NOVELTY - The reactor has a prefilter (122) receiving a fluid stream e.g. air, and filtering particulates e.g. aerosol particulates, from the stream. A plasma chamber receives the prefiltered stream and subjects the prefiltered stream to a cold plasma having high concentration of reactive species e.g. ozone, to treat the particulates. A porous catalyst (130) is located downstream of the chamber and is configured to receive the stream, where the catalyst is arranged to promote conversion of the reactive species that are contained in the stream before the stream emerges from the reactor.    USE - Used in a heating, ventilation and air conditioning (HVAC) system, vehicle e.g. aircraft, air recycling system, and within a building or workspace area, for treating aerosol particulate carried in a fluid stream e.g. air (claimed), in medical and residential applications in health-care environment e.g. hospital environment.    ADVANTAGE - The utilization of the catalyst reduces ozone that emerges from the reactor to a level that is below an ambient ozone concentration level and reduces nitrous oxide in an effluent stream to the level that is below an ambient nitrous oxide level if the ambient nitrous oxide levels are particularly high, thus providing an improved and cost effective reactor for air purification.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a catalytic converter comprising a mixing plate    (2) a catalyst electrode comprising a metal frame    (3) an air purification device comprising an ionizer    (4) an electrostatic filter comprising a porous electrode    (5) a method of operating an electrostatic filter.    DESCRIPTION OF DRAWING(S) - The drawing shows a reactor design with an ultraviolet volatile organic compounds (VOC) removal system.    Pre-filter (122)    Negative plasma generator (126)    Electrostatic filters (128)    Catalyst (130)    Negative discharge electrode (151)    Chamber walls (154)    Dielectric material (168)    Oxidation catalyst (242)    Ultraviolet light source (262)    Photocatalysts (265, 268)