Maintaining Smoke density

[magilla]

I have a simulation of 300 frames of smoke drifting above the floor. I emit over the initial 80 frames and let the smoke do its thing over the rest of the frames. However even with dissipation on zero the smoke eventually just dissolves away. It doesn't visibly drift away, the sides are blocked and there are no forces.

I have tried continuing the emission over the duration but despite manipulating the opacity curve every which way I get very visible emission patches.

How do I a) hide the emission and/or b) maintain the smoke over long durations?

[Ivaylo Katev]

can you share images or video?
you can try FT advection, it preserves the smoke amount. and DO NOT use opacity diagram, use simple smoke, this is important when physically correct result is needed.

[Svetlin.Nikolov]

(edited out)