Ion Generating Air Purifiers

With the increase in cases of asthma and allergies, manufacturers have marketed air purifiers as an aid to improved health. They come in a variety of guises: industrial or commercial, installed or portable; ozone producers, ion generators, HEPA filtration devices, or a combination of these and other types.

An ion generator, marketed as an air cleaner or air purifier, is a device that charges air particles using a corona or UV light. This process is called ionization. The device sucks in air and blows it past an electrically charged wire (electrode). Particles in the air are attracted to the electrode where they are charged with unipolar (negative or positive) ions. When the charged particles are blown out of the ionizer, they attach themselves to other airborne particles. Over time, they increase in weight and, being too heavy to stay airborne, settle on household walls, furniture and devices. Other particles attach themselves to surfaces such as ceilings through electrostatic deposition. They remain like a thin film until disturbed, when they get briefly airborne before settling elsewhere.  Since the surfaces (on which they settle) are effectively contaminated, these surfaces require periodic cleaning.

In addition these devices do not remove from the air all the charged particles that they generate.1 Some of the particles remain airborne.

Industrial ionizer models have built-in “collecting plates” on which the charged particles are deposited. Many portable devices lack this useful feature. Some portable devices lack a fan to suck in air, and hence cannot collect airborne particles that are more than a few feet away. Dust, when sucked in, further reduces their effectiveness.

Despite these shortcomings, ionic air cleaners are useful. They remove dust particles, aeroallergens and microorganisms such as bacteria from the air. Astudy by Huber 2 found that ionic air purifiers used in a dental practice were effective at killing 99% of bacteria (including Staphylococcus aureus) collected on its stainless steel plates. However, the devices do not help to remove viruses 3 or respirable particles from tobacco smoke. 4 Ozone is a by-product of ionization.5 When Waring and colleagues studied ion generators in 2011, they found that regardless of the presence of terpenes (to be found in air fresheners), ion generators emit ozone which interacts with other constituents to increase levels of formaldehyde and nonanal (an alkyl adhehyde that is a colourless, oily liquid). A comparison of portable air cleaners found that when either a plug-in liquid or solid air freshener was present, an ion generator increased concentrations of formaldehyde even as concentrations of terpenes decreased. 6 The research teamalso noted that when ion generators functioned in the presence of a plug-in air freshener that released terpenes, the result was an increased level of ultrafine respirable organic pollutants which were less than 0.7 microns in diameter. 7,8 Ozone is toxic; degrades air quality, andis hazardous to health. Longer exposures cause increased harm.

In a separate study, Grinshpun 9 and colleagues tested ionic air purifiers and noted that the devices were very effective at reducing aerosol concentrations in confined indoor spaces. But they had both a warning and a recommendation. The warning pertained to the ratio of the volume of air to the surface area of the indoor space. The ratio has to be adequate to remove aerosol particles from the air. However, a large area would require a device that produces a high rate of ions. It could also lead to the production of ozone above the regulatory standards, increased electrostatic charge, and a rate of sedimentation that would require all surfaces be cleaned regularly. Their recommendation was that an ion device that provides a high rate of ions should be used intermittently, thus reducing both the level of ozone and the sedimentation rate. Further, the ability of the device to reduce particles would also depend on whether the particle source was in the room.

Consumers should be aware of fictitious claims made in manufacturer’s advertising, and should regard all claims with suspicion – particularly those stating that the ionic air purifier provides relief from asthma, bronchitis, hay fever and other respiratory diseases. The recent British Guidelines on the Management of Asthma clearly states that ionizers are not beneficial and “are not recommended for the treatment of asthma”.10 The EPA’s website offers a variety of resources, including a guide for the comparison of portable air cleaners. Further, the EPA warns that “an air cleaner’s ability to remove some airborne pollutants is not an indication of its ability to reduce health symptoms.” 11

References

  1. http://www.epa.gov/iaq/pubs/residair.html#types-of-air-cleaners
  2. Hubar JS, Pelon W, Strother EA, Sicard FS. Reducing Staphylococcus aureus bacterial counts in a dental clinic using an Ionic Breeze air purifier: a preliminary study. Gen Dent. 2009 May-Jun;57(3):226-9.
  3. Zuraimi MS, Nilsson GI and Magee RJ. Removing indoor particles using portable air cleaners: implications for residential infection transmission. Building and Environment 2011; 46(12):2512-19. Abstract.
  4. Offerman FJ, Sezreo RG et al. Control of respirable particles in indoor air with portable air cleaners. Atmospheric Environment 1985; 19(11):1761-71. Abstract. doi:10.1016/0004-6981(85)90003-4
  5. Sublett JL, Seltzer J et al. Air filters and air cleaners: Rostrum by the American Academy of Allergy, Asthma & Immunology Indoor Allergen Committee. J Allergy Clin Immunl 2010; 125(1); 32-38.  doi:  10.1016/j.jaci.2009.08.036
  6. Waring MS, Siegel JA and Corsi RL. Ultrafine particle removal and generation by portable air cleaners. Atmospheric Environment 2008; 42(20): 5003-14
  7. Waring MS, Siegel JA. The effect of an ion generator on indoor air quality in a residential room. Indoor Air. 2011 Aug;21(4):267-76. doi: 10.1111/j.1600-0668.2010.00696.x.
  8. Hubbard HF, Coleman BK, Sarwar G, Corsi RL. Effects of an ozone-generating air purifier on indoor secondary particles in three residential dwellings. Indoor Air. 2005 Dec;15(6):432-44
  9. Grinshpun SA, Mainelis G et al. Evaluation of ionic air purifiers for reducing aerosol exposure in confined indoor spaces. Indoor Air. 2005 Aug;15(4):235-45.
  10. British Guidelines on the Management of Asthma 2014. www.brit-thoracic.org.uk. Accessed August 2015.
  11. http://www.epa.gov/iaq/pubs/airclean.html Accessed August 2015