Odor Remediation of Environmental Tobacco Smoke

Odor Remediation of Environmental Tobacco Smoke

By Normand Brais, P.Eng., M.A.Sc., Ph.D.


Environmental Tobacco Smoke or ETS is a technical term which describes the contaminants released into the air when tobacco products burn or when smokers exhale. At room temperature, many of these compounds are gaseous but most are solid ash particulate and liquid droplets called aerosol.

Particles in tobacco smoke are especially problematic to remove not because of their small size (0.1 to 1 micron), but because they are coated with tar, nicotine, phenols, and many other pungent odorous compounds. They can remain airborne for hours after smoking stops.

Due to their aerosol coating, tobacco smoke particles are not dry but rather sticky and will inevitably clog the surface of any types of air filters, making them quickly wasted and thus ruling out the solution of simple filtration. Their stickiness makes them cling to walls, carpets, fabrics, and clothing, thus impregnating the environment with a lasting nasty smell.

This article describes those technical challenges and explores from a fundamental point of view the proper use of ultraviolet photo-oxidation process as a solution to remediate the odors caused by environmental tobacco smoke.


Studies have shown that cigarette smoke contains over 3,800 chemical compounds. Some of these compounds are shown in Table 1 below. Cigarette smoke aerosols are essentially condensable gases resulting from incomplete combustion. Combustion being an oxidation process, those aerosols can be rendered less sticky and turned into dry ash by completing their oxidation. Their odors would even disappear if they could be fully oxidized down to water vapor and carbon dioxide, which are odorless compounds. If one could draw the smoke cloud directly into the combustion chamber of an industrial fume incinerator at 850 Celcius for two seconds, the odorous molecules cocktail listed in Table 1 would be completely oxidized and consequently odorless. Although it would work perfectly, this solution is obviously not economically sound.


Table 1. Chemical composition of cigarette smoke

Duration of smoke production (sec)

20 sec

550 sec

Characteristics or compound

Mainstream Smoke

Sidestream smoke

Particles (number per cigarette)



a) Solid particles and aerosols









Benzo (a) pyrene









Benzo (a) fluorene



Benzo (b/c) fluorene



Chrysene, benz (a) anthracene



Benzo (b,k,j) fluorenthrene



Benzo (e) pyrene






Dibenz (a,j) anthracene



Dibenz (a,h) anthracene, ideno-(2,3) pyrene



Benzo (g,h,i) perylene






Phenols (total)






Polonium 210, pCi



b) Gases and vapors






Carbon monoxide






Carbon dioxide






Hydrogen Cyanide















Source: Introduction to indoor air quality: a reference manual, EPA/40013-91/003



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.


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.

Table 2. Chemical Bonds Strength4

Chemical Bond

Chemical Bond Average Energy (kJ/mol)

C – C


C – H


C – N


C – O


C – S


 N – H


Therefore, the chemical bonds between carbon atoms and hydrogen, nitrogen, oxygen and sulfur atoms will be broken down by UVC ultraviolet photons, resulting broken pieces of molecules. Following this process, the broken molecules can now be further oxidized to complete their combustion and reduce their odor potential.

This oxidation can be accomplished by using a higher energy ultraviolet of 185 nm wavelength called UVV, where the second V stands for Vacuum. UVV photon have an energy of 645 kJ/mole but can only propagate into a vacuum because the dioxygen molecule in the air absorbs it and as a result gets broken up into monoatomic oxygen. At normal atmospheric pressure, UVV photons are almost totally absorbed within less than 5 mm away from a standard low pressure mercury quartz lamp UVV source. These free oxygen atoms generated by the UVV light are then able to react and complete the oxidation of the broken-down tar, nicotine, and phenols molecules.

The end products of this photo-oxidation process are then dry non-sticky ashes particles that can now be captured by adequate standard filters. This way the odors are eliminated by the oxidation process and the dry resulting particles removed by filtration.

The proper sizing to avoid oversizing of photo-oxidation system is of utmost importance. Should there be nothing to react with, the UVV generated oxygen atoms O* will react with dioxygen molecules O2 to produce ozone O3, another undesirable compound. Ozone is a not a stable molecule and will decompose naturally into normal dioxygen at ambient room temperature within 20 to 30 minutes depending upon relative humidity. The OSHA limit for 8 hours exposure is 0.05 ppm of ozone. Because the generation rate and the rate of decomposition of ozone in the absence of any smoke or other volatile contaminants in a given room size at an ambient temperature and ventilation rate can all be adequately calculated, it is possible to size an ultraviolet photo-oxidation system that will never exceed the OSHA safety limit.


This paper has described in detail the nature and composition of cigarette smoke and the consequential inherent shortcomings of classical filtration and electrostatic filters or air ionizers. Many years of experimental evidences backed by calculations based on cigarette smoke chemical composition show that the odor of cigarette smoke cannot be removed without altering the structure of the molecules responsible for the odors which are essentially tar, nicotine, and phenols. Besides thermal incineration, ultraviolet photo-oxidation has proven to be the most effective way to accomplish this by degrading and oxidizing those molecules. Their oxidation render the smoke particles dry and non-sticky which make them acceptable candidates for standard filtration. Care must be taken to adequately engineer the ultraviolet photo-oxidation system with respect to the room size and ventilation rates to keep the potential residual ozone well within the OSHA limit when the treated room becomes free from tobacco smoke.



The author is grateful to Francisco Doyon P.Eng. and Grégory Clément P.Eng. for sharing their experimental data on the effect of air ionizers on environmental tobacco smoke inside rooms of various scale.


  1. C.N. Davies, Cigarette smoke: generation and properties of the aerosol, J.Aerosol Sci. Vol 19, No.4, pp463-469, 1988.
  2. Hays, Gobbell, Ganick, Indoor Air Quality, McGraw-Hill,1995, p.58.
  3. Spengler, Samet, McCarthhy, Indoor Air Quality Handbook. McGraw-Hill, 2001.
  4. UWaterloo, Bond Lengths and Energies. n.d. Web. 21 Nov 2010.
  5. http://www.science.uwaterloo.ca/~cch…20/bondel.html EPA. Reference Guide to Odor Thresholds for Hazardous Air Pollutants Listed in the Clean Air Act Ammendments of 1990.
  6. EPA/600/R-92/047, March 1992.

Other articles that might interest you:

The Myth of HEPA Filtration

The Myth of HEPA Filtration

By Vigilair, www.vigilairsystems.com

High Efficiency Particulate Air filters (HEPA) are commonly used to achieve a significant dust and particulate control. Hospitals and companies operating clean room fabrication labs use these types of filters to reduce the particulate contamination to acceptable levels. Properly installed and maintained HEPA filters undoubtedly reduce airborne contaminants. But this fact has spawned the myth that environments serviced by HEPA filters are free from contamination.

Like all filters, HEPA filters have an efficiency curve with a minimum in the range of 0.1- 0.3 μm. The particle removal efficiency for 0.3 μm particulate is 99.99%. However, reports1,2,3 show that as many as 50% of installed HEPA filters operate well below their theoretical efficiency due to:

• incorrect installation resulting in air bypassing the filter bank

• damage during the installation or service of the air handler, especially in settings where maintenance staff lack the specific training needed to maintain HEPA filters.

• trapped viable organic matter (e.g. fungi, bacteria, mold) that has grown through the filters In many cases a combination of the above factors compromises the efficiency level of HEPA filters.

Another way to look at HEPA filter protection is to determine the particulate allowed to pass through the filter because of its inherent 0.01% inefficiency. Assume that conservatively the HEPA will be challenged with 10,000 particles in the size range of 0.1-0.3 micron per cubic foot of air every minute (cfm) and that this HEPA filter is rated at 1,000 cfm. This HEPA will allow 10,000 particles to pass through every minute or 14,400,000 every 24 hours of operation.

While it is possible to reduce or eliminate damage during filter installation with the implementation of training and good operational procedures, it is more difficult to deal with the problems presented by viable organic contamination. With the exception of high end cleanroom fabrication labs, many facilities using HEPA filters are not staffed with technicians who have the knowledge necessary to maintain the environment that HEPA filtration is designed to provide.

Air handlers equipped with HEPA filtration usually have both pre-filters and secondary filters upstream to protect the HEPA filters. This minimizes the load and improves the life of the more expensive HEPA filters. With this design larger particles entering the air handler are therefore removed before they reach the HEPA filter.

This filtration scenario works well until viable organic matter starts the growth process within the HVAC system. Conditioning coils, particularly the cooling coils, are ideal for culturing microorganisms. The constant temperatures, moisture and an abundant food source equate to laboratory conditions for growing and sustaining a multi-species microbial population4. Eventually these organisms will travel downstream and become entrapped by the HEPA filter.

Filters treated with an antibacterial preservative typically show less tendency to develop microbial growth5. Under ideal conditions for microbial growth the treatment will, at the best, delay the process.

It is one thing to stop a small inorganic dust particle but a completely different thing to stop a small living organism. The situation becomes even more cumbersome if moisture is finding its way to the filter. This establishes conditions on the filter media that are similarly ideal to the ones on the coil. Again, studies show that when filters are loaded with microbial growth and moisture, it is very likely that the same organisms can be found on the supply side of the filters7.

The picture shows a typical final filter located downstream from the cooling coil at a hospital. The organic growth on the upstream side of the filter is clearly visible as white and dark areas (see arrows). Condensation water coming off the coil virtually saturated the filter. Besides creating an ideal environment for organism growth, the water also increased the delta pressure across the filter adding 1″ (W.G.). It is quite clear that this filter has lost much of its protective properties and instead assumed a roll as an incubator of contamination. Unfortunately this situation is not rare and can be found in many air handlers varied environmental settings.

Severe contamination of the cooling coil and drain pans are the root cause of this condition. The contamination causes water and organisms to come off the coil surface and travel down to the final filter. Fouled and clogged drain pans act as a secondary reservoir for microbial growth.

Contaminated air handlers not only yield reduced filtration efficiency, they also may increase indoor air pollution. Studies of office buildings suggest that once filters are colonized with fungi, they produce Volatile Organic Compounds (VOCs) that are offgassed, adding to indoor air quality problems6,7, especially for building occupants that are immune compromised or suffer from allergies.

Building owners who install VIGILAIR® Air Handler Protection Systems experience clean coils and drain pans. Coils are returned to their ‘as designed’ efficiency and drain pans work as intended instead of exacerbating the problem. Filters remain dry and free from viable organisms. Microorganisms captured by the dry filter will find it difficult to survive and reproduce.

In summation, the HEPA filter is the highest efficiency filter available for HVAC systems. Like all filters there exists a determinable inefficiency that belies the myth of the HEPA as an ‘absolute’ solution to airborne contamination removal. The presence of microbial matter within HVAC systems raises the bar for contamination control of conditioned environments.

VIGILAIR® is a proven, highly effective system that provides an uncontaminated air handler environment. High efficiency Ultraviolet Germicidal Irradiation (UVGI) ensures that cooling coils are completely free from organic growth. VIGILAIR® UVGI compatible filters allow UVGI exposure of the filter surfaces which ensures inactivation of any organisms trapped on the filter surface.


1. Michele R. Evans, David K. Henderson, Infection Control in the Healthcare industry in the 21st Century, Hospital Engineering & Facilities Management 2005, Issue 2 pp. 58-62

2. Colin Perllman, Are Hospitals Getting Left Behind?, Cleanroom Technology, October 17, 2005

3. Andrew Streifel, Control Factors in Hospital Building Maintenance and Operations, Hospital Engineering & Facilities Management 2005, Issue 1 pp. 55- 58

4. R.B. Simmons, D.L. Price, J.A. Noble, S.A. Crow, D.G. Ahearn, Fungal Colonization of Air Filters from Hospitals, AIHA Journal (58) December 1997

5. D.L. Price, R.S. Simmons, S.A. Crow, D.G. Ahearn, Mold Colonization during Use of Preservative-Treated and Untreated Air Filters, Including HEPA Filters from Hospitals and Common Locations over an 8-year Period(1996-2003), Journal of Industrial Microbiology Vol. 32: 319-321

6. M. Möritz, H. Peters, B. Nipko, H. Rüden, Capability of Air Filters to Retain Airborne Bacteria and Molds in Heating, Ventilating and Air-conditionng (HVAC) Systems, Int. J. Hyg. Environ. Health 203, 401-409 (2001)

7. D.G. Ahearn, S.A. Crow, R.B. Simmons, D.L. Price, S.K. Mishra, D.I. Pierson, Fungal Colonization of Air Filters and Insulation in a Multi-Story Office Building: Production of Volatile Organics, Current Microbiology, Vol. 35 (1997)