Understanding How Air Purifiers Work: A Comprehensive Guide

An air purifier or air cleaner is a device which removes contaminants from the air in a room to improve indoor air quality. These devices are commonly marketed as being beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke. The commercially graded air purifiers are manufactured as either small stand-alone units or larger units that can be affixed to an air handler unit (AHU) or to an HVAC unit found in the medical, industrial, and commercial industries. Air purifiers may also be used in industry to remove impurities from air before processing. Pressure swing adsorbers or other adsorption techniques are typically used for this.

How Do Air Purifiers Work?

Most air purifiers have a relatively simple setup: a fan that sucks in air, and one or more filters. These filters ¡ª usually made from paper, fibers such as fiberglass, or a mesh ¡ª capture particles as air passes over them, before the clean air is recirculated into the living space. As air travels through the filter, particles are captured and the clean air is pushed back out into the living space. As a result, an air purifier’s filters, which are typically made of paper, mesh or fiber, have to be replaced regularly in order to maintain efficiency. The frequency with which they need to be replaced will depend on the type of air cleaner and the amount you use it, although some appliances come with washable and reusable filters.

Main Components of an Air Purifier

• Fan: A modern fan will guarantee quiet, efficient, and trouble-free operation while consuming minimal energy. This will be appreciated by those who plan to use the air purifier in the children’s room or bedroom.
• Filters: The filter is the true hero to help improve indoor air quality. The polluted air first passes through a pre-filter, responsible for filtering out the biggest dirt clusters, dust, and hair, thus protecting other filters from premature wear.
• Sensors: Sensors that react to changes in air quality are critical. Higher accuracy and faster response to changing air quality are provided by a laser sensor, so it is worth investing in an air purifier that has it.

Types of Air Purifier Technologies

There are five main types of air purifiers on the market¡ªthose that rely on HEPA air filters, activated carbon filters, electrostatic filters, ozone generators, and UV lights. These filter types can be used individually or together in one machine.

HEPA Filters

HEPA stands for “high-efficiency particulate air.” The filter technology is the result of an industrial need that became critical in the Atomic Age: high volumes of very clean air, vital for the production of microprocessors and other sensitive instruments. A HEPA filter is standardized at a minimum 99.97% efficiency rating for removing particles greater than or equal to 0.3¦Ìm (1/83,000 of an inch) in diameter. This means that for every 10,000 particles that are 0.3¦Ìm in diameter, 3 will pass through the filter, and the rest will be trapped by the filter. The diameter specification of 0.3 microns responds to the worst case, or most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency.

Activated Carbon Filters

Activated carbon filters are designed to remove volatile organic compounds, odors, and other gases from air that passes through. Adsorption is a process by which selected materials, such as volatile organic compounds, are attracted to the surface of the adsorbent material, often activated carbon. Activated carbon filters are best suited to controlling odors from VOCs commonly found in home construction and renovation. Keep in mind that not all odors are attracted to adsorbent filters. Activated carbon filters get saturated faster than mechanical filters, though, and require replacement more frequently¡ªevery three months, as opposed to every six to 12 months for mechanical filters.

Electrostatic Precipitators (ESPs)

These electronic air cleaners use an electrostatic process to charge airborne particles, which are then attracted to oppositely charged surfaces such as collector plates or other media. As the collector plates or media become more particle-laden, they start losing efficiency – so proper cleaning of collector plates or replacement of filter media will be the key to maintaining efficient filtering.

UV Purifiers

UV purifiers use ultraviolet lamps to kill microorganisms such as fungal spores, bacteria, and viruses. In residential use, UV purifiers are typically used to treat interior surfaces of HVAC systems – specifically the indoor coil used in central air conditioning or heat pump systems – where organic matter tends to accumulate. UV lamps need to be replaced annually as they become less effective over time.

Ozone Generators

Ozone generators are designed to produce ozone, a strong oxidant gas which can oxidize many other chemicals. Unlike ionizers, ozone generators are intended to produce significant amounts of ozone. Due to the below-average performance and potential health risks, it has been advised against using ozone-producing air purifiers. Ozone is a colorless gas that is found naturally in the Earth’s upper atmosphere and protects us from harmful ultraviolet solar rays, though it also can be formed at ground level. It is known to cause free-radical formation in biological systems, which damages tissues.

Effectiveness of Air Purifiers

Air purifiers are intended to remove allergens and pollutants from the air, but how well do they really work? A 2024 analysis in the journal Science of the Total Environment looked at 148 studies that considered real-world use and found that on average, filters cut the number of small particles in the air by only half. This also means that air purifiers may not perform nearly as well in real-life situations as they do in carefully controlled laboratory tests. According to that 2024 analysis, portable air cleaners removed on average 49% of 2.5-micron particles and 44% of 10-micron particles ¡ª far less than the percentages that are often promised by manufacturers.

Factors Affecting Effectiveness

• Clean Air Delivery Rate (CADR): This metric measures how much clean air an air purifier can produce in a set amount of time and space, largely depending on the surface area of the filter and the strength of the fan. Generally, the higher the CADR, the more powerful the device.
• Room Size: Be wary about manufacturers’ claims. Many air purifiers are not suitable for their claimed room sizes. Most models suitable for large rooms (350 square feet and larger) can also work well for smaller rooms at lower speeds.
• Filter Maintenance: All filters need regular replacement as specified by the manufacturer in the product user manual. If a filter is dirty and overloaded, it will not work well.

Benefits of Using Air Purifiers

Air purifiers can help rid the air inside your house from allergens, molds, and other toxins. They remove a wide range of pollutants, including fine particles, bacteria, and viruses. The British Guideline on Asthma Management from the British Thoracic Society recommends the use of air filters for the removal of pet and other allergens. Effective air purification can have a significant impact on your health and well-being. By removing pollutants from the air, an air purifier can help reduce your exposure to substances that can cause allergies, respiratory issues, and other health problems.

• Allergies: Air purifiers can reduce allergic symptoms by lightening the allergen load of your indoor air.
• Asthma: Air purifiers can lessen triggers of asthma symptoms and attacks, from contaminants like dust, smoke, and pollen.
• Dust: Your air purifier may lessen the amount of dust particles, which are usually 5 microns or less in size, within the range of most HEPA air purifiers.
• Animal Dander: Your air purifier may help reduce dander in your home from your pet cat, dog, or bird.
• Particulate Matter (PMs): HEPA air cleaners with sufficient CADR can reduce concentrations of indoor PM2.5 (the smaller particles) by an average of 50% or higher.

Choosing the Right Air Purifier

Choosing the right air purifier starts with identifying your personal needs and priorities. Consider factors such as the size of the room or area you want to purify, specific air quality concerns (such as allergies or pet dander), noise level preferences, and any additional features you may prioritize, such as energy efficiency or integration with your existing smart home ecosystem.

• Room Size: Multiply the length and width of the area in which you intend to operate the air cleaner. The result will provide you with the size of the room or area in square feet. Compare this to the maximum recommended room size on the product packaging.
• Filter Type: When shopping for mobile air purifiers, look for True HEPA as opposed to “HEPA type” or “HEPA like” filters. Choose a portable air cleaner with an activated carbon filter or other absorbent filter designed to remove gases.
• Smart Features: Smart air purifiers offer a range of advanced features and connectivity options that enhance user control, convenience, and personalization. With Wi-Fi connectivity, mobile apps, voice control, real-time monitoring, filter replacement alerts, and smart scheduling, these devices provide an elevated air purification experience.

Comparison of Air Purifier Technologies

Best Practices for Using Air Purifiers

• Position it well: If you just have one unit, put it in the room where you spend the most time. Place your air purifier in an open area.
• Clean or replace filters regularly: Clean filters or replace them every 6 to 12 months, depending on the type of filter and how dirty they are.
• Run continuously: Our years of testing have proved that a good air purifier creates and maintains excellent air quality when it is simply allowed to run continuously on a moderate setting.
• Combine with other measures: Air purifiers tend to produce better results when used alongside other pollutant-reducing measures, such as proper ventilation.

Recommended Air Purifiers

• Winix 5500-2: An exceptional performer on particulate air pollution, capturing as much as 99.9% of smoke in test rooms in just 30 minutes on high. Shop on Amazon
• Levoit Core 300: Highly rated for its smart Wi-Fi features and quiet operation, ideal for small to medium rooms. Shop on Amazon
• Medify MA-50: Praised for its effectiveness in reducing odors and allergens, though replacement filters can be costly. Shop on Amazon

Frequently Asked Questions

Do air purifiers remove all pollutants from the air?

No, air purifiers cannot remove all pollutants. HEPA filters excel at capturing particles like dust, pollen, and pet dander, while activated carbon filters tackle odors and some gases. However, they may not eliminate all gaseous pollutants or ultrafine particles. Combining air purifiers with ventilation and source control is the most effective approach.

Are air purifiers safe to use?

Most air purifiers, especially those with HEPA and activated carbon filters, are safe. However, avoid ozone-generating or ionizing purifiers, as they can produce harmful ozone, which may irritate the lungs. Always choose models certified for low ozone emissions, particularly in states like California.

How often should I run my air purifier?

For optimal results, run your air purifier continuously on a moderate setting. This ensures consistent air quality, especially in high-pollution areas or during allergy seasons. Smart purifiers can adjust automatically based on air quality sensors.

Can air purifiers help with wildfire smoke?

Yes, HEPA-based air purifiers are effective at reducing particulate matter from wildfire smoke, capturing particles as small as 0.3 microns. Ensure the purifier’s CADR is suitable for your room size for maximum effectiveness. Learn more from the EPA.

Where should I place my air purifier?

Place your air purifier in an open area, away from walls or furniture, to ensure proper airflow. Ideally, position it in the room where you spend the most time, such as the bedroom or living room, and avoid placing it near sources of pollution like gas stoves.