Spawn particles on collider surfaces in range

I am currently creating particle systems and scripts to generate giant explosions of varying sizes.

One of the effect I am trying to create is dust rising from the ground as the explosion nears. I am currently doing that with a very fast particle emitter, emitting thousands of invisible particles that generate a dust spray on collision. The results are however unsatisfying. To create nice effect, I need tens of thousands of invisible particles, which is way too much.

I am looking for a way to simply extend the spawning zone of the particle emitter, and that it automatically emits dust on every surface available.

I think the number of particles and the spawn radius size can be altered in the properties of the particle system itself. The ‘Shape’ sub-menu allows you to increase the radius. And in the starting options, there’s a variable called as ‘Max Particles’ which determine how much particles will be spawned.