E-cigarette aerosol is a complex mixture of gases and particles with a composition that is dependent on the e-liquid formulation, puffing regimen, and device operational parameters. This work investigated mainstream aerosols from a 3 rd generation device, as a function of coil temperature (315 -510 °F, correspond to 157 -266 °C), puff duration (2 -4 s), and the ratio of propylene glycol (PG) to vegetable glycerin (VG) in e-liquid (100:0 -0:100). Targeted and untargeted analyses using liquid chromatography high-resolution mass spectrometry, gas chromatography, in-situ chemical ionization mass spectrometry, and gravimetry was used for chemical characterizations. PG and VG were found to be the major constituents (> 99%) in both phases of the aerosol. Most e-cigarette components were observed to be volatile or semivolatile under the conditions tested. PG was found almost entirely in the gas phase, while VG had a sizable particle component. Nicotine was only observed in the particle phase. The production of aerosol mass and carbonyl degradation products dramatically increased with higher coil temperature and puff duration, but decreased with increasing VG fraction in the e-liquid. An exception is acrolein, which increased with increasing VG. The formation of carbonyls was dominated by the heatinduced dehydration mechanism in the temperature range studied, yet radical reactions also played an important role. The findings from this study identified open questions regarding both pathways.The vaping process consumed PG significantly faster than VG under all tested conditions, suggesting that e-liquids become more enriched in VG and the exposure to acrolein significantly increases as vaping continues. It can be estimated that a 30:70 initial ratio of PG:VG in the e-liquid becomes almost entirely VG when 60-70% of e-liquid remains during the vaping process at 375 °F (191 °C). This work underscores the need for further research on the puffing lifecycle of ecigarettes.

The sulfate anion radical (SO 4 •– ) is known to be formed in the autoxidation chain of sulfur dioxide and from minor reactions when sulfate or bisulfate ions are activated by OH radicals, NO 3 radicals, or iron. Here, we report a source of SO 4 •– , from the irradiation of the liquid water of sulfate-containing organic aerosol particles under natural sunlight and laboratory UV radiation. Irradiation of aqueous sulfate mixed with a variety of atmospherically relevant organic compounds degrades the organics well within the typical lifetime of aerosols in the atmosphere. Products of the SO 4 •– + organic reaction include surface-active organosulfates and small organic acids, alongside other products. Scavenging and deoxygenated experiments indicate that SO 4 •– radicals, instead of OH, drive the reaction. Ion substitution experiments confirm that sulfate ions are necessary for organic reactivity, while the cation identity is of low importance. The reaction proceeds at pH 1–6, implicating both bisulfate and sulfate in the formation of photoinduced SO 4 •– . Certain aromatic species may further accelerate the reaction through synergy. This reaction may impact our understanding of atmospheric sulfur reactions, aerosol properties, and organic aerosol lifetimes when inserted into aqueous chemistry model mechanisms.

The popularity of vaping cannabis products has increased sharply in recent years. In 2019, a sudden onset of electronic cigarette/vaping-associated lung injury (EVALI) was reported, leading to thousands of cases of lung illness and dozens of deaths due to the vaping of tetrahydrocannabinol (THC)-containing e-liquids that were obtained on the black market. A potential cause of EVALI has been hypothesized due to the illicit use of vitamin E acetate (VEA) in cannabis vape cartridges. However, the chemistry that modifies VEA and THC oil, to potentially produce toxic byproducts, is not well understood under different scenarios of use. In this work, we quantified carbonyls, organic acids, cannabinoids, and terpenes in the vaping aerosol of pure VEA, purified THC oil, and an equal volume mixture of VEA and THC oil at various coil temperatures (100−300 °C). It was found under the conditions of our study that degradation of VEA and cannabinoids, including Δ 9 -THC and cannabigerol (CBG), occurred via radical oxidation and direct thermal decomposition pathways. Evidence of terpene degradation was also observed. The bond cleavage of aliphatic side chains in both VEA and cannabinoids formed a variety of smaller carbonyls. Oxidation at the ring positions of cannabinoids formed various functionalized products. We show that THC oil has a stronger tendency to aerosolize and degrade compared to VEA at a given temperature. The addition of VEA to the e-liquid nonlinearly suppressed the formation of vape aerosol compared to THC oil. At the same time, toxic carbonyls including formaldehyde, 4-methylpentanal, glyoxal, or diacetyl and its isomers were highly enhanced in VEA e-liquid when normalized to particle mass.

The sulfate anion radical (SO 4 •– ) is a reactive oxidant formed in the autoxidation chain of sulfur dioxide, among other sources. Recently, new formation pathways toward SO 4 •– and other reactive sulfur species have been reported. This work investigated the second-order rate coefficients for the aqueous SO 4 •– oxidation of the following important organic aerosol compounds ( k SO4 ): 2-methyltetrol, 2-methyl-1,2,3-trihydroxy-4-sulfate, 2-methyl-1,2-dihydroxy-3-sulfate, 1,2-dihydroxyisoprene, 2-methyl-2,3-dihydroxy-1,4-dinitrate, 2-methyl-1,2,4-trihydroxy-3-nitrate, 2-methylglyceric acid, 2-methylglycerate, lactic acid, lactate, pyruvic acid, pyruvate. The rate coefficients of the unknowns were determined against that of a reference in pure water in a temperature range of 298–322 K. The decays of each reagent were measured with nuclear magnetic resonance (NMR) and high-performance liquid chromatography–high-resolution mass spectrometry (HPLC-HRMS). Incorporating additional SO 4 •– reactions into models may aid in the understanding of organosulfate formation, radical propagation, and aerosol mass sinks.

No abstract