An experimental roof coating that “eats” smog

Smog in NYC

Students at the University of California at Riverside have developed an inexpensive roof coating that in testing was able to remove 88 to 97 percent of nitrogen oxides from the air. Nitrogen oxides are responsible for the yellow, hazy appearance of smog and can be harmful to the ozone and the environment.

What exactly is this ‘miracle’ roof coating?

The roof coating is titanium dioxide, which is found in products like paint, sunblock, toothpastes and inks. Titanium dioxide, or titania as its also called, is pretty much harmless in small quantities but “possibly carcinogenic to humans” in large quantities, according to the Canadian Centre for Occupational Health and Safety. The safety of using this stuff in a roofing application is, obviously, something that would have to be studied before being mass produced and used in the roofing industry.

Safety questions aside, the results of the University study are promising. The research team, part of the Bourns College of Engineering, found the roof coating removed enough smog-inducing nitrogen oxide from the air to equal that of a car driving 11,000 miles.

How the testing was done

The researchers constructed a mini atmospheric chamber (see below), which simulates the environmental effects put on roofing tiles; e.g., rain, UV rays, humidity, etc.

Atmospheric chamber at UC Riverside

The results of the experiment were tremendously positive. The research team calculated that applying the smog-eating coating to 1 million roofs would eliminate 21 tons of nitrogen oxides per day from the air. You got to think that a roof coating like this could be invaluable in some of the smoggiest places in the U.S., such as the Los Angeles metro area.

The science behind how this all works

Nitrogen oxides are formed when fuels are burned. It then reacts with UV rays from the sun to produce what we see as smog.


The titanium dioxide applied to roofing tiles helps eliminate nitrogen oxides from the air through a catalytic reaction. The titanium dioxide reacts with the sun’s UV rays to produce a steady stream of hydroxide (OH) which in turn breaks the nitrogen oxide molecules apart. The byproducts of the reaction are water and air molecules that are able to be consumed by plants and trees.

Interestingly enough, the research found that it didn’t make a difference whether they applied a little or a lot of the coating to tiles. Both worked equally well.

Is titanium dioxide coated roofing a viable option for the future?

Early testing shows that it could be. It’s effective at cleaning the air, and it’s incredibly inexpensive. According to the researchers at UC Riverside, it would cost just $5 to coat the average size roof with titanium dioxide. Of course, don’t expect to have your local roofing contractor come over and do it for $5; travel/labor costs would drive the price way higher than that.

Roof tiles coated with titanium dioxide

Similar roofing products are already on the market, although their smog-cleaning effectiveness is questionable. There are also cool roof coatings on the market designed to reduce the heat island effect and lower heating and cooling costs.

So, roof coating products are nothing new. There’s no reason why a titanium dioxide roof coating couldn’t become a commercially available product, assuming the human and environmental safety of such a product checks out.

The UC Riverside team of scientists and engineers hopes to continue its research by testing titanium dioxide on exterior walls, driveways and roads. All testing has used white pigmented titanium dioxide, and the team hopes to also examine the effectiveness of other colors.

The testing was done exclusively on roofing tiles. There’s no mention of whether it would work on roofing shingles, slate, wood shakes or metal roofing.

Original source: UC Riverside, also referenced: