Validation Of Dispersion Models Research Articles

Uncertainty-bounded estimates of ash cloud properties using the ORAC algorithm: application to the 2019 Raikoke eruption

Abstract. Uncertainty-bounded satellite retrievals of volcanic ash cloud properties such as ash cloud-top height, effective radius, optical depth and mass loading are needed for the robust quantitative assessment required to warn aviation of potential hazards. Moreover, there is an imperative to improve quantitative ash cloud estimation due to the planned move towards quantitative ash concentration forecasts by the Volcanic Ash Advisory Centers. Here we apply the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm to Advanced Himawari Imager (AHI) measurements of the ash clouds produced by the June 2019 Raikoke (Russia) eruption. The ORAC algorithm uses an optimal estimation technique to consolidate a priori information, satellite measurements and associated uncertainties into uncertainty-bounded estimates of the desired state variables. Using ORAC, we demonstrate several improvements in thermal infrared volcanic ash retrievals applied to broadband imagers. These include an improved treatment of measurement noise, accounting for multi-layer cloud scenarios, distinguishing between heights in the troposphere and stratosphere, and the retrieval of a wider range of effective radii sizes than existing techniques by exploiting information from the 10.4 µm channel. Our results indicate that 0.73 ± 0.40 Tg of very fine ash (radius ≤ 15 µm) was injected into the atmosphere during the main eruptive period from 21 June 18:00 UTC to 22 June 10:00 UTC. The total mass of very fine ash decreased from 0.73 to 0.10 Tg over ∼ 48 h, with an e-folding time of 20 h. We estimate a distal fine ash mass fraction of 0.73 % ± 0.62 % based on the total mass of very fine ash retrieved and the ORAC-derived height–time series. Several distinct ash layers were revealed by the ORAC height retrievals. Generally, ash in the troposphere was composed of larger particles than ash present in the stratosphere. We also find that median ash cloud concentrations fall below peak ash concentration safety limits (< 4 mg m−3) 11–16 h after the eruption begins, if typical ash cloud geometric thicknesses are assumed. The ORAC height retrievals for the near-source plume showed good agreement with GOES-17 side-view height data (R=0.84; bias = −0.75 km); however, a larger negative bias was found when comparing ORAC height retrievals for distal ash clouds against Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) measurements (R=0.67; bias = −2.67 km). The dataset generated here provides uncertainties at the pixel level for all retrieved variables and could potentially be used for dispersion model validation or be implemented in data assimilation schemes. Future work should focus on improving ash detection, improving height estimation in the stratosphere and exploring the added benefit of visible channels for retrieving effective radius and optical depth in opaque regions of nascent ash plumes.

Modelling air pollution around nuclear power plants: validation of dispersion models using tracer data

The Šoštanj exercise of the Modelling and Data for Radiological Impact Assessments I Urban Environments Working Group took advantage of a set of measurement data from a 1991 tracer experiment to test atmospheric dispersion models for emissions from point sources over complex terrain. The data set included emissions of SO2 from the stacks of the Šoštanj Thermal Power Plant in Slovenia, measurements of the SO2 at a number of locations in the surrounding area up to 7 km from the plant, and meteorological data from several monitoring stations, all as measured half-hour average values. Two sets of meteorological conditions were modelled: (a) a simple situation with a strong wind blowing from a point source directly towards a monitoring station; and (b) a complex situation involving a temperature inversion and convective mixing. The modelling results enable the assessment of the capabilities of various dispersion models in handling both complex terrain and complex meteorological situations.

Modelling the atmospheric dispersion of radiotracers in small-scale, controlled detonations: validation of dispersion models using field test data

A series of modelling exercises, based on field tests conducted in the Czech Republic, were carried out by the ‘Urban’ Working Groups as part of the International Atomic Energy Agency’s Environmental Modelling for Radiation Safety II, Modelling and Data for Radiological Impact Assessment (MODARIA) I and MODARIA II international data compilation and model validation programmes. In the first two of these programmes, data from a series of field tests involving dispersion of a radiotracer, 99mTc, from small-scale, controlled detonations were used in a comparison of model predictions with field measurements of deposition. In the third programme, data from a similar field test, involving dispersion of 140La instead of 99mTc, were used. Use of longer-lived 140La as a radiotracer allowed a greater number of measurements to be made over a greater distance from the dispersion point and in more directions than was possible for the earlier tests involving shorter-lived 99mTc. The modelling exercises included both intercomparison of model predictions from several participants and comparison of model predictions with the measured data. Several models (HotSpot, LASAIR, ADDAM/CSA-ERM, plus some research models) were used in the comparisons, which demonstrated the challenges of modelling dispersion of radionuclides from detonations and the need for appropriate meteorological measurements.

Validation of dispersion models using Cabauw field experiments and numerical weather re-analysis

Validation of dispersion models using Cabauw field experiments and numerical weather re-analysis

Validation of dispersion models using Cabauw field experiments and numerical weather re-analysis

The Gaussian atmospheric dispersion model AEROPOL is validated against the classical Cabauw dispersion experiment, driven by (1) on-site meteorological data and (2) meteorological data from the numerical weather model HARMONIE. The meteorological forecast time used at the time of the release is 10 to 14 hours ahead of the analysis time. The results from the combination of AEROPOL with on-site data are slightly better than with re-analysed meteorology. The near-surface concentrations based on the combination of AEROPOL with the model forecasts are in general lower than the concentrations from the combination of AEROPOL with on-site data and are also lower than the observed concentrations. The combination of AEROPOL with meteorological model results in a mismatch between the modelled position of the plume axis with the observed plume axis. The results show a significant improvement in the HARMONIE version 38 with respect to the HARMONIE version 37.

BIOAEROSOLS AND HEALTH: CURRENT KNOWLEDGE AND GAPS IN THE FIELD OF WASTE MANAGEMENT

The development of biodegradable waste recycling leads to increased amounts of decaying organic materials handled, and encourages the conditions in which workers, households and neighbouring communities are potentially exposed to bioaerosols. The objective of this study was to assess the knowledge and gaps regarding the health risks associated to bioaerosols in the field of municipal solid waste (MSW) and commercial and industrial waste (C&IW) management. Additional objective was to identify priority issues for research in order to improve knowledge and prevention. Overall, 368 studies have been selected. Strong qualitative evidence links occupational exposure to bioaerosols in the waste industry to adverse effects on health including long-term respiratory disease, notably in the fields of composting, mechanical biological treatment (MBT) and materials recovery facilities (MRF). The literature review highlighted numerous gaps in knowledge about exposure and health effects of bioaerosols that need to be addressed to assess the risk. Most importantly, valid and standardized methods for quantitative exposure assessment are needed. Identification of environmental indicators, estimate of factors influencing the level of bioaerosol exposure at the workplace, well-designed epidemiological studies and validation of dispersion models are other priority issues.

Evaluation of multi-phase atmospheric dispersion models for application to Carbon Capture and Storage

A dispersion model validation study is presented for atmospheric releases of dense-phase carbon dioxide (CO2). Predictions from an integral model and two different Computational Fluid Dynamics (CFD) models are compared to data from field-scale experiments conducted by INERIS, as part of the EU-funded CO2PipeHaz project.The experiments studied consist of a 2 m3 vessel fitted with a short pipe, from which CO2 was discharged into the atmosphere through either a 6 mm or 25 mm diameter orifice. Comparisons are made to measured temperatures and concentrations in the multi-phase CO2 jets.The integral dispersion model tested is DNV Phast and the two CFD models are ANSYS-CFX and a research and development version of FLACS, both of which adopt a Lagrangian particle-tracking approach to simulate the sublimating solid CO2 particles in the jet. Source conditions for the CFD models are taken from a sophisticated near-field CFD model developed by the University of Leeds that simulates the multi-phase, compressible flow in the expansion region of the CO2 jet, close to the orifice.Overall, the predicted concentrations from the various models are found to be in reasonable agreement with the measurements, but generally in poorer agreement than has been reported previously for similar dispersion models in other dense-phase CO2 release experiments. The ANSYS-CFX model is shown to be sensitive to the way in which the source conditions are prescribed, while FLACS shows some sensitivity to the solid CO2 particle size. Difficulties in interpreting the results from one of the tests, which featured some time-varying phenomena, are also discussed.The study provides useful insight into the coupling of near- and far-field dispersion models, and the strengths and weaknesses of different modelling approaches. These findings contribute to the assessment of potential hazards presented by Carbon Capture and Storage (CCS) infrastructure.

A dataset for the validation of flow and dispersion models at an urban intersection

Dispersion modelling concerning air pollution caused by road traffic is reduced to a two–dimensional problem within street canyons. However, significant pollution loads are also to be expected at intersections. In this case, three–dimensional flow and dispersion structures have to be considered. For the validation of models claimed to be applicable to intersections, measurements of meteorological parameters and pollutant concentrations were performed at an urban intersection. Though those field observations are important to get information about the actual immission situation, they cannot render data to the extent necessary for model validation. Therefore, the same intersection was subjected to wind tunnel studies, whereby wind and pollution data were measured. Evaluation of results showed that, owing to the complex flow structure at an intersection, concentration distributions with a high confidence level can be gained only by a combination of field observations with wind tunnel studies and/or model runs.

Large Scale CO2 Releases for Dispersion Model and Safety Study Validation

Abstract The second phase of the CO2PIPETRANS Joint Industry Project (JIP) aims to fill knowledge gaps associated with the safe and reliable pipeline transport of CO2. The JIP has three main focus areas and technical work packages designed to address these. The work packages collect experimental data and experience on dense phase CO2 release model validation data, pipeline fracture arrest, and corrosion. This paper presents an overview of results and conclusions from the work package focusing on collection of data for validation of release models. The JIP consists of 15 partner organisations, who are: Arcelor Mittal, BP, DNV GL, Endesa, ENI, E.on Ruhrgas, Gassco, Gassnova, Health and Safety Executive (HSE) UK, Maersk Oil, Petrobras, Petroleum Safety Authority (PSA) Norway, Shell, V&M Tubes, and Vattenfall. The objective of the CO2 release model validation data work package was to collect and make available data for validating release and dispersion models for dense phase CO2. This involved releasing dense phase CO2 from large inventories through orifices ranging in size 6 mm to 150 mm onto a suitably sized array of instruments to measure the CO2 concentration and temperature profiles. The condition of the CO2 being released was up to 150 barg and 150 °C with release durations up to 10 minutes. Most of the releases were in a horizontal orientation 1m above the ground but during some of the tests the orientation was changed to be upwards, downwards to impact the ground, or into an enclosure. In addition to the CO2 releases described above, the work package also undertook rapid depressurisation of a long horizontal pipe containing 100 barg CO2 in order to collect data, amongst other aspects, on shock wave propagation. These experiments used a 200m long, 50 mm diameter pipe mounted on load cells with an orifice plate and explosive initiated bursting disk at one end. In addition to measuring data within the pipe during the rapid depressurisation tests, dispersion and temperature data was also recorded downstream of the release for release model validation purposes. The paper presents an overview of the frontier experimental work mentioned above along with discussion on the output of the data review that was subsequently completed during which recorded data was compared with model predictions. Validation of dispersion models and safety studies reduces the uncertainty and hence conservatism required in these studies thereby making design and implementation of CO2 pipelines safer and more cost effective.

In-situ database toolbox for short-term dispersion model validation in macro-tidal seas, application for 2D-model

Appropriate field data are required to check the reliability of hydrodynamic models simulating the dispersion of soluble substances in the marine environment. This study deals with the collection of physical measurements and soluble tracer data intended specifically for this kind of validation.The intensity of currents as well as the complexity of topography and tides around the Cap de La Hague in the centre of the English Channel make it one of the most difficult areas to represent in terms of hydrodynamics and dispersion. Controlled releases of tritium—in the form of HTO—are carried out in this area by the AREVA-NC plant, providing an excellent soluble tracer. A total of 14,493 measurements were acquired to track dispersion in the hours and days following a release. These data, supplementing previously gathered data and physical measurements (bathymetry, water-surface levels, Eulerian and Lagrangian current studies) allow us to test dispersion models from the hour following release to periods of several years which are not accessible with dye experiments. The dispersion characteristics are described and methods are proposed for comparing models against measurements.An application is proposed for a 2 dimensions high-resolution numerical model. It shows how an extensive dataset can be used to build, calibrate and validate several aspects of the model in a highly dynamic and macrotidal area: tidal cycle timing, tidal amplitude, fixed-point current data, hodographs.This study presents results concerning the model's ability to reproduce residual Lagrangian currents, along with a comparison between simulation and high-frequency measurements of tracer dispersion.All physical and tracer data are available at 〈http://doi.pangaea.de/10.1594/PANGAEA.762253〉. This tool for validation of models in macro-tidal seas is intended to be an open and evolving resource, which could provide a benchmark for dispersion-model validation.

228Ra and 226Ra in coastal seawater samples from the Ubatuba region: Brazilian southeastern coastal region

The present work reports 228Ra and 226Ra results obtained during the 4th Submarine Groundwater Discharge (SGD) intercomparison experiment realized in Ubatuba, November 2003, aiming to test the methodologies on a fractured crystalline rocks system. Although with distinct objectives, it was decided to participate in this experiment in order to verify if radium isotopes could be used to determine water mixing rates in this region and to test the laboratory capability to perform, later on, a marine dispersion model validation at Angra dos Reis reactor site, located nearby. The results show that the SGD model constrains seems to be valid, at least for a distance of 20 km offshore, that corresponds to the distance between the reactor site and Ilha Grande, a 193-km2 island existing at this site and probably an additional SGD source. Salinity, barium and silica results are also reported and their relation to 228Ra concentrations is discussed.

Indicators of performance of dispersion models and their reference values

A methodology of validation of dispersion models is analysed in this paper for situations when measurements, corresponding to a given set of governing meteorological parameters, are contaminated with stochastic noise resulting from the turbulent nature of atmospheric processes. Deterministic dispersion models in these situations predict certain non-stochastic values of concentrations and, therefore, cannot reproduce measured patterns of stochasticity. Resulting discrepancies are reflected in all indicators of performance of the models. The values of these indicators are estimated in this paper for an idealized case of a 'perfect model' that can predict exact values of characteristics of the probability distribution function of measured concentrations in assumption that this PDF can be fitted with a lognormal distribution. The estimates obtained can be used as reference values of the indicators of performance of dispersion models.