The APS-200 PM 2.5 has a state of the art cartridge that is unique from the traditional Airocide Cartridge. The two are not interchangeable. If you have purchased the APS-200 PM2.5 unit; this is the cartridge to buy. We still make it easy. Just replace the Reaction Chambers when the indicator light starts blinking, approximately once a year. *For extreme environments, we recommend replacing the APS200 PM2.5 reaction chamber every six months. Regrettably, due to the high volume of business this month we are out of stock on this item. If you place an order today, expect it to ship the first week of April.