Ahh, so it sounds like you would be basically getting a mostly PG throat hit and a bit of the tobacco with it.
I had heard that before, but IIRC it doesn't change to the oxide in ecigs does it? Otherwise that would be a serious problem for the entire vaping community.
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I tried vaping pipe tobacco at 480F and 490F on my Arizer E Q to test the 477F boiling point idea. To be honest it didn't feel any different as far as the nicotine delivered than when I vape at 446F and 428F and 410F (the arizers preset temps). It was slightly more harsh and at 490F the tobacco eventually started to combust. So I am not sure what that means, you are correct on the nicotine boiling point, but possibly the point that it vaporizes out is much lower. When I do vape at the "suggested temperature" for tobacco (350F I believe) I get almost nothing. No feeling nor barely any vapor, so I think the higher temperatures are needed. Around 410-440 seems to be the sweet spot on my E Q.
PG does turn into Propylene oxide in ecigs, this is precisely what the study I refer to found unfortunately.
More of a problem still is the fact that the same study found that VG also leads to production of Glycidol, another probable carcinogen in ecig tanks. Both PG and VG were found to produce these toxic byproducts when used in an ejuice mixture, or just vaped straight without mixing it with anything else. It is a serious problem for the entire vaping community. It may be less of a carcinogenic mixture to inhale ejuice vapor than cigarette smoke - but they are still both demonstrably carcinogenic aerosol mixtures to inhale!
Man we have not been acquainted here before, but those who know me around these parts will assure you that I am not so much an amateur on these topics. The boiling point is the temperature at which the vapor pressure of the compound (liquid) is the same as the ambient pressure (whether local barometric pressure or the pressure inside a chamber under vacuum). This causes the compound to leave the liquid phase and enter the vapor phase (vaporization). The boiling point is the literal temperature at which you can expect a thin film of a given compound to vaporize.
If you heat a substance (especially a complex mixture of compounds) to a lower temperature than the boiling point of the desired active, a liquid solution will potentially have a cumulative boiling point (that is the entire solution will vaporize) that is lower, or higher, depending on the mixture of compounds and each of their respective vapor pressures etc. However when we are vaporizing dry tobacco, you then have many variables such as where the nicotine deposits are physically found in each granule/crumb of the mixture of ground tobacco and the temperature at the point that the heat source manages to impart to the material being vaporized (perhaps somebody more knowledgeable on the tobacco biology than myself might chime in on this?). You may find that even at lower nominal temps on your vaporizer than the boiling points from the scholarly literature, some nicotine enters the vapor phase due to uneven heating/nucleation points at various different sites on the load. This is what I'm talking about when I mention nicotine transfer efficiency variations above.
The problems with vaporizing tobacco at the boiling point of nicotine are as follows:
1. that temp might be hot enough to lead to combustion or pyrolisis of all/some of the load.
2. Even where 1. is not met, we can reasonably expect that a much greater amount of nicotine will enter the user's body from the same tobacco as what would be expected to enter the user from combusting said tobacco (vaporizers do not continue burning off into the air in-between inhales, they also do not degrade or decompose the nicotine into other compounds to the extent that combustion/smoking does). One might be inhaling much more nicotine when vaping tobacco at the boiling point of nicotine vs combusting it.
What I was suggesting above is that I believe that Phillip Morris' engineers may have considered this potential problem and decided to use a lower temp (so as to only partially boil some of the nicotine content out) and use a cloudy PG 'filler' rather than risk a product that gives people uncomfortable or even toxic doses of nicotine which are more difficult to dose for the user. I may be wrong on this of course, this may be coincidence.
