- Experts say a lab study on “passive vaping” does not reflect what bystanders actually breathe in real life.
- The experiment used a machine to pump vape aerosol into a tiny sealed chamber, which critics say can exaggerate exposure levels.
- Roberto A. Sussman says bystanders inhale exhaled vapour from people, not freshly generated aerosol from a device.
- He also questions whether the flavour chemicals tested are representative of most nicotine vapes.
A recent laboratory study examining how vape emissions change over time indoors has been cited as evidence of potential risks from “passive vaping”. But experts say the experimental set-up does not reflect how vaping happens in everyday environments and could overstate bystander exposure.
The study, “Chemical Transformation of Vaping Emissions under Indoor Atmospheric Aging Processes” by Linhui Tian, Wonsik Woo, and Ying-Hsuan Lin, was published in Chemical Research in Toxicology in 2025. It investigated how vape aerosols behave when they are left to “age” in indoor air, including air containing ozone (O₃).
Roberto A. Sussman, a researcher at the National Autonomous University of Mexico (UNAM), says the experiment was competently performed but argues its conclusions should not be applied to real-world passive vaping.
He describes it as “an interesting and correctly conducted experiment,” but adds that “its results have no relevance to assess the risks of exposure of bystanders to environmental vaping aerosols”.
What the researchers did
In the study, aerosols were generated using a vaping machine rather than a human user. The machine produced vapour from different liquid formulations and injected it into a sealed chamber with a volume of 2 cubic metres — roughly comparable to a very small phone booth.
Three types of liquids were tested: a basic solvent mixture of propylene glycol and vegetable glycerin (PG/VG), the same mixture with added terpenes (aroma chemicals such as α-pinene or geraniol), and a commercial mixture described as containing terpene-like chemicals.
The researchers compared “fresh” aerosol in clean air with “aged” aerosol in air containing ozone. According to Sussman, there is some ambiguity in the paper about how long aerosols were left in the chamber, noting: “Judging from Table S2, the aging condition involved 30 minutes, but figures 1A and 1B shows aerosols standing during two hours.”
What the study reported
As summarised by Sussman, the authors measured particle size and concentration under different conditions. They reported that ozone exposure increased the formation of ultra-fine particles when terpenes were present, while aerosols made only from PG/VG were not affected in the same way.
The authors also reported that “aged” aerosols showed a lower threshold concentration for in vitro toxicity, while noting that oxidation of terpenes in secondary organic aerosols is already known to induce oxidative stress.
Based on these findings, the paper concluded that terpenes play an important role in vape emissions and suggested measures to reduce passive exposure, including designated vaping areas and improved ventilation.
Why critics say this is not “passive vaping”
Sussman’s main objection is that the study did not examine what bystanders are actually exposed to.
“The authors have not examined environmental e-cigarette aerosols, but laboratory aerosols within an unrealistic framework disconnected with real life usage of the devices,” he said.
In everyday settings, bystanders are exposed to what a person exhales after vaping, not to freshly generated aerosol straight from a device. Sussman argues that this difference is crucial. “Machine generated e-cigarette aerosol might be an appropriate proxy for inhaled (ie active) aerosol, but not for the environmental vape aerosols exhaled by users,” he said.
He points out that the human body retains much of what is inhaled. According to figures he cites, users retain “94 per cent of nicotine, 92 per cent of PG, 86 per cent of VG” and “97 per cent of aldehydes”. As a result, what is exhaled into the surrounding air is far less concentrated and chemically different from what a machine produces.
The problem with a tiny sealed space
Another key criticism relates to the size of the test chamber. Sussman says a 2 m³ enclosure does not represent real indoor spaces where vaping typically occurs. “A small 2 m³ telephone booth enclosure is completely unrepresentative of any real indoor volume in which users of e-cigarettes would normally puff,” he said.
Injecting aerosol into such a small, sealed space can create concentrations far higher than those found in homes, offices, or public venues. Sussman says this approach can lead to “artificially large concentrations” that may be orders of magnitude higher than in more realistic indoor environments, even a small office.
Are the flavours representative?
Sussman also questions whether the study’s focus on terpenes reflects typical nicotine vapes. He notes that the strongest effects reported by the authors were linked to ozone-driven reactions involving terpene flavourings.
“Another problem is the authors’ usage of terpene compounds as the only flavor chemicals,” he said. While terpene-like chemicals can be present in nicotine liquids, he says they usually appear alongside many other flavour compounds. Using terpenes alone at relatively high concentrations may be more relevant to some cannabis products than to most nicotine vapes.
A wider debate about lab realism
Sussman’s critique aligns with concerns raised in other research about laboratory methods used to assess vape exposure. In a 2025 review published in Contributions to Tobacco & Nicotine Research, Sébastien Soulet and Roberto A. Sussmann argued that some lab studies generate aerosols under conditions that do not reflect consumer use, potentially producing overheated, aldehyde-rich vapour that users would find unpleasant and avoid.
Taken together, these critiques do not dispute that chemical changes can occur in vape aerosols under certain conditions. Instead, they question whether experiments conducted in small sealed chambers with machine-generated aerosol can reliably inform discussions about real-world “passive vaping” exposure.
