Aerosol studies

      Aerosol studies on smoke-free products

      Aerosol assessment, or extract assessment for oral products, is a foundational part of our smoke-free product assessment program. By design, our smoke-free products do not burn tobacco. This decision is based on the fact that the process of burning in a cigarette leads to the release of thousands of chemicals with around 100 of those classified as harmful or potentially harmful.

      Aerosol studies are the foundation of smoke-free product assessment

      Developing smoke-free products that release lower levels of harmful chemicals, and conducting aerosol studies to confirm this fact, is a critical first step for product assessment. The aerosol studies we have conducted on our inhalable smoke-free products, specifically our Tobacco Heating System (THS), confirmed the absence of combustion processes and that this lack of combustion indeed results in the release of significantly lower levels of harmful chemicals. In other words, the aerosol of THS is significantly different from the smoke of a cigarette. Importantly, THS is not risk free and contains nicotine, which is addictive.

      Determining whether a smoke-free product releases lower levels of harmful chemicals compared with cigarette smoke is critical to the next steps of our assessment program. Once this point is confirmed, we can already begin to determine whether that leads to the expected lower toxicity. Meanwhile, we continue our aerosol assessment even as we gather results from clinical studies, insights into product acceptance and consumer behavior, as well as some early results in our long-term studies.

      You can find a summary of our entire product assessment program in the PMI Science Booklet, and our publications, most of which are open-access, can be found via the publications library.

      Jump to a specific result from our aerosol studies:

      • No burning, no smoke

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      • Lower levels of harmful chemicals

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      • Liquid droplets, no solid particles

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      • No adverse effect on indoor air quality

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      • Similar results in different environments and puffing regimes

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      The Tobacco Heating System does not burn tobacco nor create smoke

      We have conducted several aerosol studies to demonstrate the absence of combustion in THS, these include temperature measurements, experiments demonstrating the absence of net exothermic processes (i.e., processes that produce more heat than is put in), and measurements of constituents that typically indicate combustion. In addition, since burning requires oxygen, we have tested THS in an oxygen-free atmosphere. The combustion demonstration provides an overview of how that works. The results of our research showed that oxygen does not play a major role in the thermo-chemical degradation (the breakdown of chemicals in the presence of heat) of the THS tobacco or the aerosol formation. In short: combustion does not occur during THS use. 

      Our studies also show that the aerosol of THS does not contain solid particles, which are produced when tobacco is burned. Smoke, on the other hand, is a kind of aerosol that is created as a result of combustion and high temperature pyrolysis, and it contains both liquid and solid particles. Thus, the aerosol of THS is not smoke.

      These are some of the main publications that support the above conclusions:

      An experimental investigation into the operation of an electrically heated tobacco system
      Investigation of solid particles in the mainstream aerosol of the Tobacco Heating System THS2.2 and mainstream smoke of a 3R4F reference cigarette
      Evaluation of the Tobacco Heating System 2.2. Part 3: Influence of the tobacco blend on the formation of harmful and potentially harmful constituents of the Tobacco Heating System 2.2 aerosol

      The Tobacco Heating System’s aerosol contains significantly lower levels of harmful chemicals compared with cigarette smoke

      We measured a number of harmful chemicals in the aerosol of THS and compared them with the levels found in the smoke of a standard reference cigarette (3R4F) according to our PMI-58 list of constituents. A 90-95% reduction on average of the levels of these harmful chemicals in THS aerosol was observed. We have published the data comparing the levels of harmful chemicals in THS aerosol and cigarette smoke. In addition to these data, we have also assessed the aerosol of THS according to the FDA-93 list compared with cigarette smoke and published these data accordingly. We have summarized the list of some of the methods we used to make this assessment, and the methods themselves can be found in our publications library.

      There is a 10-fold reduction in the number of chemical constituents identified in the aerosol of the Tobacco Heating System that were also found in cigarette smoke 

      The comprehensive chemical characterization of THS aerosol using untargeted analytical screening methods revealed that a total of 532 chemical constituents (including water, glycerin, and nicotine, which were measured using different methods) were present at concentrations at or above 100 ng/heated tobacco unit. The identities for 80% of all chemical constituents measured using untargeted screening, representing more than 96% of the total determined mass, were confirmed using purchased reference chemicals. All compounds that were detected in THS aerosol at or above 100 ng/heated tobacco unit were also found to be present in smoke from the standard reference cigarette 3R4F. Only a minority of compounds in THS aerosol were present at concentrations exceeding those measured in cigarette smoke.

      By comparing the smoke from a cigarette and the aerosol from a heated tobacco product (HTP), where both products contained the same blend of tobacco with no added flavorants, we eliminated possible confounding factors in order to focus on the difference of heating and burning. This unique approach reaffirmed our initial findings that THS aerosols hold fewer harmful chemicals than cigarette smoke, with no new tobacco-related compounds introduced as a result of heating the tobacco rather than burning it.

      Potential toxicological effects of compounds that were more abundant in the aerosol of the Tobacco Heating System than in cigarette smoke, were considered to be outweighed by the substantial decrease in harmful chemicals in THS aerosol relative to cigarette smoke

      To identify any potential new hazards presented by exposure to THS aerosol, untargeted differential screening was performed, which specifically looked for chemicals that were significantly more concentrated in THS aerosol compared with cigarette smoke of the standard reference cigarette 3R4F. The compounds that were found to be significantly higher in THS aerosol compared with cigarette smoke, including three compounds that were unique to THS aerosol (all with concentrations lower than 100 ng/heated tobacco unit), were submitted for toxicological evaluation. Four compounds were subsequently highlighted to be of potential toxicological concern. These compounds are present in the aerosol at levels below the level of toxicological concern, and the U.S. Food and Drug Administration concluded that “Although some of the chemicals are genotoxic or cytotoxic, these chemicals are present in very low levels and potential effects are outweighed by the substantial decrease in the number and levels of HPHCs [harmful and potentially harmful constituents] found in CC [combusted cigarettes].”

      Read about the research that supports these conclusions: 

      Evaluation of the Tobacco Heating System 2.2. Part 2: Chemical composition, genotoxicity, cytotoxicity, and physical properties of the aerosol
      Comprehensive chemical characterization of the aerosol generated by a heated tobacco product by untargeted screening
      Non-targeted analytical comparison of a heated tobacco product aerosol against mainstream cigarette smoke: does heating tobacco produce an inherently different set of aerosol constituents?
      Non-targeted analytical comparison of a heated tobacco product aerosol against mainstream cigarette smoke: does heating tobacco produce an inherently different set of aerosol constituents?

      The Tobacco Heating System’s aerosol consists of droplets of similar size as those found in cigarette smoke

      Droplet size is important for user satisfaction, and also for increasing the likelihood that adult smokers who choose to continue using tobacco completely switch to THS. When tobacco is heated in THS, the aerosol that is produced consists of small liquid droplets suspended in a gas. The typical size of the droplets in the THS aerosol has been engineered to be similar to the droplet and particle sizes found in cigarette smoke. The correct particle size distribution contributes to our goal of creating a sensory experience comparable to smoking.

      Learn more about these results in this publication:

      Evaluation of the Tobacco Heating System 2.2. Part 2: Chemical composition, genotoxicity, cytotoxicity, and physical properties of the aerosol
      Evaluation of the Tobacco Heating System 2.2. Part 2: Chemical composition, genotoxicity, cytotoxicity, and physical properties of the aerosol

      Using the Tobacco Heating System indoors does not adversely affect overall indoor air quality

      In addition to the aerosol studies described above, we also assess the quality of indoor air during the use of a smoke-free product by measuring air quality markers in accordance with international guidelines. Our studies showed that when THS was in use, the levels of 21 out of the 24 compounds measured did not increase beyond the levels already present as background in our dedicated indoor air quality room. Only nicotine, acetaldehyde, and glycerin were measurably higher than the background, although well below the exposure limits established in air quality guidelines.

      These are some of our main publications with results on the topic of indoor air quality:

      Air quality assessment of the Tobacco Heating System 2.2 under simulated residential conditions
      Comparison of the impact of the Tobacco Heating System 2.2 and a cigarette on indoor air quality
      Validation of selected analytical methods using accuracy profiles to assess the impact of a Tobacco Heating System on indoor air quality

      Robust product measurements that reflect real-life conditions

      Our smoke-free product development process follows the principle of “Quality by Design” as described by J. M. Juran, in addition to all the other guidelines and standards we follow for our product assessment. For us, this means that the products are specifically designed to eliminate or reduce the levels of harmful chemicals found in the aerosol compared with those found in cigarette smoke. After products leave the factory, they can stay in storage for a certain period of time and be exposed to large variations in humidity and temperature conditions, and careful thought is given to these parameters.

      We also take into account the fact that different people have different puffing behaviors, and that these behaviors may be very different from the conditions that we simulate in the laboratory. Therefore, we use a variety of puffing regimes and test our products in a range of conditions that resemble real-life scenarios to gain a better understanding. 

      Related articles
      FDA's list of HPHCs
      See the levels of toxicants in THS aerosol compared with cigarette smoke according to the FDA-93 list.
      PMI's aerosol chemistry list of 58 constituents
      We regularly monitor the levels of harmful chemicals. See which chemicals are part of the PMI 58 list.
      Untargeted assessment strategy
      See the methods and results behind our comprehensive, untargeted screening of smoke-free product aerosols.
      Tobacco Heating System mainstream aerosol compared with reference cigarette smoke
      We observed an average of 90-95% reduction of the levels of HPHCs in the THS aerosol.
      Product stability and robustness
      See how our Tobacco Heating System (THS) results stand up under different climatic conditions and puffing patters.
      Method for generating and testing aerosol from THS
      Method for generating and testing aerosol from THS
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      Indoor air quality of smoke-free products
      Discover the impact of smoke-free products on indoor air quality. Our research, conducted in controlled environments, reveals that the tobacco heating system (THS) aerosol has minimal impact on indoor air quality.
      Illustration of comprehensive chemical characterization of the THS aerosol
      Comprehensive chemical characterization of the aerosol generated by the Tobacco Heating System
      Discover how untargeted screening confirms reduced levels of harmful chemicals in THS aerosol compared to cigarette smoke.
      Why cigarette combustion is the biggest problem with smoking
      Learn how cigarette combustion releases harmful chemicals and why switching to smoke-free products may reduce the harmful effects of smoking.

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      Reduced Risk Products ("RRPs”) is the term we use to refer to products that present, are likely to present, or have the potential to present less risk of harm to smokers who switch to these products versus continuing smoking. PMI has a range of RRPs in various stages of development, scientific assessment and commercialization. All of our RRPs are smoke-free products that deliver nicotine with far lower quantities of harmful and potentially harmful constituents than found in cigarette smoke.