UV Lights and Formaldehyde

Regarding UV Lights…

Imagine if, in an effort to clean the air more efficiently, you were involuntarily introducing chemicals more dangerous than the ones you were trying to scrub.

Concordia University researchers have found that this exact situation is happening with a type of air filter called photocatalytic oxidation (PCO), a product already on the market. The chemical by-product? Formaldehyde, a known human carcinogen.

In a paper published in the journal Building and Environment, recent doctoral graduate Lexuan Zhong and her supervisor Fariborz Haghighat present the findings of their independent testing of the PCO systems, which filter air using ultraviolet light. This is the first time the systems have been independently tested.

“We were shocked that some of the gases to come through the system are more dangerous than the original gas,” says Haghighat, who is a professor with the Department of Building, Civil and Environmental Engineering and Concordia University Research Chair of Energy and Environment.

The battle against chemical contaminants is a challenge because gases come from so many sources–carpets, paint, treated wood. And then there are all the perfumed products we use individually. “Sometimes the concentration of gases inside the building is almost ten times more than outside,” says Haghighat. While regulations limit percentages of chemicals in the air, there are fewer governing specific technologies.

“Because it’s new technology and the public accepts whatever the industry says, if a company says it is working they believe it. But it has not been tested by a standards organization. Usually that takes time,10 to 15 years,” he says.


Concordia University. Note: Content may be edited for style and length.

Journal Reference:

Lexuan Zhong, Fariborz Haghighat. Photocatalytic air cleaners and materials technologies – Abilities and limitations. Building and Environment, 2015; 91: 191 DOI: 10.1016/j.buildenv.2015.01.033


Concordia University. “Certain air filters using photocatalytic oxidation have dangerous by-product, study shows: Dangerous by-products released by a filter already in commercial use.” ScienceDaily. ScienceDaily, 15 July 2015. <>

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