This is been discussed before in here, but I notice this article went into a lot of detail of what was actually found in the test.
This article says that electronic cigarette free radical production are 140 times less than real cigarettes.
They tested:
A Cig-a-like, a Ego, and dripping methods.
Show the difference between, PG based vs. VG based e-liquids.
Also Nicotine vs. no nicotine e-liquids.
http://ecigarettereviewed.com/Study-e-cig-dripping-worse-for-lungs
This article says that electronic cigarette free radical production are 140 times less than real cigarettes.
They tested:
A Cig-a-like, a Ego, and dripping methods.
Show the difference between, PG based vs. VG based e-liquids.
Also Nicotine vs. no nicotine e-liquids.
http://ecigarettereviewed.com/Study-e-cig-dripping-worse-for-lungs