Japanese-Invented Roof Tiles Neutralize Auto Pollution

A pollution-fighting titanium-dioxide coating for roofing tiles and paving materials that was invented in Japan has gained acceptance in Europe and is now starting to catch on in the US.

A Los Angeles-area company called Boral Roofing has recently introduced its version, which it calls “Smog-Eating Tiles”. Each year a 2,000-square-foot home covered with Boral roof tiles will break down the amount of harmful nitrogen oxides (NOx) — the major component of auto exhaust pollutants — generated by about 10,000 miles of driving.

When ultraviolet light hits titanium dioxide, it releases free electrons, producing “free radicals” that actively break down pollutants like NOx gases (molecules of varying proportions of nitrogen and oxygen) or VOCs (volatile organic compounds like carbon dioxide).

As a bonus, the reaction of the nitrous oxides with the titanium dioxide produces a coating of calcium nitrate, a common garden fertilizer, that washes off in rain.

Perhaps the most important quality of titanium dioxide is that it’s economical. The coating adds only $600-$1,000 to the cost of the average roof.

Boral Roofing is probably the first construction company in the US to introduce titanium dioxide coatings to roofing tiles, but Alcoa is the first US company to produce the coating for use on the sides of buildings. Late last year it released Ecoclean, a titanium dioxide coating on aluminum panels used for covering the sides of buildings, typically highrises.

Ecoclean panels boast about the same level of NOx-fighting ability as Boral Roofing’s roof tiles. The NOx emissions of about four cars are neutralized by 1,000 square meters (about 10,500 sq-ft) of the material.

Fortunately for humanity’s prospects of turning titanium dioxide into an exciting ally in fighting pollution, it is naturally a brilliant white. That makes it an ideal coating for use in sunny regions where a major problem is reducing cooling costs.

Yet another property that expands its range of potential uses is its transparency in thin layers, making it useful on skylights and windows.

Fortunately titanium dioxide isn’t toxic. It’s already used in great abundance in toorthpaste, sunscreen and cosmetics.

Titanium-dioxide-coated building materials have gained increasingly widespread use in Japan during the past several years where Mitusubishi markets paving stones coated with the compound and Toto uses it to coat ceramic tiles. High-profile architectural projects using the material include the spacey Jubilee Church in Rome and the fantastical “Iceberg” project in Denmark.

In Europe the coating is now being mandated by many new construction regulations. In Britain and Belgium governments have launched projects to measure the real-world effectiveness of the coating in reducing pollution.

A two-year trial in the London borough of Camden, using a titanium-dioxide-containing paint made by a firm called Cristal showed up to a 65% reduction in pollution levels a short distance from a wall coated with the paint.

In Brussels Photopaq coated the interior of the Leopold II tunnel with titanium dioxide and carried out two weeks of detailed measurements of its impact on the air inside the tunnel. While the test showed promising results but Photopaq is also trying to see whether titanium dioxide may produce any harmful compounds in the process of reacting with NOx like nitrous acid or ozone. So far no significant amounts of harmful compounds have been detected being released.

“Tests in urban settings determined that some pollutants, such as nitrogen oxides, which are a major pollutant contained in exhaust gases, could be reduced by 20-70%,” concluded the European Commission’s Environmental Technologies Action Plan.

A recent UK air quality study by MIT pollution experts Steve Yim and Steven Barrett found that pollution created by traffic causes 13,000 premature deaths a year, more than the number of people killed by road accidents.

Air pollution causes more than two million deaths a year worldwide, according to WHO director of health and environment Maria Neira.

The use of titanium dioxide-coated materials may be especially important in cities like Los Angeles which continues to top the list of cities suffering most from ozone pollution caused by road traffic.