The Science of Carbon Filtering

Stephen Andrews
06 Dec 2021

Carbon filters improve air quality and can prevent the spread of marijuana smell. Filters with activated carbon are common items in grow rooms, especially in places where the ventilation is poor. In this article, we explain how carbon filters work.

Carbon filters are commonly used to remove the smell of marijuana in grow rooms. The filter uses activated carbon to eliminate smell particles and other impurities invisible to the human eye but that can be present in the air. The contaminants are trapped in the granules of activated carbon, which is basically charcoal treated with oxygen. 

When carbon is subjected to oxygen, the chemical reaction opens up a many many tiny pores between the carbon atoms. Special manufacturing techniques are used to create highly-porous crystals of activated charcoals that can "adsorb" organic particles such as odors, tastes, or colors. The carbon particles are big enough to hold in the particles trapped from the air. 

What's the Difference Between Absorption and Adsorption? 

Adsorption is only one letter different than absorption, and it's an entirely different physical/chemical process. When a particular substance adsorbs something, such as active carbon, it basically attaches to it. Adsorption is the quality of a solid compound to attract and trap gas, liquid, or dissolved solid molecules to its surface. As liquid or air comes into contact with active charcoal, intermolecular forces draw molecules into the millions of pores dotting the carbon surface. 

Pollution masks would be an example of adsorption from our daily lives. Masks are made of two or more layers of fabric, and between the layers, there is activated carbon either in the form of granules or a filter sheet. Whatever its form, the carbon acts as a purifier, allowing clean air to go inside the nostrils while dust and smoke particles are captured in the filter. The activated carbon element is the adsorbent, while the dust and smoke particles are adsorbates. 

Adsorption is different from absorption because molecules that are being absorbed rather than adsorbed are taken inside the material. An example for that is cotton wool used for bandages. As an absorbent, cotton wool can soak up the blood from an open wound. It's something that adsorbent materials don't do. 

It's easy to distinguish absorbents from adsorbents. Adsorption does not change its adsorbent visually. Odor molecules are simply "swallowed" in the process, without changing the volume, color, or any other property of the adsorbent. In contrast, after cotton wool is applied for wound treatment, its volume changes, it becomes red and wet, and feels different on the touch. 

how active carbon works and filters the air
A micrograph of activated charcoal in water. The fractal-like shape of the particles hints at their vast surface area. Each particle in this image has a surface area of several square feet. This image is at a scale of 6.236 pixels/μm; the entire image covers a region of approximately 1.13 by 0.69 mm. Photo credit: Zephyris on Wikimedia, CC BY-SA 3.0

How Carbon Filtering Works?

The surface of an activated charcoal piece has countless sites for bonding. When certain particles hover around the carbon surface, they attach to it and stay there. Activated charcoal is superior in trapping volatile organic compounds (such as paint, varnishes, adhesives, air fresheners, etc.), and it will only remove certain impurities circulating in the air; it's not affecting all particles. 

Activated carbon can filter odors, hydrocarbons, and oil vapors from the air. Filters are available in solid carbon, impregnated foam materials, powder, and cloth. Filters do need to be changed regularly, every few months or so, depending on the type of filter, the size of the cannabis grow room, or the plants that are being grown

Carbon also has other superpowers, which might not be very relevant for cannabis growers. But, important, they can also be utilized to catch radon in the air, a naturally-occurring radioactive gas associated with causing lung cancer. 

The purification qualities of active carbon have found a wide range of use, from utilization in processing facilities to coffee machines, air conditioning units, aquariums, and essential exhaust fans that filter the air of unwanted odors

When was the last time you changed your carbon filter?

Also read on Soft Secrets:

Cannabis Botany Terminology for Beginners

A Beginner’s Guide To Flowering Cannabis

A Beginner’s Guide to Training Cannabis Plants

Stephen Andrews