Water-soluble inorganic ions of size-differentiated atmospheric particles from a suburban site of Mexico City

During the MILAGRO campaign, March 2006, eight-stage cut impactors were used to sample atmospheric particles at Tecámac (T1 supersite), towards the northeast edge of the Mexico City Metropolitan Area, collecting fresh local emissions and aged pollutants produced in Mexico City. Particle samples were analyzed to determine total mass concentrations of Ca²⁺, Mg²⁺, NH₄ ⁺, K⁺, Cl^?, SO₄ ^2?, and NO₃ ^?. Average concentrations were 22.1 ± 7.2 μg m^?3 for PM₁₀ and 18.3 ± 6.2 μg m^?3 for PM_1.8. A good correlation between PM₁₀ and PM_1.8, without influence from wind patterns, indicates that local emissions are more important than the city’s pollution transported to the site, despite the fact that Tecámac is just 40 km away from Mexico City. A lack of diurnal patterns in the PM_2.5/PM_1.8 ratio supports this conclusion. The inorganic composition of particles suggests that vehicles, soil resuspension, and industries are the main pollutant sources. Finally, the particles were found to be neutralized, in agreement with observations in the Mexico City Metropolitan Area.     

Short-term effects of gamma ray bursts on oceanic photosynthesis

We continue our previous work on the potential short-term influence of a gamma ray bursts on Earth’s biosphere, focusing on the only important short-term effect on life: the ultraviolet flash which occurs as a result of the retransmission of the γ radiation through the atmosphere. Thus, in this work we calculate the ultraviolet irradiances penetrating the first hundred meters of the water column, for Jerlov’s ocean water types I, II and III. Then we estimate the UV flash potential for photosynthesis inhibition in the whole photic zone, showing that it can be important in the first tens of meters of the water column.     

Metal partitioning in sediments and mineralogical controls on the acid mine drainage in Ribeira da Água Forte (Aljustrel,Iberian Pyrite Belt,Southern Portugal)

This work focuses on the geochemical processes taking place in the acid drainage in the Ribeira da Água Forte, located in the Aljustrel mining area in the Iberian Pyrite Belt. The approach involved water and stream sediment geochemical analyses, as well as other techniques such as sequential extraction, Mössbauer spectroscopy, and X-ray diffraction. Ribeira da Água Forte is a stream that drains the area of the old mine dumps of the Aljustrel mine, which have for decades been a source of acid waters. This stream flows to the north for a little over than 10 km, but mixes with a reduced, organic-rich, high pH waste water from the municipal waste water pools of the village. This water input produces two different results in the chemistry of the stream depending upon the season: (i) in the winter season, effective water mixing takes place, and the flux of acid water from the mine dumps is continuous, resulting in the immediate precipitation of the Fe from the acid waters; (ii) during the summer season, acid drainage is interrupted and only the waste water feeds the stream, resulting in the reductive dissolution of Fe hydroxides and hydroxysulfates in the stream sediments, releasing significant quantities of metals into solution. Throughout the year, water pH stays invariably within 4.0–4.5 for several meters downstream of this mixing zone even when the source waters come from the waste water pools, which have a pH around 8.4. The coupled interplay of dissolution and precipitation of the secondary minerals (hydroxides and sulfates), keeps the system pH between 3.9 and 4.5 all along the stream. In particular, evidence suggests that schwertmannite may be precipitating and later decomposing into Fe hydroxides to sustain the stream water pH at those levels. While Fe content decreases by 50% from solution, the most important trace metals are only slightly attenuated before the solution mixes with the Ribeira do Rôxo stream waters. Concentrations of As are the only ones effectively reduced along the flow path. Partitioning of Cu, Zn and Pb in the contaminated sediments also showed different behavior. Specific/non-specific adsorption is relevant for Cu and Zn in the upstream branch of Ribeira da Água Forte with acid drainage conditions, whereas the mixture with the waste water causes that the association of these metals with oxyhydroxide to be more important. Metals bound to oxyhydroxides are on the order of 60–70% for Pb, 50% for Cu and 30–60% for Zn. Organic matter is only marginally important around the waste water input area showing 2–8% Cu bound to this phase. These results also show that, although the mixing process of both acid and organic-rich waters can suppress and briefly mitigate some adverse effects of acid drainage, the continuing discharge of these waste waters into a dry stream promotes the remobilization of metals fixed in the secondary solid phases in the stream bed back into solution, a situation that can hardly be amended back to its original state.     

Changes in the composition and structure of Mediterranean rocky-shore communities following a gradient of nutrient enrichment: descriptive study and test of proposed methods to assess water quality regarding macroalgae

Changes in the species composition and structure of Mediterranean macroalgal-dominated communities from the upper sublittoral zone are described along a gradient of nutrient enrichment coming from a urban sewage outfall. Ulva-dominated communities only appear close to the sewage outfall. Corallina-dominated communities replace ulvacean algae at intermediate levels of nutrient enrichment. Cystoseira-dominated communities thrive in the reference site but already appear at nutrient levels that are threefold higher than those reported from unpolluted sites. Assemblage variability of Cystoseira-dominated communities decreases along the gradient of nutrient enrichment. Methods based on the functional-form groups of macroalgae to assess the water quality provide equivocal results at intermediate levels of nutrient enrichment because species belonging to the same group can display a completely different response to pollution. Alternatively, methods based on indicator species showed correlated evidence among species abundances and pollution levels and seem to have better performances in water quality assessment.     

Rocky-shore communities as indicators of water quality: a case study in the Northwestern Mediterranean

The collection of 152 samples from the upper sublittoral zone along the rocky coasts of Catalonia (Northwestern Mediterranean) was carried out in 1999 in order to test the suitability of littoral communities to be used as indicators of water quality in the frame of the European Water Framework Directive. Detrended correspondence analysis were performed to distinguish between different communities and to relate communities composition to water quality. Samples collected in reference sites were included in the analysis. Mediterranean rocky shore communities situated in the upper sublittoral zone can be used as indicators of the water quality: there is a gradient from high to bad status that comprises from dense Cystoseira mediterranea forests to green algae dominated communities. The geographical patterns in the distribution of these communities show that the best areas are situated in the Northern coast, where tourism is the main economic resource of the area, and the worst area is situated close to the metropolitan zone of Barcelona with high population and industrial development. Thus, Mediterranean sublittoral rocky shore communities are useful indicators of water quality and multivariate analysis are a suitable statistical tool for the assessment of the ecological status.     

Hydrogenated fulleranes and the anomalous microwave emission of the dark cloud LDN 1622

We study the rotation rates and electric dipole emission of hydrogenated icosahedral fullerenes under the physical conditions of the dark cloud (DC) LDN 1622. The abundance of fullerenes is estimated by fitting theoretical photoabsorption spectra to the characteristics of the ultraviolet (UV) bump extinction in DCs. The UV bump appears to be well reproduced by a mixture of fullerenes following a size-distribution power law, which gives progressively lower abundances as the radius of the fullerene increases. We infer abundances of the order of  0.2 × 10⁻⁶  n (H ₂)  for C₆₀. A significant fraction of these molecules are expected to be hydrogenated. We compute the electric dipole rotational emission from these fullerene hydrides, taking into account rotational excitation and damping processes. The recent detection of anomalous microwave emission (5–60 GHz) in LDN 1622 by Casassus et al. can be explained as the result of electric dipole radiation from hydrogenated fullerenes. The bulk of the emission (10–30 GHz) appears to be associated with 60–80 carbon atom fulleranes with a degree of hydrogenation of C:H ≈ 3:1. A small contribution (∼10 per cent) of these molecules residing in the surrounding cold neutral medium and/or photodissociation region of the cloud is required to fit the high-frequency tail (40–60 GHz) of the emission.     

HD 172189, a Cluster Member Binary System with a δ Scuti Component in the Field of View of COROT

Photometric and spectroscopic results for the star HD 172189, member of the open cluster IC 4756 in the summer field of the space mission COROT, are presented. From photometric observations in the Strömgren system carried out at various epochs, its binary nature as well as the presence of a δ Scuti-type pulsating component have been discovered. The frequency analysis of the whole dataset confirms a dominant frequency of 19.5974 c d^?1 with a maximum amplitude near 0.02 mag plus other frequencies in the range 18–20 c d^?1. A preliminary orbital solution from the light curve and from four FEROS spectra reveals two similar components of around 1.5 M _⊙ orbiting with a period of 5.702 d.     

A Model to Test the Internal Structure of the G31.41+0.31 Hot Molecular Core

We investigate the physical conditions of the material around massive protostars by modelling the so-called hot molecular cores. We present a model for the spectral energy distribution (SED) as well as the ammonia line emission of the G31.41+0.31 hot core. We find that the best fit to the SED is achieved by assuming a density distribution corresponding to the collapse of a magnetized logatropic sphere. On the other hand, the line emission is reproduced by adopting a gas phase ammonia abundance increasing towards the center of the core, as a result of the release of the ammonia molecules trapped in ice grain mantles.