UDINEE: Evaluation of Multiple Models with Data from the JU2003 Puff Releases in Oklahoma City. Part I: Comparison of Observed and Predicted Concentrations

Abstract

In a complex environment such as an urban area, accurate prediction of the atmospheric dispersion of airborne harmful materials such as radioactive substances is necessary for establishing response actions and assessing risk or damage. Given the variety of urban atmospheric dispersion models available, evaluation and inter-comparison exercises are vital for assessing quantitatively and qualitatively their capabilities and differences. To that end, the European Commission/Directorate General Joint Research Centre with support from the European Commission/Directorate General-Migration and Home Affairs, and with the contribution of the U.S. Defense Threat Reduction Agency, launched the Urban Dispersion INternational Evaluation Exercise (UDINEE) project. Within UDINEE, nine atmospheric dispersion models are evaluated and intercompared. Sulphur hexafluoride concentrations from puffs released near the ground during the Joint Urban 2003 (JU2003) field experiment are used in UDINEE to evaluate atmospheric dispersion models. The JU2003 experiment is chosen because UDINEE aims at the better understanding of modelling capabilities for radiological dispersal devices in urban areas, and the neutrally-buoyant puff releases performed in the JU2003 experiment are the closest scenario to this purpose. The present study evaluates the capability of models at simulating the presence and concentration levels of the tracer at sampling locations. The fraction of predicted concentrations and time-integrated concentrations within a factor-of-two of observations are less than 0.36 and 0.4 respectively. The analysis reveals an improvement in the performance of models by using time-varying inflow conditions. Since the simulation of the dispersion of puff release is particularly challenging, the results of UDINEE could constitute a benchmark for future model developments.

UDINEE: Evaluation of Multiple Models with Data from the JU2003 Puff Releases in Oklahoma City. Part II: Simulation of Puff Parameters

“…As in Hernández-Ceballos et al (2019), the statistical measures presented in the previous sections show variability among different models in the simulation of the puff dispersion.…”

“…In the context of UDINEE, six modelling groups from Europe and two modelling groups from North America simulated the dispersion of the puff releases that occurred during the JU2003 experiment. The nine ADMs, listed below, have been evaluated; for more information see Hernández-Ceballos et al (2019). Pardyjak andBrown 2001, 2002).…”

“…This result is in agreement with the increase in the complexity of matching the observed puff concentrations with increasing the distance of the sampling site from the release point. Hernández-Ceballos et al (2019) report that the models tend to increasingly underestimate concentration as the puff moves away from the source. This behaviour is strongly influenced by the complex circulations and turbulence patterns generated by the buildings in the built-up urban area.…”

“…In our study, we examine how the models simulate the puff passage at the measurement locations (a companion study is devoted to the comparison of observed and predicted concentration levels, see Hernández-Ceballos et al 2019). We evaluate for each puff and sampler the model capability to match the peak concentration, the peak and puff arrival times, and the time duration (the period over which concentrations exceed 10% of the peak concentration).…”

Urban Dispersion Modelling Capabilities Related to the UDINEE Intensive Operating Period 4

“…The presented study and analysis were realized within the Urban Dispersion International Evaluation Exercise (UDINEE) project, led by the Joint Research Centre (JRC European Commission) (Hernández-Ceballos et al 2017). The main goal of the project is to evaluate various urban atmospheric dispersion models for use in emergency preparedness and response.…”