An extreme ultraviolet exposure apparatus includes a radiation system configured to supply a beam of extreme ultraviolet radiation; a support configured to support a patterning device, the patterning device configured to pattern the beam of extreme ultraviolet radiation according to a desired pattern; a substrate table having an area configured to support a substrate; a projection system configured to project the patterned beam of extreme ultraviolet radiation onto a target portion of the substrate, the projection system comprising a reflective optical system; wherein at least a part of the apparatus that during use of the apparatus is exposed to the beam of extreme ultraviolet radiation is coated with a coating, the coating comprising a metal oxide, or a photocatalyst, or a semiconductor, or any combination thereof.