Your Air Purifier May Be Trapping Pollutants Instead of Eliminating Them
Most people buy an air purifier without understanding what it can actually remove. Air quality researcher Dr. Jaspreet Dhau explains how HEPA filters, CADR ratings, VOCs, and filtration technologies affect indoor air quality.
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The air inside most American homes carries a longer list of pollutants than most people realize. Wildfire smoke has made indoor air quality a household conversation in California, but the more persistent hazards are quieter: cooking emissions from gas stoves, volatile organic compounds released from paint and furniture, mold spores traveling through under-ventilated rooms, and fine particles shed from synthetic textiles.
A systematic review of residential exposure studies published in the International Journal of Environmental Research and Public Health found that indoor pollutant concentrations, including VOCs and particulate matter, routinely exceed outdoor levels, with the home environment itself a primary driver of exposure.
Air purifiers have followed that awareness into the market, and sales have grown accordingly. But most people shopping for one don’t know that trapping a pollutant and destroying it are fundamentally different outcomes, and that most devices accomplish only one.
“While wildfire smoke has rightfully drawn attention to air quality concerns, many people overlook the everyday pollutants already present in their homes,” says Dr. Jaspreet Dhau, Vice President of Research and Development at Molekule, where he leads development of PECO technology, a photochemical oxidation process designed to break down pollutants at the molecular level rather than collect them on a filter. “Because people spend most of their time indoors, these pollutants can accumulate, particularly in homes with limited ventilation. The result is that indoor air quality can be just as, if not more, concerning than outdoor air quality.”
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Understanding CADR and Room Sizing: How to Choose the Right Air Purifier
Dhau has spent two decades studying indoor air, which puts him in a position to explain what the marketing language around purifiers often obscures. “When evaluating an air purifier, consumers should focus on objective performance metrics rather than marketing claims,” Dhau notes. The most important of those is the Clean Air Delivery Rate, or CADR, which measures how efficiently a purifier cleans the air in a given space. “A CADR of 200 to 400 or more cubic feet per minute is a strong range for medium and larger living spaces,” he explains. Equally important is air changes per hour, the number of times a purifier can filter the entire volume of air in a room within a single hour. For households managing allergies, asthma, or smoke exposure, Dhau recommends targeting four to five air changes per hour. “More frequent air changes generally result in cleaner indoor air because contaminants are removed more consistently.”
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Room sizing is the most common mistake consumers make at the point of purchase, according to Dhau. The Association of Home Appliance Manufacturers offers a guideline that many shoppers miss: a purifier’s CADR should be at least two-thirds of the room’s square footage. A 450-square-foot living room requires a unit with a CADR of at least 300. “Many consumers purchase units that are undersized for their space, and this limits an air purifier’s overall effectiveness,” he says.
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Comparing Air Filter Technologies: HEPA, Carbon, and Beyond
Beyond sizing, the choice of filtration technology determines what a purifier can actually do. HEPA filters are mechanical systems that capture at least 99.97 percent of particles measuring 0.3 microns or larger, and they remain, according to Dhau, “one of the most widely trusted filtration technologies for particulate removal.” A 2022 study in the International Journal of Environmental Research and Public Health measured real-world HEPA performance in household environments and found a mean reduction in indoor fine particulate matter from 33.5 to 17.2 micrograms per cubic meter, cutting the indoor-to-outdoor ratio by more than 37 percentage points under optimal conditions.
For shoppers comparing models, Dhau flags a specification trap: “Several air purification systems use lower-efficiency filters due to energy constraints and system limitations. Air units with a lower-efficiency filter may provide a higher CADR rating due to higher volume of airflow passing through it.” The MERV rating, which measures single-pass filtration efficiency, is the cleaner benchmark. The higher the MERV, the more each pass through the filter actually captures.
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Activated carbon filters address a different problem, absorbing gases and VOCs rather than capturing particles, making them particularly useful in homes with gas cooking, recent renovations, or furniture off-gassing. A 2023 study in Environmental Science and Technology found that gas and propane combustion from kitchen stoves emits benzene, a known carcinogen, in addition to elevating indoor particulate levels during cooking. Researchers measured benzene concentrations in kitchens during and after stove use at levels that exceed what most people associate with outdoor air pollution, and the effect was pronounced in homes without adequate ventilation.
UV-based systems target biological contaminants by exposing microorganisms to ultraviolet light in ways that can reduce the viability of certain bacteria and viruses. “UV technology is typically used as a supplemental feature rather than a replacement for particle filtration,” Dhau points out, noting that these systems are most relevant in homes with immunocompromised occupants or histories of mold growth. Ionizers, which release charged particles to cause airborne contaminants to settle or become easier to capture, work best when paired with traditional filtration, according to Dhau. “It’s important to carefully review product specifications because some ionization technologies can generate ozone as a byproduct, which can be an irritant for people with asthma or other respiratory conditions,” he says.
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Maximizing Performance: Air Purifier Placement and Source Control
Placement decisions affect performance in ways most consumers don’t account for after bringing a unit home. Purifiers need clear airflow around them, and Dhau is specific: “Ideally, they should be placed in open areas where air can circulate freely.” For the greatest benefit, he recommends positioning a purifier within the breathing zone for the room’s primary activity, three to six feet from a desk in a home office, a few feet from the bed in a bedroom.
“Placing the air purifier near a pollution source, for example, a new piece of furniture in your house, helps in bringing a greater benefit in improving the indoor air quality,” he notes. “Also, if your kitchen lacks a proper or efficient range hood, having an air purification unit in the kitchen brings greater relief in reducing pollutants generated during cooking.”
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For larger homes with separate rooms, hallways, or irregular layouts, Dhau recommends prioritizing the spaces where people spend the most time, bedrooms, living rooms, and home offices, rather than assuming a single high-capacity unit will cover everything. Maintenance is equally consequential. “Even high-performing air purifiers become less effective if filters are not replaced according to the manufacturer’s recommendations,” he says. “Regular filter replacement ensures the system continues operating at its intended performance level.”
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For households that want to improve air quality without a purifier purchase, source control is the highest-leverage starting point. “One of the most effective steps is controlling the pollution at the source,” Dhau explains. “This can include choosing low-VOC paints and cleaning products, avoiding synthetic air fresheners, and limiting the use of products that release unnecessary chemicals into the air.”
When outdoor air quality allows, opening windows to increase fresh air circulation helps dilute indoor pollutants. Running kitchen exhaust fans while cooking and bathroom ventilation fans during showers further reduces moisture, odors, and airborne contaminants.
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Regular vacuuming with a HEPA-filter vacuum, washing bedding frequently, and using damp cloths for dusting keep allergens from becoming airborne. “The biggest improvements come from a combination of source control, ventilation, routine cleaning, and effective air purification when needed,” Dhau notes.
Gas stove use without a functioning range hood remains one of the most consistent sources of spikes in indoor particulate matter and benzene in residential environments, according to Kashtan’s research, and it’s a variable that no purifier eliminates on its own. Source control and filtration work as a system. A HEPA unit running in the kitchen during and after cooking, paired with an exhaust fan that actually vents to the outside rather than recirculating air, addresses the problem in a way that either approach alone does not.
