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.

Atmospheric formic acid (FA) and acetic acid (AA) mixing ratios are often underestimated in atmospheric models, particularly over areas with high biogenic influence. We investigated the aqueous hydroxyl radical (OH) oxidation of 2methyltetrol, one of the largest components of secondary organic aerosols (SOAs) that are produced from the oxidation of isoprene, and compare its chemistry to the non-methylated C 4 polyol analogue, erythritol. We studied the kinetics and reaction products of the aqueous 2-methyltetrol (2-MT) + OH and erythritol (E) + OH reactions using 1 H and 13 C nuclear magnetic resonance spectroscopy and high-performance liquid chromatography coupled with high-resolution mass spectrometry. We found that the aqueous oxidation of aliphatic alcohols, such as E and 2-MT, are strong sources of small acids. Nearly all 2-MT is converted to FA, AA, and carbon dioxide (CO 2 ) under atmospherically relevant OH exposures. Suppression of volatile acid partitioning into the gas phase increased the observed yields of volatile products in solution by up to 80%, as quantified by experiments with low headspace. The influence of solution pH on the yields of FA and AA (or their carboxylates) was also investigated in the range of pH 2−9 for the 2-MT + OH reaction. Solution pH strongly influenced the concentrations of FA and AA via their gas−aqueous partitioning, gross production yields, and radical-induced decarboxylation reactions. The data are adequately reproduced with a kinetic model; however, different reaction mechanisms are needed for the low and high pH chemistries. Fewer stable reaction intermediates were observed for 2-MT compared to E and at high pH compared to low pH, providing insight into the decomposition pathways of 2-MT. On the basis of the substantial production yields and partitioning of FA and AA in the aqueous photooxidation of 2-methyltetrol, aqueous aging of isoprene-derived SOA may contribute to FA and AA emissions to the atmosphere that are currently missing from models.

The hydroxyl radical (OH) oxidation of the most abundant nonmethane volatile organic compound emitted to the atmosphere, isoprene (C5H8), produces a number of chemical species that partition to the condensed phase via gas-particle partitioning or form condensed-phase compounds via multiphase/heterogeneous chemistry to generate secondary organic aerosols (SOA). The SOA species in aerosol water or cloud/fog droplets may oxidize further via aqueous reaction with OH radicals, among other fates. Rate coefficients for compounds in isoprene’s photochemical cascade are well constrained in the gas phase; however, a gap of information exists for the aqueous OH rate coefficients of the condensed-phased products, precluding the atmospheric modeling of the oxidative fate of isoprene-derived SOA. This work investigated the OH-initiated oxidation kinetic rate coefficients (k OH) for six major SOA compounds formed from the high-NO and low-NO channels of isoprene’s atmospheric oxidation and one analog, most of which were synthesized and purified for study: (k 1) 2-methyltetrol [MT: 1.14 (±0.17) × 109 M–1 s–1], (k 2) 2-methyl-1,2,3-trihydroxy-4-sulfate [MT-4-S: 1.52 (±0.25) × 109 M–1 s–1], (k 3) 2-methyl-1,2-dihydroxy-3-sulfate [MD-3-S: 0.56 (±0.15) × 109 M–1 s–1], (k 4) 2-methyl-1,2-dihydroxy-but-3-ene [MDE: 4.35 (±1.16) × 109 M–1 s–1], (k 5) 2-methyl-2,3-dihydroxy-1,4-dinitrate [MD-1,4-DN: 0.24 (±0.04) × 109 M–1 s–1], (k 6) 2-methyl-1,2,4-trihydroxy-3-nitrate [MT-3-N: 1.12 (±0.15) × 109 M–1 s–1], and (k 7) 2-methylglyceric acid [MGA: pH 2:1.41 (±0.49) × 109 M–1 s–1; pH 5:0.97 (±0.42) × 109 M–1 s–1]. The second-order rate coefficients are determined against the known k OH of erythritol in pure water. The decays of each reagent were measured with nuclear magnetic resonance (NMR) and high-performance liquid chromatography-high resolution mass spectrometry (HPLC-HRMS). The aqueous photooxidation fates of isoprene-derived SOA compounds are substantial and may impact the SOA budget when implemented into global models.

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 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.