There have been some studies on ecigs, I think the only other concern besides nicotine may be formaldehyde, but, it's a very small concern.
Here is a graph from a study where 3 ecig cartridges were vaped in a closed off space:
On thing to note, as was noted in the study, humans naturally exhale formaldehyde, so some, or most of that was not from the ecig.
Unfortunately, mainstream media did not note that in news reports, instead they claimed ecigs have 20% of that of regular cigarettes. They obviously included the 10ppb that was already in the room before the test began, and they didn't divide the increase per cartridge vaped. If they had, the number would have been 3% based on that graph, and on top of that, as stated in the study, regular exhalation would have caused some or most of that increase. The news reports lumped in acetaldehyde with formaldehyde in the 20% statistics, even though studies showed the levels of acetaldehyde were about 1/425th of the amount in cigarettes, and all of that may have been also been from natural acetaldehyde exhalation. Acetaldehyde is formed when sugars reach a burning temperature, which shouldn't happen in a regular vape. What also wasn't noted, is that the liver breaks down alcohol into acetaldehyde, it is actually the cause of hang overs, so one beer produces waaaaay more that even a regular cigarette.
If the levels of formaldehyde concerns you, please note, regular indoor air contains up to 80ppb, while without regular formaldehyde exhalation factored in, the e cigarette produced about 3 or 4ppb
Also, the tar in cigarettes is by far the most harmful part of cigarette smoke, which there is none of in ecigs. Factoring that into the rest, that would put ecigs at >1% as dangerous as regular cigarettes. That's a number I can live with.
edit: Also many food contains formaldehyde, a pear has 38.7 60mg/k that makes the part per billion in an ecig seem like literally nothing
Artificial sweeteners also break down into formaldehyde, at much higher levels than any ecig could produce even over a long period of time, so one diet soda leads to far more exposure.
