UPDATE***

BUY ACTIVATED CHARCOAL POWDER, TABLETS, CAPSULES, BULK

4x8 screen size perfect for air filtration
Carbon source is Coconut. Best there is, confirmed by NASA
They let you buy small quantities

$23 for a bit more than a gallon.

This will make the best air filter available. The basic design and construction is very simple, and this type of carbon is the best you can get.

Another note: A common scent masking system may cover up the smell to humans, but the weed molecules are still in the air. Activated carbon is the single most effective means to trap the organic molecules in question.

This doen't mean it's sniffer dog-proof. There will still be plenty of molecules for fido if he's close by.