Air purifiers producing ozone make air dirtier

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Air purifiers producing ozone make air dirtier

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.

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

and

Technology.

" 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 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 hour.

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

environment.

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.