Study Finds RCI Devices Increase Indoor Ozone and Are Relatively Ineffective at Particle Removal

By Jim Rosenthal, 2/10/2007

This study shows that the RCI (radiant catalytic ionization) Air Cleaning Devices produce fairly significant levels of ozone and are less effective than a standard air filter at removing 2 micron sized particles.

Researchers at the University of Cincinnati have found that the RCI "air cleaning device" produces a significant amount of ozone and is relatively ineffective at removing particles from the air. Their study written by Sergey Grinshpun, et. al. and entitled "Control of Aerosol Contaminants in Indoor Air" was published in Environmental Science and Technology, Vol. 41, No. 2, 2007.

The product tested was supplied by Ecoquest and it combines unipolar ion emissions and photocatalytic oxidation promoted by the "radiant catalytic ionization" (RCI) technique. The researchers found that when an RCI device was placed in a 24.3 cubic meter chamber (10'X11'X8') it increased the ozone level in the chamber from 6 ppb to over 50 ppb in just 35 minutes. The FDA has established 50 ppb of ozone as the maximum allowable level in a room with an ozone generating medical device. However, currently no federal agency regulates the ozone allowed for household air cleaning devices. The researchers also found that the RCI device pushed the level of ozone in a "bathroom" sized chamber over the 50 ppb in just 5 minutes. This would indicate that the "radiant catalytic ionization" (RCI) technology has the potential to create unsafe levels of ozone in small, poorly ventilated rooms. The researchers point out that the RCI devices "were tested in non-ventilated chambers (no air exchange) as it is known that portable air cleaners are perceived to be primarily beneficial in poorly ventilated spaces."

The manufacturers and marketers of the RCI product claim that the device is effective at removing particles from the air. However, when the researchers tested the particle removal efficiency of the device, they found that after 120 minutes of continuous operation in the 10'X11'X8' chamber it was less effective than a standard pleated filter in removing 2 micron sized particles. The filter was in a system set to provide just 2.5 air exchanges per hour.

Using NACL particles of various sizes as the challenge particles the study showed that the RCI device had a Clean Air Delivery Rate (CADR) of 32.4 cfm on particles at .041 microns, a CADR of 32.1 cfm on particles at 0.13 microns, a CADR of 29.4 on 0.499 micron particles and a CADR of 23.5 on particles of 2 microns. Most homes have a higher air infiltration rate than this. In other words, in a ventilated space the net effect of running the RCI device would be zero on these particle sizes.

The researchers compared the particle removal performance of the RCI device with a MERV 8 pleated filter. The MERV 8 pleated filter is tested to have an average efficiency of greater than 70% on particles of 3 microns and above. It is not particularly effective at smaller sized particles and there are no claims made that it is. For example, in recent tests performed by LMS Technologies a MERV 8 filter had an efficiency of 5.5% on 0.4 micron sized particles and an efficiency of 59.9% on 2 micron sized particles. This study found that the RCI device was twice as effective at removing 0.4 micron sized particles as a MERV 8 filter. One would assume that this would give an efficiency for the RCI device on 0.4 micron sized particles of less than 15%. In the case of 2 micron sized particles the MERV 8 filter (with 2.5 ACH) was more efficient than the RCI device. So, in other words, the MERV 8 filter running at a moderate level of usage would do a better job at removing particles of 2 microns and above in a whole house than the RCI device could do while running continuously in a 110 square foot room.

This conclusion was supported by the fact that the researchers tested the particle removal efficiency of the HEPA (High Efficiency Particulate Arresting) filter attached to the test chamber. They found that while running the system at a rate that would provide 2.5 air changes per hour (this works out to be just 37.4 cfm) the HEPA filter was 3 times more effective at removing particles than the RCI device. Most stand alone HEPA air purifiers designed for one room use will provide approximately 100 cfm on medium. This would mean that a stand alone HEPA in this same chamber would be 8 times more effective at removing particles than the RCI device. Further comparison testing is required to confirm this conclusion.

The researchers also tested the photocatalytic oxidation process of the RCI device on cell structures. In the smaller 3'X4'X8' chamber they concluded that the high concentrations of hydroxyl radicals and other Reactive Oxygen Species (ROS) had detrimental effects on cell structures. These effects included the destruction of the outer membrane of cells, the alteration of the cell DNA and RNA, and the oxidation of enzymes causing inhibition of cell respiration and cell death. These tests were conducted on virus and bacteria samples that have relatively thin cell walls. However, Hydroxyl Radicals and other ROS's are classified as "free radicals" and have been known to have a link in humans for diseases ranging from alzheimers to heart attacks. The effects of large concentrations of airborn free radicals was not included in this research. Further testing would certainly be warranted.

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