Air purifiers usually consist of a filter, or multiple filters, and a fan that sucks in and circulates air. As air moves through the filter, pollutants and particles are captured and the clean air is pushed back out into the living space. Typically, filters are made of paper, fiber (often fiberglass), or mesh, and require regular replacement to maintain efficiency. Most filters on the market are designed to capture particles like dust and pollen, but don’t catch gases like VOCs (volatile organic compounds) or radon. That would require an adsorbent, like activated carbon. In fact, the Environmental Protection Agency (EPA) warns that the functionality of air purifiers is limited in terms of filtering out gases, and that you must frequently replace filters for optimal functionality, usually about every three or so months.