Chemical composition of e-cigarette aerosol

The chemical composition of e-cigarette aerosol is relatively complex, mainly including the following seven aspects.

1. Nicotine and secondary alkaloids. Nicotine is one of the main components of e-cigarette aerosol. In 2014, Goniewicz et al. [30] studied the e-cigarettes that are popular in the UK market and found that the atomization efficiency of nicotine is about 10% to 81%. For every 300 puffs of e-cigarettes, the nicotine release amount ranges from 2 to 15 mg. The delivery efficiency of nicotine from e-cigarette liquid to the human body is related to the nicotine content in the liquid, the atomization efficiency and the bioavailability. The higher the three, the higher the delivery efficiency [31]. The degradation products of nicotine are secondary alkaloids. Some studies have found that secondary alkaloids have been detected in e-cigarette aerosols containing nicotine [32].
2. Carbonyl compounds. There are literature reports on the detection of carbonyl compounds in e-cigarette aerosols [33-34]. Uchiyama et al. [35] tested 363 e-cigarette aerosols from 13 brands, among which formaldehyde, acetaldehyde, acrolein, glyoxal and methylglyoxal were detected. Carbonyl compounds were detected in samples from 9 of the 13 brands. Studies in the United States have shown that the formaldehyde content in e-cigarette aerosols is related to the power of the e-cigarette, and the higher the power, the higher the formaldehyde release in the aerosol, even exceeding that of traditional cigarettes [36].
3. Glycerin and propylene glycol. Glycerin, propylene glycol or a mixture of the two generally account for about 90% of the mass of e-cigarette liquid, and their proportion in e-cigarette aerosol is also high. Pellegrino et al. [37] found that the proportion of 1,2-propylene glycol and glycerol in e-cigarette aerosol is similar to their proportion in liquid. In addition, some studies have found that aldehydes and ketones may be produced after heating glycerin and propylene glycol [38].
4. Volatile and semi-volatile organic compounds. The aerosols produced by substances such as flavors and tobacco extracts added to e-cigarette liquids may contain volatile and semi-volatile organic compounds [39]. Laugesen et al. [40] detected p, m-xylene, propylene glycol, styrene and other substances in e-cigarette aerosols. Goniewicz et al. [41] tested 12 types of e-cigarette aerosols. For every 150 puffs of e-cigarettes, the toluene release ranged from 0.2 to 6.3 μg, and the p-(m-)-xylene release ranged from 0.1 to 0.2 μg.
5. Tobacco-specific nitrosamines (TSNA). Alkaloids in tobacco are nitrosated to form TSNA, which is a strong carcinogen. Goniewicz et al. [41] detected trace concentrations of TSNA in e-cigarette aerosols. There are reports on the analysis of N-nitrosonornicotine, 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N-nitrosoanatabine and N-nitrosoanatabine in e-cigarette aerosols [42-43]. Some studies have found that TSNA in aerosols is a prototype transfer of TSNA in tobacco liquid, and the TSNA content in aerosols can be inferred based on the TSNA content in tobacco liquid [44].
6. Polycyclic aromatic hydrocarbons and phenolic compounds. There are also reports on the detection of polycyclic aromatic hydrocarbons and phenolic compounds in e-cigarette aerosols. Schober et al. [45] analyzed the levels of e-cigarette pollutants in indoor air after 9 volunteers smoked e-cigarettes in a well-ventilated room for 2 hours and found that the concentration of polycyclic aromatic hydrocarbons that may cause cancer increased by 20%. Wang Chao et al. [46] detected 6 polycyclic aromatic hydrocarbons, including naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and fluorene, in 13 e-cigarette liquid samples. Cai Junlan et al. [32] summarized the various harmful substances detected in e-cigarette aerosols in a review, including phenolic compounds such as o-cresol, m-cresol, and p-cresol.
7. Non-metallic elements and metallic elements. Non-metallic elements and metallic elements are not only present in e-cigarette liquids, but may also be present in their aerosols. Goniewicz et al. [41] detected 3 metal elements, cadmium, nickel, and lead, in e-cigarette aerosols. Williams et al. [47] detected the non-metallic element silicon and 20 other metal elements, some of which had aerosol release levels higher than those in traditional cigarette smoke.

Reference:

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