectors, including mainstreaming climate considerations into existing policies and plans, and pursuing no- and low-regrets strategies. Despite the positive momentum in recent years, barriers to implementation still impede action in all sectors and across scales. The most significant barriers include lack of funding, policy and institutional constraints, and difficulty in anticipating climate change given the current state of information on change. However, the practice of adaptation can advance through learning by doing, stakeholder engagements (including “listening sessions”), and sharing of best practices. Efforts to advance adaptation across the U.S. and globally will necessitate the reduction or elimination of barriers, the enhancement of information and best practice sharing mechanisms, and the creation of comprehensive adaptation evaluation metrics.     

Concentrations of organophosphate esters and brominated flame retardants in German indoor dust samples

While it is known that the ingestion of indoor dust contributes substantially to human exposure to the recently restricted polybrominated diphenyl ethers (PBDEs), the situation for one class of potential replacements, i.e. organophosphate esters (OPEs), used in a variety of applications including as flame retardants has yet to be fully characterised. In this study, surface dust from twelve different cars from various locations throughout Germany were analysed for eight OPEs, decabromodiphenyl ethane (DBDPE), and eight PBDEs. In five cars, tris-(1,3-dichloro-2-propyl) phosphate (TDCPP) was the dominant compound with concentrations up to 620 μg g(-1) dust. High concentrations of tri-cresyl phosphate (TCP) (up to 150 μg g(-1)) were also detected in two samples of car dust. Dust from ten offices in the same building in Ludwigsburg, Germany was also analysed. In these samples, tri (2-butoxyethyl) phosphate (TBEP) predominated with an average concentration of 7.0 μg g(-1) dust, followed by tris (1-chloro-2-propyl) phosphate (TCPP) at 3.0 μg g(-1) and triphenyl phosphate (TPhP) at 2.5 μg g(-1) dust. Although caution must be exercised given the relatively small database reported here; this study provides evidence that cars and offices from Germany are significantly more contaminated with OPEs than PBDEs. Average concentrations of ΣOPEs were ten times higher in car than in office dust. This is the first study to provide data on a wide range of OPE concentrations in German indoor dust samples.     

Assessment of Spatiotemporal Varying Relationships Between Rainfall,Land Cover and Surface Water Area Using Geographically Weighted Regression

Traditional regression techniques such as ordinary least squares (OLS) are often unable to accurately model spatially varying data and may ignore or hide local variations in model coefficients. A relatively new technique, geographically weighted regression (GWR) has been shown to greatly improve model performance compared to OLS in terms of higher R ² and lower corrected Akaike information criterion (AIC_C). GWR models have the potential to improve reliabilities of the identified relationships by reducing spatial autocorrelations and by accounting for local variations and spatial non-stationarity between dependent and independent variables. In this study, GWR was used to examine the relationship between land cover, rainfall and surface water habitat in 149 sub-catchments in a predominately agricultural region covering 2.6 million ha in southeast Australia. The application of the GWR models revealed that the relationships between land cover, rainfall and surface water habitat display significant spatial non-stationarity. GWR showed improvements over analogous OLS models in terms of higher R ² and lower AIC_C. The increased explanatory power of GWR was confirmed by the results of an approximate likelihood ratio test, which showed statistically significant improvements over analogous OLS models. The models suggest that the amount of surface water area in the landscape is related to anthropogenic drainage practices enhancing runoff to facilitate intensive agriculture and increased plantation forestry. However, with some key variables not present in our analysis, the strength of this relationship could not be qualified. GWR techniques have the potential to serve as a useful tool for environmental research and management across a broad range of scales for the investigation of spatially varying relationships.     

Using diatom indices for water quality assessment in a subtropical river, China

Diatoms have been regularly used as bioindicators to assess water quality of surface waters. However, diatom-based indices developed for a specific geographic region may not be appropriate elsewhere. We sampled benthic diatom assemblages in the upper Han River, a subtropical river in China, to evaluate applicability of 14 diatom-based indices used worldwide for water quality assessment. A total of 194 taxa from 31 genera were identified in the dry season and 139 taxa from 23 genera in the wet season. During the dry season, significant relationships were found for all but one of the diatom-based indices (Index Diatom Artois–Picardie) with one or more physical and chemical variables including nutrients and ion concentrations in river waters. The Biological Diatom Index (IBD) and diatom-based eutrophication/pollution index (EPI-D) were strongly related to trophic status and ionic content, while Watanabe’s Index was related to organic pollution and conductivity. Yet, the diatom indices showed weak relationships with physical and chemical variables during the wet season. It suggests that diatom-based indices developed in Europe can be applied with confidence as bioindicators of water quality in subtropical rivers of China, at least during base-flow conditions.     

Significance of Regional Source Contributions to Urban PM-10 Concentrations

Based on data collected in St. Louis, Philadelphia and other eastern U.S. cities, we conclude that a significant fraction of the PM-10 concentration is "background." In these urban areas the background fraction ranges from 35 to 80 percent of the daily, monthly or annual concentration. The bulk of the background appears to be of regional origin. The average chemical makeup of eastern U.S. PM-10 is sulfate as SO₄, 21-34 percent; crustal material, 14-39 percent; "unknown" (carbonaceous matter, ammonium, nitrate and water), 36-51 percent, all of which is difficult to apportion to specific sources. Dispersion modeling using a local source inventory can account only for a small portion of the total PM-10 mass. Emission roll-back of local sources may have a limited effect on reducing total concentrations of PM-10.     

Estimate of Contribution of Jet Aircraft Operations To Trace Element Concentration at or near Airports

Samples of ASTM type A jet fuel were analyzed for trace element content by instrumental neutron activation techniques. Forty-nine elements were sought. Only ten, aluminum, gold, indium, lanthanum, titanium, vanadium, barium, dysprosium, tellurium, and uranium, were observed at levels above the detection limits encountered; of these only aluminum, titanium, and barium were present at concentrations greater than 0.1 ppm. Estimates of exhaust gas. concentrations are made, and the ambient contribution at or near airports is calculated by using the Los Angeles International Airport dispersion model. It is shown that the ambient contribution is about an order of magnitude below typical urban levels for virtually all elements sought.     

Dehalogenation of polychlorinated biphenyls and polybrominated diphenyl ethers using a hybrid bioinorganic catalyst

The environmentally prevalent polybrominated diphenyl ether (PBDE) #47 and polychlorinated biphenyls (PCBs) #28 and #118 were challenged for 24 hours with a novel biomass-supported Pd catalyst (Bio-Pd(0)). Analysis of the products via GC-MS revealed the Bio-Pd(0) to cause the challenged compounds to undergo stepwise dehalogenation with preferential loss of the least sterically hindered halogen atom. A mass balance for PCB #28 showed that it is degraded to three dichlorobiphenyls (33.9%), two monochlorobiphenyls (12%), and biphenyl (30.7%). The remaining mass was starting material. In contrast, while PCB #118 underwent degradation to yield five tetra- and five trichlorinated biphenyls, no less chlorinated products or biphenyl were detected, and the total mass of degraded products was 0.3%. Although the Bio-Pd(0) material was developed for treatment of PCBs, a mass balance for PBDE #47 showed that the biocatalyst could prove a potentially useful method for treatment of PBDEs. Specifically, 10% of PBDE #47 was converted to identifiable lower brominated congeners, predominantly the tribrominated PBDE #17 and the dibrominated PBDE #4, 75% remained intact, while 15% of the starting mass was unaccounted for.