Breathe Naturally - October 2, 2023

Activated Carbon Filters: What Do They Remove from Your Air?

Activated carbon filters are a common component of many air purifiers and HVAC systems. As air passes through the porous carbon material, pollutants and odors are removed, leaving cleaner air behind. But what exactly does activated carbon filter out of the air? Here’s an in-depth look at what these filters can and can’t trap.

How Activated Carbon Air Filters Work

The porous structure of activated carbon contains millions of tiny pores and tunnels. As air passes through, pollutant molecules get caught in these nooks and crannies through a process called adsorption. The pollutants stick to the surface of the pores via intermolecular forces. The massive surface area of activated carbon filters—often hundreds of square meters per gram—provides exponentially more sites for contaminants to adhere to. This allows the filters to adsorb a significant quantity of pollutants from the air.

Activated carbon filters are especially effective at trapping gasses and odors. The pollutant molecules are drawn into the pores like a magnet due to attractive forces at the surface. Activated carbon can adsorb a wide array of gasses, making it useful for general air purification.

Large Particles

While tiny odor molecules readily adhere to activated carbon, large particles like dust, dirt, and hair are captured on the front side of the carbon filter. Over time this will begin to restrict air flow through your unit, so we recommend brushing your filters off or replacing them on a regular basis.

In an air purifier, a carbon pre-filter catches large particles before they reach the HEPA filter, extending the lifespan of the more expensive HEPA filter. A HEPA filter will capture the microscopic particles that pass through the carbon filter, making them the perfect combination for air purification.

A higher quality of air for the ones you love

Volatile Organic Compounds

One major class of pollutants that activated carbon filters excel at removing is volatile organic compounds (VOCs). VOCs are emitted as gases from a variety of household products, building materials, paints, cleaners, and more. Common examples include formaldehyde, benzene, xylene, methylene chloride, and chloroform. Exposure to VOCs can cause eye, nose, and throat irritation along with headaches, loss of coordination, and damage to the liver, kidneys, and central nervous system.

When VOCs pass through an activated carbon filter, the molecules get trapped in the pores through adsorption. This prevents them from accumulating in indoor air and causing health issues. Studies have shown activated carbon filters can remove over 90% of VOCs from the air in some cases.

The ability of the filter to remove VOCs depends on a few factors. These include the amount of activated carbon, contact time, pore size distribution, and strength of the adsorptive forces. But in general, activated carbon is highly effective at trapping the majority of VOCs. Air purifiers with activated carbon filters can greatly reduce VOC levels in your home.


Another gas that activated carbon filters remove is ozone. Ozone generators purposely produce ozone to sterilize and deodorize air. However, breathing in too much ozone can cause chest pain, coughing, and throat irritation. Activated carbon filters provide a defense against excess ozone in indoor environments.

Ozone readily adheres to the surface of the pores in activated carbon. This prevents it from circulating freely through the air and causing potential health issues. Activated carbon filters have been shown to reduce ozone levels by up to 90% in controlled studies.

So if using an ozone generator for air purification, be sure to pair it with activated carbon filtration. The carbon will adsorb much of the ozone produced to keep levels in the safe range. An activated carbon filter can also remove residual ozone pollution that drifts indoors from outdoor air.


Pollen, pet dander, mold spores, and dust mite allergens are common indoor air contaminants. But can activated carbon filters remove these allergens? Unfortunately, the answer is no.

The particle size of most allergens ranges from 0.5 to 100 microns. This is much too large to be trapped within the nanoscale pores of activated carbon. Allergens will simply pass through an activated carbon filter without being captured.

To remove allergens, an air purifier needs a HEPA filter specifically designed to capture ultrafine particles. HEPA filters have a very tight mesh that traps particles as small as 0.3 microns through mechanical filtration. The filters can capture over 99% of particles that pass through them. So while activated carbon filters excel at removing gases and odors, a HEPA filter is required to reduce airborne allergens.

Investing in the proper air purifier filter improves respiratory health by reducing allergens, chemicals, dust and other irritants in your indoor air. Check and change air purifier filters regularly to maintain performance. Cleaner air filters mean cleaner, healthier air in your home.

Bacteria and Viruses

Like allergens, bacteria and viruses are also too large to be trapped by activated carbon. Most bacteria range from 0.2 to 10 microns in size. Viruses are even smaller, with most around 0.02 to 0.3 microns. With pore sizes starting around 1-2 nanometers (0.001-0.002 microns), activated carbon filters have no capacity to remove microbial contaminants.

To disinfect air of bacteria and viruses, an air purifier needs to utilize UV-C light or photocatalytic oxidation technology. For example, UV-C lamps emit short-wavelength ultraviolet light that damages microbial DNA/RNA and renders pathogens inactive. Photocatalytic filters use a catalyst activated by light to produce oxidizing molecules that destroy cell structures. But activated carbon itself provides no disinfection capability.

On the other hand, HEPA filters will help capture bacteria and viruses that pass through the carbon filters. Further euphuizing the importance of using both a HEPA filter and carbon filter to purify your air.

Smoke Odors

Lighting a scented candle or running an air purifier with an activated carbon filter are two ways to remove smoke odors from rooms. The porous structure of activated carbon can trap smoke components through adsorption. This eliminates the lingering odor of cigarettes, cigars, wildfires, or burnt food from the air.

Studies have found that air purifiers with activated carbon filters can reduce smoke odors by 85% or more in indoor environments. The filters continue working until the pores fill up with contaminants. Once saturated, the filters need to be replaced to maintain smoke & odor removal.

For severe smoke pollution, however, activated carbon filters have limits. Large amounts of smoke quickly clog up the pores, limiting effectiveness. Long-term smoke damage may also require re-painting or replacing smoke-permeated furnishings. But for occasional smoke removal, activated carbon filters can eliminate odors in short order.

Carbon Monoxide

Carbon monoxide is a poisonous, odorless gas produced by incomplete combustion. Sources include gas stoves, furnaces, fireplaces, and vehicle exhaust. Unfortunately, activated carbon does not effectively remove carbon monoxide from air.

The adsorptive forces between carbon monoxide molecules and activated carbon are relatively weak. Carbon monoxide does not readily stick to the pores like other pollutants. As a result, most carbon monoxide passes through activated carbon filters without being captured.

Specialized carbon monoxide absorbers are needed to remove this toxic gas. These contain materials like hopcalite catalyst that oxidize carbon monoxide into less harmful compounds. Activated carbon filters used in air purifiers help with many indoor air pollutants, but provide little defense against deadly carbon monoxide.

When To Replace Activated Carbon Filters

The capacity of activated carbon filters becomes exhausted over time depending on the quality of air in your home. Once they become completely saturated, they are no longer effective at removing pollutants. Some signs that your activated carbon filters need replacing include:

  • Reemergence of smoke, chemical, or other odors
  • Reduced airflow through vents
  • Filter has turned grey in color
  • More than 6 months since last filter change

Most manufacturers recommend replacing activated carbon filters every 2-3 months. But earlier replacement may be needed for those with pets, smokers in the home, or using ozone generators. Check the product specs for your specific air purifier for recommendations on filter replacement intervals.

Activated carbon air filters offer a simple, low-cost way to help clean indoor air. Their microscopic pore network is highly effective at trapping gases, VOCs, smoke odors, and other molecular contaminants. However, they do not capture particles like carbon monoxide and allergens or kill pathogens.

A multi-layer air purification system with pre-filters, activated carbon, and HEPA filtration provides the most comprehensive defense against indoor air pollution. But even as a standalone filter, activated carbon offers powerful odor and chemical removal that provides cleaner, healthier indoor air.