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Abstract Deposition of atmospheric nitrate (NO 3 −) in precipitation can be an important source of reactive nitrogen (N) to ecosystems, particularly in regions with high nitrogen oxide (NO x = nitric oxide (NO)+nitrogen dioxide (NO 2)) emissions. However, high resolution deposition data are lacking for most systems. We conducted hourly precipitation sampling across six growing season storms in a forested area historically subjected to some of the highest levels of chronic N deposition in the United States. To characterize the influence of electricity generating unit (EGU), vehicle, and biogenic NO x emissions on NO 3 − deposition, we calculated the total NO x emitted from these sources within a 100 km radius of air mass back trajectories determined for Fernow Experimental Forest (West Virginia, USA). We combined these emissions estimates with established 15N isotope values for NO x sources in a three end-member mixing model to predict source-based δ15N values of deposition reaching the study site on an hourly basis. To evaluate the effect of NO x oxidation pathways on measured δ15N-NO 3 - values, we compared observed hourly isotope values to a coupled δ15N and Δ17O array representing N isotope exchange between atmospheric oxidized N molecules. Within individual events, δ15N, δ18O, and Δ17O values ranged by as much as 19.5‰, 28.9‰, and 13.8‰, respectively. This extreme short-term isotopic variability suggests a dynamic mix of NO x sources, oxidation pathways, and fractionation processes contributing to HNO 3 formation. During every storm, precipitation δ15N-NO 3 - values were lower than those expected to result from predominant HNO 3 formation pathways or oxidation of estimated NO x emissions along back trajectories, suggesting a systematic underestimation of NO x contributions to atmospheric HNO 3 formation from isotopically depleted soil emissions. Together, these analyses represent the most comprehensive assessment to date relating high temporal resolution δ15N-NO 3 - observations to NO x emission sources, oxidation chemistry, and isotopic fractionation effects. We present the first observations of extreme intra-storm δ15N, δ18O, and Δ17O variability, emphasizing the need for improved constraints on soil NO x emissions, forest canopy effects, and their role in atmospheric NO 3 − deposition and isotope dynamics in forests. Highlights • Triple NO 3 − isotopes in wet deposition demonstrate extreme intra-storm variability. • Anthropogenic and biogenic NO x sources contribute to precipitation NO 3 − formation. • Intra-system N recycling may be an important source of wet NO 3 − deposition. [ABSTRACT FROM AUTHOR]

Stirred-flow cell experiments were performed to investigate the kinetics of uranyl [U(VI)] desorption from a contaminated sediment collected from the Hanford 300 Area at the U.S. Department of Energy Hanford Site, Washington. Three influent solutions of variable pH, Ca and carbonate concentrations that affected U(Vl) aqueous and surface speciation were used under dynamic flow conditions to evaluate the effect of geochemical conditions on the rate of U(VI) desorption. The measured rate of U(UI) desorption varied with solution chemical composition that evolved as a result of thermodynamic and kinetic interactions between the solutions and sediment The solution chemical composition that led to a larger disequilibrium between adsorbed U(VI) and equilibrium adsorption state yielded a faster desorption rate. The experimental results were used to evaluate a multirate, surface complexation model (SCM) that has been proposed to describe U(VI) desorption kinetics in the Hanford sediment that contained complex adsorbed U(VI) in mass transfer limited domains (Lui et al. Water Resour. Res. 2008, 44, W08413). The model was modified and supplemented by including multirate, ion exchange reactions to describe the geochemical interactions between the solutions and sediment With the same set of model parameters, the modified model reasonably well described the evolution of major ions and the rates of U(VI) desorption under variable geochemical and flow conditions, implying that the multirate SCM is an effective way to describe U(VI) desorption kinetics in subsurface sediments. [ABSTRACT FROM AUTHOR]

The article provides information concerning the experiment for the inorganic chemistry laboratory in the U.S. The sunlight-induced photosynthesis and characterization of pentacarbonyl tungsten and the kinetics of its ligand-exchange reactions are published experiments for the inorganic chemistry laboratory. The educational objectives of the latter experiment are to promote student understanding of the relation between kinetics, mechanisms, and the role of solvents in ligand-exchange reactions. The aim of the present experiment is to teach the chemical interpretation of a voltammogram.