Impact of Lagrangian transport on lower-stratospheric transport timescales in a climate model

We investigate the impact of model trace gas transport schemes on the representation of transport processes in the upper troposphere and lower stratosphere. Towards this end, the Chemical Lagrangian Model of the Stratosphere (CLaMS) was coupled to the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and results from the two transport schemes (Lagrangian critical Lyapunov scheme and flux-form semi-Lagrangian, respectively) were compared. Advection in CLaMS was driven by the EMAC simulation winds, and thereby the only differences in transport between the two sets of results were caused by differences in the transport schemes. To analyze the timescales of large-scale transport, multiple tropical-surface-emitted tracer pulses were performed to calculate age of air spectra, while smaller-scale transport was analyzed via idealized, radioactively decaying tracers emitted in smaller regions (nine grid cells) within the stratosphere. The results show that stratospheric transport barriers are significantly stronger for Lagrangian EMAC-CLaMS transport due to reduced numerical diffusion. In particular, stronger tracer gradients emerge around the polar vortex, at the subtropical jets, and at the edge of the tropical pipe. Inside the polar vortex, the more diffusive EMAC flux-form semi-Lagrangian transport scheme results in a substantially higher amount of air with ages from 0 to 2 years (up to a factor of 5 higher). In the lowermost stratosphere, mean age of air is much smaller in EMAC, owing to stronger diffusive cross-tropopause transport. Conversely, EMAC-CLaMS shows a summertime lowermost stratosphere age inversion – a layer of older air residing below younger air (an “eave”). This pattern is caused by strong poleward transport above the subtropical jet and is entirely blurred by diffusive cross-tropopause transport in EMAC. Potential consequences from the choice of the transport scheme on chemistry–climate and geoengineering simulations are discussed

Electrochemical Investigation of the Corrosion Behavior of API 5L-X65 Carbon Steel in Carbon Dioxide Medium

The corrosion behavior of API 5L-X65 carbon steel in a carbon dioxide (CO2)-saturated solution was investigated by electrochemical measurements (polarization curves, Levich plots, and electrochemical impedance spectroscopy) with a rotating disk electrode. Different experimental conditions such as hydrodynamics, immersion time, and temperature were considered. From the polarization curves, it was shown that both the anodic and cathodic current densities decreased as the electrode rotation speed, the immersion time, and the temperature increased. This behavior was in agreement with the impedance results obtained at the corrosion potential. It was shown that the corrosion processes were initially controlled by mass transport but they became under activation control for longer immersion times. Scanning electron microscopy was used to characterize the corrosion products. For short immersion times (2 h and 6 h), the corrosion products mainly deposited on the cathodic sites (pearlitic zones) of the carbon steel surface forming a heterogeneous layer, whereas they covered the whole electrode surface after longer periods (>15 h). At a microscale, localized corrosion, as a result of galvanic coupling between pearlite and ferrite, was also observed

Effect of Dissolved Oxygen, Sodium Bisulfite, and Oxygen Scavengers on Methane Hydrate Inhibition

© 2018 American Chemical Society. Numerous chemical additives are added to monoethylene glycol (MEG) injection streams to maintain and protect assets as well as to ensure steady production of hydrocarbons. Oxygen scavengers are injected for the purpose of lowering dissolved oxygen to levels that do not pose the risk of corrosion. In this study, the effect of dissolved oxygen and some oxygen scavengers on gas hydrate inhibition was investigated. Results reveal that high levels of dissolved oxygen may promote the formation of hydrates due to the reaction of dissolved oxygen with impurity components such as iron carbonate that may exist in the MEG solution, thus decreasing overall MEG quality. Sodium bisulfite had negligible effect on hydrate inhibition at low concentrations but showed greater inhibition performance at higher concentrations due to the electrostatic attraction between ions and water molecules. A proprietary oxygen scavenger showed hydrate promotion effect, which suggests that proprietary chemical additives should undergo extensive compatibility and risk analysis. An erythorbic acid-based oxygen scavenger showed minor inhibition performance albeit at small concentration, possibly due to hydrogen bonding between hydroxyl groups of its components with water molecules