Utilizing activated carbon, the Blueair 500/600 Series SmokeStopTM replacement filter is designed for environments with heavy gaseous pollutants, made specifically to fit the 501, 503, 510, 550E, 555EB, 601, 603, and 650E Blueair purifiers. Using almost 4 lbs of carbon, activated with magnesium dioxide and copper oxide, the 500/600 Series SmokeStop Filter removes tobacco smoke, ethylene oxide, odors, and harmful VOCs from your home environment. In addition the SmokeStop filter uses HEPASilent technology, which is certified to remove 99.97% of particles down to 0.1 microns in size, such as dust, pollen, bacteria, and mold spores. This filter uses a gradient structure with thermally bonded fibers, free of chemicals and binders, which are naturally anti-bacterial, and fiber shedding resistant. Blueair recommends changing the filter in your air purifier every 6 months. The use of a SmokeStop filter may lower an air purifier’s airflow and CADR.