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Published on June 5th, 2014 | by Tina Casey


Students Invent Smog-Eating House — For Only $5!

June 5th, 2014 by  

A team of students has calculated that for the low cost of $5.00, your home could be transformed into a smog-eating house that could eliminate pollution-causing nitrogen oxides from the air just by sitting there. The secret sauce is a coating of titanium dioxide (TiO2), and $5.00 reflects the cost of just enough TiO2 to coat the roof tiles of a typical home.

Smog-eating coatings are not exactly a brand new thing (see here and here, for example), but the real breakthrough is a method that the students devised for calculating the amount of nitrogen oxides that can be removed.

That’s a key point because it makes all the difference between a feel-good coating and a useful investment of your $5.00.

smog eating house

Courtesy of College of Engineering (TiO2 tiles l., c., uncoated tile r.).

What Difference Can A Smog-Eating House Make?

Plenty. The students, from the University of California – Riverside’s Bourns College of Engineering, calculated that the annual equivalent removal for a typical TiO2-coated roof would be the nitrogen oxides emitted by a car driven 11,000 miles yearly.

That’s because TiO2 is a photocatalyst, meaning that it interacts with sunlight to break down nitrogen oxides and other organic matter in smog (kind of the reverse of what happens in photosynthesis). The photocatalytic effect can reach matter floating near the coated surface, as well as matter that actually comes into contact with the surface.

As a catalyst, TiO2 does not get “used up” during the process.

When you add up the numbers, that’s pretty impressive. The figures work out to 21 tons of nitrogen oxides removed daily per one million TiO2-coated roofs.

By way of comparison, the nitrogen oxides load in southern California is about 500 tons daily, so 21 tons is a pretty good chunk (specifically, that area is the South Coast Air Quality Management District, which covers Orange County as well as urban parts of Los Angeles, Riverside and San Bernardino counties).

How To Measure Smog-Eating Tiles

To get a read on the efficiency of a smog-eating house, the students cobbled together a sealed environment from wood, Teflon, and PVC piping.

They placed TiO2-coated tiles in the chamber and connected it to a source of nitrogen oxides. When the chamber was exposed to ultraviolet light, the TiO2 was activated, just as it would be under natural sunlight, and it began to break down the nitrogen oxides.

The results were impressive. The readings indicated that the coated tiles removed from 88 percent to 97 percent of the nitrogen oxides.

Although there’s at least one essential caveat — the experiment did not take windy conditions into account, for example — the students did make one discovery that could lead to the more efficient use of titanium dioxide coatings.

They found that the amount of nitrogen oxides removed did not vary, no matter thickly the TiO2 was applied. Specifically, they found that one tile with a relatively thin coat removed as much as another tile that had about 12 times more.

Titanium Dioxide To The Rescue

TiO2 is a common substance (think: white paint, cosmetics, etc.) that has been playing a big role in clean tech, for example as an element in advanced fuel cells and photovoltaic cells.

In regards to solar cells, TiO2 recently popped up in a new development from Northwestern University that we dubbed a “coal-killing solar cell,” based on the mineral perovskite.

The smog-eating house angle first came to our attention back in 2011, when Alcoa rolled out a TiO2 coating in combination with its proprietary pre-painted aluminum architectural panels.

We’re not familiar with Alcoa’s methodology, but according to the company’s calculations a typical building with about 10,000 square feet of coated panels would offset about four cars daily.

For the record, in tree-equivalency, that works out to about 80 trees.


Alcoa also notes that commercial building owners get a sustainability + aesthetic twofer from the coating/panel combo:

When it rains, water doesn’t bead on the surface. Instead, it collapses and runs evenly off the building, taking most of the broken down pollutants with it. That means lower maintenance costs for owners, and a consistently cleaner image for the building over time.

As for smog-eating roadways, Pureti is the US company that crossed our radar a couple of years ago. Pureti has translated its TiO2 technology for a range of applications, including glass and photovoltaic surfaces as well as cement, stucco, or concrete (think: stadiums and building facades as well as roadways).

As with Alcoa, Pureti notes that you get some additional benefits aside from the pollution-eating factor, particularly in terms of keeping exterior surfaces clean and attractive simply with ambient precipitation, without the need for power-washing or chemical treatments.

Pureti also checks in with a threefer, since you get odor control (“smoke, pet,food, or human”) too.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

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