When marijuana is smoked, how does it interact with the surrounding air? (i.e. does it dissipate? How does the smoke travel, move and thin out over time?) What are the processes involved when the smoke grows in size and thins out as it expands?

I’m trying to figure out how marijuana smoke interacts with surrounding air after it is smoked. So, after someone blows out the smoke, how long does it take to dissipate into the air? I’m trying to get as technical of an answer as possible but still be easily understandable. Reason I ask is because a friend who lives in a dorm room (who DOES NOT smoke marijuana) is being accused of smoking marijuana in his room and I’m trying to help provide him a defense.

Thank you



  1. 0 Votes

    Marijuana smoke isn’t necessarily special; it’s just smoke.  Smoke is a mixture of gases, usually water vapor and whatever the burned item was (in this case marijuana).  It rises because of convection currents in the air (hot molecules are lighter than cool molecules–the smoke has been burning so of course it’s hotter than the surrounding air).  Once the smoke mixes with the air (this is an eventuality) it falls to the ground as soot or dust, but this shouldn’t be anything perceptible.  It may fall to the ground more immediately, however, if it is a humid day or if the smoke mixes with air that already has a lot of water vapor in it.  The unseen water in the air would cause the smoke to travel downward.  If your friend really doesn’t smoke, it’s possible that marijuana smoke from another user traveled up and into the ventilation system, and then “fell” into his room if in fact his room was more humid than where the smoke came from.

  2. 0 Votes

    If it was actually coming from the ventilation, it is very likely that whomever was smoking was also blowing the smoke directly into the vents, and that your friend had his fans blowing in (unawares), or that they had one helping it along on their. While the mechanics of the passive can explain it, you’ll find that most situations like that inspire a quirky ingenuity in those trying to mask their recreation. 

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