The European Commission Atmospheric Observatory

A comprehensive set of essential atmospheric variables have been measured in 2018 at the European Commission Atmospheric Observatory on the site of the historical EMEP-GAW station of the JRC in Ispra to continue the assessment of the impact of European policies and international conventions on air pollution and climate forcing that started in 1985. The variables we measure at the Atmospheric Observatory in Ispra include greenhouse gas concentrations (CO2, CH4), radon (222Rn) activity concentration, short-lived gaseous and particulate pollutant concentrations (CO, SO2, NO, NO2, O3, NMHCs, PM2.5 and its main ionic and carbonaceous constituents), atmospheric particle micro-physical characteristics (number concentration and size distribution) and optical properties (light scattering and absorption in-situ, light scattering and extinction vertical profiles remotely), eutrophying and acidifying species (sulphate, nitrate, ammonium) wet deposition. Vegetation - atmosphere exchanges (CO2, O3, H2O and heat) are measured at our Mediterranean Forest Flux Station of San Rossore, backed up by meteorological and pedological measurements.JRC.C.5-Air and Climat

A single-point modeling approach for the intercomparison and evaluation of ozone dry deposition across chemical transport models (Activity 2 of AQMEII4)

A primary sink of air pollutants and their precursors is dry deposition. Dry deposition estimates differ across chemical transport models, yet an understanding of the model spread is incomplete. Here, we introduce Activity 2 of the Air Quality Model Evaluation International Initiative Phase 4 (AQMEII4). We examine 18 dry deposition schemes from regional and global chemical transport models as well as standalone models used for impact assessments or process understanding. We configure the schemes as single-point models at eight Northern Hemisphere locations with observed ozone fluxes. Single-point models are driven by a common set of site-specific meteorological and environmental conditions. Five of eight sites have at least 3 years and up to 12 years of ozone fluxes. The interquartile range across models in multiyear mean ozone deposition velocities ranges from a factor of 1.2 to 1.9 annually across sites and tends to be highest during winter compared with summer. No model is within 50 % of observed multiyear averages across all sites and seasons, but some models perform well for some sites and seasons. For the first time, we demonstrate how contributions from depositional pathways vary across models. Models can disagree with respect to relative contributions from the pathways, even when they predict similar deposition velocities, or agree with respect to the relative contributions but predict different deposition velocities. Both stomatal and nonstomatal uptake contribute to the large model spread across sites. Our findings are the beginning of results from AQMEII4 Activity 2, which brings scientists who model air quality and dry deposition together with scientists who measure ozone fluxes to evaluate and improve dry deposition schemes in the chemical transport models used for research, planning, and regulatory purposes

Further Cryogenic Separation and Mass Spectrometry Developments: Towards Ambient Air Methane Clumped Isotopes Measurements

The multiply-substituted isotopologues of methane are of significant interest due to their increased ability to distinguish between methane formation and destruction processes, in comparison to singly-substituted isotopologues, as shown previously by Thiagarajan et al.(2022) and Sivan et al.(2022). Methane isotopologues, unlike the isotopologues of carbon dioxide, do not easily transition towards thermodynamic equilibrium in the atmosphere and therefore, ambient air methane isotopologues, offer constraints on the atmospheric methane sources and sinks (Chung and Arnold, 2021). These processes potentially offer new insight into the causes of variation in methane concentrations in the last two decades. We present developments in the separation of the components of air, using a helium-cooled cryostat. Working on both pre-concentrated air mixtures and laboratory created gas mixtures, we extract methane from the contaminants and other atmospheric gases using the cryostat, applicable to a minimum methane concentration of ~1% (Stolper et al., 2015), then we analyse using a TFS Ultra HR-IRMS. We demonstrate that our cryostat separations successfully extract methane and krypton from laboratory gas mixtures containing the components of atmospheric air, without causing methane fractionation. We also present further developments in measuring and calibrating the isotopologues of methane by high-resolution mass spectrometry. We successfully created thermodynamically equilibrated samples of methane in the 250-500oC range using a nickel catalyst and are working on the 1-250oC range using a γ-Al2O3 catalyst (Eldridge et al., 2019). It is essential to have an extensive calibration curve to best constrain the effects of scale compression on the calculated deltas and therefore reduce sources of further error, hence the extension of this calibration range. Further work will add additional reference and sample points to the absolute reference frame created by the equilibrated samples, optimise the cryogenic/gas chromatographic purification methods for more complex gas mixtures, and optimise the IRMS workflow to reduce the necessary air sample sizes

Rocking response of structures with shallow foundations on thin liquefiable layers

In the event of earthquake-induced liquefaction, structures with shallow foundations can suffer excessive settlement and rotation. In this paper, the rotational response of structures with shallow foundations resting on liquefiable layers with thickness equal to or smaller than the width of the foundation is examined through a series of dynamic centrifuge experiments. Moment–rotation backbone curves are extracted and the corresponding evolution of rocking stiffness with increasing rotation is depicted, in normalised terms. A stiffness attenuation relation is proposed, which can be used for simplified predictions of maximum and residual rotation using rotational spring and dashpot models. Two such examples are presented, one using an iterative, equivalent-linear rotational spring approximation, and one using Masing's rules for cyclic response, extended with Pyke's hypothesis. Non