How does fallout from an airburst differ from fallout from a surface burst?

The primary difference between fallout from an airburst and a surface burst lies in the amount of radioactive debris generated and the resulting intensity of local contamination.

• Airburst: When a nuclear weapon is detonated in the air, the residual radiation is primarily composed of the weapon's own debris. Because the fireball does not touch the ground, it does not vaporize large quantities of soil or surface materials, resulting in minimal local fallout.1
• Surface Burst: When an explosion occurs on or near the surface, the fireball interacts directly with the ground. This process sucks large amounts of soil, water, and other materials into the rising cloud. These materials become highly radioactive as they mix with the weapon's fission products. This creates significant early (local) fallout, which settles within the first 24 hours and can contaminate large areas, posing an immediate and extreme biological hazard.1

While both types of explosions produce delayed, worldwide fallout consisting of fine particles dispersed by winds, the surface burst is uniquely characterized by the intense, localized deposition of radioactive material caused by the inclusion of surface debris.21