Mercury Accumulation in Tree Rings: Observed Trends in Quantity and Isotopic Composition in Shenandoah National Park, Virginia

Recent studies have shown that mercury (Hg) concentrations in tree rings have the potential to archive historical Hg exposure from local, regional, and global sources. The southeastern United States has received elevated Hg deposition, yet no studies have evaluated tree ring Hg in this region. Here, we quantify Hg accumulation and isotopic composition in tree rings collected in Shenandoah National Park, Virginia. Cores were collected from three individuals of three tree species—white oak (Quercus alba), northern red oak (Quercus rubra), and pitch pine (Pinus rigida)—within the northern, central, and southern areas of the Park (n = 27 cores). The cores were analyzed for Hg content in 10‐year increments, with some cores dating back to the early 1800s. Overall, tree ring Hg concentrations (ranging from below detection to 4.4 ng/g) were similar to other studies and varied between species, with pitch pine having higher concentrations than the deciduous species. The most notable feature of the tree ring Hg time series was a peak that occurred during the 1930s through 1950s, coinciding with the use of Hg at a local industrial facility. Atmospheric modeling indicates that potential emissions from the plant likely had a stronger impact on the southern region of the Park, consistent with the latitudinal gradient in tree ring Hg concentrations. Mass‐dependent and mass‐independent fractionation of Hg isotopes suggests contributions from both regional anthropogenic and local industrial sources during this period. This study demonstrates the potential usefulness of tree ring dendrochemistry for identifying historical sources of atmospheric Hg exposure.Key PointsTree ring mercury levels in Shenandoah National Park, Virginia, were similar to those measured in other North American forestsTree ring mercury peaked during the 1930s to 1950s, coinciding with mercury use at an industrial facility near the southern end of the ParkMercury isotopes suggest a local source at this time, demonstrating the potential of dendrochemistry to identify historical sourcesPlain Language SummaryFor many years scientists have used tree rings to reconstruct past climate. Increasingly, tree rings are being used to document the historical exposure of trees to pollutants. In this study, we cored trees in Shenandoah National Park, Virginia, dated the tree rings, and then measured the amount of mercury stored within decadal core increments. We were surprised to find that mercury levels peaked in the 1930s to 1950s, even though global mercury emissions continued to rise throughout the past century, mostly as a by‐product of energy production. Our findings suggest that the trees were exposed to a local pollutant source during this earlier time period, perhaps from a nearby industrial plant that used mercury in the production of rayon. By examining the chemistry of wood within tree rings, we can get a clearer picture of when and where human activities have affected air pollution over recent centuries.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153685/1/jgrg21576_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153685/2/jgrg21576.pd

Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation

High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected

Genotyping Validates the Efficacy of Photographic Identification in a Capture-Mark-Recapture Study Based on the Head Scale Patterns of the Prairie Lizard (\u3ci\u3eSceloporus consobrinus\u3c/i\u3e)

Population studies often incorporate capture‐mark‐recapture (CMR) techniques to gather information on long‐term biological and demographic characteristics. A fundamental requirement for CMR studies is that an individual must be uniquely and permanently marked to ensure reliable reidentification throughout its lifespan. Photographic identification involving automated photographic identification software has become a popular and efficient noninvasive method for identifying individuals based on natural markings. However, few studies have (a) robustly assessed the performance of automated programs by using a double‐marking system or (b) determined their efficacy for long‐term studies by incorporating multi‐year data. Here, we evaluated the performance of the program Interactive Individual Identification System (I3S) by cross‐validating photographic identifications based on the head scale pattern of the prairie lizard (Sceloporus consobrinus) with individual microsatellite genotyping (N = 863). Further, we assessed the efficacy of the program to identify individuals over time by comparing error rates between within‐year and between‐year recaptures. Recaptured lizards were correctly identified by I3S in 94.1% of cases. We estimated a false rejection rate (FRR) of 5.9% and a false acceptance rate (FAR) of 0%. By using I3S, we correctly identified 97.8% of within‐year recaptures (FRR = 2.2%; FAR = 0%) and 91.1% of between‐year recaptures (FRR = 8.9%; FAR = 0%). Misidentifications were primarily due to poor photograph quality (N = 4). However, two misidentifications were caused by indistinct scale configuration due to scale damage (N = 1) and ontogenetic changes in head scalation between capture events (N = 1). We conclude that automated photographic identification based on head scale patterns is a reliable and accurate method for identifying individuals over time. Because many lizard or reptilian species possess variable head squamation, this method has potential for successful application in many species

Development of a detector for inertial sensing of positronium at AEgIS (CERN)

The primary goal of the AEgIS collaboration at CERN is to measure the gravitational acceleration on neutral antimatter. Positronium (Ps), the bound state of an electron and a positron, is a suitable candidate for a force-sensitive inertial measurement by means of deflectometry/interferometry. In order to conduct such an experiment, the impact position and time of arrival of Ps atoms at the detector must be detected simultaneously. The detection of a low-velocity Ps beam with a spatial resolution of (88 ± 5) μm was previously demonstrated [1]. Based on the methodology employed in [1] and [2], a hybrid imaging/timing detector with increased spatial resolution of about 10 μm was developed. The performance of a prototype was tested with a positron beam. The concept of the detector and first results are presented

High-resolution MCP-TimePix3 imaging/timing detector for antimatter physics

We present a hybrid imaging/timing detector for force sensitive inertial measurements designed for measurements on positronium, the metastable bound state of an electron and a positron, but also suitable for applications involving other low intensity, low energy beams of neutral (antimatter)-atoms, such as antihydrogen. The performance of the prototype detector was evaluated with a tunable low energy positron beam, resulting in a spatial resolution of approximate t

Positronium laser cooling via the 13S1^3S-23P2^3P transition with a broadband laser pulse

We report on laser cooling of a large fraction of positronium (Ps) in free-flight by strongly saturating the $1^3S$-$2^3P$ transition with a broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is produced in a magnetic and electric field-free environment. We observe two different laser-induced effects. The first effect is an increase in the number of atoms in the ground state after the time Ps has spent in the long-lived $3^3P$ states. The second effect is the one-dimensional Doppler cooling of Ps, reducing the cloud's temperature from 380(20) K to 170(20) K. We demonstrate a 58(9) % increase in the coldest fraction of the Ps ensemble.Comment: 6 pages, 5 figure

Control system for ion Penning traps at the AEgIS experiment at CERN

The AEgIS experiment located at the Antiproton Decelerator at CERN aims to measure the gravitational fall of a cold antihydrogen pulsed beam. The precise observation of the antiatoms in the Earth gravitational field requires a controlled production and manipulation of antihydrogen. The neutral antimatter is obtained via a charge exchange reaction between a cold plasma of antiprotons from ELENA decelerator and a pulse of Rydberg positronium atoms. The current custom electronics designed to operate the 5 and 1 T Penning traps are going to be replaced by a control system based on the ARTIQ & Sinara open hardware and software ecosystem. This solution is present in many atomic, molecular and optical physics experiments and devices such as quantum computers. We report the status of the implementation as well as the main features of the new control system

Chromosomal localization of the transcription factor YY1 in the mouse and human

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47010/1/335_2004_Article_BF00360552.pd