Abstract: In one aspect, the invention provides a gas treatment apparatus (1) comprising a gas-flow path and a plurality of reactor units (5)-(7) through which gas to be treated may flow arranged in series along the path. The reactor units (5)-(7) are adapted to generate a non-equilibrium plasma. This aspect of the invention may be used for decomposing pollutant materials in a gas (e.g. air). When air is being treated, the apparatus of this aspect of the invention is advantageously provided, downstream of the final reactor unit in series, with at least one catalyst bed (8) incorporating a catalyst capable of decomposing ozone.