Scientific paper
Scientific paper
A Review of More Than 20 Years of Aerosol Observation at the High Altitude Research Station Jungfraujoch, Switzerland (3580 m asl)
Among the worldwide existing long-term aerosol monitoring sites, the Jungfraujoch (JFJ) belongs to the category where both free tropospheric (FT) conditions and influence from planetary boundary layer (PBL) injections can be observed. Thus, it is possible to characterize free tropospheric aerosol as well as the effects of vertical transport of more polluted air from the PBL. This paper summarizes the current knowledge of the key properties for the JFJ aerosol, gained from the large number of in-situ studies from more than 20 years of aerosol measurements at the site. This includes physical, chemical and optical aerosol properties as well as aerosol-cloud interactions and cloud characteristics. It is illustrated that the aerosol size distribution and the aerosol chemical composition are fairly constant in time due to the long distance from aerosol sources, and that many climate relevant aerosol properties can be derived due to this behavior.
Scientific paper
A transition metal oxofluoride offering advantages in electrocatalysis and potential use in applications
The recently described solid solution ( Co,Ni,Mn)(3)Sb4O6F6 has proved stable and efficient as a catalyst for electrocatalytic water oxidation. The end component Co3Sb4O6F6 was found to be most efficient, maintaining a current density of j = 10 mA cm(-2) at an overpotential of 443 mV with good capability. At this current density, O-2 and H-2 were produced in the ratio 1 : 2 without loss of faradaic current against a Pt-cathode. A morphological change in the crystallite surface was observed after 0.5 h, however, even after 64.5 h, the overall shape and size of the small crystallites were unaffected and the electrolyte contained only 0.02 at% Co. It was also possible to conclude from in situ EXAFS measurements that the coordination around Co did not change. The oxofluorides express both hydrophilic and hydrophobic surface sites, incorporate a flexible metalloid element and offer the possibility of a mechanism that differs from other inorganic catalytic pathways previously described.
Scientific paper
Bioconcentration of Dissolved Organic Compounds from Oil Sands Process-Affected Water by Medaka (Oryzias latipes): Importance of Partitioning to Phospholipids
bases
,
chemicals
,
fish
,
mass spectrometry
,
mixtures
,
model
,
naphthenic acids
,
parameter
,
surrogate
The complex mixture of dissolved organics in oil sands process-affected water (OSPW) is acutely lethal to fish at environmentally relevant concentrations, but few bioconcentration factors (BCFs) have been measured for its many chemical species. Japanese medaka (Oryzias latipes) were exposed to 10% OSPW, and measured BCFs were evaluated against predicted BCFs from octanol water distribution ratios (D-OW) and phospholipid membrane water distribution ratios (D-MW). Two heteroatomic chemical classes detected in positive ion mode (SO+, NO+) and one in negative mode (O-2(-), also known as naphthenic acids) had the greatest D-MW, values, as high as 10 000. Estimates of D-MW were similar to and correlated with D-OW for O+, O-2(+), SO+, and NO+ chemical species, but for O-2 and SO2 species the D-MW values were much greater than the corresponding D-OW, suggesting the importance of electrostatic interactions for these ionizable organic acids. Only SO+, NO+, and O-2(-) species were detectable in medaka exposed to OSPW, and BCFs for SO+ and NO+ species ranged from 0.6 to 28 L/kg, lower than predicted (i.e., 1.4-1.7 X 10(3) L/kg), possibly because of biotransformation of these hydrophobic substances. BCFs of O-2(-) species ranged from 0.7 to 53 L/kg, similar to predicted values and indicating that phospholipid partitioning was an important bioconcentration mechanism.
Scientific paper
Carbon isotope composition of carbohydrates and polyols in leaf and phloem sap of Phaseolus vulgaris L. influences predictions of plant water use efficiency
Scientific paper
Unexpectedly acidic nanoparticles formed in dimethylamine-ammonia-sulfuric-acid nucleation experiments at CLOUD
alkylaminium sulfates
,
atmospheric particles
,
chemical composition
,
ci-api-tof
,
growth-rates
,
mass spectrometry
,
oxidation
,
particle formation
,
phase
,
secondary organic aerosol
New particle formation driven by acid-base chemistry was initiated in the CLOUD chamber at CERN by introducing atmospherically relevant levels of gas-phase sulfuric acid and dimethylamine (DMA). Ammonia was also present in the chamber as a gas-phase contaminant from earlier experiments. The composition of particles with volume median diameters (VMDs) as small as 10 nm was measured by the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Particulate ammonium-to-dimethylaminium ratios were higher than the gas-phase ammonia-to-DMA ratios, suggesting preferential uptake of ammonia over DMA for the collected 10-30 nm VMD particles. This behavior is not consistent with present nanoparticle physicochemical models, which predict a higher dimethylaminium fraction when NH3 and DMA are present at similar gas-phase concentrations. Despite the presence in the gas phase of at least 100 times higher base concentrations than sulfuric acid, the recently formed particles always had measured base : acid ratios lower than 1 : 1. The lowest base fractions were found in particles below 15 nm VMD, with a strong size-dependent composition gradient. The reasons for the very acidic composition remain uncertain, but a plausible explanation is that the particles did not reach thermodynamic equilibrium with respect to the bases due to rapid heterogeneous conversion of SO2 to sulfate. These results indicate that sulfuric acid does not require stabilization by ammonium or dimethylaminium as acid-base pairs in particles as small as 10 nm.
Scientific paper
Highly functionalized organic nitrates in the southeast United States: Contribution to secondary organic aerosol and reactive nitrogen budgets
Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene-and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gas-particle equilibrium and (ii) have a short particle-phase lifetime (similar to 2-4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment.
Scientific paper
Enhanced availability of mercury bound to dissolved organic matter for methylation in marine sediments
bioavailability
,
complexation
,
dissolution
,
dom
,
estuarine sediment
,
fluorescence
,
marine
,
mercury
,
methylation
,
methylmercury production
,
rates
,
sediment
,
sulfate-reducing bacteria
,
sulfide nanoparticles
The forms of inorganic mercury (Hg-II) taken up and methylated by bacteria in sediments still remain largely unknown. From pure cultures studies, it has been suggested that dissolved organic matter (DOM) may facilitate the uptake either by acting as a shuttle molecule, transporting the Hg-II atom to divalent metal transporters, or by binding Hg-II and then being transported into the cell as a carbon source. Enhanced availability of Hg complexed to DOM has however not yet been demonstrated in natural systems. Here, we show that Hg-II complexed with DOM of marine origin was up to 2.7 times more available for methylation in sediments than Hg-II added as a dissolved inorganic complex (Hg-II (aq)). We argue that the DOM used to complex Hg-II directly facilitated the bacterial uptake of Hg-II whereas the inorganic dissolved Hg-II complex adsorbed to the sediment matrix before forming bioavailable dissolved Hg-II complexes. We further demonstrate that differences in net methylation in sediments with high and low organic carbon content may be explained by differences in the availability of carbon to stimulate the activity of Hg methylating bacteria rather than, as previously proposed, be due to differences in Hg-II binding capacities between sediments. (C) 2016 Elsevier Ltd. All rights reserved.
Scientific paper