However, any impurities present may also be transferred, and other substances can be formed if the device is not operating correctly, for example if the heating coil gets too hot and causes thermal degradation of the e-liquid constituents or components of the e-cigarette, or there are reactions between constituents and/or degradation products. Some of the potential impurities and degradation/reaction products are toxic.
The characteristics of the aerosol depend mainly on the power applied to the heating coil, the physical characteristics of the formulation (viscosity, wettability and so on) and the specific heat capacity of the formulation. In addition, the pressure drop, airflow rate and aerosol density, may vary between and within devices.
In an investigation of numerous cartridges and refills, formulations were tested in sixteen devices with a smoking simulator using puffing parameters derived from user puffing profiles. This delivered nicotine yields of 0.3±0.2mg – 8.7±1.0mg (from 150 puffs) and 0.5±0.1mg – 15.4±2.1mg (from 300 puffs).
A further study investigated the yields generated from 10 puffs of an e-cigarette under two puffing regimes and three durations. The findings suggested that moving from ISO to intense puffing parameters (puff volume, duration and frequency) shows around 50% increase in particulate matter (PM) and nicotine yields – much less than the approximate threefold increase seen with conventional cigarettes; but that there were significant differences between different devices in terms of sensitivity to puff duration.
Recent analysis has shown that the other alkaloids and degradation products can be present at between 0 and 4.4% of the nicotine content, but for most of the samples tested were present at 1-2% of the nicotine.
Recent analyses have reported the presence of carbonyl compounds (formaldehyde, acetaldehyde, acrolein, and o-methylbenzaldehyde), volatile organic compounds (toluene and p-, m-xylene), tobacco-specific nitrosamines (NNN and NNK) and certain heavy metals (cadmium, nickel, lead) in the aerosols produced by a range of e-cigarettes, but at levels 9-450 times lower than the typical levels in cigarette tobacco smoke.