Anthonykay8737

The atmosphere is a significant global reservoir for mercury (Hg) and its isotopic characterization is important to understand sources, distribution, and deposition of Hg to the Earth's surface. To better understand Hg isotope variability in the remote background atmosphere, we collected continuous 12-h Hg0 samples for 1 week from two high elevation sites, Camp Davis, Wyoming (valley), and Mount Bachelor, Oregon (mountaintop). The samples collected at Camp Davis displayed strong diel variation in δ202Hg values of Hg0, but not in Δ199Hg or Δ200Hg values. We attribute this pattern to nightly atmospheric inversions trapping Hg in the valley and the subsequent nighttime uptake of Hg by vegetation, which depletes Hg from the atmosphere. At Mount Bachelor, the samples displayed diel variation in both δ202Hg and Δ199Hg, but not Δ200Hg. We attribute this pattern to differences in the vertical distribution of Hg in the atmosphere as Mount Bachelor received free tropospheric air masses on certain nights during the sampling period. Near the end of the sampling period at Mount Bachelor, the observed diel pattern dissipated due to the influence of a nearby forest fire. The processes governing the Hg isotopic fractionation differ across sites depending on mixing, topography, and vegetation cover.The Qinghai-Tibetan Plateau is experiencing unprecedented temperature rises and changes in plant community composition owing to global warming. Few studies focused on the combined effects of warming and changes in species composition on soil respiration (Rs). We conducted a 4-year experiment (2015-2018) to examine the influences of warming and dominant plant species removal on Rs and its autotrophic (Ra) and heterotrophic (Rh) components along an elevation gradient (3200, 3700, and 4000 m) for alpine meadow of the Qinghai-Tibetan Plateau. Results showed that warming positively affected Rs, and the stimulation of Rs gradually diminished at 3200 m but remained stable at 3700 and 4000 m as warming progressed. Warming did not influence Ra at all sites. Dominant species removal produced hysteretic behavior that decreased Ra (29%) at 3700 m but increased Ra (55%) at 4000 m in 2018. No significant effect of dominant species removal on Rh was observed. Significant interactive effects of warming and dominant species removal were detected only on Ra at 3700 and 4000 m. OTX015 Accordingly, under future warming, soil organic matter decomposition at higher elevation will enhance positive feedback to atmospheric CO2 concentration more than that at lower elevation, thus accelerating soil organic carbon loss.The recent discovery of magnetic nanoparticles (NPs) in human brain tissue has raised concerns regarding their source and neurotoxicity. As previous studies have suggested that magnetite in urban dust may be the source, we collected urban magnetic dust and thoroughly characterized the nature of ambient urban magnetic dust particles prior to investigating their neurotoxic potential. In addition to magnetite, magnetic dust contained an abundance (∼40%) of elemental iron (Fe0). The coexistence of magnetite and elemental iron was found in magnetic dust particles of inhalable ( less then 10 μm) and nanoscale ( less then 200 nm) size ranges with these particles small enough to enter the human brain via the respiratory tract and olfactory bulbs. The magnetic dust also contained nonferrous water-soluble metals (particularly Cu) that can induce formation of reactive oxygen species (ROS). Previous studies used engineered pure-magnetite for in vitro ROS studies. However, while magnetite was present in all magnetic dust particles collected, engineered pure-magnetite was relatively unreactive and contributed minimally to the generation of ROS. We fill a critical knowledge gap between exposure to heterogeneous ambient iron-particles and in vitro experiments with engineered versus ambient, incidental iron-bearing nanoscale minerals. Our work points to the need to further investigate the presence and properties of magnetic NPs in respirable dust with respect to their potential role in neurodegeneration.Ag-Mn catalysts with excellent water resistance and ozone decomposition activity were successfully synthesized by simple precipitation and impregnation methods. Under a relative humidity of 65% and space velocity of 840,000 h-1, the 6%Ag/α-Mn2O3-I catalyst showed 99% conversion of 40 ppm O3 after 6 h, which was far superior to the performance of the 6%AgMnO x -C (49%), 6%Ag/MnCO3-I (32%), and α-Mn2O3 (5%) catalysts. Physicochemical characterization indicated that the chemical state of Ag on the Ag-Mn catalysts determined the O3 decomposition activity of the catalysts. The Ag species on the 6%Ag/α-Mn2O3-I catalyst were mainly metallic silver nanoparticles (Agn0), which exhibited much better ozone decomposition performance than the Ag1.8Mn8O16 and oxidized silver clusters (Agnδ+) existing on the 6%Ag/MnCO3-I and 6%AgMnO x -C catalysts. The 6%Ag/α-Mn2O3-I catalyst still had above 85% ozone conversion after 60 h under a relative humidity of 65% and space velocity of 840,000 h-1. The slight deactivation of the catalyst was ascribed to the oxidation of Agn0, and its activity could be completely recovered by treatment at 350 °C under an N2 atmosphere, which indicated that it is a promising catalyst for ozone decomposition. This research provides guidance for the subsequent development of Ag-Mn catalysts for ozone decomposition with high activity.Efforts of using data assimilation to improve PM2.5 forecasts have been hindered by the limited number of species and incomplete vertical coverage in the observations. The common practice of initializing a chemical transport model (CTM) with assimilated initial conditions (ICs) may lead to model imbalances, which could confine the impacts of assimilated ICs within a day. To address this challenge, we introduce an initial error transport model (IETM) approach to improving PM2.5 forecasts. The model describes the transport of initial errors by advection, diffusion, and decay processes and calculates the impacts of assimilated ICs separately from the CTM. The CTM forecasts with unassimilated ICs are then corrected by the IETM output. We implement our method to improve PM2.5 forecasts over central and eastern China. The reduced root-mean-square errors for 1-, 2-, 3-, and 4-day forecasts during January 2018 were 51.2, 27.0, 16.4, and 9.4 μg m-3, respectively, which are 3.2, 6.9, 8.6, and 10.4 times those by the CTM forecasts with assimilated ICs.