An air cleaning device (20; 30; 40) for removing aerosol particles from an air stream, the device comprising: (a) a particle charger (22; 32) comprising a housing (22a; 32a) and an electrode arrangement therein for generating air ions in the air stream, the particle charger having a particle charging zone within which, in use, aerosol particles in the air stream are electrically charged via collision with the air ions; (b) a filter (26; 36) for precipitating electrically charged aerosol particles from the air stream moving through the device; and (c) an air mover (25; 35), comprising a casing (25a; 35a) as a separate component from the housing of the particle charger, for moving the air stream through the device; wherein, in use of the device, the particle charger and the air mover are provided upstream of the filter; and wherein the housing of the particle charger has an inlet and an outlet and the casing of the air mover has an inlet and an outlet, and either: (i) the outlet of the housing of the particle charger is hermetically sealed to the inlet of the casing of the air mover in the direction of intended air flow through the device; or (ii) the outlet of the casing of the air mover is hermetically sealed to the inlet of the housing of the particle charger in the direction of intended air flow through the device, wherein in alternative (i) the outlet of the housing of the particle charger and the inlet of the casing of the air mover and in alternative (ii) the outlet of the casing of the air mover and the inlet of the housing of the particle charger are provided with a common cross-sectional area with a high degree of accuracy such that the housing of the particle charger and the casing of the air mover together define the volume through which the air stream must flow in order to pass through the filter, with no additional surrounding housing, cowling, ductwork or the like being required, whereby, in use of the device, all air entering the device has to pass through both the particle charger and the air mover. (a) a particle charger (22; 32) comprising a housing (22a; 32a) and an electrode arrangement therein for generating air ions in the air stream, the particle charger having a particle charging zone within which, in use, aerosol particles in the air stream are electrically charged via collision with the air ions; (b) a filter (26; 36) for precipitating electrically charged aerosol particles from the air stream moving through the device; and (c) an air mover (25; 35), comprising a casing (25a; 35a) as a separate component from the housing of the particle charger, for moving the air stream through the device; wherein, in use of the device, the particle charger and the air mover are provided upstream of the filter; and wherein the housing of the particle charger has an inlet and an outlet and the casing of the air mover has an inlet and an outlet, and either: (i) the outlet of the housing of the particle charger is hermetically sealed to the inlet of the casing of the air mover in the direction of intended air flow through the device; or (ii) the outlet of the casing of the air mover is hermetically sealed to the inlet of the housing of the particle charger in the direction of intended air flow through the device, wherein in alternative (i) the outlet of the housing of the particle charger and the inlet of the casing of the air mover and in alternative (ii) the outlet of the casing of the air mover and the inlet of the housing of the particle charger are provided with a common cross-sectional area with a high degree of accuracy such that the housing of the particle charger and the casing of the air mover together define the volume through which the air stream must flow in order to pass through the filter, with no additional surrounding housing, cowling, ductwork or the like being required, whereby, in use of the device, all air entering the device has to pass through both the particle charger and the air mover. wherein, in use of the device, the particle charger and the air mover are provided upstream of the filter; and wherein the housing of the particle charger has an inlet and an outlet and the casing of the air mover has an inlet and an outlet, and either: (i) the outlet of the housing of the particle charger is hermetically sealed to the inlet of the casing of the air mover in the direction of intended air flow through the device; or (ii) the outlet of the casing of the air mover is hermetically sealed to the inlet of the housing of the particle charger in the direction of intended air flow through the device, (i) the outlet of the housing of the particle charger is hermetically sealed to the inlet of the casing of the air mover in the direction of intended air flow through the device; or (ii) the outlet of the casing of the air mover is hermetically sealed to the inlet of the housing of the particle charger in the direction of intended air flow through the device, wherein in alternative (i) the outlet of the housing of the particle charger and the inlet of the casing of the air mover and in alternative (ii) the outlet of the casing of the air mover and the inlet of the housing of the particle charger are provided with a common cross-sectional area with a high degree of accuracy such that the housing of the particle charger and the casing of the air mover together define the volume through which the air stream must flow in order to pass through the filter, with no additional surrounding housing, cowling, ductwork or the like being required, whereby, in use of the device, all air entering the device has to pass through both the particle charger and the air mover.