An apparatus for removing particulate matter from a gas stream containing particulate matter, the apparatus including: a mist-producing element that mixes a gas stream entering the apparatus with liquid droplets; and a down flow Wet Electrostatic Precipitator (WESP) pass section having ionizing electrodes that electrically charge the particulate matter and the intermixed liquid droplets, and collecting surfaces in the form of an array of polygonal tubes, wherein the collecting surfaces are under the influence of an electrical field to attract and remove electrically-charged particulate matter and intermixed liquid droplets from the gas stream. An embodiment utilizing two down-flow Wet Electrostatic Precipitator (WESP) sections (i.e., a first pass section and a second pass section), each of which includes ionizing electrodes that electrically charge the particulate matter and the intermixed liquid droplets, and collecting surfaces in the form of an array of polygonal tubes, wherein the collecting surfaces are under the influence of an electrical field to attract and remove electrically-charged particulate matter and intermixed liquid droplets from the gas stream is also disclosed, as is a method for removing particulate matter.