An electronic air cleaner 20 has a fan 27, driven by electric motor 28, to draw dirty air through filter 21 to remove larger dust particles and then on through an electrostatic precipitator cell consisting of an ioniser 22 and a collector 23 which has two sheets 24, 25 of open-celled reticulated polyester loaded with activated carbon electrically connected to the 4.1 kV and zero potential terminals respectively. Accordingly the charged dirt particles are deposited on the collector (23), which also acts to adsorb gaseous materials from the airstream and to remove ozone produced in the ioniser (22). Once sheets 24, 25 are no longer effective in so cleaning the airstream, the sheets (24, 25) are removed and discarded with new sheets (24, 25) being put in their place.