Replacement Prefilter / Model 681 Model 681 large room air purifier uses a combination of filtration processes to provide you with a HEPA filter air purifier, an activated carbon filter air purifier and/or an ionic air purifier all in one unit. The negative-ion generator, photo-catalyst pre-filter, HEPA filter, activated carbon filter and optional herbal sterilization filter combine to eliminate and absorb household odors, smoke, germs and harmful gases.

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