Apparatus and method for atomic layer deposition on a surface of a substrate (6) in a treatment space. A gas supply device (15, 16) is present for providing various gas mixtures to the treatment space (1, 2). The gas supply device (15, 16) is arranged to provide a gas mixture with a precursor material to the treatment space for allowing reactive surface sites to react with precursor material molecules to give a surface covered by a monolayer of precursor molecules attached via the reactive sites to the surface of the substrate. Subsequently, a gas mixture comprising a reactive agent capable to convert the attached precursor m molecules to active precursor sites is provided. A plasma generator (10) is present for generating an atmospheric pressure plasma in the gas mixture comprising the reactive agent, the plasma generator being arranged remote from the treatment space (1, 2).