Cavity ringdown spectrum of the forbidden (A)over-tilde(2)E('')←(X)over-tilde(2)A(2)(') transition of NO_3: Evidence for static Jahn-Teller distortion in the (A)over-tilde state

The Jahn-Teller effect in the first two excited states of the nitrate radical NO3 has yet to be experimentally elucidated. In this paper, direct evidence of strong Jahn-Teller interactions in the A state is presented from the first complete absorption spectrum of the A(2)E(')←X(2)A(2)(') transition of NO3 in the gas phase in the region 5900-9000 cm(-1), at moderate resolution (0.15 cm(-1)). The observed spectrum is consistent with Herzberg-Teller selection rules, and reveals strong linear and quadratic Jahn-Teller interactions in the A state. Several of the vibronic bands have been tentatively assigned, including nu(2),nu(3), an irregular progression in nu(4), and combination bands involving nu(1). Our assignments are consistent with the previous works of Weaver [A. Weaver, D. W. Arnold, S. E. Bradforth, and D. M. Neumark, J. Chem. Phys. 94, 1740 (1991)] and Hirota [E. Hirota, T. Ishiwata, K. Kawaguchi, M. Fujitake, N. Ohashi, and I. Tanaka, J. Phys. Chem. 107, 2829 (1997)] The band origin is not observed, in accord with the selection rules, but is determined to be T-0=7064 cm(-1) from the observation of the 4(1)(0) hot band at 6695.7 cm(-1). Rotational contour analysis of this band indicates that the upper state is an asymmetric rotor, establishing that NO3 undergoes static Jahn-Teller distortion in the ground vibrational level of the A state

New insights into the Jahn–Teller effect in NO_3 via the dark à 2E" state

The recent cavity ringdown (CRD) measurement of the forbidden Ã^2 E"←X~^2 A2' transition of the nitrate radical NO_3 reveals a rich, well-resolved spectrum in the near-infrared. The spectroscopic detail provides a new window onto the Jahn–Teller (JT) and pseudo-Jahn–Teller (PJT) effects in NO_3. This paper reviews the current experimental evidence for vibronic coupling in the à state and discusses the theoretical issues in the context of new preliminary EOMIP/CCSD and CCSD(T) calculations. The theoretical results to date indicate that the à 2E" state of NO_3 undergoes a relatively strong JT distortion which may require inclusion of higher order vibronic couplings. The intensity of this transition may involve multiple intensity borrowing mechanisms via PJT coupling among the X~, à and B~ states

Atmospheric mercury inputs in montane soils increase with elevation: evidence from mercury isotope signatures

The influence of topography on the biogeochemical cycle of mercury (Hg) has received relatively little attention. Here, we report the measurement of Hg species and their corresponding isotope composition in soil sampled along an elevational gradient transect on Mt. Leigong in subtropical southwestern China. The data are used to explain orography-related effects on the fate and behaviour of Hg species in montane environments. The total- and methyl-Hg concentrations in topsoil samples show a positive correlation with elevation. However, a negative elevation dependence was observed in the mass- ependent fractionation (MDF) and mass-independent fractionation (MIF) signatures of Hg isotopes. Both a MIF (D199Hg) binary mixing approach and the traditional inert element method indicate that the content of Hg derived from the atmosphere distinctly increases with altitude.publishedVersio

Assessing Air–Surface Exchange and Fate of Mercury in a Subtropical Forest Using a Novel Passive Exchange-Meter Device

Embargo until 01 April 2020acceptedVersio

Mercury Biogeochemical Cycling: A Synthesis of Recent Scientific Advances

The focus of this paper is to briefly discuss the major advances in scientific thinking regarding: a) processes governing the fate and transport of mercury in the environment; b) advances in measurement methods; and c) how these advances in knowledge fit in within the context of the Minamata Convention on Mercury. Details regarding the information summarized here can be found in the papers associated with this Virtual Special Issue of STOTEN

System design and evaluation of intermodal transport solutions

The aim of this report is to outline a possible intermodal transport solution for temperature sensitive shipments on a pilot international European route and identify what’s required of this system in order to be competitive

Recent advances in understanding and measurement of Hg in the environment: Surface-atmosphere exchange of gaseous elemental mercury (Hg-0)

The atmosphere is the major transport pathway for distribution of mercury (Hg) globally. Gaseous elemental mercury (GEM, hereafter Hg0) is the predominant form in both anthropogenic and natural emissions. Evaluation of the efficacy of reductions in emissions set by the UN's Minamata Convention (UN-MC) is critically dependent on the knowledge of the dynamics of the global Hg cycle. Of these dynamics including e.g. red-ox reactions, methylation-demethylation and dry-wet deposition, poorly constrained atmosphere-surface Hg-0 fluxes especially limit predictability of the timescales of its global biogeochemical cycle. This review focuses on Hg-0 flux field observational studies, namely the theory, applications, strengths, and limitations of the various experimental methodologies applied to gauge the exchange flux and decipher active sub-processes. We present an in-depth review, a comprehensive literature synthesis, and methodological and instrumentation advances for terrestrial and marine Hg0 flux studies in recent years. In particular, we outline the theory of a wide range of measurement techniques and detail the operational protocols. Today, the most frequently used measurement techniques to determine the net Hg-0 flux (>95% of the published flux data) are dynamic flux chambers for small-scale and micrometeorological approaches for large-scale measurements. Furthermore, top-down approaches based on Hg-0 concentration measurements have been applied as tools to better constrain Hg emissions as an independent way to e.g. challenge emission inventories. This review is an up-dated, thoroughly revised edition of Sommar et al. 2013 (DOI: 10.1080/10643389.2012.671733). To the tabulation of >100 cited flux studies 1988-2009 given in the former publication, we have here listed corresponding studies published during the last decade with a few exceptions (2008-2019). During that decade, Hg stable isotope ratios of samples involved in atmosphere-terrestrial interaction is at hand and provide in combination with concentration and/or flux measurements novel constraints to quantitatively and qualitatively assess the bi-directional Hg-0 flux. Recent efforts in the development of relaxed eddy accumulation and eddy covariance Hg-0 flux methods bear the potential to facilitate long-term, ecosystem-scale flux measurements to reduce the prevailing large uncertainties in Hg-0 flux estimates. Standardization of methods for Hg-0 flux measurements is crucial to investigate how land-use change and how climate warming impact ecosystem-specific Hg-0 sink-source characteristics and to validate frequently applied model parameterizations describing the regional and global scale Hg cycle. (C) 2020 Elsevier B.V. All rights reserved

Enhanced concentrations of dissolved gaseous mercury in the surface waters of the Arctic Ocean

During an almost three months long expedition in the Arctic Ocean, the Beringia 2005, dissolved gaseous mercury (DGM) was measured continuously in the surface water. The DGM concentration was measured using an equilibrium system, i.e. the DGM in the water phase equilibrated with a stream of gas and the gas was thereafter analysed with respect to its mercury content. The DGM concentrations were calculated using the following equation, DGM = Hg eq / k H\u27 where Hg eq is the equilibrated concentration of elemental mercury in the gas phase and k H\u27 is the dimensionless Henry\u27s law constant at desired temperature and salinity. During the expedition several features were observed. For example, enhanced DGM concentration was measured underneath the ice which may indicate that the sea ice acted as a barrier for evasion of mercury from the Arctic Ocean to the atmosphere. Furthermore, elevated DGM concentrations were observed in water that might have originated from river discharge. The gas-exchange of mercury between the ocean and the atmosphere was calculated in the open water and both deposition and evasion were observed. The measurements showed significantly enhanced DGM concentrations, compared to more southern latitudes. \ua9 2008 Elsevier B.V. All rights reserved