Which dispersion type is described as “Like a spherical release but occurs at ground level”?

Which dispersion type is described as “Like a spherical release but occurs at ground level”?

• A. Spherical dispersion
• B. Circular dispersion
• C. Hemispherical dispersion
• D. Cloud dispersion pattern

Answer: (C)

When a release happens at ground level, the ground plane acts as a boundary that prevents downward spread. A release in open space would expand in all directions like a sphere, but the lower half is blocked by the ground, so you get a hemispherical dispersion pattern: the plume spreads outward and upward from the source, forming a hemisphere with the flat face along the ground. This geometric idea captures why the pattern looks like a sphere cut in half by the surface. The other patterns describe different spreading geometries: a circular dispersion implies spread mainly in the horizontal plane without the same vertical expansion, and cloud dispersion reflects a more wind-influenced, evolving plume shape rather than a simple geometric form.

When a release happens at ground level, the ground plane acts as a boundary that prevents downward spread. A release in open space would expand in all directions like a sphere, but the lower half is blocked by the ground, so you get a hemispherical dispersion pattern: the plume spreads outward and upward from the source, forming a hemisphere with the flat face along the ground. This geometric idea captures why the pattern looks like a sphere cut in half by the surface. The other patterns describe different spreading geometries: a circular dispersion implies spread mainly in the horizontal plane without the same vertical expansion, and cloud dispersion reflects a more wind-influenced, evolving plume shape rather than a simple geometric form.