Comparison of 3R4F cigarette smoke and IQOS heated tobacco product aerosol emissions

Abstract

In this study, the smoke from a 3R4F research cigarette and the aerosol generated by the Heated Tobacco Product IQOS, also referred to as the Tobacco Heating System (THS) 2.2 in the literature, were compared. The objective was to characterize the gas and suspended particulate matter compositions in the mainstream smoke from a combusted 3R4F cigarette and in the aerosol generated by IQOS during use. The results indicated that the determined aerosol emissions from IQOS were notably lower than in the cigarette smoke under a Health Canada Intense puffing regimen. As an interesting detail in this study, the maximum nicotine concentrations within a puff were practically the same in both the 3R4F smoke and the IQOS aerosol, but the average concentration was lower for the IQOS aerosol. For both products, water constituted a significant proportion of the particulate matter, although it was substantially higher in the IQOS aerosol. Furthermore, combustion-related solid particles observed in the 3R4F smoke contained elements such as carbon, oxygen, potassium, calcium, and silicon. In contrast, IQOS aerosol particulate matter was composed of semi-volatile organic constituents with some minor traces of oxygen and silicon. The particulate matter found in the IQOS aerosol was volatile, which was especially noticeable when exposed to the electron beam of the scanning electron microscope (SEM) and Transmission Electron Microscope (TEM).

Keywords: Combustible cigarette; Heated tobacco; Low emissions; Particulate matter; Volatile matter.

Fig. 1

Schematics of the experimental setup. 1) PDSP inlet line connector (with a tobacco product) inside the plastic box, 2) PDSP outlet, 3) cross-connector at the location of hot dilution and 4) cross-connector splitting the sample flow for the two sampling lines and an exhaust line

Fig. 2

Comparison of gas mass concentrations (mg/m³) for 3R4F smoke and IQOS aerosol at 20 °C. The concentration ratio IQOS / 3R4F [%] is displayed

Fig. 3

Comparison of the gaseous and particulate matter emissions from 3R4F and IQOS. The values are extracted from the results of this study (Table 1) and literature (Table 2). The comparison of particulate matter emissions is marked with green circles in the figure. IQOS A: NO_x, B: C₂H₄O, C: CO, D: C₁₀H₁₄N₂, E: TPM; 3R4F a: NO, b: HCN, c: NO_x, d: C₁₀H₁₄N₂, e: C₂H₄O, f: TPM, g: CO

Fig. 4

Picture showing the filters with the collected particulate matter of IQOS aerosol and 3R4F smoke. Filter (a) was obtained after using 17 IQOS heated tobacco sticks. Filters (b) and (c) were obtained after smoking 4 and 8 3R4F cigarettes, respectively. The dilution ratio was the same for all tested samples

Fig. 5

Elements observed in the tobacco wrap papers of the studied products (3R4F and IQOS). The tobacco wrap paper in IQOS tobacco sticks (middle figure) had two layers: The outer paper was similar to the 3R4F paper (top), whereas the inner layer appeared to be an Al foil (bottom). The major difference in the paper was that potassium was not observed in the IQOS paper. The calcium was found to be attributed to the paper fillers and pigments. The platinum signal is attributed to the conductive coating of the samples

Fig. 6

Elements observed in the tobacco material from a 3R4F cigarette (top) and from an IQOS tobacco stick (bottom). The observed elements are typical for living plant organisms. The platinum signal is attributed to the conductive coating of the samples

Fig. 7

SEM micrograph of 3R4F smoke sample. Several individual particles are visible as pale grey coloured areas on the carbon film. Scale bar is 1 µm, testing at 20 °C

Fig. 8

STEM analysis of an individual 3R4F smoke particle in Fig. 7. On top is a HAADF micrograph (scale bar is 20 nm, testing at 20 °C) and at the bottom are the EDX elemental maps of the observed elements (Oxygen (O), Magnesium (Mg), Aluminium (Al), Silicon (Si), Potassium (K), and Iron (Fe)). Copper is omitted as it arises from the grid. The EDX maps show typical uniform distribution of multi-elemental composition of particles observed in the in-organic 3R4F samples

Fig. 9

Dark field STEM micrograph and EDX elemental maps for the observed elements of a 3R4F smoke particle (scale bar is 500 nm, testing at 200 °C). Two larger carbon-rich particles are indicated with rectangles. The elemental maps show imbedded in these two larger particles several smaller particles having multi-component elemental composition. Otherwise, the elements are those found in the tobacco samples from a 3R4F cigarette (see Fig. 6)

Fig. 10

SEM micrographs (a,b) and TEM/EDX (c,d) analysis of the collected particulate matter from 3R4F smoke (sampling at high gas phase concentration of smoke), which was heated to 200 °C for an hour in a furnace in an air atmosphere to vaporize the excess carbonaceous material. The grid sample prior heating is shown in (a). The copper grid and carbon foil areas are indicated with lines in the figure. The whole sample is covered with featureless organic material, no individual particles are visible. In (b) is the SEM micrograph of the sample after heating showing several particles (some indicated by arrows). According to the TEM analyses (c, d), the particles (some indicated by arrows in (c)) composed mainly of potassium (K). The X-ray spectrum in (d) is measured from the particle visible inside the circle in (c)

Fig. 11

SEM micrograph of the IQOS aerosol sample collected at 20 °C. The aerosol appears as agglomerate chains (some indicated by arrows) on the carbon film

Fig. 12

STEM/EDX elemental maps of an IQOS low mass aerosol sample. In (a) is a HAADF micrograph showing analysed frame after EDX mapping. The arrow in (a) and the corresponding silicon map indicate strong silicon diffusion along the carbon foil during the EDX mapping. The elemental maps are rather noisy. The observed particles in elemental maps are indicated by circles. Aluminium and calcium particles seem to be oxides. Silicon map is also in oxide form as there is a weak increase in oxygen content towards the edges of the frame (similar as with silicon)

Fig. 13

SEM micrographs of a sample of the collected particulate matter from the IQOS aerosol, which was used in the heating experiment at 200 °C. (a): the collected material is shown prior to heating and (b): after heating showing film-like structures that were hardly visible in SEM

Fig. 14

TEM micrograph (a) and STEM HAADF image (b) of a sample of the collected particulate matter from the IQOS aerosol heated at 200 °C in a dry air flow for one hour. The X-ray spectrum in (c), and its magnification below, show the elemental content of the sample. The deposited particulate matter in (b) appeared to be composed mainly of carbon and oxygen (originating from the glycerol additive) together with nitrogen (nitrogen map given in inset in b). In addition, small amounts of Si, Ca and Fe were observed in the heated sample. The (amorphous) grainy structure of the sample may be due to small Fe clusters produced during the heating