The EPA study referenced below reported PCO devices installed in portable air cleaners did not effectively remove any of the test VOCs present at the low concentrations normally found in indoor air. This study compared the VOC-removal efficiencies of 15 air cleaners that use different types of technology. A mixture of 16 VOCs commonly found indoors was used. The report indicated that the PCO devices studied might not work as advertised. The findings also showed that some devices appear not to have fully implemented PCO technology.
A review of the literature suggests that more research is needed to further advance PCO as an effective technology in removing low levels of gaseous contaminants from the indoor air of residences. This additional research should include many important performance characteristics that influence the effectiveness of PCO cleaners, such as whether:
A decrease in light irradiance with illumination time inhibits performance. Photocatalyst deactivation in the presence of chemicals such as toluene, benzene, ethanol, or hexamethyldisilazane decreases performance. An increase in reaction temperature or water vapor content increases the PCO reaction rate. Competitive adsorption between gaseous contaminants affects the PCO reaction mechanism.
Estimated costs of PCO technology are significantly higher than those of activated carbon technology. A major factor influencing PCO costs is the intensity of UV light required at the inlet to destroy a range of VOCs at the low concentrations that typify IAQ problems.
PCO of certain VOCs may create by-products that are indoor pollutants if the system’s design parameters and catalyst metal composition do not match the compound targeted for decomposition, particularly in the presence of multiple reactive compounds commonly found in residential settings. One study reported that no detectable by-products formed during the PCO of 17 VOCs using titanium dioxide under the experimental conditions.
However, two studies on the degradation of 4 chlorinated VOCs found by-products including phosgene and chlorides. In addition, the PCO of trichloroethylene in air using titanium dioxide as the catalyst yielded as by-products carbon monoxide, phosgene, carbon dioxide, hydrogen chloride, and chlorine.
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