## 5 Results  
### Respiratory Droplets Emission  
From the evidence and data examined in Section 3, it is plausible to assume that droplet emission in smoking and vaping (at least MTL style) can be reasonably inferred from outcomes of studies in Table 2 with comparable exhaled tidal volumes (see Table S2), including outcomes of studies mentioned previously that examined breath holds.  
The studies we summarized and listed in Table 2 only involve mouth breathing, but they share some common respiratory features with vaping and smoking: oral inspiration with usage of MPs (in vaping), as well as qualitatively similar exhalation velocities and respiratory parameters, namely inhalation/exhalation times and tidal volumes. However, there are also differences: smoking and vaping do not involve the nose occlusion of these experiments, but involve suction which the subjects of the latter experiments did not experience. While the absence of NCs would imply a tidal volume very close to rest values in MTL smoking and vaping, this absence is compensated by the increase due to the need to overcome airflow resistance through suction. The decrease of droplet emission from the mouth/oropharynx hold in MTL topography (absent in normal breathing) was a detected outcome in two of the studies listed in Table 2. We have then the following inferences regarding emission of respiratory droplets:  
* **MTL vaping and smoking** (and even DTL vaping not involving deep inspiration). The outcomes displayed in Table S2 and Table 2 suggest that exhaled respiratory particles (droplets or nuclei) in mean tidal volumes \(V_{T}=700\)-\(900\,\text{cm}^{3}\) are overwhelmingly in the submicron range (typically peaking at \(d_{r}=0.3\)-\(0.8\,\text{\mu m}\)), with respiratory particle number densities well below \(n_{r}=1\,\text{cm}^{-3}\) and a small rate of droplet emission. Assuming \(V_{T}=0.75\) L, we have \(N_{r}=6\)-200 per exhalation. Since the distribution of \(N_{r}\) in the 10 outcomes listed in Table 2 is strongly skewed towards the range \(N_{r}<30\) with only three studies reporting \(N_{r}>150\), the median value \(N_{r}=40\) and median deviation 67.28 provide a more representative description than the mean value \(N_{r}=79.82\) and standard deviation 74.66. We also assume that the wide individual variation reported in these respiratory studies should also apply to vaping, including the existence of a small minority of outlier individuals that can be thought of as \"super emitters\" reaching over \(N_{r}\sim 500\)-1000 per exhalation.
* **DTL vaping**. It involves a spectrum of deeper respiratory intensity than MTL vaping and thus should involve a higher rate of droplet emission. A reasonable estimation of emitted droplets in the DTL regime is furnished by the intense DTL (2-3 L exhalation) breathing at fractional residual capacity in [95] and by high end emitters in [90; 98], leading to possible emission rates approaching 1000/L. However, this style of vaping is practiced by a small minority of vapers (roughly 10-20%, see Figure S1), while extreme vaping with big clouds (the so-called \"cloud chasers\") is even less frequently practiced in competitions or exhibitions. Evidently, this type of extreme vaping cannot be sustained for long periods and is not representative even of DTL vapers.  
While the inferred droplet numbers in the upper end of high-intensity DTL vaping can be comparable with low end numbers for vocalizing, the latter involves modes with larger mean droplet diameters because of distinct droplet generation processes (see [92; 94; 101]).