Photometric Monitoring of Electronic Cigarette Puff Topography

Abstract

To study and monitor the adverse health consequences of using electronic cigarettes, a user's puff topography, which are quantification parameters of the user's vaping habits, plays a central role. In this work, we introduce a topography sensor to measure the mass of total particulate matter generated in every puff and to estimate the nicotine yield. The sensor is compact and low-cost, and is integrated into the electronic cigarette device to promptly and conveniently monitor the user's daily puff topography. The topography sensor is comprised of a photometric sensor and a pressure sensor. The photometric sensor measures the mass concentration of the aerosol, based on scattering of near-infrared light from airborne particles, while the pressure sensor measures the flow rate. The topography sensor was tested under various conditions including a wide range of atomizer power, puff duration, and inhalation pressure. The sensor's accuracy was validated by comparing the sensor's readings with reference measurements, and the results matched closely with the trends reported by existing studies on electronic cigarettes. An example application for tracking a user's puff topography was also demonstrated. Our topography sensor holds great promise in mitigating the health risks of vaping, and in promoting quality control of electronic cigarette products.

Keywords: aerosol; atomizer; e-liquid; electronic cigarette; nicotine; particulate matter; photometric sensor; pressure sensor; puff topography; vaping.

Figure 1

Working principle of the e-cig topography sensor. (a) Schematic of a “smart e-cigarette” equipped with a built-in topography sensor comprised of a photometric sensor, a pressure sensor, and a microcontroller unit (MCU). Example of (b) optical signal and (c) inhalation pressure collected from the photometric sensor and the pressure sensor, respectively. (d) Schematic of the photometric sensor for detecting an e-cigarette aerosol concentration.

Figure 2

A prototype smart e-cigarette with an e-cig topography sensor. (a) Integration of the e-cig topography sensor assembly with a commercial e-cigarette module. (b) Photograph of the e-cig topography sensor assembly. (c) Photographs of the core components of the sensors, compared to the size of a U.S. penny coin. (d,e) Photographs of the constructed smart e-cigarette prototype.

Figure 3

Algorithm for sensor signal processing. (a) Raw signals collected from the photometric sensor and the pressure sensor. (b) Baseline-subtracted optical signal and inhalation pressure. (c) Determination of the puff duration with a threshold on the optical signal. (d) Calculation of the numerical integral of $S\left(t\right)\sqrt{\Delta P\left(t\right)}$ during the identified puff.

Figure 4

Experimental setup for reference measurements of the mass of TPM in the puff. (a) Schematic of the experimental setup. (b) Photograph of the constructed setup with a homemade vaping machine. (c) Flow chart of the control sequences used in each measurement of e-cigarette aerosols.

Figure 5

Effects of atomizer power on the e-cigarette aerosol output. (a) Example signals acquired from the e-cig topography sensor. Plots of sensor signals for different atomizer powers specified by line styles. Solid line: 20 W; dashed line: 30 W; dotted line: 40 W. (b) Mass of TPM in the puff measured from the e-cig sensor (red) and from the reference setup (black) versus atomizer power.

Figure 6

Effects of puff duration on the e-cigarette aerosol output. (a) Example signals acquired from the e-cig topography sensor. Plots of sensor signals for different button-pusher durations specified by line styles. Solid line: 1.5 s; dashed line: 2.0 s; dotted line: 2.5 s. (b) Mass of TPM in the puff measured from the e-cig topography sensor (red) and from the reference setup (black) versus button-pusher duration.

Figure 7

Effects of inhalation pressure on the e-cigarette aerosol output. (a) Example signals acquired from the e-cig topography sensor. Plots of sensor signals for different inhalation pressures specified by line styles. Solid line: low pressure (around 300 Pa); dashed line: medium pressure (around 450 Pa); dotted line: high pressure (around 600 Pa). (b) Mass of TPM in the puff measured from the e-cig topography sensor (red) and from the reference setup (black) versus peak inhalation pressure.

Figure 8

Effects of atomizer conditions (cold or warmed-up coil) on the e-cigarette aerosol output. (a) E-cig topography sensor signals acquired during the first three puffs from the smart e-cigarette starting to operate from a cold atomizer coil. The rising edges of the optical signals are marked with arrows. (b) Mass of TPM in the puff measured from the e-cig topography sensor (red triangles), from the reference setup (black circles), and aerosol temperature (blue squares), versus the puff number, as the coil was warmed up in one trial. (c) Mass of TPM versus the puff number as the coil is warmed up with experiments repeated in three cycles. Statistic quantities (mean and standard deviations), are plotted.

Figure 9

Tracking a user’s puff topography with the e-cig topography sensor. Photograph of (a) the user testing the smart e-cigarette and (b) the display on the device showing the results after one puff. (c) Sensor signals acquired during the first puff for 20 W atomizer power. The data points for this acquisition are marked as dashed circles on the curves in (d,f,g). (d) Mass of TPM in the puff and estimated nicotine yield from multiple puffs using 20 W and 25 W atomizer power. (e) Statistical quantity (mean and standard deviations) of the user’s puff topography for 20 W and 25 W atomizer power, respectively, attained from the puffs shown in (d). (f) Puff duration and (g) peak inhalation pressure acquired from the user’s puffs using 20 W and 25 W atomizer power.