An electrostatic filter (sometimes called a precipitator) will pull particles as small as cigarette smoke out of air circulated through it, but this has some potential drawbacks for a darkroom.
First, all of the devices I've seen that do this have status lights on them -- you'd have to disable those for film loading, or filter them even for B&W printing. Second, by their nature, these devices can intermittently arc between the high voltage plates, which will produce a short-lived but brilliant light source; same problem as the status lights, but less predictable. They need the plates cleaned regularly, and cleaning these can be a chore (they're typically fairly large and have rather small spacing between elements). I had one for years in my bedroom, but I had to simply get used to going back to sleep after the "snap" of an arc discharge.
HEPA filters aren't prone to arcing, but still have status lights and need the filter elements cleaned or replaced on a regular basis.
One option that might work well is to install a filter with a built-in fan that blows into a darkroom ventilator -- the device is outside the dark area, but blows the cleaned air in to the darkroom through a light trap of some kind.
