Systems and methods of pyrolyzing gaseous hydrocarbons include a reaction chamber and a plenum in fluid communication therewith. A light source directs electromagnetic radiation through a window into the reaction chamber. A first recirculation conduit connected between an offtake and an intake of the reaction chamber recirculates to the intake of the reaction chamber a portion of an aerosol product from the offtake of the reaction chamber. A filter operatively associated with the offtake of the reaction chamber receives un-recirculated amounts of the aerosol product and produces a retentate that includes particulate matter removed from the aerosol product. First and second gas separators operatively associated with the filter separate hydrogen and unreacted hydrocarbons from a filtrate of the filter. A second recirculation conduit connected between the second gas separator and the intake of the plenum recirculates unreacted hydrocarbons from the filtrate to the plenum.