Open Access

Table 1

Uncertainty categories.

Examples Description
Category 1 Release rate
Wind direction
These are the most influential parameters. The amount or rate of material released often relies on measurements that are not available in the early phase of an incident and work by Astrup and Mikkelsen (2010) has shown that observed wind directions can differ from the NWP wind directions by up to 25° in flat terrain and more in more complex terrain.
Category 2 Plume rise or release height
Wind speed
Release timing
These are parameters that are often, but not always, influential. For example, the release timing could be influential if the timing of the release coincides with a change of wind direction or a precipitation event, otherwise it may only impact the time until the plume arrives and will have little impact on quantities integrated over a time period.
Category 3 Precipitation
Wet and dry scavenging parameters
Particle size distribution
These are parameters that are not relevant to all scenarios but can be very influential in some circumstances. When precipitation does occur, it can have a big impact on the amount of material deposited on the ground. In addition, the location of rainfall generated by convection can be difficult to predict accurately.
Category 4 Atmospheric stability
Boundary layer depth or mixing height Vertical and horizontal diffusion parameters
Parameters that only have a moderate influence.
Category 5 Resolution of the terrain
Surface roughness Model time step
Model grid cell size Vertical source profile
Ambient temperature
These parameters were not found to be particularly influential in the reviewed studies but could be influential in some circumstances.

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