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 by product 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.
The public needs to be aware that every air purification approach has its limitation, and ionization air purifiers are no exception, Sergey Nizkorodov, assistant professor of chemistry at UCI and co-author of the study, has said. These air purifiers cannot 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 and shortness of breath and throat irritation.
Nizkorodov and two students 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 vapour 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 two 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.Source: Bio-Medicine