AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Use of Piezobalance to Determine Volatility of E-Cigarette Aerosol
LANCE WALLACE, Wayne Ott, Kai-Chung Cheng, Tongke Zhao, Lynn M. Hildemann, US EPA (retired)
Abstract Number: 112 Working Group: Indoor Aerosols
Abstract Some aerosols, such as nitrates, are volatile, and can escape from filters while being collected for gravimetric analysis. Recently e-cigarette liquids containing glycerin have become popular and their aerosol emissions appear to be volatile in part. Therefore collection by filters for gravimetric analysis might not provide useful data on density or source strengths. The Piezobalance (piezoelectric microbalance) provides a real-time measure of mass accumulating on its crystal surface. It can also quantify the mass leaving the surface due to volatilization. We present a general method for determining the fraction of mass that is volatilized as a function of time. After a source containing volatile material is turned on, the Piezobalance frequency increases from a baseline to a peak value, and then decreases as the crystal loses mass. The amount of the decrease divided by the amount of the increase over a period of time is the fraction F(t) of the aerosol that is lost during that time. If the decay is followed long enough for the frequency to achieve an asymptotic (steady-state) value, then this ratio is the total volatile fraction Finf. If we have a series of measurements of the observed fraction F(t) at different times t, then we can fit an asymptotic curve of the form
F(t) = Finf(1-exp(-t/tau))
to estimate the two unknown parameters Finf and time constant tau (time from the beginning of the decay period to reach 1-1/e of the final concentration). From 88 experiments, we find that the fraction (Finf) of e-cigarette aerosol containing glycerin = 88% (SE 11%). The time constant tau = 16 (SE 4) minutes. The method is general and can apply to other aerosol mixtures. One of particular interest is aerosol from marijuana liquid.