Abstract: A cigarette smoking article achieves very low levels of CO and other gas phase components by means of substantial air dilution, but has an acceptable pressure drop and sufficient delivery of particulate matter to provide a flavorful smoke. The filter has two sections, an upstream section which has substantially no pressure drop thereacross and a downstream section which provides substantially all the pressure drop of the filter. Dilution air is admitted to the upstream section of the filter to mix with mainstream smoke before it passes through the downstream section of the filter and thereby reduce the CO and gas phase levels in the smoke.