# How much air could an activated charcoal bag or baking soda box actually purify / deodorize?

Someone I know recently bought a set of small stylish and expensive cloth bags (roughly paperback book sized) filled with activated bamboo charcoal, that you place in a room and it purportedly purifies the air of the room and eliminates odors. Similar claims have been made for open boxes of baking soda in a refrigerator.

My initial reaction is skepticism, mostly from a possibly-wrong intuition that the physics don't make sense; I also don't see any studies of the effectiveness of either product, and web searches just reveal a lot of SEO affiliate pages, blog marketing and the like. And this seems the type of situation that would be rife with confirmation bias ("I definitely think I smell a difference").

So down to the physics of it - in, say, a 4 x 4 x 3 meter (48 m^3) room, with a small bag of charcoal (say 12 x 12 x 6 cm, or 864 cm^3), how long would it take for say 95% of the air to pass through the bag due to gas diffusion, typical air convection, etc.? Or looked at another way, how much air volume would the bag "process" per hour? The interior is little charcoal pieces with an apparently high surface area. If a stinky carpet covering the floor of the room were off-gassing a given volume of gas per minute, could the bag keep up?

• I am not a physicist, but I would be very surprised, if it turned out that a large percentage of the air would go through the bag at all without directing its flow with something like a fan. On the other hand, when you put eg, a bunch of flowers in the room, the odour does permeate the room, so there is quite some movement. Commented Jun 14, 2019 at 4:55
• I would imagine this wildly depends on air composition, altitude, temperature, how well room is sealed, physical/checmical properties of the odor particles... But you can do much better by testing. A box with a rug, a box with charcoal, a box with a similar rug and charcoal. Test the scent reduction in the box with both, and test the weight difference between the charcoal bags. Easy peasy. Commented Jun 22, 2019 at 12:25
• I was hoping it'd be simpler to just do ballpark calculations than setting up a whole experiment in my house that relies on the subjectivity of the nose etc. E.g. if charcoal magically absorbs every bad smell that passes through the bag, is it plausible that enough of the smelly-gasses would diffuse or convect through the bag & room? Commented Jun 23, 2019 at 16:12
• FWIW: There's a limit to how much "stuff" the charcoal would be able to adsorb, and the rate at which it approached that limit would depend on how much "stuff" was in the air. Commented May 22, 2020 at 18:13
• Typical air velocities in rooms are of order 0.1 m/s based on the link below. I guess you could use that and multiply by the cross sectional area of your filter to get volume of air/second. designingbuildings.co.uk/wiki/Indoor_air_velocity Commented May 22, 2020 at 20:18