For a small impact it is assumed that effects would be 1000 times less then the Alvarez Asteroid. Therefore only 5000 Tg of dust would be ejected into the atmosphere. It was assumed that the dust would first be centered around the impact site in a 1000 km area and dispersed uniformly by the wind.
For a medium impact the total amount of dust ejected into the atmosphere would be 75,000 Tg, uniformly distributed over the entire earth.
Coagulation (the precipitation of particles due to collision) was accounted for in the medium impact case but not in the Alvarez or small impact case.
Particle size of the dust was assumed to be 2.5 µm.
Present day geography of the continents was used.
The initial heat caused by the impact was not included in any of the scenarios.