Training on atmospheric dispersion in urban environments

Table of contents


1. Introduction

Releases of hazardous material can occur in urban environments, and are potentially threatening to life and health. These releases may result from industrial accidents, transportation accidents (e.g. tanker truck or railroad spills) or they may be deliberate (e.g. terrorist attack using a chemical, radioactive or biological agent).

In order to provide the best possible service when an atmospheric release of a dangerous agent occurs in urban zones, responders need to have a basic understanding of urban wind patterns.

The urban environment produces very complex wind patterns, as everyone can experience walking in the downtown area of a large city. These make it impossible for basic atmospheric transport models (ATM) to correctly estimate the evolution of a plume. At accident sites, evaluations are often based on Gaussian models which do not consider the impact of buildings. The Environmental Emergency Response Section of Environment Canada (EC-EERS) has been developing a system called the Canadian Urban Dispersion Model (CUDM), that is capable of providing atmospheric dispersion guidance in urban areas. EER Section is leading a project to bring this prototype of CUDM to a fully operational status. However, EC-EERS has developed an expertise and some tools in urban modeling. This training will give readers an improved understanding of the wind patterns encountered in large urban centres and the effects of those patterns on the dispersion of hazardous agents.

Because of the complexities of urban winds, it is not possible to have general rules for plume transport and dispersion that work for every case. However, this course should help emergency responders, managers, and training personnel become familiar with some of the more common patterns of plume transport and dispersion that develop in built-up areas.

2. Training Objectives:

This web-based course is focused on atmospheric dispersion in urban areas. The training gives a description of the basic principles of dispersion, with specific attention to urban zones.

Introduction to this training on atmospheric dispersion in built-up areas and its objectives are presented, respectively in Section 1 and Section 2.
Section 3 describes the dispersion process and factors that influence dispersion.
Section 4 presents effects of buildings on atmospheric dispersion.
Section 5 is a basic overview of dispersion models.
Section 6 presents the atmospheric dispersion modeling in urban areas, and a brief description of the Canadian urban dispersion modeling system.
The Section 7 presents a fictional chemical release scenario and steps through some common situations that may occur in an urban environment. In some situations, the emergency responder will find that unexpected, counter-intuitive flow phenomena occur. Section 8 presents an application of the CUDM system for hypothetical scenarios in some Canadian cities.

By the end of this training, the reader should be able to describe:

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