Source: Introduction to indoor air quality: a reference manual, EPA/40013-91/003
AIR FILTRATION AND IONIZATION LIMITATIONS AGAINST TOBACCO SMOKE
Inspection of Table 1 shows that filtration alone could not handle cigarette smoke aerosols. Past experience has shown that the very small sub-micron size of the particles requires expensive HEPA filters that become tar coated and consequently clogged very quickly.
Besides classic filtration, there is another well-known way to remove sub-micron particulates from the air. Electrostatic air filters also called air ionizers have this capability. Instead of capturing particles mechanically like classic filters, the idea behind electrostatic or electronic filtration is to electrically charge the particles so that they will migrate due to electrical forces toward nearby surfaces. The same effect is obtained by rubbing a balloon on one’s hair and then sticking it to a wall. Eventually, the balloon loses its charge and falls back to the floor.
Many of the popularly called “smoke eaters” use the electrostatic principle to collect smoke particles on metal plates. The effect of ionizers on the smoke particles in the air is the same, except that they have no collecting plates and the charged particles end up sticking on the walls and surfaces of the room. It is worth noting that since the cigarette particles are sticky with tar, they will overtime coat all the room surfaces with pungent smelly yellow-brown tar extract.
Experiences with ionizers into small volumes like a hand jar is quite conclusive where the smoke particles of one cigarette can be easily dispersed toward to jar walls within 15 to 20 seconds. However when repeating the same experience in a larger volume like a 3m x 3m x 3m room, the time required to clear the air from the same amount of smoke goes up to several hours!
The explanation for this loss of effectiveness as the room size increases is rooted into basic fundamental physics of electrostatic forces: the Coulomb Law, which states that the electrical forces between charged particles decreases with the square of their distance. The Coulomb Law implies that when the distance is doubled, the electrical force is reduced by a factor of 4. When comparing the electrical forces in the small jar where the particles are within less than a few centimeters from one another and from a nearby wall with that of a room of a few meters wide, the electrostatic forces responsible for the dispersion of the smoke particles are down by the square of the ratio of 1 meter to 1 centimeter i.e. the square of 100 or 10,000 times less electrical force !
This fundamentally explains why experiment based on removing the same number of smoke particles in a normal size room takes several hours (10,000 + seconds) whereas the old sales-pitch demonstration videos performed in a hand size container takes seconds. Not only air ionization does not remove the odors due to the walls and surface tar coating effect, but their electrostatic actions are way too slow to have any significant cleaning effect except in a small jar. On top of their ineffectiveness, the fact that room surfaces will get gummy as they accumulate the electrically charged tar particles instead of using some internal cleanable capture plates like in all electrostatic smoke eater units, the air ionizers are in fact an ill-conceived version of an electrostatic smoke eater and an overall bad idea.
EFFECT OF ULTRAVIOLET LIGHT ON CIGARETTE SMOKE
When ultraviolet UV-C light photons hit a tar or nicotine molecule, they carry enough impact energy to break the interatomic chemical bonds and shatter the molecule into many smaller molecules. The energy of germicidal UV photons at 254 nm wavelength is 470 kJ/mole, an energy greater than the energy of all the chemical bonds listed in Table 2. By comparison, visible light with an average wavelength of 550 nm has photon energy of only 217 kJ/mol.
It is therefore quite clear that some bonds within tar, nicotine and phenols molecules in the smoke can be broken down by UV-C irradiation but not by visible light.