Stop smoke fading when character walks into it?

I am pretty new to Unity so I only have a little understanding of the particle systems.

Question: How can I stop smoke from fading when it is approached by the player.

Explanation and Context: I have smoke coming from a vent in the ground and I would like the smoke to completely obscure the players vision when they enter it. I have turned Max particle size under Renderer in the particle system editor to 1 so the particles will take up the whole screen, yet they seem to lose opacity when approached. If i stand directly above the source, it is as if there is no smoke at all. I would very much appreciate any advice. Thanks