Ozonolysis purifiers emit ozone at higher levels with the goal of oxidizing volatile organic compounds in the air, but that consequently can cause health problems as well, U.S. researchers said Wednesday.
High levels of airborne particles can aggravate asthma and cardiovascular problems, and have been linked to high death and lung cancer rates, said the researchers at the University of California in Irvine (UCI).
Excess ozone can damage the lungs, causing chest pain, coughing, shortness of breath and throat irritation, according to the researchers.
They claimed that cleaning products containing chemicals that produce a lemon smell can dirty the air when used with indoor air purifiers that produce even a small amount of ozone.
Ozone from the purifiers react in the air with unsaturated volatile organic compounds such as limonene -- a chemical added to cleaning supplies that give them a lemon fragrance -- to create additional microscopic particles, they said.
"The public needs to be aware that every air purification approach has its limitation, and ionization air purifiers are no exception," said Sergey Nizkorodov, an assistant professor of chemistry at UCI and a 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," Nizkorodov said.
The research appeared online on Wednesday in Environmental Science and Technology.
According to Nizkorodov, certain ionic purifiers emit ozone as a byproduct of ionization that is used for charging airborne particles and electrostatically attracting them to metal electrodes.
Nizkorodov and two of his students placed an ozone-emitting air purifier in the middle of a sparsely furnished office, along with a large fan to better mix the air.
At timed intervals, limonene vapor was injected in the room, and samples were taken and analyzed for ozone and particulate matter levels, Nizkorodov said.
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 about 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.
However, when limonene was added, 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 made little change in the overall particle level, Nizkorodov said.