How to remove partially a shader or particle?

Hi everyone, I am trying to get a particular effect. My game consists of a player that moves on a 2D space (even though my environment is set in 3D) and needs to eat some gas like hydrogen/nitrogen/etc... What I would like to achieve is an effect like a "rubber/eraser" so when the player moves on this gas, it will disappear. I achieved a good cloudy gas effect with shaders but I don't like that when the player collides with the shader it just disappear. Moreover, I need a large area of gas so I think that instantiating many objects with shaders can cause performance issues.

Does someone know how to achieve this? For me is also fine to change completely the strategy.

Thanks!