Ozone, friend or foe?

As an engineer involved in the business of indoor air purification I have interest in all technologies that could benefit and improve the effectiveness of air purifiers. Ozone certainly is interesting as there are many claims for its ability to sanitize and deodorize. There is much debate and scientific data on ozone so let’s take a look.

Stratospheric ozone
In these times, we have become educated to the protection received from the earth’s upper stratospheric layer in shielding our planet from the sun’s harmful ultraviolet rays. Few, if any, appear to disbelieve the scientific studies regarding the beneficial effects of ozone in our stratosphere. Ozone in the stratosphere is mostly produced from ultraviolet (UV) rays reacting with oxygen and is often referred to as "good ozone".

Tropospheric ozone
In the lower atmosphere (troposphere) UV rays not only react with oxygen to produce ozone, they also reacts with products of combustion and with volatile organic compounds (VOC’s) that we release into the atmosphere. This combination of reactions can lead to high concentrations of ozone in certain densely populated and industrial areas. The National Ambient Air Quality Standard (NAAQ) maximum allowable ambient ozone level is regulated to 75ppb (parts per billion) within any 8 hour period. Tropospheric ozone is often referred to as "bad ozone".

Further discussion
Let us get one thing clear before we start looking at effects of indoor ozone. Ozone is ozone regardless of how it is produced or where it resides, if the ozone is deemed "good" it is O3, if ozone is deemed "bad" it is O3.
Apparently the intent of referring to ozone as "good" is that it is located in an uninhabited section of the atmosphere and therefore does not endanger human health and is actually beneficial in shielding us from harmful UV rays. On the other hand "bad ozone" is in the troposphere frequented by human, animal and plant life that suffers ill effects when ozone levels exceed tolerable levels.

Indoor ozone and air purifiers
Ozone has several applications in food processing, manufacturing, disinfecting, pest control, eradication of parasites, deodorizing and water purification. With all these useful applications it is easy to see how ozone air purification devices have developed and it is also easily understood why they have come under scrutiny from several regulatory bodies.

There is much documented scientific evidence regarding adverse health effects when regulatory ozone levels are exceeded. Some scientists are proposing that maximum indoor ozone levels should be lowered due to ozone’s known reactivity with certain cleaners, air fresheners and perfumes. When ozone reacts with some household cleaners and perfumes studies have shown that other toxins such as formaldehyde can be formed.

In consideration of current scientific evidence regarding the known and possible health hazards by the use of air purifiers producing ozone, I have to commend the California Air Resource Board (CARB) for pioneering the regulation of air purifiers sold in their state. In consideration of the use of ozone we should remember the motto "Do No Harm". Ozone may have useful applications but in that use we should exhibit great care. Those interested in developing ozone purification may wish to join the "International Ozone Association" http://www.io3a.org

Others that are issuing warning or cautions regarding the use of indoor air purification using ozone are:
Environmental Protection Agency (EPA) http://www.epa.gov/iaq/pubs/ozonegen.html
Arizona Department of Health Services http://www.azdhs.gov/phs/oeh/invsurv/air_qual/moldcleanup.htm
Minnesota Department of Health http://www.health.state.mn.us/divs/eh/air/ozone.htm
Texas Department of State Health http://www.dshs.state.tx.us/iaq/SchoolsGuide.shtm#Portable_a
California Department of Health http://www.propertyid.com/govbooklets/govbookletsmoldfaq.pdf
State of Michigan http://www.michigan.gov/documents/FY2002_PAC_Annual_Report_79447_7.pdf
Health Canada http://www.hc-sc.gc.ca/ewh-semt/air/in/poll/ozone/index-eng.php
State of Alaska http://www.epi.hss.state.ak.us/bulletins/docs/b1997_36.htm
Connecticut Department of Public Health http://www.ct.gov/dph/cwp/view.asp?A=3116&Q=400514
The Federal Trade Commission (FTC) http://www.ftc.gov/speeches/varney/toyour.shtm
The Hartford www.thehartford.com/corporate/losscontrol/CFLC/56ozone.pdf

For those interested in further reading (scientific data, argument and ozone safety data):
Assessing Potential Health Effects & Establishing Ozone Exposure Limits for Ozone-Generating Air Cleaners - R. Shaughnessy, Ph.D 66pages
http://www.cpsc.gov/library/foia/foia07/os/aircleaners.pdf
Indoor Air Chemistry: Cleaning Agents, Ozone and Toxic Air Contaminants - William W. Nazaroff, University of California, Berkeley 207pages
http://www.arb.ca.gov/research/apr/past/01-336_a.pdf
Ozone Regulations Assembly Bill 2276 - Applied Ozone Systems (manufacture ozone devices) http://www.appliedozone.com/ozone_news.html
Ozone safety - http://www.io3a.org/Ozone-Safety-Article.pdf
Experimental characterization of portable ion generators - P Zhao, JA Siegel* and RL Corsi, University of Texas, Austin http://www.ce.utexas.edu/prof/Siegel/papers/conference/mullen_2005_ion_ia2005.pdf