A lithographic projection apparatus is disclosed. The apparatus includes a
radiation system for providing a beam of radiation, and a support for
supporting a patterning device. The patterning device serves to pattern
the beam of radiation according to a desired pattern. The apparatus also
includes a substrate support for supporting a substrate, a projection
system for projecting the patterned beam of radiation onto a target
portion of the substrate, and a purge gas supply system. The purge gas
supply system includes a purge gas mixture generator that includes a
moisturizer that is arranged for adding moisture to a purge gas to
generate a purge gas mixture, and a purge gas mixture outlet connected to
the purge gas mixture generator for supplying the purge gas mixture to at
least part of the lithographic projection apparatus.