DESC: The Blueair 200SF Smokestop filter is an optional filter that contains highly activated carbon.  It's recommended for use in rooms where heavy gaseous pollutants such as cigarette smoke or VOCs (Volatile Organic  Compounds) are present. On first use, you may notice a slight odor coming from the active carbon, but this will dissipate quickly.  Compatible Models: Blueair 201, 203, 205, 250E, 270E air purifiers.