, said apparatus comprising: a conduit for providing a flow of liquid carbon dioxide; aperture coupled to said conduit for subjecting said flow of liquid carbon dioxide to a pressure expansion to create a flow of carbon dioxide snow particles; a metallic electrically conductive tube for receiving said flow of carbon dioxide snow particles and imparting to said flow of carbon dioxide snow particles a negative electrostatic charge as a result of physical engagement between said flow of carbon dioxide snow particles with a surface of said conductive tube; conductive material of