DCAR proceedings: Overview

The following text is the section 'Overview' from the proceedings of the workshop "Objectives for Next Generation of Practical Short-Range Atmospheric Dispersion Models".

The workshop was organized by DCAR (Danish Centre for Atmospheric Research).

The proceedings are now out of print, but certain sections of the proceedings are available via the Word Wide Web.

Contents of this document

• 1.1 Overview
  • General
  • Contents
  • Workshop discussions

H.R. Olesen, National Environmental Research Institute, Denmark
T. Mikkelsen, Risų National Laboratory, Denmark

The present workshop - "Objectives for Next Generation of Practical Short-Range Atmospheric Dispersion Models" - has come about as a result of an action started in 1991 for increased cooperation and harmonisation within atmospheric dispersion modelling. This action is experienced as particularly relevant at the present time, because recent developments in dispersion science have paved the way for a new generation of models with physically more justifiable parameterisations of dispersion processes. Moreover, recent improvements in computer skills and the widespread availability of small personal computers have furthered the practical use of such models.
The focus of the workshop was on the management of model development and the definition of model objectives, rather than on detailed model contents. It was the intention to identify actions that can be taken in order to improve the development and use of atmospheric dispersion models.
The workshop dealt with two types of models, namely models for regulatory purposes and models for real-time applications.
The workshop program consisted of lectures and discussions in plenum as well as work groups where the following topics were treated:

Work Group I:    Scientific basis for next-generation
                 models.
Work Group II:   Requirements concerning model capabilities
                 and model output.
Work Group III:  Data bases and principles for model
                 evaluation.

The workshop was directed towards an audience of both model developers and model users. It attracted approximately 120 participants from many different, mainly European, countries and with different backgrounds, as can be seen in Fig. 1.

Fig. 1: Distribution of participants by country.

More details on the background and the objectives of the workshop can be found in Paper 1 (by H.R. Olesen) in this volume.

The present volume consists of the following material:

• Summaries: this overview, a resolution, and summaries of the discussions that took place in the three work groups.
• Papers and abstracts: papers presented at the plenary sessions and in the work groups, and a few additional papers by participants.
• Practical information: inter alia related to electronic information exchange which was the subject of some interest at the workshop.

The discussions opened up for a broad exchange of opinions. They reflected the fact that the participants had a variety of backgrounds. Thus, not all relevant matters concerning practical short-range dispersion models could be treated in depth. However, a number of important problems were identified, and some were discussed in detail, pointing to further work needed.
There was a consensus among the participants at the workshop that the presently used regulatory models are in principle outdated. This was expressed in a resolution passed by the participants during the final session, with the following wording:

• The practical atmospheric dispersion models which are presently used for regulatory purposes are based on 25-year old research (Pasquill-Gifford type stability classes, simple Gaussian dispersion schemes, i.a.). During the past 25 years, research in atmospheric dispersion has progressed substantially, thus rendering the presently used regulatory models outdated. Consequently, there is now a need for development and practical implementation of computer codes based on our present knowledge of atmospheric dispersion.

• The development of state-of-the-art practical models for regulatory purposes.
• The establishment of standard data bases for model verification, based on both past and future experiments.
• Harmonisation within the field of regulatory models.

As to the discussions in the work groups, some important conclusions are stated below. More details can be found in the summaries of the work groups and elsewhere in the proceedings.
A question often raised in the discussion was "Why are new models needed?". Every model user has certain requirements to models, and key questions to be answered by the modelling community are "How well do existing and forthcoming models fit the various needs? Where can improvements be made?"
From the discussions it appeared that the question of how well the models are fit for purpose is not at all easy to answer. Generally, models are developed and documented in a rather disorganized manner, and there seems to be a lack of basic standards and tools which would make it feasible to make statements on model merits in a satisfactory way. One major problem in the present situation is that current models have severe shortcomings of which the users are often unaware. Also, models are often used outside of their proper field of applicability.
In order to improve the "modelling culture" several actions were suggested. These are presented in the work group summaries; here, some of the most important are summarized:

• There should be systematic comparisons of model predictions versus existing data sets from experiments. Further, the areas in which more experiments are needed should be identified.

A contribution towards a more systematic model evaluation procedure will be a workshop planned for September 1993 on "Scientific Intercomparison of Advanced Practical Atmospheric Dispersion Models". The planning of this workshop was discussed in Work Group III.

• Model users should be aware of the uncertainties inherent in model calculations. Work should be undertaken on how to determine model uncertainties and how to present them to the model users.
• There should be an action for setting up guidelines for model development and documentation. The aim is to promote more correct use of models.
• There should be an action for harmonisation of meteorological input for "next-generation models".
• One or more electronic Bulletin Board Services (BBS) or similar services should be established to help in the coordination of model development and management.

We hope that the reader will feel inspired to go on spending some time on the many interesting papers contained in this volume.

The editors

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Initiative on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes