We all know that charcoal filters are used in a number of air purifiers to remove odors, gases, and various chemicals from the air.

But how do charcoal filters work? And, what are the main physical principles behind their efficiency?

Before going into more detail, let us see what charcoal is in the first place.

Simply put, charcoal is carbon, C, a chemical element.

Charcoal is basically just one of the several modifications of carbon. Carbon is something that all living organisms have – hence we may say that entire life on our planet is carbon based.

How is charcoal produced?

It is produced from wood.

There are four main components of any type of wood: water, carbon, ash, and volatile organic compounds that evaporate during normal combustion. But, when you heat a piece of wood at high temperatures (above 1,000 degrees F). When you do that in a sealed box to prevent oxygen from coming in, what is left at the end of the process is charcoal – pure carbon.

Can you use any form of charcoal and expect to have an efficient filter that works well?

No, not at all. Here is the deal.

activated carbon
Activated carbon

Charcoal filters for air purification are made from active or activated carbon.

Now, activated charcoal is produced from ordinary charcoal by using special techniques that ensure opening up a huge number of tiny pores in the carbon matrix.

Specifically this happens when charcoal is exposed to a higher dose of oxygen influx.

These high oxygen doses create the pores and the end result is having a huge surface area. There is as many as 2,000 square meters per just 1 gram of the original material.

This extremely large surface area allows capturing and filtering many different types of impurities that pass through the activated charcoal.

What is Being Filtered

This enormous surface area within each activated charcoal filter is what absorbs odors, toxins, harmful substance from gases, organic substance, and various liquids.

It causes adhering of impurities that pass through it. These various pollutants remain attached to and basically trapped on the surface of the charcoal. A good example of harmful substance trapped on the surface of activated carbon is chlorine.

Because the carbon filter is so fine, and given that many gases are carbon based, these filters are great at removing odors, cigarette smoke, cooking smells, and fumes.

Without a doubt organic chemicals are most efficiently removed. In contrast, most of the inorganic chemicals won’t be removed.

Volatile organic compounds, also referred to as VOCs, belong to the group of organic chemical compounds that are easily removed. Here we have substances such as Benzene, Xylene, Toluene, and oils.

What is not being filtered

It is important to know that certain chemicals and certain impurities are NOT attracted by the carbon surface at all. They pass these carbon filters without any problem. Examples of such materials that do not bond well on the carbon surface are nitrates, sodium, fluoride, and microbes.

It is also important to know that ONCE ALL active surface areas are filled with trapped chemicals, the charcoal filters stop working altogether. Even before that happens, the filter loses its efficiency and that’s the time to replace your carbon filter.

How to Know When to Replace Your Charcoal Filter

Some manufacturers have installed smart indicators to tell you when you need to replace your charcoal filter. If your unit doesn’t have one of these, you can do the following.

Measure the weight of the filter before you start using the machine. Then monitor the weight over time and look for significant deviations from the starting baseline weight.

Once the charcoal filter starts to lose efficiency, it will start leaking odors, indicating that it is saturated. You can smell this or use chemical detectors for special vapors and gases in the filtered air.

Charcoal Filters for Water Filtration

Water filtration is not really what you have to deal with if you have an air cleaner.

However it is important to know about one potential issue with water and charcoal.

Charcoal filters can be used to filtrate water. In this case you should make sure that the pores are free from bacteria as much as possible. Water makes a favorable breeding ground for various bacteria. Most drinking water in municipal areas is free from bacteria, so there is nothing to worry about.

But if the charcoal filter has not been used for some time, always make sure to let tap water run for a minute or so before use. This will ensure that the filtered water has much lower concentration of potential bacteria.