A novel high-resolution small ion spectrometer to study ion nucleation of aerosols in ambient indoor and outdoor air

An electrically based ion spectrometer is described, capable of measuring particle sizes and mobilities from molecular ions (small ions) to aerosol particles across a size range of 0.4 to 30 nm in diameter. It consists of a single cylindrical capacitor divided into three electrically insulated sections. The current arriving at the central section is measured by an electrometer and represents the ion flux over a known range of mobilities determined by the applied voltage. The applied voltage is scanned in steps to measure the ion fluxes over a large number of overlapping mobility ranges. The recorded signal and the response function of the instrument are unfolded using a maximum entropy procedure to give a high-resolution measured mobility spectrum. The maximum entropy approach offers a considerable improvement over traditional aspiration collectors and can approach the resolution of a drift tube system. In this way, the spectrometer successfully overcomes the diffusion limit to small ion resolution. Illustrative spectra are shown, demonstrating for the first time the presence of some resolved structure within the small ion spectrum at the highest mobilities. It is demonstrated that the actual mobility spectrum of small ions falls in the range 0.8–2.0 × 10⁻⁴ m² V⁻¹ s⁻¹. This represents a narrower range than that previously measured which is attributed to improved spectral resolution in the present work.     

The effect of adsorbed lipid on pyrite oxidation under biotic conditions

The chemolithoautotrophic bacterium, Acidithiobacillus ferrooxidans, commonly occurs in acid mine drainage (AMD) environments where it is responsible for catalyzing the oxidation of pyrite and concomitant development of acidic conditions. This investigation reports on the growth of this bacterial species on the pyrite surface and in the aqueous phase at a pH close to 2 as well as the role of adsorbed lipid in preventing pyrite dissolution. Both acid washed pyrite and acid-washed pyrite coated with lipids were used as substrates in the studies. The choice of lipid, 1,2-bis(10,12-tricosadiynoyl)-sn-Glycero-3-Phosphocholine lipid (23:2 Diyne PC), a phosphocholine lipid, was based on earlier work that showed that this lipid inhibits the abiotic oxidation rate of pyrite. Atomic force microscopy showed that under the experimental conditions used in this study, the lipid formed ~4–20 nm layers on the mineral surface. Surface-bound lipid greatly suppresses the oxidation process catalyzed by A. ferrooxidans. This suppression continued for the duration of the experiments (25 days maximum). Analysis of the bacterial population on the pyrite surface and in solution over the course of the experiments suggested that the pyrite oxidation was dependent in large part on the fraction of bacteria bound to the pyrite surface.     

The chronology and long term dynamics of a low energy river system: the Kelvin Valley,central Scotland

The long term (Holocene) channel and floodplain dynamics of a low gradient, low energy, fine grained aggradational fluvial system within a formerly glaciated landscape in central Scotland, the Kelvin Valley, are described from a series of sediment stratigraphic transects and 12 ¹⁴C assays in a headwater reach between Kirkintilloch and Kilsyth. The ¹⁴C assays and dated archaeological sites on the floodplain together suggest that the River Kelvin ceased to aggrade more than 2000 years ago, probably much more, so the 4–6 m of channel and floodplain deposits are almost entirely of early to mid‐Holocene age. The Kelvin Valley is characterized, despite its low flow characteristics, by a highly variable floodplain architecture, in which some transects suggest long term channel stability and strong partitioning of floodplain sedimentation and others indicate high channel mobility. This variation makes the application of general models of fluvial evolution difficult. Copyright © 2007 John Wiley & Sons, Ltd.     

Knowledge gaps in our perceptual model of Great Britain's hydrology

There is a no lack of significant open questions in the field of hydrology. How will hydrological connectivity between freshwater bodies be altered by future human alterations to the hydrological cycle? Where does water go when it rains? Or what is the future space–time variability of flood and drought events? However, the answers to these questions will vary with location due to the specific and often poorly understood local boundary conditions and system properties that control the functional behaviour of a catchment or any other hydrologic control volume. We suggest that an open, shared and evolving perceptual model of a region's hydrology is critical to tailor our science questions, as it would be for any other study domain from the plot to the continental scale. In this opinion piece, we begin to discuss the elements of and point out some knowledge gaps in the perceptual model of the terrestrial water cycle of Great Britain. We discuss six major knowledge gaps and propose four key ways to reduce them. While the specific knowledge gaps in our perceptual model do not necessarily transfer to other places, we believe that the development of such perceptual models should be at the core of the debate for all hydrologic communities, and we encourage others to have a similar debate for their hydrologic domain.     

Fire decreases near‐surface hydraulic conductivity and macropore flow in blanket peat

Many peatlands have been subjected to wildfire or prescribed burning, but it is not known how these fires influence near‐surface hydrological processes. Macropores are important flowpaths in the upper layers of blanket peat and were investigated through the use of tension disc infiltrometers, which also provide data on saturated hydraulic conductivity. Measurements were performed on unburnt peat (U), where prescribed burning had taken place 2 years (B2), 4 years (B4) and >15 (B15+) years prior to sampling, and where a wildfire (W) had taken place 4 months prior to sampling. Where there had been recent burning (B2, B4 and W), saturated hydraulic conductivity was approximately three times lower than where there was no burning (U) or where burning was last conducted >15 years ago (B15+). Similarly, the contribution of macropore flow to overall infiltration was significantly lower (between 12% and 25% less) in the recently burnt treatments compared to B15+ and U. There were no significant differences in saturated hydraulic conductivity or macropore flow between peat that had been subject to recent wildfire (W) and those that had undergone recent prescribed burning (B2 and B4). The results suggest that fire influences the near‐surface hydrological functioning of peatlands but that recovery in terms of saturated hydraulic conductivity and macropore flow may be possible within two decades if there are no further fires. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantification of particle-induced inflammatory stress response: a novel approach for toxicity testing of earth materials

Background

Reactive oxygen species (ROS) are vital regulators of many cellular functions in the body. The intracellular ROS concentration is highly regulated by a balance between pro-oxidants and anti-oxidants. A chronic excess of pro-oxidants leads to elevated ROS concentrations and inflammation, possibly initiating or enhancing disease onset. Mineral-induced generation of ROS, the role of minerals in upregulating cellular ROS, and their role in the development of several occupational diseases are now widely recognized. However, there is no standard protocol to determine changes in ROS production in cells after exposure to mineral dust or earth materials in general. In this study, a new method for determining the degree of cellular toxicity (i.e., cytotoxicity) of particles is described that will help bridge the gap in knowledge.

Results

By measuring the production of ROS and the viability of cells, an inflammatory stress response (ISR) indicator is defined. This approach normalizes the ROS upregulation with respect to the number of viable cells at the time of measurement. We conducted experiments on a series of minerals and soils that represent materials that are inert (i.e., glass beads, anatase, and a soil with low trace element content), moderately reactive (i.e., soil with high trace element content), and highly reactive (i.e., pyrite). Inert materials generated the lowest ISR, averaging 350% compared to the control. Acid washed pyrite produced the highest ISR (1,100 fold higher than the control). The measurements conducted as a function of time showed a complex response. Most materials showed an increase in ISR with particle loading.

Conclusions

The amount of cellularly generated ROS and cell viability combined provide a better understanding of particle-induced oxidative stress. The results indicate that some earth materials may solicit an initial burst of ROS, followed by a second phase in which cell viability decreases and ROS production increases, leading to a high ISR value. Hence, measurements conducted over a range of particle loading combined with multiple data measurements up to 24 hours can provide new insights in the possible effect of exposure to earth materials on human health.     

Phenylalanine as a hydroxyl radical-specific probe in pyrite slurries

The abundant iron sulfide mineral pyrite has been shown to catalytically produce hydrogen peroxide (H₂O₂) and hydroxyl radical ( ^. OH) in slurries of oxygenated water. Understanding the formation and fate of these reactive oxygen species is important to biological and ecological systems as exposure can lead to deleterious health effects, but also environmental engineering during the optimization of remediation approaches for possible treatment of contaminated waste streams. This study presents the use of the amino acid phenylalanine (Phe) to monitor the kinetics of pyrite-induced ^. OH formation through rates of hydroxylation forming three isomers of tyrosine (Tyr) - ortho-, meta-, and para-Tyr. Results indicate that about 50% of the Phe loss results in Tyr formation, and that these products further react with ^. OH at rates comparable to Phe. The overall loss of Phe appeared to be pseudo first-order in [Phe] as a function of time, but for the first time it is shown that initial rates were much less than first-order as a function of initial substrate concentration, [Phe]_o. These results can be rationalized by considering that the effective concentration of ^. OH in solution is lower at a higher level of reactant and that an increasing fraction of ^. OH is consumed by Phe-degradation products as a function of time. A simplified first-order model was created to describe Phe loss in pyrite slurries which incorporates the [Phe]_o, a first-order dependence on pyrite surface area, the assumption that all Phe degradation products compete equally for the limited supply of highly reactive ^. OH, and a flux that is related to the release of H₂O₂ from the pyrite surface (a result of the incomplete reduction of oxygen at the pyrite surface). An empirically derived rate constant, K _pyr , was introduced to describe a variable ^. OH-reactivity for different batches of pyrite. Both the simplified first-order kinetic model, and a more detailed numerical simulation, yielded results that compare well to the observed kinetic data describing the effects of variations in concentrations of both initial Phe and pyrite. This work supports the use of Phe as a useful probe to assess the formation of ^. OH in the presence of pyrite, and its possible utility for similar applications with other minerals.     

Evaluating methods for quantifying cation exchange in mildly calcareous sediments in Northern Alberta

Cation exchange capacity (CEC) and exchangeable cation composition are important properties in defining water–sediment interactions in contaminant transport scenarios, such as the seepage of process-affected water from oil sands tailings impoundments. At present, detailed characterization of these properties has been overlooked in the surficial Pleistocene sediments of the Athabasca Oil Sands region in Canada. Although a great variety of methods for determining CEC exist and continue to be developed, there is a deficiency in detailed comparisons amongst these methods in the literature, and consequently uncertainty still remains as to which extractants/methods are most suitable for use with sediments containing partially soluble carbonate salts. The present study (1) conducts an up-to-date evaluation of several distinct methods for their suitability in characterizing cation exchange properties in mildly calcareous sediments; using them to (2) evaluate the sorptive capacity and easily displaceable cations of mildly calcareous, surficial sediments near Fort McMurray, Alberta. Four conceptually different CEC methods were chosen: (a) a summation method (Lithium Chloride extractant); (b) a method that displaces an index cation after intermediary washes (Sodium Acetate–Ammonium Acetate); (c) a method using a high affinity cation complex (Silver Thiourea); and (d) a titration method using an organic cationic dye (Methylene Blue). Exchangeable cations were characterized using the Lithium Chloride and Silver Thiourea methods. Analysis suggests that the Methylene Blue test is least impacted by the presence of carbonate mineral phases. Results from field sediments suggest that the exchangeable cations, in decreasing abundance, consist of Ca > Mg > K > NH₄ > Na; while the CEC was found to be 4.7 ± 2.7 meq 100 g⁻¹ in the clay-rich glacial till, 0.7 ± 0.0 meq 100 g⁻¹ in the underlying sand and 4.1 ± 2.3 meq 100 g⁻¹ in the till-sand transition zone.     

Ti-in-zircon thermometry applied to contrasting Archean metamorphic and igneous systems

Ti-in-zircon thermometry with SHRIMP II multi-collector has been applied to two well-documented Archean igneous and metamorphic samples from southern West Greenland. Zircons from 2.71 Ga partial melt segregation G03/38 formed in a small (< 1 m³), closed system within a mafic rock under high pressure granulite facies conditions. Results of 14 Ti analyses present a mean apparent zircon crystallization temperature of 679 ± 11 °C, underestimating independent garnet-clinopyroxene thermometry by 20–50 °C but consistent with reduced a_TiO2 in this system. 36 spot analysis on 15 zircons from 3.81 Ga meta-tonalite G97/18, with an estimated magmatic temperature > 1000 °C, yield a low-temperature focused normal distribution with a mean of 683 ± 32 °C, further demonstrated by high resolution Ti mapping of two individual grains. This distribution is interpreted to represent the temperature of the residual magma at zircon saturation, late in the crystallization history of the tonalite. Hypothetically, Ti-in-zircon thermometry on Eoarchaean detrital zircons sourced from such a high temperature tonalite would present a low-temperature biased image of the host magma, which could be misconstrued as being a minimum melt granite. Multiple analyses from individual zircons can yield complex Ti distributions and associated apparent temperature patterns, reflecting cooling history and local chemical environments in large magma chambers. In addition to inclusions and crystal imperfections, which can yield apparent high temperature anomalies, zircon surfaces can also record extreme (> 1000 °C) apparent Ti temperatures. In our studies these were traced to ⁴⁹Ti (or a molecular isobaric interference) contamination derived from the double sided adhesive tape used in sample preparation, and should not be assigned geological significance.     

A Lagrangian approach to nonlinear modeling of anti-roll tanks

This paper presents two novel nonlinear models of u-shaped anti-roll tanks for ships, and their linearizations. In addition, a third simplified nonlinear model is presented. The models are derived using Lagrangian mechanics. This formulation not only simplifies the modeling process, but also allows one to obtain models that satisfy energy-related physical properties. The proposed nonlinear models and their linearizations are validated using model-scale experimental data. Unlike other models in the literature, the nonlinear models in this paper are valid for large roll amplitudes. Even at moderate roll angles, the nonlinear models have three orders of magnitude lower mean square error relative to experimental data than the linear models.