Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide

Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere has been estimated from observations and modelling studies using low-resolution oceanic emission scenarios derived from top-down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt (Halocarbons in the Ocean and Atmosphere) database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1 degrees x 1 degrees grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds' distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global sea-to-air concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr(-1) for CHBr3, 0.78/0.98 Gmol Br yr(-1) for CH2Br2 and 1.24/1.45 Gmol Br yr(-1) for CH3I (robust fit/ordinary least squares regression techniques). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic regions. "Hot spots" for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our flux calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An under-representation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom-up emission estimate and top-down approaches.

Marine snow studies in the Northeast Atlantic Ocean: distribution, composition and role as a food source for migrating plankton

During a 25 d Lagrangian study in May and June 1990 in the Northeast Atlantic Ocean, marine snow aggregates were collected using a novel water bottle, and the composition was determined microscopically. The aggregates contained a characteristic signature of a matrix of bacteria, cyanobacteria and autotrophic picoplankton with inter alia inclusions of the tintiniid Dictyocysta elegans and large pennate diatoms. The concentration of bacteria and cyanobacteria was much greater on the aggregates than when free-living by factors of 100 to 6000 and 3000 to 2 500 000, respectively, depending on depth. Various species of crustacean plankton and micronekton were collected, and the faecal pellets produced after capture were examined. These often contained the marine snow signature, indicating that these organisms had been consuming marine snow. In some cases, marine snow material appeared to dominate the diet. This implies a food-chain short cut wherby material, normally too small to be consumed by the mesozooplankton, and considered to constitute the diet of the microplankton can become part of the diet of organisms higher in the food-chain. The micronekton was dominated by the amphipod Themisto compressa, whose pellets also contained the marine snow signature. Shipboard incubation experiments with this species indicated that (1) it does consume marine snow, and (2) its gut-passage time is sufficiently long for material it has eaten in the upper water to be defecated at its day-time depth of several hundred meters. Plankton and micronekton were collected with nets to examine their vertical distribution and diel migration and to put into context the significance of the flux of material in the guts of migrants. “Gut flux” for the T. compressa population was calculated to be up to 2% of the flux measured simultaneously by drifting sediment traps and <5% when all migrants are considered. The in situ abundance and distribution of marine snow aggregates (>0.6 mm) was examined photographically. A sharp concentration peak was usually encountered in the depth range 40 to 80 m which was not associated with peaks of in situ fluorescence or attenuation but was just below or at the base of the upper mixed layer. The feeding behaviour of zooplankton and nekton may influence these concentration gradients to a considerable extent, and hence affect the flux due to passive settling of marine snow aggregates.

Chemotaxis of macrophages is abolished in the Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is a rare disease characterized by microthrombocytopenia, eczema and immune deficiency. In this study a direct-viewing chemotaxis chamber was used to analyse chemotactic responses of WAS neutrophils and macrophages in stable linear concentration gradients. In five patients with classic WAS, chemotaxis of macrophages but not of neutrophils was found to be abolished, whereas the speed of random motility of both cell types was found to be indistinguishable from control cells. This supports the existence of an essential functional link, previously suggested by biochemical studies, between Cdc42, WAS protein (WASp) and the actin cytoskeleton in primary human macrophages. Moreover, these data suggest that Cdc42-WASp-mediated filopodial extension is a requirement for chemotaxis but not for chemokinesis in these cells. Abnormal directional cell motility of macrophages and related antigen-presenting cells may play a significant part in the immune deficiency and eczema of WAS.

Experimental validation of the performance of a microreactor for the high-throughput screening of catalytic coatings

In this paper, the results of computational fluid dynamics simulations of flow, temperature, and concentration distributions used in the design of a microreactor for the high-throughput screening of catalytic coatings (Mies et al., Chem. Eng. J. 2004, 101, 225) are compared with experimental data, and good agreement is obtained in all cases. The experimental results on flow distribution were obtained from laser Doppler anemometry measurements in the range of Reynolds numbers from 6 to 113. The measured flow nonuniformity in the separate reactor compartments was below 2%. The temperature distribution was obtained from thermocouple measurements. The temperature nonuniformity between the reactor compartments was below 3 K at a maximum heat production rate of 1.3 W in ethylene oxidation at 425 degrees C over CuO/Al2O3/Al coatings. With respect to concentration gradients, a deviation from the average rate of reaction of only 2.3% was obtained at realistic process conditions in the ethylene ammoxidation process over identical Co-ZSM-5 coatings in all reactor compartments. The cross talking noise between separate compartments does not exceed 0.1% when the reactor parts have a smooth surface finish. This illustrates the importance of ultraprecision machining of surfaces in microtechnology, when interfaces cannot be avoided.

In situ, high-resolution imaging of labile phosphorus in sediments of a large eutrophic lake

Understanding the labile status of phosphorus (P) in sediments is crucial for managing a eutrophic lake, but it is hindered by lacking in situ data particularly on a catchment scale. In this study, we for the first time characterized in situ labile P in sediments with the Zr-oxide diffusive gradients in thin films (Zr-oxide DGT) technique at a two-dimensional (2D), submillimeter resolution in a large eutrophic lake (Lake Taihu, China, with an area of 2338km²). The concentration of DGT-labile P in the sediment profiles showed strong variation mostly ranging from 0.01 to 0.35mgL^-1 with a considerable number of hotspots. The horizontal heterogeneity index of labile P varied from 0.04 to 4.5. High values appeared at the depths of 0-30mm, likely reflecting an active layer of labile P under the sediment-water interface (SWI). Concentration gradients of labile P were observed from the high-resolution 1D DGT profiles in both the sediment and overlying water layers close to the SWI. The apparent diffusion flux of P across the SWI was calculated between -21 and 65ngcm^-2d^-1, which showed that the sediments tended to be a source and sink of overlying water P in the algal- and macrophyte-dominated regions, respectively. The DGT-labile P in the 0-30mm active layer showed a better correlation with overlying water P than the labile P measured by ex situ chemical extraction methods. It implies that in situ, high-resolution profiling of labile P with DGT is a more reliable approach and will significantly extend our ability in in situ monitoring of the labile status of P in sediments in the field.

Exogenous RNA interference exposes contrasting roles for sugar exudation in host-finding by plant pathogens

Plant parasitic nematodes (PPN) locate host plants by following concentration gradients of root exudate chemicals in the soil. We present a simple method for RNA interference (RNAi)-induced knockdown of genes in tomato seedling roots, facilitating the study of root exudate composition, and PPN responses. Knockdown of sugar transporter genes, STP1 and STP2, in tomato seedlings triggered corresponding reductions of glucose and fructose, but not xylose, in collected root exudate. This corresponded directly with reduced infectivity and stylet thrusting of the promiscuous PPN Meloidogyne incognita, however we observed no impact on the infectivity or stylet thrusting of the selective Solanaceae PPN Globodera pallida. This approach can underpin future efforts to understand the early stages of plant-pathogen interactions in tomato and potentially other crop plants.

Simulated variations in atmospheric CO2 over a Wisconsin forest using a coupled ecosystem-atmosphere model

Ecosystem fluxes of energy, water, and CO2 result in spatial and temporal variations in atmospheric properties. In principle, these variations can be used to quantify the fluxes through inverse modelling of atmospheric transport, and can improve the understanding of processes and falsifiability of models. We investigated the influence of ecosystem fluxes on atmospheric CO2 in the vicinity of the WLEF-TV tower in Wisconsin using an ecophysiological model (Simple Biosphere, SiB2) coupled to an atmospheric model (Regional Atmospheric Modelling System). Model parameters were specified from satellite imagery and soil texture data. In a companion paper, simulated fluxes in the immediate tower vicinity have been compared to eddy covariance fluxes measured at the tower, with meteorology specified from tower sensors. Results were encouraging with respect to the ability of the model to capture observed diurnal cycles of fluxes. Here, the effects of fluxes in the tower footprint were also investigated by coupling SiB2 to a high-resolution atmospheric simulation, so that the model physiology could affect the meteorological environment. These experiments were successful in reproducing observed fluxes and concentration gradients during the day and at night, but revealed problems during transitions at sunrise and sunset that appear to be related to the canopy radiation parameterization in SiB2.

Motion of the dayside polar cap boundary during substorm cycles: II. Generation of poleward-moving events and polar cap patches by pulses in the magnetopause reconnection rate

Using data from the EISCAT (European Incoherent Scatter) VHF and CUTLASS (Co-operative UK Twin- Located Auroral Sounding System) HF radars, we study the formation of ionospheric polar cap patches and their relationship to the magnetopause reconnection pulses identified in the companion paper by Lockwood et al. (2005). It is shown that the poleward-moving, high-concentration plasma patches observed in the ionosphere by EISCAT on 23 November 1999, as reported by Davies et al. (2002), were often associated with corresponding reconnection rate pulses. However, not all such pulses generated a patch and only within a limited MLT range (11:00–12:00 MLT) did a patch result from a reconnection pulse. Three proposed mechanisms for the production of patches, and of the concentration minima that separate them, are analysed and evaluated: (1) concentration enhancement within the patches by cusp/cleft precipitation; (2) plasma depletion in the minima between the patches by fast plasma flows; and (3) intermittent injection of photoionisation-enhanced plasma into the polar cap. We devise a test to distinguish between the effects of these mechanisms. Some of the events repeat too frequently to apply the test. Others have sufficiently long repeat periods and mechanism (3) is shown to be the only explanation of three of the longer-lived patches seen on this day. However, effect (2) also appears to contribute to some events. We conclude that plasma concentration gradients on the edges of the larger patches arise mainly from local time variations in the subauroral plasma, via the mechanism proposed by Lockwood et al. (2000).

Advanced source apportionment of size-resolved trace elements at multiple sites in London during winter

Trace element measurements in PM10–2.5, PM2.5–1.0 and PM1.0–0.3 aerosol were performed with 2 h time resolution at kerbside, urban background and rural sites during the ClearfLo winter 2012 campaign in London. The environment-dependent variability of emissions was characterized using the Multilinear Engine implementation of the positive matrix factorization model, conducted on data sets comprising all three sites but segregated by size. Combining the sites enabled separation of sources with high temporal covariance but significant spatial variability. Separation of sizes improved source resolution by preventing sources occurring in only a single size fraction from having too small a contribution for the model to resolve. Anchor profiles were retrieved internally by analysing data subsets, and these profiles were used in the analyses of the complete data sets of all sites for enhanced source apportionment. A total of nine different factors were resolved (notable elements in brackets): in PM10–2.5, brake wear (Cu, Zr, Sb, Ba), other traffic-related (Fe), resuspended dust (Si, Ca), sea/road salt (Cl), aged sea salt (Na, Mg) and industrial (Cr, Ni); in PM2.5–1.0, brake wear, other traffic-related, resuspended dust, sea/road salt, aged sea salt and S-rich (S); and in PM1.0–0.3, traffic-related (Fe, Cu, Zr, Sb, Ba), resuspended dust, sea/road salt, aged sea salt, reacted Cl (Cl), S-rich and solid fuel (K, Pb). Human activities enhance the kerb-to-rural concentration gradients of coarse aged sea salt, typically considered to have a natural source, by 1.7–2.2. These site-dependent concentration differences reflect the effect of local resuspension processes in London. The anthropogenically influenced factors traffic (brake wear and other traffic-related processes), dust and sea/road salt provide further kerb-to-rural concentration enhancements by direct source emissions by a factor of 3.5–12.7. The traffic and dust factors are mainly emitted in PM10–2.5 and show strong diurnal variations with concentrations up to 4 times higher during rush hour than during night-time. Regionally influenced S-rich and solid fuel factors, occurring primarily in PM1.0–0.3, have negligible resuspension influences, and concentrations are similar throughout the day and across the regions.

NONLINEAR SURFACE-WAVE EXCITATIONS IN THE BENARD-MARANGONI SYSTEM

We examine the appearance of surface waves governed by Burgers and Korteweg-de Vries equations in a shallow viscous heated fluid. We consider waves triggered by a surface-tension variation induced by both temperature and concentration gradients. We also establish the range of parameters for which the above-mentioned equations appear.

Adsorption of dihydrogen phosphate ion on platinum electrodes in aqueous media monitored by probe-beam deflection

Probe-beam deflection (PBD) was used to monitor concentration gradients of anions adjacent to the surface of a platinum electrode in acidic aqueous media containing H3PO4. PBD can measure the potential-dependent extent of adsorption of H2PO4- on the Pt electrode surface and permits the Langmuir isotherm to be fitted to the experimental data. The value thus obtained for the surface concentration was 1.3 × 10-11 mol mm -2, or 1.7 atoms of Pt per H2PO4-. Also, the electron transfer number obtained was 0.24, signifying an incomplete transfer of charge, and the equilibrium constant is 1.80 suggesting a reversible adsorption process. © 2005 Elsevier B.V. All rights reserved.

Determinação de complexos de urânio em solo usando a técnica de difusão em filmes finos por gradiente de concentração (DGT)

This paper proposes to assess the lability of complexes of uranium in soil using the technique of Diffusion in Thin Films by concentration gradients (DGT) in the vicinity the Osamu Utsumi mine, located in the municipality of Caldas - MG. The technique is based on the 1ª Fick Law, where metal complexes diffuse through a gel, which in turn is adsorbed on a resin. The metals adsorbed are recovered by an analytical technique and quantified by optical emission spectrometer with plasma inductively coupled (ICP-OES) or mass spectrometry with inductively coupled plasma (ICP-MS)

Avaliação da membrana de troca aniônica DE 81 como ligante ba técnica de difusão em filmes finos por gradientes de concentração (DGT) para a determinação de Cromo VI

It is known that there is a wide variety of bioavailable trace metals in aquatic systems, and its determination is fundamental to predict impacts to organisms in these environments. However, the determination of the total concentration of chemicals in aquatic systems, despite its importance, does not provide necessary information for decision making or even may lead to misinterpretation of the procedures and potential risks to the system in question. This study aimed to use the technique of diffusion in thin films by concentration gradients (DGT) to evaluate the anion exchange membrane Whatman DE 81 as binder alternative in determining Cr (VI). Experiments were carried out to determine the diffusion coefficients for the material used diffusion (agarose gel). The behaviors of the binders were analyzed before the main variables of the systems, immersion time, pH and ionic strength. Then was made the assessment of potential interferences, to finally proceed with testing using actual samples in the laboratory and in situ

Dually fluorescent silica nanoparticles

The cationic dyes 9-aminoacridine (9AA) and safranine (Sf) were entrapped into silica spheres of about 0.2 mu m diameter prepared by modified Stober method. The fluorescent materials are investigated by steady-state and time-resolved emission, in addition of confocal fluorescence microscopy. Silica particles containing 9-aminoacridine (SP9AA) and safranine (SPSf or both dyes (SPSf9AA) are emissive particles. When both dyes are present in the same particle but loaded in sequential stages 9AA emission is quenched as a consequence of energy transfer from 9AA (donor) to Sf (acceptor). This result suggests that particle growing processes where the acceptor is incorporated first into the core do not prevent donor/acceptor pairs to be close due to an overlay of the concentration gradients of both dyes in a radial core-shell like distribution. (C) 2010 Elsevier B.V. All rights reserved.

EFFECTS OF ION LIMITING CONDITIONS ON THE BEHAVIOR OF MICROFLUIDIC DEVICES

Finite numbers of ions are present in microfluidic devices. This leads to ion limiting effects in microfluidic channels and electrode surfaces. These effects include electrode surface changes and ion concentration gradient formation across microfluidic channels, and can influence microfluidic device behavior. A literature survey on the use of electrochemical analysis techniques in micro- and nanofluidic devices was carried out, which puts into perspective the importance of electrode surface changes with regards to analytical microfluidic applications. Surface changes in Pt wire electrodes under various physiological buffer and electric field conditions were investigated using cyclic voltammetry (CV), SEM-EDS and XPS. Effects of surface changes on electrochemical analysis performance of Pt wire and thin film electrodes were investigated. Electrode surfaces were subjected to varying phosphate buffer and electric field conditions, and their CV performance was monitored. Electrode surfaces were also studied with SEM-EDS. Two studies of ion concentration gradient formation in microfluidic channels were conducted. In the first, concentration gradients of H+ and OH- ions generated on electrode surfaces were found to cause significant pH decreases in certain buffer and electric field conditions, which was also found to play a key role in iDEP manipulation of proteins. The role of electrode surface reactions in this case shows the importance of understanding electrode surface changes in microfluidic devices. In the second study of ion concentration gradient formation, Cl- ion concentration gradient formation was attempted to be quantified upon electric field application across a KCl solution. Electrokinetic transport of the Cl- indicating fluorophore MQAE contributed significantly to the fluorescence microscopy signals collected, complicating Cl- quantification as a function of position and time. It was shown that a dielectric coating on electrode surfaces is effective at preventing MQAE electrokinetic transport.