Lessons Learned from Unintentional Aerosols - Safety of Nanomaterials along Their Lifecycle - page 101

5.4 CLASSES OF UNINTENTIONAL AEROSOLS

5.4.1 t oBaCCo s moke
Cigarette smoke is a familiar example of an aerosol with abundant nanoparticles.
Many of these unintentional nanoparticles, such as those in cigarette smoke, were
not known or poorly described simply because investigators lacked the technologies
to identify, count, and characterize particles smaller than 100 nm. Thus, as we look
at the literature for tobacco smoke or air pollution particulates, there is a gradual
progression, which increasingly includes a discussion and quantification of nanoma-
terials. This is not because they were absent in earlier decades but that investigators
failed to look for nanoparticles. They lacked adequate technologies. For example,
mass sampling tells us nothing about size unless an appropriate size-selective filter
is used prior to mass sampling.
Hundreds of millions of individuals are exposed to either active or passive
tobacco smoke. As shown in Figure 5.1, tobacco smoke is composed of polydisperse
particles, all submicronic (Ning et al. 2006). Figure 5.1 clearly shows that particle
numbers depend on time for both low tar and high tar cigarettes. Particle density
is so high that particle collisions and resulting agglomeration are common. As
time increases by a factor of 10, the numbers of particles are substantially reduced.
However, under all conditions, there are a significant number of particles smaller
than 100 nm.
A recent study compared conventional cigarettes with electronic cigarettes, which
generate aerosols of water, nicotine, and propylene glycol (PG) or vegetable glycerin
(VG) (Zhang et al. 2013). A scanning mobility particle sizer (SMPS) was used to

2.0 × 10 5

330s LT
2010s LT
3630s LT
330s HT
1950s HT
3570s HT

1.6 × 10 5

1.2 × 10 5

8.0 × 10 4

4.0 × 10 4

0.0

10 100 1000

Particle diameter/nm

FIGURE 5.1 Nanoparticles in environmental tobacco smoke (number concentration pro-
duced by two high tar and two low tar cigarettes with increasing time). Investigators at Hong
Kong Polytechnic University used a scanning mobility particle sizer (SMPS; TSI Model
3934) to characterize both size and particle number. (Reprinted from Sci. Total Environ ., 367,
Ning, Z. et al., Experimental study of environmental tobacco smoke particles under actual
indoor environment, 822-830, Copyright 2006, with permission from Elsevier.)