1. Atmospheric Dispersion Modelling.
Lab. Seminar
Atmospheric Dispersion Modelling.
Jae San Kim
Dept. of Nuclear and Quantum Engineering
Korea Advanced Institute of Science and Technology

2. Outline
1. Introduction
1.1 Background
1.2 Practical Application of Atmospheric Dispersion Model.
1.3 The limitation of Atmospheric Dispersion Model
1.4 Dispersion Model to Use
2. The Explanation of Atmospheric Dispersion Model.
2.1 Basic Principles of Atmospheric Dispersion.
2.2 Gaussian Models.
3. Application.
3.1 Gaussian - Plume models.
3.2 Advanced dispersion models.
4. Discussion
5. Conclusions and Further Works
Korea Advanced Institute of Science and Technology

3. 1. Introduction 1.1 Background
Atmospheric Dispersion Model
Mathematical simulation of the physics and chemistry governing the transport, dispersion and transformation of pollutants in the atmosphere.
Means of estimating downwind air pollution concentrations given information about the pollutant emissions and nature of the atmosphere.
Meteorology is fundamental for the dispersion of pollutants because it is the primary factor determining the diluting effect of the atmosphere. Therefore, it is important that meteorology is carefully considered when modelling.
Korea Advanced Institute of Science and Technology

4. 1. Introduction 1.2 Practical Application of Atmospheric Dispersion Model.
What dispersion modelling can be used for
The most common use of dispersion modelling is to assess the potential environmental and health effects of discharges to air from industrial or trade premises.
Models are particularly valuable for assessing the impacts of discharges from new activities and to estimate likely changes as a result of process modifications.
Modelling results can also be used for:
Assessing compliance of emissions with air quality guidelines and standards.
Planning new facilities.
Managing existing emissions
Identifying the main contributors to existing air pollution problems
Assessing the risks and planning for the management of rare events such as accidental hazardous substance releases
Korea Advanced Institute of Science and Technology

5. 1. Introduction 1.3 The limitation of Atmospheric Dispersion Model
Even the most sophisticated atmospheric dispersion model cannot predict the precise location, magnitude and timing of ground-level concentrations with 100% accuracy.
However, most models used today (especially the US EPA approved models) have been through a thorough model evaluation process and the modelling results are reasonably accurate, provided an appropriate model and input data are used.
Errors are introduced into results by the inherent uncertainty associated with the physics and formulation.
Korea Advanced Institute of Science and Technology

6. 1. Introduction 1.4 Dispersion Model to Use
When choosing the most appropriate model, the principal issues to consider are:
The complexity of dispersion (e.g. terrain and meteorology effects)
The potential scale and significance of potential effects, including the sensitivity of the receiving environment.
Figure 1 illustrates the types of models typically applied to particular scenarios, depending on their scale and complexity.
Figure 1. Type of model typically applied according to the complexity of the problem.
Korea Advanced Institute of Science and Technology

7. 2. Explanation of Atmospheric Dispersion Model 2
2. Explanation of Atmospheric Dispersion Model 2.1 Basic Principles of Atmospheric Dispersion
Materials released into the air in particulate or gaseous form at the scene of an accident are dispersed as they are transported downwind, and diffuse vertically and laterally according to the degree of turbulence in the atmosphere.
Most commonly used mathematical representations of atmospheric dispersion are based on a Gaussian plume model, developed by Pasquill (1961).
The predominant force in plume transport is the wind; i.e., gases, aerosols, and particles dispersed in the air move predominantly downwind.
The greatest concentration of material in a plume is along the plume centerline.
Aerosols, gases, and other materials in a plume diffuse spontaneously from regions of higher concentration to regions of lower concentration.
Korea Advanced Institute of Science and Technology

8. 2. Explanation of Atmospheric Dispersion Model 2.2 Gaussian models
In Gaussian models for a “puff” release (for an idealized instantaneous, perfectly spherical release), the concentration of the material in the puff has a normal distribution along the two axes perpendicular to wind direction (Figure 2).
Source clouds for releases associated with transportation accidents should be modeled as puff releases.
Figure 2. Diagram of Gaussian Dispersion.
Korea Advanced Institute of Science and Technology

9. 2. Explanation of Atmospheric Dispersion Model 2.2 Gaussian models
Persons in the path of such an aerosol plume inhale material as the plume passes, and inhaled particles are deposited in their lungs in proportion to the time-integrated concentration [X, units of Ci-sec/m³ or Sv-sec/m³] of the aerosol.
For radioactive materials, the value of X at any point downwind of the release location is directly proportional to the total activity of the released aerosol species [Q, units of activity; curies (Ci) in RADTRAN 5] and is inversely proportional to the wind speed (u, units of m/sec).
One way of describing the behavior of X as one moves away from a release location is to tabulate values of the dilution factor X/Q for a given wind speed versus downwind distance or versus isopleth area.
Korea Advanced Institute of Science and Technology

10. 3. Application 3.1 Gaussian- Plume models.
Gaussian-plume models are widely used, well understood, easy to apply, and until more recently have received international approval.
The Gaussian-plume formula is derived assuming ‘steady-state’ conditions. That is, the Gaussian-plume dispersion formulae do not depend on time.
Although plume models do not have large meteorological data requirements, the meteorology is a crucial component, and good-quality data are needed.
Gaussian-plume models are generally applicable when:
The terrain is not steep or complex
The meteorology may be considered uniform spatially
There are few periods of calm or light winds.
Korea Advanced Institute of Science and Technology

11. 3. Application 3.2 Advanced dispersion models.
Although Gaussian-plume models are commonly used for regulatory impact assessments, other advanced dispersion models are available.
Their demands on resources are far higher than those of Gaussian-plume models. That is, The use of advanced models does involve much greater meteorological input data demands.
Advanced models should be used when:
Meteorological conditions vary across the modelling domain and therefore are not compatible with a steady-state model.
Sources or receptors are located in complex terrain, which affects the meteorological as well as the plume-dispersion characteristics.
Korea Advanced Institute of Science and Technology

12. 3. Application 3.2 Advanced dispersion models.
CALPUFF
CALPUFF (a puff model) has recently been accepted by the US EPA as a guideline model to be used in all regulatory applications involving the long-range (>50km) transport of pollutants.
It can also be used on a case-by-case basis in situations involving complex flow and non-steady-state cases from fence-line impacts to 50 km.
Roadway emissions modelling
Assessing the effects of emissions from vehicles and their transport and transformation at the urban scale is complex.
Figure 3 is a schematic representation of the emission and mixing processes associated with vehicle emissions. Thermal and mechanical turbulence occurring behind a vehicle contributes to mixing the emissions, so that the air behind a vehicle is relatively well-mixed.
In many situations the modelling of roadway emissions is carried out using a Gaussian-plume model configured to emulate the dispersion of contaminants from this type of line source.
line source − a long, narrow source such as a roadway, conveyor belt, or roofline vent along a long, narrow building (usually a line source must be redefined as a chain of volume sources for modelling)
Korea Advanced Institute of Science and Technology

13. 3. Application 3.2 Advanced dispersion models.
Figure 3. The effect of thermal and mechanical turbulence combining to produce a well-mixed zone of contaminants.
Korea Advanced Institute of Science and Technology

14. 4. Discussion
Atmospheric dispersion modelling is an essential tool in air quality management by providing the link between environmental effects and discharges to air.
The estimation of atmospheric dispersion behavior is subject to numerous sources of uncertainty.
These include ones arising from the approximation represented by the model itself, those attributable to the range of choice available in relation to the user-defined parameters, and the incompleteness of our knowledge of dispersion behavior.
The model user should give some estimate of the uncertainty that attaches to the results.
If this is done much of the apparent disagreement between models, measured values may be encompassed within the ranges of uncertainty.
Korea Advanced Institute of Science and Technology

15. 5. Conclusion and Further Study.
In RADTRAN 5, Atmospheric Dispersion is very important factor to perform the risk assessment.
Considering more accurate atmospheric dispersion, the results of SNF transportation risk assessment will be more reliable.
As yet, the data regarding the Atmospheric Dispersion is from the weather of the United States. So we will study to know the domestic data for the Atmospheric Dispersion.
Further Study.
The study for Sensitivity and uncertainty analysis.
More specifically Reviewing the Atmospheric Dispersion model.
Korea Advanced Institute of Science and Technology

16. 6. Reference.
Rex Britter, Paul Mason, David Thomson. “ATMOSPHERIC DISPERSION MODELLING: GUIDELINES ON THE JUSTIFICATION OF CHOICE AND USE OF MODELS” ,May 1995
Barry Carbon. “Good Practice Guide for Atmospheric Dispersion Modelling”. June 2004
K. S. Neuhauser, F. L. Kanipe and R. F. Weiner, RADTRAN 5 Technical Manual, SAND , May 2000
EPA. Draft User’s Guide for the Industrial Source Complex (ISCST3) Dispersion Models. EPA-454/ B a. US Environmental Protection Agency: North Carolina.
Consulting Air pollution Modelling Meteorology CITPUFF – A regional Gaussian puff model. URL:
Korea Advanced Institute of Science and Technology