Melissa Coffin | July 23, 2013
This blog post, originally shared in the Pharos Signal, includes information about parts of Pharos that are no longer available. Please use it for historical reference and for the other useful information it contains.
Can building products make the environment cleaner and healthier? Has the first generation of "pollution-eating," "regenerative" materials arrived?
A growing number of products are claiming to remove everything from VOCs from interior environments to auto-exhaust on highways. The apparent wizardry behind some of these products is the photocatalysis of titanium dioxide. In nanoscale form, titanium dioxide in these products' surface layers can react with ultraviolet light to catalyze a chemical reaction that breaks some pollutants down into non-hazardous molecules, carbon dioxide, and water.
European researchers have confirmed, for example, that cement enriched with titanium dioxide can reduce NOx airborne pollutant levels in a laboratory setting. But as is so often the case, lab conditions differ significantly from many real world applications. Indeed follow up experiments outdoors showed that variations in sun and wind can significantly alter performance. Further, one recent study indicates that under more real-life conditions, such as changes in humidity levels, the titanium dioxide reacted to actually create the very pollution it was intended to destroy.
Assuming that these products perform as advertised, is it reasonable to assume that the breakdown products wash harmlessly away? Not quite. The use of nano-particles is still largely unstudied for impacts on human health and environmental safety. There is some evidence that nano-scale titanium dioxide may be carcinogenic or cause genetic damage in animals. The possible release of titanium dioxide nanoparticles raises potential health concerns and nitrogen molecules from degraded pollutants in storm water runoff could increase the eutrophication problems caused by phosphate and nitrate runoffs from agriculture, lawns, and waste facilities that already clog many lakes and streams with algae and starve them of oxygen.
Finally, cement kilns are major producers of the smog producing compounds. We have not been able to find a study of how the benefits of smog-eating cement compare to the impacts of smog-eating cement production.
Pollution-eating products could play an important role in creating a truly regenerative material economy. They also could end up being just another form of greenwash. Right now, it's too early to tell and manufacturer claims seem to exceed the available data.
For more detailed information including extensive citations, see our companion blog.