An exposed electrode negative air ion device, either stand-alone or mounted in an exposed environment 56 as part of a negative air ion panel system 50. Each device comprises: (a) an electronics module 22, the electronics module 22 including a negative voltage generator 22B; and (b) an exposed electrode 10, the exposed electrode 10 including a mat surface 11 of intertwined individual fibres electrically connected to the negative voltage generator 22B. The mat surface 11 has a minimum mean resistance of RMIN to restrict a maximum capacitive current discharge below a capacitive current discharge detection threshold. The negative voltage generator 22B is configured to generate a negative voltage source 23 from a power supply 21 within a set of electrical parameters. The set of electrical parameters includes a maximum preset negative voltage of VMAX and a maximum operating current, the maximum operating current set below or equal to a direct current detection threshold.