Tyre Weights an Overlooked Diffuse Source of Lead and Antimony to Road Runoff

Lead (Pb) remains elevated in road runoff and roadside dust, which has been attributed to legacy lead in surface soils from leaded petrol. However, “lead” tyre weights, an alloy of 95% Pb and 5% Sb, may be a relatively unrecognised diffuse source of Pb and Sb as they are still used in many countries. An unknown number of these weights drop off tyre rims and deposit on the road where they are abraded and dispersed, potentially causing adverse environmental effects. The type, number and weight of tyre weights lost from motor vehicles were characterised for a range of roading infrastructures and motor vehicle intensities in a 38 month long study of a 6.9 km length of road in Hamilton City, New Zealand. Overall, 1070 tyre weights with a combined mass of 18.6 kg were collected. About 96.4% of the collected weights were made of “lead”, which is an alloy of 95% Pb and 5% Sb, indicating tyre weights can be a major source of Pb and Sb in urban areas. The tyre weight distribution on roads used in this study depended mainly on traffic density and the prevalence of “start stop” patterns in traffic flow influenced by roundabouts and intersections. “Lead” tyre weights should be phased out and replaced with environmentally benign materials.

A dying radio AGN in the ELAIS-N1 field

We use low-frequency GMRT observations and 1.4 GHz VLA archival data to study the radio spectrum of a dying radio galaxy discovered in the field of ELAIS-N1. With a linear size of ˜ 100 kpc at a redshift z ˜ 0.33, the diffuse source J1615+5452 exhibits a steep spectral index and a convex radio spectrum. Its radio morphology also seems to lack compact features such as a nuclear core, relativistic jets and hotspots. We record a spectral curvature Δα ≍ -1 and a synchrotron age estimated between 34 - 70 Myr. These characteristics suggest that J1615+5452 is most likely a remnant radio AGN that has spent more than half of its total lifetime in the quiescence phase. The detection of such an elusive source is important since it represents the final phase in the evolution of a radio galaxy unless the nuclear core gets replenished with fresh particles and undergoes a restarting activity.

Dynamic Diffuse-Source Upscaling in High-Contrast Systems

Summary Traditional upscaling methods are dependent on steady-state (SS) concepts of flow, whereas flow simulation itself is used for the calculation of pressure and saturation transients, which can be considered as a sequence of pseudosteady-state (PSS) solutions. In high-contrast or low-permeability systems, neither the SS nor the PSS limits need to be reached within each coarse-cell volume during a simulation timestep, introducing a potentially significant bias into an upscaling or downscaling calculation. We use an asymptotic pressure analysis for transient flow, dependent on the diffusive time of flight, to improve the resolution of these dynamic effects. We introduce a novel upscaling approach with two major differences from SS upscaling. First, we transition from SS- to PSS-flow solutions. This has been shown to provide identical results to SS upscaling in one dimension, but to have improved localization for upscaling in two and three dimensions. Specifically, there is no longer an explicit dependence upon global pressure boundary conditions. Development of this PSS upscaling approach has also required the introduction of a new transmissibility-weighted pressure-averaging definition instead of the pore-volume (PV) -weighted pressure average used for SS flow. The second difference is in using pressure-transient concepts to identify well-connected subvolumes within a coarse-cell volume. The local source/sink terms during the transient are no longer solely proportional to porosity, as in the PSS limit. Instead, these terms now include a spatial dependence obtained from the asymptotic transient pressure approximation. This dependence is especially important for high-contrast or low-permeability systems. The methodology we have developed is an application of the concepts of the diffusive time of flight and transient drainage volume to obtain source functions that capture both the early- and late-time limits of the transient-flow patterns. Diffuse-source (DS) functions are introduced within each fine cell of a coarse-cell pair, consistent with the transients and with a specified total flux between the coarse cells. The ratio of this flux to the averaged pressure drop is used to obtain the effective transmissibility between the cell pair. The application of pressure-transient concepts has allowed us to develop completely local upscaling and downscaling calculations. A characteristic time is determined for which a well-connected subvolume for each coarse-cell pair is sufficiently close to PSS. This enables us to distinguish between well-connected and weakly connected pay while upscaling. Unlike SS upscaling calculations, which explicitly impose flow on the boundaries of an upscaling region and implicitly couple the local problem to a global flow field, these calculations are completely local. The methodology is tested on SPE10 (Christie and Blunt 2001) with permeability variations over eight orders of magnitude, making it a high-contrast example. We also test the method on a low-net/gross onshore tight gas reservoir consisting of thin fluvial channels undergoing primary depletion. The comparisons of performance prediction with fine-scale numerical simulation and SS upscaling demonstrate the accuracy of the proposed approach. NOTE: Supplement available in Supporting Information section.