Indoor concentrations of PM10, TVOCs, CO2 and airborne nicotine significantly increased during a vaping convention in Maryland that attracted more than 1,000 people in April 2016, markedly impairing indoor air quality. TVOCs and CO2 concentrations, moreover, further increased during the cloud competitions, a time during the convention when people competed to produce the largest aerosol plumes. The detection of airborne nicotine, a specific marker not related to other sources of air pollution, supports that e-cigarettes are a major source of indoor air pollutants during vaping conventions. To the best of our knowledge, this is the first study to measure particulate matter, gases and airborne nicotine during a vaping convention with a large number of attendees. As e-cigarettes have become more popular [2], indoor e-cigarette use is a source of concern.
An increasing number of studies have assessed the impact of e-cigarette aerosol on indoor air quality, with mixed results. A study by Schripp (2013) using an 8-m3 emission chamber found an increase in ultrafine particles (FP/UFP) and VOCs after e-cigarette use compared to background air [13]. In an observational study comparing PM2.5 measured during 1 h in the home of an e-cigarette user living in a smoke-free home, PM2.5 concentrations were higher compared to non-e-cigarette users living in smoke-free homes [10]. Another study using a laboratory room as an exposure chamber suggested that e-cigarette use was a source of secondhand exposure to nicotine but not to PM2.5 or VOCs [14]. Two doses of 70-ml e-cigarette aerosol were generated for each of the 12 experiments in this study and the mean 1-h concentration of nicotine was 2.51 μg/m3. Schober et al. showed an increase in indoor polynuclear aromatic hydrocarbons (PAHs) and airborne nicotine by mimicking a real vaping session of three volunteers using one e-cigarette each in a 45 m3 room. They found the mean PM2.5 was 197 μg/m3 during the sessions, which was 33-fold higher than the concentration in the same room without use of e-cigarettes [24]. However, most previous studies were conducted in a chamber or an artificial environment, which may be different from real-world conditions. Additionally, previous studies assessed contaminants generated by a small number of e-cigarettes. Our study is the first evaluation of indoor air quality during a real vaping convention, characterized by a large number of people using e-cigarettes simultaneously [25].
In our study, the estimated 24-h time-TWA PM10 was 1,800 μg/m3, which is 12 fold higher than the National Ambient Air Quality Standards (NAAQS) 24-h TWA PM10 limit (150 μg/m3) established by the United States Environmental Protection Agency (EPA) and 36-fold higher than the air quality standards of the European Commission (50 µg/m3). The peak PM10 concentration reached 17,860 μg/m3. Furthermore, for more than 50% of the time during the vaping convention, the PM10 concentration stayed over 10,000 μg /m3, reaching the TWA inhalable particle guideline of the American Conference of Governmental Industrial Hygienists. This indicates a potential occupational hazard to PM10 exposure for vendors attending the whole event, and similar events frequently. Outdoor mean concentrations were calculated as 33 μg/m3 (median of 12 μg/m3).
Of note, the aerosol that is released from electronic cigarettes is a mix of volatile components with a high vapor pressure, and thus it undergoes rapid changes that result in changes in size distribution. This is one of the reasons we chose to collect PM10 instead of PM2.5, although some authors (Ingebrethsen et al. [23].) have described e-cigarette aerosols in the ultrafine to fine particle sizes. Two limitations of our sampling are that we did not calibrate the SidePak at the high concentrations found at the convention, and that the SidePak is calibrated against Arizona dust, which has very different optical properties from the aerosol encountered at this venue. Nevertheless, we have reasonable confidence in our real-time PM10 results because the integrated samples collected simultaneously (using filter calibration is an accepted protocol for direct reading devices) match the SidePak TWA within 1%. In addition, real-time concentrations dropped to baseline during our time outside the venue, as shown in Fig. 2.
The median indoor TVOC concentrations of 0.13 ppm during the vaping convention was 2-fold higher than that of outdoor TVOC concentrations, suggesting that e-cigarettes are a source of TVOCs. However, we expected the difference between indoor and outdoor TVOC concentrations to be higher given the dense plumes observed during the event; the relatively small difference may reflect some problem with the sensor at the high concentrations found in the venue. Alternatively, some of the VOCs in the aerosol may have an IP greater than the lamp’s energy and were not being ionized, or we may be losing particle-bound VOCs that are filtered out by the inlet membrane. The major organic compounds found in inhaled e-cigarette aerosol are propylene glycol and glycerol [15]. Goniewicz et al. reported that toxic or carcinogenic VOCs including formaldehyde, acetaldehyde, acrolein, toluene, and p,m-xylene were found in most of the 12 types of e-cigarette aerosol generated in their study [12]. However, few studies have characterized VOCs in the exhaled aerosol.
The average indoor nicotine concentration of 124.7 μg/m3 in our study was similar to secondhand smoke nicotine measured in nightclubs and pubs when cigarette smoking was permitted in the US [26] and Canada (94.5 μg/m3) [27]. This concentration is 88 times higher than the average concentration of 1.42 μg/m3 measured in waterpipe cafes in Baltimore [28]. Secondhand tobacco smoke causes both fatal and nonfatal cardiac disease [29, 30]. Some but limited evidence also supports that e-cigarette aerosol can induce cardiovascular disease [30]. Additional studies are needed to evaluate whether individual compounds of hazardous VOCs and/or aerosol nicotine generated from e-cigarettes can impact people’s health.
Outdoor NO2 concentrations were about twice the indoor NO2, as we expected [31]. Indoor NO2 concentrations in the venue did not exceed the recommended exposure limit of 1 ppm from the National Institute for Occupational Safety and Health (NIOSH). Indoor NO2 concentration with a mean of 0.10 ppm and a peak concentration of 0.49 ppm exceeded the US National Ambient Air Quality Standards (NAAQS) of 1-h daily maximum of 100 ppb (0.10 ppm), indicating potential health risks, especially to susceptible and vulnerable populations including asthmatics and disproportionately exposed groups. The indoor NO2 concentrations, however, were possibly related to outdoor concentrations and not due to the use of e-cigarettes [25].
The CO2 concentrations are typically used as an indicator of the ventilation adequacy and occupant densities, as there was no other source of CO2 other than normal respiration in the venue based on our observation. The difference between median indoor and outdoor CO2 concentration was 422 ppm, almost 60% of the guideline of a 700-ppm difference from the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) (ANSI/ASHRAE 62-2001). The comparison of the indoor/outdoor CO2 concentration difference in the ASHRAE guideline is used to determine if air exchange and ventilation are satisfactory. Our finding indicates that if we were only to use CO2 concentrations, ventilation would be determined adequate during the convention. However, as can be seen from Fig. 1, the venue was not being ventilated adequately. This could be explained by interference of some of the aerosol components with the CO2 sensor. The sensor in our probe detects CO2 in the infrared wavelengths. Ideally, other gas molecules do not absorb light at the same wavelength as CO2, and do not affect the amount of light reaching the detector; however, some cross-sensitivity is possible, and the unknown nature of the e-cigarette mix makes interference likely. Furthermore, condensation on the sensor may lead to errant readings. Even though relative humidity (RH) was not of concern, some components of the aerosol may be condensing on the sensor. We also noted that ventilation was being reduced on purpose, especially during the competitions, as organizers called for closing of doors and windows in order to increase the visibility of the generated plumes. Higher PM10 and TVOC concentrations were closely correlated with elevated CO2 concentrations, supporting that exhaling was the major source of PM10 and TVOCs (Fig. 3). Increased indoor use of e-cigarettes and poor ventilation conditions will increase the indoor PM10 and TVOCs levels from vaping, thus aggravating the indoor air quality.
A limitation of this study was that we only conducted sampling in one vaping convention, so we cannot generalize to all scenarios. Additional variables such as ventilation rate and number of active e-cigarette users need to be quantitatively measured for future studies. In addition to PM10, TVOCs, NO2 and nicotine—the chemicals measured in our study—other potential toxic components related to indoor air quality should be assessed, including PM2.5, ultra-fine particles, individual components of VOCs such as PAHs, TSNAs, aldehydes and 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK). Another limitation of our study is that our VOC and PM instruments are typically used for screening purposes, and were not calibrated at high concentrations. Thus, the results are most useful when considering relative concentrations. In order to validate VOC results, integrated samples, such as sampling with sorbent tubes analyzed with gas chromatography may need to be used in future studies.
Our study has several strengths. First, our air sampling was conducted outside of the laboratory setting and in a real-world situation with a large number of people using e-cigarettes. This avoids potential differences associated with the aerosol generated by smoking machines and shows the real indoor air quality conditions in a vaping convention, including the amount of people, venue size, ventilation conditions, and large varieties of e-cigarette devices and e-liquids. Another strength is that we collected some integrated samples to validate our PM results. In addition, personal sampling was conducted by carrying backpacks, reflecting breathing zone exposure of convention attendees.
Our study confirms that e-cigarette aerosol is a major source of indoor air pollution of PM10, TVOCs, and air nicotine, which impairs indoor air quality. Attendees and vendors are exposed to high concentrations of hazardous pollutants during a vaping convention. The findings raise an occupational concern for e-cigarette vendors who attend vaping conventions on a regular basis in addition to being exposed at local vape shops during working hours, as well as other venue workers such as food vendors and cleaning personnel. Furthermore, extremely high concentrations of e-cigarette aerosol may cause third-hand exposure, since it can be expected that the surfaces in the exhibition hall become impregnated with deposited aerosol (solvents and nicotine), and nicotine exposure may happen via direct skin contact.
The FDA finalized a rule in August 2016 extending their regulatory authority to all e-cigarette products; however, the rule does not restrict their use in public places. A 2017 report [31] lists 12 US states and over 600 local laws restricting use of e-cigarette use in indoor public places. However, Maryland does not have a state ban, and only Baltimore city and three counties have restrictions on e-cigarettes in public places. Baltimore County, where the convention was held, has no restriction [9]. These results can inform FDA policy by supporting restricting use of e-cigarettes indoors, and recommending worker protections at vaping venues, such as vape shops and lounges. Protections may include increased ventilation, and requiring extensive cleaning procedures after each convention, to minimize potential third-hand exposure to future users of the venue.
