To increase the effectiveness of the electrostatic precipitation I upgraded the high voltage DC source to have both positive and negative voltages. This effectively doubles my voltage. I use the negative poll to charge incoming air and the positive poll the absorb the charged particulates. I can place grounding grids in intermediate positions if need be.

I accomplished this by placing another 5 stage Cockroft-Walton multiplier (that has backward facing diodes) to the existing single high voltage transformer. Here is the circuit I followed.

This extra multiplier circuit that provided the negative polarity conveniently fit in the space on the board left between the transformer and the other multiplier.

Testing showed that it indeed works. The arcs between the high voltage positive to high voltage negative are about twice as long as those between positive to ground and negative to ground.