A fan includes a base and a nozzle mounted on the base. The base includes an impeller and a motor for driving the impeller to generate an air flow. The nozzle includes an air inlet, an air outlet, and an annular casing which defines a bore through which air from outside the fan is drawn by air emitted from the air outlet. An electrostatic precipitator is located within the bore of the nozzle for treating the air drawn through the bore.