A novel synthesis of the N-13 labeled atmospheric trace gas peroxynitric acid

Radioactively labeled trace gases have been successfully used to study heterogeneous chemistry of atmospheric relevance. Here we present anew synthesis of gas-phase peroxynitric acid labeled with 13N (H13NO4) to study the interaction of HNO4 with ice and snow surfaces. Ayield of about 30% for HNO4 was determined. The main by-products were HNO3 and HNO2. Exposure of an ice packed bed flow tube to these species revealed that the interaction with the surface scale in the order HNO3ߙ>ߙHNO4ߙ=ߙHNO2ߙ>ߙNO

Transformation of 2-line ferrihydrite to goethite at alkaline pH

The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH >= 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life,t_1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 hours at pH = 14.0. Calculated first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log_10 k = log_10 k_0 + a*pH^E3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow re-dissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions

Al-doped Fe2O3 as a support for molybdenum oxide methanol oxidation catalysts

We have made high surface area catalysts for the selective oxidation of methanol to formaldehyde. This is done in two ways – (i) by doping haematite with Al ions, to increase the surface area of the material, but which itself is unselective and (ii) by surface coating with Mo which induces high selectivity. Temperature programmed desorption (TPD) of methanol shows little difference in surface chemistry of the doped haematite from the undoped material, with the main products being CO2 and CO, but shifted to somewhat higher desorption temperature. However, when Mo is dosed onto the haematite surface, the chemistry changes completely to show mainly the selective product, formaldehyde, with no CO2 production, and this is little changed up to 10% Al loading. But at 15 wt% Al, the chemistry changes to indicate the presence of a strongly acidic function at the surface, with additional dimethyl ether and CO/CO2 production characteristic of the presence of alumina. Structurally, X-ray diffraction (XRD) shows little change over the range 0–20% Al doping, except for some small lattice contraction, while the surface area increases from around 20 to 100 m2 g−1. Using X-ray absorption spectroscopy (XAS) it is clear that, at 5% loading, the Al is incorporated into the Fe2O3 corundum lattice, which has the same structure as α-alumina. By 10% loading then it appears that the alumina starts to nano-crystallise within the haematite lattice into the γ form. At higher loadings, there is evidence of phase separation into separate Al-doped haematite and γ-alumina. If we add 1 monolayer equivalent of Mo to the surface there is already high selectivity to formaldehyde, but little change in structure, because that monolayer is isolated at the surface. However, when three monolayers equivalent of Mo is added, we then see aluminium molybdate type signatures in the XANES spectra at 5% Al loading and above. These appear to be in a sub-surface layer with Fe molybdate, which we interpret as due to Al substitution into ferric molybdate layers immediately beneath the topmost surface layer of molybdena. It seems like the separate γ-alumina phase is not covered by molybdena and is responsible for the appearance of the acid function products in the TPD

Microbial activity affects sulphur in biogenic aragonite

Carbonates that exhibit obvious diagenetic alteration are usually excluded as archives in palaeoenvironmental studies. However, the potential impact of microbial alteration during early diagenesis is still poorly explored. To investigate the sensitivity of sulphur concentration, distribution, oxidation state and isotopic composition in marine aragonite to microbial alteration, Arctica islandica bivalves and Porites sp. corals were experimentally exposed to anaerobic microbial activity. The anoxic incubation media included a benthic bacterial strain Shewanella sediminis and a natural anoxic sediment slurry with a natural microbial community of unknown species. Combined fluorescence microscopy and synchrotron‐based analysis of the sulphur distribution and oxidation state enabled a comparison of organic matter and sulphur content in the two materials. Results revealed a higher proportion of reduced sulphur species and locally stronger fluorescence within the pristine bivalve shell compared to the pristine coral skeleton. Within the pristine bivalve specimen, reduced sulphur was enriched in layers along the inner shell margin. After incubation in the anoxic sediment slurry, this region revealed rust‐brown staining and a patchy S2‐ distribution pattern rather than S2‐‐layers. Another effect on sulphur distribution was rust‐brown coloured fibres along one growth line, revealing a locally higher proportion of sulphur. The δ34S value of carbonate‐associated sulphate remained largely unaffected by both incubation media, but a lower δ34S value of water‐soluble sulphate reflected the degradation of insoluble organic matter by microbes in both experiments. No significant alteration was detected in the coral samples exposed to microbial alteration. The data clearly identified a distinct sensitivity of organically bound sulphur in biogenic aragonite to microbial alteration even when “traditional” geochemical proxies such as δ18OCARB or δ13CCARB in the carbonate didn’t show any effect. Differences in the intensity of microbial alteration documented are likely due to inherent variations in the concentration and nature of original organic compositions in the samples

Phosphorus speciation in the organic layer of two Swedish forest soils 13-24 years after wood ash and nitrogen application

Application of wood ash to forests can restore pools of phosphorus (P) and other nutrients, which are removed following whole tree harvesting. Yet, the mechanisms that affect the fate of ash-P in the organic layer are less well known. Previous research into the extent to which ash application leads to increased P solubility in the soil is contradictory. We combined synchrotron P K-edge XANES spectroscopy, mu-XRF microscopy, and chemical ex-tractions to examine the speciation and solubility of P. We studied organic horizons of two long-term field ex-periments, Riddarhyttan (central Sweden), which had received 3, 6, and 9 Mg ash ha -1, and Ro center dot dalund (northern Sweden), where 3 Mg ash ha- 1 had been applied alone or combined with N every-three years since 2003. At the latter site, we also determined P in aboveground tree biomass. Overall, the ash application increased P in the organic layer by between 6 and 28 kg P ha -1, equivalent to 17-39 % of the initial P content in the applied ash. At Ro center dot dalund, there was 4.6 kg Ca-bound P ha- 1 (9.5 %) in the ash treatment compared to 1.6 kg ha- 1 in the ash + N treatment and < 0.4 kg ha- 1 in the N treatment and the control. At Riddarhyttan, only the treatment with the highest ash dose had residual Ca-bound P (3.8 kg ha -1). In contrast, the ash application increased Al-bound P (p < 0.001) with up to 15.6 kg P ha -1. Moreover, the ash increased Olsen-P by up to two times. There was a strong relationship between the concentrations of Olsen-P and Al-bound P (R2 = 0.83, p < 0.001) as well as Fe-bound P (R2 = 0.74, p = 0.003), suggesting that the ash application resulted in an increased amount of relatively soluble P associated with hydroxy-Al and hydroxy-Fe compounds. Further, there was an 18 % increase in P uptake by trees in the ash treatment. By contrast, repeated N fertilization, with or without ash, reduced Olsen-P. The lower P extractability was concomitant with a 39 % increase in plant P uptake in the N treatment, which indicates elevated P uptake in response to higher N availability. Hence, the application of wood ash increased Al-bound P, easily available P, and P uptake. N fertilization, while also increasing tree P uptake, instead decreased easily available P and did not cause a shift in soil P speciation

Quantifying the hydration structure of sodium and potassium ions: taking additional steps on Jacob's Ladder

The ability to reproduce the experimental structure of water around the sodium and potassium ions is a key test of the quality of interaction potentials due to the central importance of these ions in a wide range of important phenomena. Here, we simulate the Na+ and K+ ions in bulk water using three density functional theory functionals: (1) the generalized gradient approximation (GGA) based dispersion corrected revised Perdew, Burke, and Ernzerhof functional (revPBE-D3) (2) the recently developed strongly constrained and appropriately normed (SCAN) functional (3) the random phase approximation (RPA) functional for potassium. We compare with experimental X-ray diffraction (XRD) and X-ray absorption fine structure (EXAFS) measurements to demonstrate that SCAN accurately reproduces key structural details of the hydration structure around the sodium and potassium cations, whereas revPBE-D3 fails to do so. However, we show that SCAN provides a worse description of pure water in comparison with revPBE-D3. RPA also shows an improvement for K+, but slow convergence prevents rigorous comparison. Finally, we analyse cluster energetics to show SCAN and RPA have smaller fluctuations of the mean error of ion-water cluster binding energies compared with revPBE-D3

Phosphorus speciation in the organic layer of two Swedish forest soils 13–24 years after wood ash and nitrogen application

Application of wood ash to forests can restore pools of phosphorus (P) and other nutrients, which are removed following whole tree harvesting. Yet, the mechanisms that affect the fate of ash-P in the organic layer are less well known. Previous research into the extent to which ash application leads to increased P solubility in the soil is contradictory. We combined synchrotron P K-edge XANES spectroscopy, µ-XRF microscopy, and chemical extractions to examine the speciation and solubility of P. We studied organic horizons of two long-term field experiments, Riddarhyttan (central Sweden), which had received 3, 6, and 9 Mg ash ha−1, and Rödålund (northern Sweden), where 3 Mg ash ha−1 had been applied alone or combined with N every-three years since 2003. At the latter site, we also determined P in aboveground tree biomass. Overall, the ash application increased P in the organic layer by between 6 and 28 kg P ha−1, equivalent to 17–39 % of the initial P content in the applied ash. At Rödålund, there was 4.6 kg Ca-bound P ha−1 (9.5 %) in the ash treatment compared to 1.6 kg ha−1 in the ash + N treatment and < 0.4 kg ha−1 in the N treatment and the control. At Riddarhyttan, only the treatment with the highest ash dose had residual Ca-bound P (3.8 kg ha−1). In contrast, the ash application increased Al-bound P (p < 0.001) with up to 15.6 kg P ha−1. Moreover, the ash increased Olsen-P by up to two times. There was a strong relationship between the concentrations of Olsen-P and Al-bound P (R2 = 0.83, p < 0.001) as well as Fe-bound P (R2 = 0.74, p = 0.003), suggesting that the ash application resulted in an increased amount of relatively soluble P associated with hydroxy-Al and hydroxy-Fe compounds. Further, there was an 18 % increase in P uptake by trees in the ash treatment. By contrast, repeated N fertilization, with or without ash, reduced Olsen-P. The lower P extractability was concomitant with a 39 % increase in plant P uptake in the N treatment, which indicates elevated P uptake in response to higher N availability. Hence, the application of wood ash increased Al-bound P, easily available P, and P uptake. N fertilization, while also increasing tree P uptake, instead decreased easily available P and did not cause a shift in soil P speciation

Multimodal correlative imaging and modelling of phosphorus uptake from soil by hyphae of mycorrhizal fungi.

Funder: U.S. Department of Energy through the LANL/LDRD ProgramFunder: G. T. Seaborg InstitutePhosphorus (P) is essential for plant growth. Arbuscular mycorrhizal fungi (AMF) aid its uptake by acquiring P from sources distant from roots in return for carbon. Little is known about how AMF colonise soil pore-space, and models of AMF-enhanced P-uptake are poorly validated. We used synchrotron X-ray computed tomography to visualize mycorrhizas in soil and synchrotron X-ray fluorescence/X-ray absorption near edge structure (XRF/XANES) elemental mapping for P, sulphur (S) and aluminium (Al) in combination with modelling. We found that AMF inoculation had a suppressive effect on colonisation by other soil fungi and identified differences in structure and growth rate between hyphae of AMF and nonmycorrhizal fungi. Our results showed that AMF co-locate with areas of high P and low Al, and preferentially associate with organic-type P species over Al-rich inorganic P. We discovered that AMF avoid Al-rich areas as a source of P. Sulphur-rich regions were found to be correlated with higher hyphal density and an increased organic-associated P-pool, whilst oxidized S-species were found close to AMF hyphae. Increased S oxidation close to AMF suggested the observed changes were microbiome-related. Our experimentally-validated model led to an estimate of P-uptake by AMF hyphae that is an order of magnitude lower than rates previously estimated - a result with significant implications for the modelling of plant-soil-AMF interactions