The prediction of the probability density function (PDF) of a pollutant concentration within atmospheric flows is of primary importance in estimating the hazard related to accidental releases of toxic or flammable substances and their effects on human health. This need motivates studies devoted to the characterization of concentration statistics of pollutants dispersion in the lower atmosphere, and their dependence on the parameters controlling their emissions. As is known from previous experimental results, concentration fluctuations are significantly influenced by the diameter of the source and its elevation. In this study, we aim to further investigate the dependence of the dispersion process on the source configuration, including source size, elevation and emission velocity. To that end we study experimentally the influence of these parameters on the statistics of the concentration of a passive scalar, measured at several distances downwind of the source. We analyze the spatial distribution of the first four moments of the concentration PDFs, with a focus on the variance, its dissipation and production and its spectral density. The information provided by the dataset, completed by estimates of the intermittency factors, allow us to discuss the role of the main mechanisms controlling the scalar dispersion and their link to the form of the PDF. The latter is shown to be very well approximated by a Gamma distribution, irrespective of the emission conditions and the distance from the source. Concentration measurements are complemented by a detailed description of the velocity statistics, including direct estimates of the Eulerian integral length scales from two-point correlations, a measurement that has been rarely presented to date.

We investigate the reliability of a meandering plume model in reproducing the passive scalar concentration statistics due to a continuous release in a turbulent boundary layer. More specifically, we aim to verify the physical consistency of the parametrizations adopted in the model through a systematic comparison with experimental data. In order to perform this verification, we take advantage of the velocity and concentration measurements presented in part I of the present study (Nironi et al., Boundary-Layer Meteorol, 2015) particularly concerning estimates of the Eulerian integral length scales and the higher order moments of the concentration probability density function. The study is completed by a sensitivity analysis in order to estimate the effects of the variations of the key parameter to the model results. In the light of these results, we discuss the benefits and shortcomings of this modelling approach and its suitability for operational purposes.

PurposeThe research activity presented in this paper has the objective of developing models for the evaluation of technological risk and loss of production due to failures, which are among the criterions that enable the choice of optimal scenarios for energy supply. This activity is based on the European Project “Risk of Energy Availability: Common Corridors for Europe Supply Security” (REACCESS), which aims to develop an analytical tool to analyse scenarios for future secure European Union (EU) energy supply.Design/methodology/approachThe paper proposes an innovative approach, since nowadays a generalised analytic model for risk assessment in large‐scale energetic systems does not exist. In particular, the methodology adopted includes models to assess risk for people safety, risk for the environment and availability for corridors and the related infrastructures. As regards technological risk, accidents producing loss of lives in the population and environmental damage are taken into account; while for the loss of production primary attention is paid to technical failures and maintenance.FindingsSince the analytic models developed perform a large‐scale assessment, they must be flexible and simplified to adapt to different situations and to be easily updated when different future scenarios are investigated. Details of the analysis depend on the precision of data collected and inserted in the models. The damage assessment is affected by deficiency and uncertainties related to territorial and statistical data. Nevertheless, the outcomes obtained for each energy commodity are reasonable and often comparable to literature data.Originality/valueBased on this study output, technological risk can be considered, more systematically than in the past, in the selection of EU strategies for future energy supply. The corridors social cost is included in future strategies selection, in addition to purely economical and environmental evaluations.

International audienceno abstrac