How much air can an ioniser clean? Here's my suggestion.

An ioniser can generate around 2.5 microamps per needle. Conservatively perhaps1 microamp per needle. (See for example an experiment on youtube, or commercial documentation).

The charge on an electron is 1.6 x 10^{-19}^{}coulombs.

So 1 coulomb is 1/(1.6 x 10^{-19}) electrons = 6.25 x 10^{18} electrons.

So 1 microamp is 6.25 x 10^{12} electrons per second.

Next the ISO9 clean room standard for city air is 35 x 10^{6} particles per cubic meter.

So 1 particle occupies 1/(35 x 10^{6}) cubic meters, (at least arithmetically)

Assuming that the current is distributed by Brownian motion and self repulsion, as 1 electron on 1 particle (as in Millikan's Oil Drop experiment for example), we get that the charge at least theoretically could be distributed into:

(6.25 x 10^{12})/(35 x 10^{6}) cubic meters = 176,000 cubic meters of air

By cube root this corresponds to a cube of air 56 meters on each side.

In addition this volume is charged every second!

The assumption then is that if the charged particle comes near to an earthed surface, it is drawn to the surface and sticks, so cleaning the air.

Does this make sense? Can anyone improve this estimate? This seems to imply that ionisers could be put on lamposts to clean the air in a city, never mind in a room.