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output ozone generator to
mold and odors.
In Presence Of
Fragrant Cleaning Products, Air Purifiers
That Emit Ozone Can Dirty The Air
— Indoor air
purifiers that produce even small quantities of ozone may actually make the
air dirtier when used at the same time as household cleaning products,
scientists at UC Irvine have discovered.
"The public needs to be aware that every
air purification approach has its limitation, and ionization air purifiers
are no exception," said Sergey Nizkorodov, assistant professor of chemistry
at UCI and co-author of the study. (Credit: Image courtesy of
University of California - Irvine)
Ozone emitted by purifiers reacts in the air with unsaturated
volatile organic compounds such as limonene – a chemical added to cleaning
supplies that gives them a lemon fragrance – to create additional
microscopic particles, scientists found. Certain ionic purifiers emit ozone
as a byproduct of ionization used for charging airborne particles and
electrostatically attracting them to metal electrodes. Ozonolysis purifiers
emit ozone at higher levels on purpose with the ostensible goal of oxidizing
volatile organic compounds in the air.
This research appeared online this morning in Environmental Science
“The public needs to be aware that every air purification approach
has its limitation, and ionization air purifiers are no exception,” said
Sergey Nizkorodov, assistant professor of chemistry at UCI and co-author of
the study. “These air purifiers can not only elevate the level of ozone, a
formidable air pollutant in itself, but also increase the amount of harmful
particulate matter in indoor air.”
High levels of airborne particles can aggravate asthma and
cardiovascular problems, and have been linked to higher death and lung
cancer rates. Excess ozone can damage the lungs, causing chest pain,
coughing, shortness of breath and throat irritation.
Nizkorodov and students Ahmad Alshawa and Ashley Russell conducted
their experiment in a sparsely furnished office with a floor area of about
11 square meters. They placed an ozone-emitting air purifier in the middle
of the room along with a large fan to better mix the air. At timed
intervals, limonene vapor was injected in the room. Samples of the air were
taken about one meter from the purifier and analyzed for ozone and
particulate matter levels.
The researchers tested two types of air purifiers – a commercial
ionic purifier that emits about 2 milligrams of ozone per hour, and an
ozonolysis purifier that emits approximately 100 milligrams of ozone per
Continuous operation of the ionic purifier without limonene
resulted in a slight reduction in the average particle concentration, while
operation of the ozonolysis purifier resulted in no detectable effect on the
particle level. When limonene was added to the room, the particle
concentration shot up in both cases, on some occasions up to 100 times the
original level. Adding limonene to the room when a purifier was not
operating produced little change in the overall particle level.
The scientists also developed a mathematical model that precisely
matched their experimental observations. This model can be used to predict
whether a given air purifier will make the air dirtier in a given indoor
Scientific data on indoor air purifiers will be important as
officials begin the process of regulating air purifiers that emit ozone. In
September 2006, California Gov. Arnold Schwarzenegger signed into law
Assembly Bill 2276, requiring the California Air Resources Board to develop
regulations that will set emission standards and procedures for certifying
and labeling the devices.
“State regulators should set a strict limit on the amount of ozone
produced by air purifiers to protect the public from exposure to unhealthy
ozone and particulate matter levels,” Nizkorodov said.
The National Science Foundation funded this study.