Do Air Purifiers Actually Work?
The promise of an air purifier is an enticing one: An appliance designed to cleanse the air in your home, getting rid of all the impurities including odors, smoke, dust, and pet dander. Given the fact that indoor air can have levels of certain pollutants up to five times higher than outdoor air, we get it. Some models may even be able to target bad air that creeps into your apartment or home, especially if you live in an area affected by pollution, or natural disaster.

Most people shouldn't be worried about exposure to temporary pollutants like smoke or exhaust in the air outside your home, as they dissipate over time, explains Ryan Roten, D.O., an emergency medicine doctor with Redlands Community Hospital in California. "In the short term, people will have asthma-like symptoms, primarily, or symptoms closer to allergies or sinusitis, including stuffy nose and a bit of a cough," says Dr. Doten, who has been treating patients with underlying respiratory illnesses as mass wildfires rage along the West Coast and air quality reaches new lows. "If the smoke is dense enough, you might have some headaches due to carbon dioxide, and those with issues like asthma or COPD will have it worse in the moment."

Air purifier can indeed neutralize some of the threat posed by air pollution and by indoor activities. In reality, though, not all air purifiers necessarily live up to their marketing hype.

How do air purifiers work?
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.

That means, in addition to the purchase price of an air purifier, you should also factor in operating costs and filter replacement costs. Operational costs can easily amount to $50 annually, since you should be running air purifiers near constantly to garner the benefits. Filter replacements can run upwards of $100 a year all told.

How frequently you will have to change filters varies based upon the purifier type and usage. Some filters are reusable and washable, but they require meticulous maintenance, so you don't usually find them on the most effective air purifiers. Reusable filters are generally better at removing larger particles from the air, like dust mites and pollen. You'll also find UV (ultraviolet light) filters on the market, which often claim to destroy biological impurities like mold or bacteria, but many require higher wattage and greater exposure to be effective (not to mention some bacteria is UV-resistant).

Other air purifiers use ionizers to help attract particles like static — negative ions bond to dust and allergens and make them settle out of the air. If you're interested in buying desktop air purifier that uses ionizers, make sure it does not produce ozone, a gas made up of three oxygen atoms that is often marketed as helping break down pollutants, because ozone could be a lung irritant and further aggravate asthma conditions. Usually the air purifiers with ozone will have that listed on packaging or in the marketing descriptions.

What are air purifiers supposed to filter out — and do they actually do it?
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.

Many air purifiers are good at filtering pollutant particles out of the air (dust, smoke, pollen, etc.), but they are not necessarily very good at removing gaseous pollutants like VOCs or radon from the air that may accumulate from adhesives, paints, or cleaning products. Allergens that are embedded into furniture or flooring are also not captured by them.

Additionally, the effectiveness of air purifiers in real-world situations likely won’t mimic those of controlled conditions in a lab (what those "99% effectiveness" claims are referring to!). The location, installation, flow rate, and how long it is operating for will all vary, as will the conditions in the space. In addition, there are other things happening in your home that may effect the efficacy like ventilation (open or closed windows), and new particles are constantly emerging, so the air may not as filtered as the claims may have you believe.

Can air purifiers filter the outdoor air that enters your home?
Sometimes, non-organic air pollutants — like the VOCs we mentioned previously — can originate from outside your home. "There are all sorts of scenarios in structure fires where large doses of smoke inhalation may lead to cyanide toxicity. But that would largely need to be someone who was standing directly in or near the fire: Those people are brought to emergency rooms immediately," Dr. Roten explains. "Generally, outside pollution or smoke or temporary bad air isn't a constant concern for bystanders."

But the right kind of purifier can address any environmental air qualities in your locale. Using nearby wildfires as an example, Dr. Roten adds that a HEPA filter-equipped purifier is your best bet: "Anything that has a true HEPA filter in it is probably adequate enough to filter out most all the large particles that would be concerning," he says. "Most of the smoky smell will also be addressed as well."

So… should I buy an air purifier?
Before you do, know that air purifiers are not a cure-all. There is very little medical evidence to support that air purifiers directly help improve your health or alleviate allergies and respiratory symptoms. That’s due in part to the fact that it is very difficult to separate the effects of known air-quality pollutants in your home from other environmental and genetic factors. (For instance, how are the furnishings and ventilation in your home affecting you in addition to any indoor pollutants?) But if you are an allergy or asthma sufferer, an air purifier with a HEPA filter may be helpful for you as it will be good at removing fine airborne particles.

What is a HEPA filter?
HEPA is an acronym for High Efficiency Particulate Air. HEPA filters capture variously sized particles within a multi-layered netting usually made out of very fine fiberglass threads (much thinner than the size of a human hair strand!) with varying sized gaps. The filter is airtight, and comprised of a dense sheet of small fibers pleated and sealed in a metal or plastic frame.

The air purifier's fan draws air into the filter and particulates are captured in the filter. The larger particles (ones bigger than the fibers) are captured via impaction (particle crashes into the fiber), mid-sized particles are captured by interception (particle touches the fiber and is captured), and ultra-fine particles are captured by diffusion (while zig-zagging the particle will eventually hit and stick to the fiber).

What should I look for in an air purifier?
CADR (clean-air delivery rate) rating. This measures the cleaning speed of the purifier for removing smoke, dust, and and pollen. Look for a CADR of at least 300, above 350 is really great.

Size guidelines. For proper efficacy, you need a model designed to work in the room size. Choose a model that is designed for an area larger than the one you are outfitting it for if you want to operate it at a lower, quieter setting.

AHAM (Association of Home Appliance Manufacturers) Verified mark. AHAM’s standards are design to ensure the safety, efficiency and performance of many home care appliances, including air purifiers. The standards are designed to provide a common understanding between manufacturers and consumers to help make the purchasing process simpler. While voluntary, most reputable air purifiers have undergone this certification program, which often provides a CADR rating and size guidelines.

True HEPA. True HEPA filters are effective at removing ultra fine particles (think: dust, dander, pollen, mold and other common allergens in the home). The industry standard for such is that the unit must be able to remove at least 99.97% of particulates measuring 0.3 micron diameter in a lab setting. Remember, it is important to note that in real life settings, the actual efficacy of these devices would be far less as new pollutants are constantly emerging. Note that there is no industry standard for the terms "HEPA-like" or "HEPA-type," and are mostly used as marketing ploys to get consumers to purchase the product.

What are other ways I can improve the air quality in my home?
The best advice is to address the source of indoor air pollution and ventilate your home. If you are looking to supplement the work of your home air purifiers or see if you can get by without one, we recommended trying these steps to help reduce indoor air irritants:

Keep your windows open when it's safe to do so to prevent locking irritants into rooms (especially when air purifiers aren’t running!). Create a stronger cross draft by opening windows on opposite sides of the room if possible.

Vacuum often. If you are on the market for a vacuum, opt for one that is sealed, has a bag and is HEPA-certified. They’re better at trapping dust instead of sending it back into the air. The Good Housekeeping Institute recommends the Miele U1 Maverick SHAE0.

Regularly change air filters to properly maintain HVAC equipment and maximize effectiveness. Dr. Roten adds that sourcing a HEPA-specific filter for your circulation system can provide additional filtration: "It's [going to] recirculate the air in your house a bit better with each pass."

Use an exhaust fan in the kitchen (and bath and laundry areas if possible). Switch it on before preheating the oven or firing up the burners, and leave it running for a few minutes after you’re done cooking.

Minimize the use of candles or lighting wood fires and ban smoking inside the home. Reducing pollutant sources is a surefire way to improve air quality.


Sources of Air Pollution in a Car
There are many reasons for poor air quality in a vehicle. Some were mentioned above and here is a list of the most common sources of pollution you may encounter.

Odors

Cigarette smoke

Carbon Monoxide and exhaust fumes from other cars

Carbon Dioxide

Pet Dander

Particulate matter like dust, mold, pollen and bacteria



Most of the items in this list are gases (the first four). Gases are difficult to remove with an air purifier since they are incredibly small and require advanced gas filter media. We go into detail in our comprehensive air purifier guide for how to effectively remove them.

The pet dander, dust and pollen are airborne particulates and larger than gases. To remove them you need a HEPA air filter as the solutions for gas removal are not effective. Particulate matter is best captured in a net like the fibers of a HEPA filter. Gases in contrast are often adsorbed into a material like activated carbon.

So, from an air purifier perspective it depends upon what you need the air cleaner to do before you can identify the best solution.

Strategies to Clean the Air
There are 3 main strategies to clean the air in any environment. This applies to a home, the office or in a vehicle.

Source control – remove the source of the issue. In a car this can be difficult since you don’t have a choice but to drive on the road.

Ventilation – this is achieved by circulating air from the outside or by rolling down the windows. Again, this can be difficult depending upon the weather conditions or pollution on the roads.

Air Cleaning – using an air filter to remove the pollutants.



This list is sorted in the order of importance. So, source control is the first choice, followed by ventilation and then air cleaning.

Purpose of Your Car’s Air FilterCars come with an air filter. What is interesting is that the purpose is the same as the air filter in your air conditioning or furnace heating system. And that is to protect the equipment and not your health.

In most cases this is a low efficiency pleated filter. This means it will filter out the larger particles only which is most important in maintaining the operation of your vehicle.

The same issue exists with your HVAC filter in that the fans are not strong enough to pull air through a higher efficiency filter. So, your car air filter will only remove the biggest pollen or dust particles. And not the finer particles that you breathe into your lungs.

Furthermore, imagine if you wanted to remove fumes and emissions from vehicle exhaust. In other words, the gases we listed above. This issue is even harder since a bank of carbon has more air flow resistance and therefore requires a stronger fan to pull the air through.

We looked at developing a better filter that could be placed in a car however we determined this was not practical since the fans in a car are just not strong enough. The result would be much lower air flow. This would create a strain on the fan as well as poorer performance in the air conditioning.

So, it’s a difficult problem to solve given the limitations. In addition, it takes a good amount of energy to move air through a filter that is effective and there is not a lot of power in a cigarette lighter adaptor.

And this leads us to the current car air purifier solutions.

How Car Air Purifiers Work
For the most part, car air purifiers work on the same principles as a room air purifier although they are much smaller in size. It’s more like a mini or personal air purifier with a limited power source.

Here is a listing of the most common technologies. We will examine each in more detail below.

Negative ion generator – also referred to as a car air ioniser.

HEPA filter

Activated Carbon filter

Ozone generator

Air Freshener



Negative Ion Generator
The negative ionizer works by emitting a negative charge into the air. There is no filter to catch the particles. This is simply an electronic device and most often is plugged into a cigarette lighter. This car air ionizer requires little power.

The concept is that negative ions clean the air of particulates by attaching to the dust, pollen or mold spores and then they are more easily attracted to a surface.

However, this does not address the most common issue and that is gas, smoke and odor removal. The only way a negative ioniser could remove any gas is if it creates ozone. This is problematic since ozone is a lung irritant and considered air pollution. We are not meant to breathe in ozone and should avoid it.

HEPA Filter
A HEPA air filter is the best technology to remove airborne particulates and it does so safely. The problem we have seen with HEPA filters in car air purifiers is that they are much too small to be effective and/or are not true HEPA.

As we explain in 5 reasons to buy air purifiers, the bigger the filter is and the higher efficiency it has the better it will do in cleaning the air. You simply cannot cut corners and make a tiny filter or one with a low efficiency. It won’t be able to filter much.

Recently, Tesla came out with what they call the Biodefense HEPA filtration system in one of their car models. It seems they did the right thing and built a strong enough fan to power the air through a HEPA filter. The gap that we see with this is that HEPA is not effective for gases. And gases are the primary reason people buy a car air purification system. Gases like car fumes will pass right through the HEPA air filter fibers. For something like cigarette smoke removal, the HEPA air filter will remove the smoke particles but not the smoke odors.

Activated Carbon Filter
A filter with activated carbon is good in removing many of the gases associated with smoke removal and car fumes. The problem here is that it requires a good amount (more than a pound in a car) as well as a good air flow. The car air purifier we has seen do not have strong enough motors or enough carbon to remove the pollutants.

In addition, you simply cannot put a container of active carbon in your car and expect it to clean the air.

Furthermore, carbon is not effective for all gases. You often will want additional gas filter media or a treated carbon to have a more complete solution.

For HEPA and activated carbon to work you need more power and you don’t have that with the cigarette adaptor or enough space in the car for an air cleaner that is effective.

Ozone Generator
An ozone generator works as its name implies and that is to create ozone. While ozone can be very effective in gas removal it is terrible to breathe in. And extremely bad if you have a respiratory issue like asthma, COPD or bronchitis.

As far as I know car air cleaners are not regulated like room air purifiers for ozone.

The only time you would want to use an ozone generator would be in a car when no people are present to remove odors. For example, if you need to remove smoke odors from a car interior, you could use an ozone generator to “shock” the car.

Other than that, you should stay away from ozone.

Air Freshener
An air freshener works by masking odors in a car. It does not remove any odors but rather gives off its own odor so you do not notice the odor you are wanting to avoid.

An air freshener introduces gases into your car. It’s not an ideal solution since you breathe in whatever they give off.

Do Car Air Purifiers Work?
Given what we have described above we have no confidence that a car air purifier will provide the clean air you are looking for.

The problems are real, however the solutions simply are not effective. In my opinion, they are quite gimmicky and if they produce ozone you are introducing pollution into your car. This goes against our philosophy of providing products that are effective and safe. So, this is not a product we have any interest in making or selling.

However, there is one solution we have seen in military use that could be effective but would require an installation in a vehicle. This is like a whole house or commercial air purification system for a car where you have a separate fan and filter bank. To work effectively you would have to give up some space, say in your trunk as well as go through an installation process.

Another solution would be to wear a mask. This will filter out many of the particles however unless you are wearing a respirator with a filter you will likely not be able to filter out the gases. When I am in China and wear a mask, I can still smell the pollution as well as tobacco smoke odors so I know even a N95 mask has limitations.