Smog has long been a ubiquitous presence in urban areas around the world. It is a major contributor to respiratory illness and can cripple a city’s ability to function, to say nothing of it’s psychological effects. Each city approaches the problem in their own way, from high taxes on vehicles to industrial restrictions. Now, researchers have developed a specially coated roofing tile that can reduce pollutants by 88-97% on contact.
Smog is created from the exhaust of gas-burning engines like cars and motorbikes. When nitrogen oxides from engines mix with sunlight and heat, they create the lingering, persistent pollution that hangs in the air.
The World Health Organization estimates that air pollution exposure kills seven million people every year, which equals an eighth of total global deaths and makes it the single largest environmental health risk. Pollution levels are highest, with corresponding jumps in fatalities, in low- and middle-income counties, particularly in South-East Asia and the Western Pacific region. Reducing air pollution in urban areas is a critical step to saving the lives of millions of people.
Researchers coated standard ceramic roofing tiles with the titanium oxide, which is common, inexpensive, and already used in a variety of consumer products like sunscreen and toothpaste. When nitrogen oxide molecules in smog come in contact with the coating on the tiles, it sticks and breaks down into less harmful compounds. The tiles can then be washed by hose or left to be cleaned by the rain. The accumulated smog particles drain off and enter the ground, where they are a welcome source of nitrogen that helps plants grow.
Ceramic tiles are a ubiquitous material for roofing in many hot areas (though they tend to crack in areas with large temperature variations), giving this technology the potential for widespread distribution. Critically, titanium oxide is abundant and cheap. Researchers estimate adding the chemical to the roof of a standard house would cost just $5.00, and would absorb the equivalent pollution of a car driving nearly 18,000 km.
It’s difficult to pinpoint when this technology first emerged. Articles around the internet (example here) have credited students at the University of California, Riverside, with developing the technique. However, a company called Boral PR has been manufacturing and selling the tiles for several years, and a study from the University of Milan came to similar conclusions in 2012.
While the special coating is an excellent weapon against air pollution in wealthier areas of the globe, ceramic tiles are still considerably more expensive than alternatives commonly used in poorer areas of the Global South. Work is still needed to bring this innovation to some of the world’s most polluted cities at a cost that keeps it accessible.
One promising use of the technology that may prove to have more global reach is the introduction of titanium dioxide into paving materials for roads. In 2012, the Chicago Department of Transportation unveiled a two-mile stretch of Cermak Road they hail as the greenest street in the country, in part thanks to its smog-eating abilities. Last year, the same experiment was done by researchers at Eindhoven University of Technology and implemented in the Dutch city of Hengelo, reducing pollution up to 45% in ideal weather conditions.
Have you used anti-smog tiles on your home or worked with titanium dioxide in paving projects? Have you heard of this technology branching out into a development context? Tell us about it in the comments below.
This article first appeared in the summer of 2014.