Method for estimating the volatility of aerosols using the piezobalance: Examples from vaping e-cigarette and marijuana liquids

Abstract

We present a new method to estimate the fraction of an aerosol mixture that is volatile, as well as the time required for evaporation from a collecting surface. The method depends on an instrument (the Piezobalance) designed to measure the accumulated mass on a quartz crystal that can also measure the subsequent loss of mass due to evaporation. Commercially available e-liquids or marijuana liquids were heated using an e-cigarette device or a vapor pen, inhaled, and exhaled into a closed unventilated room (volume = 43 and 33 m3) in each of two residences. From a set of 88 measurements on an e-liquid containing 99.7% “vegetable glycerin” (VG), we estimate the fraction of the e-cigarette aerosol that is volatile to be 88% (95% confidence interval (CI) 77–99%). We also estimate the time to reach 95% of the total loss of the volatile material from the crystal to be 47 min (CI 33–60 min). For pure propylene glycol (PG) liquid, we measured extremely high rates of evaporation, finding that 8–16 rapid-fire puffs were required to reach a high concentration at just 0.65 m distance. From 124 experiments on three types of marijuana cartridges, the corresponding estimates of the volatile fraction of exhaled marijuana aerosol were normally 5–7% for liquids heated to moderate temperatures (N = 106), but 25–34% for liquids heated to high temperatures (N = 18). In the latter case, the time to reach 95% of the total loss of volatile material was on the order of 5–10 h. This indicates the importance of volatility considerations in affecting exposure to indoor aerosols from these two common sources. Secondhand exposures to PM2.5 from e-cigarette aerosols are likely to be short-lived for most scenarios, whereas we show that secondhand PM2.5 exposures from marijuana vaping aerosols can be substantial and long-lived after a single puff. Practical implicationsThe method presented here is general and can be used on almost any aerosol mixtures. It has the advantage of requiring a single instrument that can measure both the source strength and decay rates of the aerosol created by the source and also the fraction of collected material that is volatile. The method identified a major difference in the expected exposure to e-cigarette aerosols vs. marijuana aerosols from vaping. The method should be of interest to investigators who study particulate air pollution and to companies that manufacture air monitoring systems. A number of important sources of indoor aerosol mixtures (e.g., cooking, candle use, incense, etc.) remain to be investigated for volatility effects using this method.