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The impact of transient reoxidation environments on the chemical morphology evolution of nonmetallic oxide inclusions in rare‐earth‐treated bearing steel is investigated using FactSage thermodynamic simulation calculations, vacuum induction furnace experiments, and high‐temperature laser confocal microscopy experiments. Thermodynamic calculations indicate a direct correlation between the initial rare‐earth content and the oxygen required to transform Ce2O2S to CeAlO3 during secondary oxidation. Furthermore, a higher initial rare‐earth content leads to a more extensive and complete conversion to CeAlO3. Vacuum induction furnace experiments reveal that the inclusions transform from Ce2O2S to CeAlO3 and Al2O3 and eventually into composite oxide clusters. This results in a significant increase in inclusions, with near‐spherical Ce2O2S inclusions transforming into aggregated CeAlO3, leading to an increase in the average inclusion size from 2.4 to 4.2 μm. Laser confocal scanning microscopy experiments show that CeAlO3 exhibits a higher tendency to aggregate than Ce2O2S inclusions, the primary factor contributing to the observed increase in the average inclusion size after secondary oxidation. The results of this study provide theoretical guidance for mitigating the adverse effects of rare‐earth secondary oxidation on bearing steels, particularly in terms of inclusion control. [ABSTRACT FROM AUTHOR]

The impact of rare earth treatment on the chemical morphology evolution of non-metallic inclusions in bearing steel under different initial cleanliness conditions was studied through simulation. Thermodynamic calculations indicate that at an oxygen content of 0.001%, the evolution route of inclusions with increasing Ce content was Al2O3 → CeAl11O18 + CeAlO3 → CeAlO3 + Ce2O2S → Ce2O2S → Ce2O2S + CeS. As the initial oxygen content decreases, the proportion of CeAlO3 decreases, leading to easier conversion of CeAlO3 to Ce2O2S. Vacuum induction furnace experiments demonstrated that with an oxygen content of 0.001%, an increase in Ce content results in a gradual rise in the proportion of inclusions in steel sized 1~2 μm. In contrast, the proportion of inclusions sized 2~5 μm decreases. Consequently, the overall content of inclusions in steel decreases, along with a reduction in both the number density and average size of inclusions. Introducing bearing steel melt with approximately 0.01% Ce rare earth to bearing steel with initial oxygen contents of 0.0005%, 0.001%, and 0.0015% showed an evolution of inclusions from Ce2O2S and CeS to Ce2O3, CeAlO3, etc. The average inclusion size significantly increased from 0.7 μm to 2.16 μm. Morphologically, the transition of inclusions from precipitated to polymerized forms occurred as the initial oxygen content rose. High-temperature laser confocal microscopy experiments demonstrated that inclusions in low cleanliness conditions tend to agglomerate more than those in high cleanliness conditions, contributing to the increase in average size. [ABSTRACT FROM AUTHOR]

Due to the strong reducibility and chemical activity of rare earths, the diffusion behavior and secondary oxidation of rare earths in the steel liquid will also have a significant impact on the modified products when rare earths are added to bearing steel, resulting in poor control of distribution behavior. Therefore, this paper studies the influence of time factors on the evolution of rare earth inclusions. The inclusion evolution behavior at different times when the bearing steel was treated with rare earths and subjected to secondary oxidation was simulated at 1873 K (1600 °C). At a cerium content of 0.012% in steel and a secondary oxidation of 0.0025%, the cerium content in steel and the total oxygen (T.O.) content in steel were determined at the 30 s, 3 min, 5 min, and 7 min after the addition and the inclusions were characterized by automatic scanning electron microscopy. The results demonstrated the formation of a cerium-enriched zone after the addition of the cerium alloy to the steel. As time progressed, a considerable number of inclusions were generated in the cerium-enriched zone, which subsequently disappeared. The trend in the composition of the inclusions can be described as Al2O3 → Ce2O2S + CeS → Ce2O2S. The final composition of the inclusions matches the thermodynamic phase diagram. Following the addition of the transient oxidant Fe2O3 to the molten steel, an oxygen-enriched zone was formed. As time progressed, a considerable number of inclusions were generated in the oxygen-enriched zone and subsequently disappeared. The trend of inclusions composition was as follows: Ce2O3 + CeAlO3 + Al2O3 → Ce2O3 + CeAlO3 → Ce2O2S + CeAlO3. The final inclusion composition coincides with the thermodynamic phase diagram. [ABSTRACT FROM AUTHOR]

The effect of the addition of 2CaO·SiO2 solid particles on dephosphorization behavior in carbon-saturated hot metal was investigated. The research results showed that the addition of 2CaO·SiO2 particles have little influence on desilication and demanganization, and the removal of [Si] and [Mn] occurred in the first 5 min with different conditions where the contents of 2CaO·SiO2 particles addition for the conditions 1, 2, 3, 4, and 5 are 0, 2.2, 6.4, 8.6, and 13.0 g, respectively. The final dephosphorization ratios for the conditions 1, 2, 3, 4, and 5 are 61.2%, 66.9%, 79.6%, 63.0%, and 78.1%, respectively. The dephosphorization ratio decreases with the increase of 2CaO·SiO2 particles in the first 3 min. The reason for this is that the dephosphorization process between hot metal and slag containing C2S phase consisted of two stages: Stage 1, [P] transfers from hot metal to liquid slag and Stage 2, the dephosphorization production (3CaO·P2O5) in liquid slag reacts with 2CaO·SiO2 to form C2S–C3P solid solution. The increase of 2CaO·SiO2 particles increases the viscosity of slag and weakens the dephosphorization ability of the stage 1. The SEM and XRD analyses show that the phase of dephosphorization slag with the addition of different 2CaO·SiO2 particles is composed of white RO phase, complex liquid silicate phase, and black solid phase (C2S or C2S–C3P). Because the contents of C2S–C3P and 2CaO·SiO2 in slag and the dephosphorization ability of the two stages are different, the dephosphorization ability with different conditions is different.

Megacities are major sources of anthropogenic fossil fuel CO2 (FFCO2) emissions. The spatial extents of these large urban systems cover areas of 10 000 km2 or more with complex topography and changing landscapes. We present a high-resolution land-atmosphere modelling system for urban CO2 emissions over the Los Angeles (LA) megacity area. The Weather Research and Forecasting (WRF)-Chem model was coupled to a very high-resolution FFCO2 emission product, Hestia-LA, to simulate atmospheric CO2 concentrations across the LA megacity at spatial resolutions as fine as ∼ 1 km. We evaluated multiple WRF configurations, selecting one that minimized errors in wind speed, wind direction, and boundary layer height as evaluated by its performance against meteorological data collected during the CalNex-LA campaign (May-June 2010). Our results show no significant difference between moderate-resolution (4 km) and high-resolution (1.3 km) simulations when evaluated against surface meteorological data, but the high-resolution configurations better resolved planetary boundary layer heights and vertical gradients in the horizontal mean winds. We coupled our WRF configuration with the Vulcan 2.2 (10 km resolution) and Hestia-LA (1.3 km resolution) fossil fuel CO2 emission products to evaluate the impact of the spatial resolution of the CO2 emission products and the meteorological transport model on the representation of spatiotemporal variability in simulated atmospheric CO2 concentrations. We find that high spatial resolution in the fossil fuel CO2 emissions is more important than in the atmospheric model to capture CO2 concentration variability across the LA megacity. Finally, we present a novel approach that employs simultaneous correlations of the simulated atmospheric CO2 fields to qualitatively evaluate the greenhouse gas measurement network over the LA megacity. Spatial correlations in the atmospheric CO2 fields reflect the coverage of individual measurement sites when a statistically significant number of sites observe emissions from a specific source or location. We conclude that elevated atmospheric CO2 concentrations over the LA megacity are composed of multiple fine-scale plumes rather than a single homogenous urban dome. Furthermore, we conclude that FFCO2 emissions monitoring in the LA megacity requires FFCO2 emissions modelling with ∼ 1 km resolution because coarser-resolution emissions modelling tends to overestimate the observational constraints on the emissions estimates.

According to the United States Environmental Protection Agency (US EPA), emissions from oil and gas infrastructure contribute 30 % of all anthropogenic methane (CH4) emissions in the US. Studies in the last decade have shown emissions from this sector to be substantially larger than bottom-up assessments, including the EPA inventory, highlighting both an increased importance of methane emissions from the oil and gas sector towards their overall climatological impact, and the need for independent monitoring of these emissions. In this study we present continuous monitoring of regional methane emissions from two oil and gas basins using tower-based observing networks. Continuous methane measurements were taken at 4 tower sites in the northeastern Marcellus basin from May 2015 through December 2016, and 5 tower sites in the Delaware basin in the western Permian from March 2020 through April 2022. These measurements, an atmospheric transport model, and prior emission fields, are combined using an atmospheric inversion to estimate monthly methane emissions in the two regions. This study finds the mean overall emission rate from the Delaware basin during the measurement period to be 146-210 Mg CH4 h-1 (energy-normalized loss rate of 1.1-1.5 %, gas-normalized rate of 2.5-3.5 %). Strong temporal variability in the emissions was present, with the lowest emission rates occurring during the onset of the COVID-19 pandemic. In the Marcellus, this study finds the overall mean emission rate to be 19-28 Mg CH4 h-1 (gas-normalized loss rate of 0.30-0.45 %), with relative consistency in the emission rate over time. These totals align with aircraft top-down estimates from the same time periods. In both basins, the tower network was able to constrain monthly flux estimates within ± 20 % uncertainty in the Delaware and ± 24 % uncertainty in the Marcellus. The results from this study demonstrate the ability to monitor emissions continuously and detect changes in the emissions field, even in a basin with relatively small emissions and complex background conditions. [ABSTRACT FROM AUTHOR]

Formulations describing a new shallow-convection parameterization intended for mesoscale models have been described in a companion paper, Part I. In the present paper the convection scheme is tested and evaluated against observed datasets in both marine and continental environments. Additional experiments explore the sensitivity of the scheme to changes in model vertical resolution, key parameters of the closure, and the cloud-dissipation mechanisms. The new shallow-convection scheme uses a hybrid mass flux closure that adjusts linearly between two closure options based on (i) boundary layer turbulent kinetic energy (TKE) for very shallow clouds and (ii) convective available potential energy (CAPE) for deep clouds. Meanwhile, cloud mass detrained from convective updrafts acts as the source for a second class of subgrid clouds having nearly neutral buoyancy, which can persist for hours. Performance of the convection submodel is found to be quite reasonable in four cases covering a range of conditions. In a marine application taken from the Atlantic Stratocumulus Transition Experiment (ASTEX), a 1D column of air undergoes Lagrangian advection as it gradually transitions from a stratus environment at 41[degrees]N to a trade-cumulus environment at 30[degrees]N. Characteristics of the simulated cloud fields agree rather well with ASTEX observations in this weakly forced environment, including distributions of cloud fraction, cloud water, precipitation, and cloud liquid water path, and with simulations from other cloud-predicting models. The three other cases simulate various continental convective regimes (stratocumulus, cumulus humilis, and cumulonimbus) observed at the Atmospheric Radiation Measurement (ARM) Program Cloud and Radiation Testbed (CART) Southern Great Plains (SGP) ARM CART Central Facility in Lamont, Oklahoma. Verifications of the evolving cloud area, base height, cloud depth, and liquid water pathlength in these cases show that the shallow-convection scheme can adapt to different synoptic environments and the rapidly changing conditions associated with strong surface fluxes.

A shallow-convection parameterization suitable for both marine and continental regimes is developed for use in mesoscale models. The scheme is closely associated with boundary layer turbulence processes and can transition to either a deep-convection scheme in conditionally unstable environments or to an explicit (resolved scale) moisture scheme in moist stable environments. The shallow-convection mass-closure assumption uses a hybrid formulation based on boundary layer turbulent kinetic energy (TKE) and convective available potential energy (CAPE), while the convective trigger is primarily a function of boundary layer TKE. Secondary subgrid clouds having nearly neutral buoyancy can form as shallow-convective updrafts detrain mass to their environment. Called neutrally buoyant clouds (NBCs), these can be dissipated through lateral and vertical mixing, light precipitation, ice-crystal settling, and cloud-top entrainment instability (CTEI). The shallow-convection scheme is developed and demonstrated in a 1D version of the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) mesoscale model (MM5) which includes a 1.5-order turbulence parameterization that predicts the TKE, an atmospheric radiation submodel, and an explicit moisture submodel. The radiation calculation includes the feedback effects of the subgrid NBCs predicted by the shallow-convection parameterization. Results from initial applications in both marine and continental environments are consistent with the observed characteristics of the mesoscale thermodynamic structures and local cloud-field parameters. A subsequent paper (Part II) presents more complete verifications in different environments and results of sensitivity experiments.