In this article we introduce the activated carbon air filter and how carbon works. You will learn what activated carbon is and when it works well. And what you need to watch out for.
Case for Carbon
While HEPA filters are great at removing things like dust and pollen they aren’t so good at removing odors.
In fact, they are quite poor.
Odors are gases. The gases will simply pass right through the HEPA filter fibers. Examples are cigarette smoke smell, cooking odors, air pollution near a highway, etc.
If you read our article on the HEPA air purifier you may have seen a true HEPA filter is rated for particle removal at 0.3 microns in size. The trouble with odors like smoke or pet odors is that they are much, much smaller.
Activated Carbon Air Filter
So, to solve this problem air purifier companies include carbon in the air purifier. Raw carbon on it’s own is not effective. To make it work it is baked into a charcoal like substance. In this state it is known as activated carbon.
Activated carbon has some special properties. Namely, that it can absorb gases. This means that as the odors are passing through your filter, the carbon can capture them.
Activated carbon has many tiny crevices that work great for catching the odors. It works well with smoke odors and VOC (volatile organic compounds).
One gram of activated carbon has a surface area greater than 32,000 square feet. It’s incredible how much surface area this creates to adsorb odors.
While carbon works well in removing most odors it is not effective for all.
The most notable gas carbon is not effective with is formaldehyde. Formaldehyde is common in building materials. Think furniture, flooring, and carpeting.
In this case a substance like potassium permanganate is sometimes used. This can capture things like formaldehyde that carbon can struggle with.
Charcoal versus Carbon
Charcoal is a substance of carbon and ash that is usually made from coal, wood, coconut shell or petroleum. It is most often the items used as a briquette for cooking.
Activated charcoal is essentially the same as activated carbon. Activated charcoal is charcoal that is heated with a gas that causes the charcoal to develop the crevices.
Types of Carbon in Air Filters
As we have researched carbon we have found that most of the carbon air filters from China use coal or petroleum based activated carbon. For American made filters we see more use of coconut shell based carbon. This is a more eco friendly option. From what we have read it seems more available in the US.
Here is an overview of how carbon is classified.
Powder Activated Carbon
Carbon that is broken down into fine powder is called PAC. Powder activated carbon. This is less than 1mm in diameter. The benefit to this is that you get a ton of surface area to adsorb odors. And you will not need as much to get the same fresh air smell. The downside is it does not last as long.
Granular Activated Carbon
GAC or granular activated carbon is commonly used in air filters. These are the pellets of carbon. They offer a good balance of odor removal ability and lifespan. It does not have the amount of surface area that you get with PAC however it lasts much longer.
Carbon is sometimes treated with silver, potassium permanganate or other substances to give the filter better performance. In the section below we cover some of the gaps in what carbon can do. By impregnating a substance onto GAC you give it the ability to remove a wider range of gases.
This is how they filter water. Granular activated carbon has a treatment to remove the sulfides and make it clean. Some air filters use this same method. A treatment is applied to the carbon to make it effective for difficult gases like natural gas or formaldehyde.
Zeolite and Potassium Permanganate
As mentioned above, activated carbon is not effective for all gases. For carbon air filters, the most common substances used to fix this gap is to use zeloite or potassium permanganate.
Both of these are good gases absorbers.
Zeolite is a natural mineral that is made up of aluminium, silicon and oxygen. The most common use of zeolite is in laundry detergent. It is also commonly found in kitty litter. Similar to being an additive in carbon air filters, zeolite is also used in aquariums to complement the activated carbon.
Potassium permanganate is a salt and a strong oxidizing agent. This means it can cause substances to lose electrons. This is cool since it can convert ozone O3 into oxygen O2. And it does not generate toxic byproducts.
We have never experienced this however in researching carbon online we have read about a few people who had the carbon re-release the odors.
This happens when the filter is old and the carbon has been used up. We are not aware of how to tell when it’s time to change the carbon filter. Other than to follow the recommended filter replacement schedule. You may not want to put it off too long if you’ve pulled a lot of odors from the air.
See our article about smoke air purifiers to learn more about carbon air purifiers and how to get fresh air.
In this article we provide an overview for how carbon works. We explain activated carbon filters and what they are effective for.
Carbon is not effective for all gases but is good for most.