Thank you, Alberto C Macchi,

When you add the bubbles to the Volume mesh, they will not show up anymore

Here is a setup with a few ideas. Will this bring it closer to where you'd like it?
CV4_2025_drs_25_FLia_21.c4d

Screenshot 2025-07-09 at 9.50.31 AM.jpg

I used the first Volume as a Field to "kill" the particles when they moved out.
The surface indicates that they are leaving, while an extra Cloner provides the internal Bubbles.

All the best