A bottle or box packed with activated charcoal, run passively (no fan) to adsorb airborne particulates and some VOCs from indoor air, a cheap complement to ventilation, not a substitute for it. Caveat, not smoothed over: the source tutorial gives no airflow or performance figures, and a passive (unpowered) filter has limited real throughput without forced air movement through the media, treat the mechanism as plausible but unverified until corroborated.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.