Replacement Carbon+ filter set for the Blueair Pro L air purifiers. The Pro L Carbon+ Filter acts as an add-on to the Pro L Particle and SmokeStop filters, providing extra protection against gaseous pollutants using a sheet of activated carbon. This add-on is designed for removal of heavy gaseous pollutants. Approximately 1-4 lbs (depending on the unit) of additional activated carbon, work in the form of hundreds of pellets to trap dangerous chemicals and annoying odors. Includes 2 Carbon+ V-shaped polypropylene pleated filters for removing pollutants such as dust, pollen, bacteria, virus, pet dander, mold spores and other airborne particles down to 0.1 micron in size with additional sheets of activated carbon to remove gaseous pollutants. Since polypropylene fibers are waterproof, Blueair purification systems do not require the use of chemical-based bacteriostats or mold inhibitors. Instead of absorbing the moisture in which bacteria thrive, polypropylene repels water and naturally prevents bacteria, mold and mildew from reproducing inside the filter. Replace filter every 6 months.