Smog-Eating Roof Tiles

Here is a cute example of a positive externality:

A California company is selling a “smog-eating” concrete tile roof that it says neutralizes the nitrogen oxides spewed by automobiles.

Boral Roofing says each year, one of its concrete tile roofs on a typical 2,000-square-foot house can break down the same amount of nitrogen oxides as a car’s engine typically produces during 10,800 miles of driving.

When sunlight hits the roof, it activates titanium dioxide, which breaks down the nitrogen oxides in the air into oxygen and nitrates, the company say. The tiles’ smog-fighting ability was proved in extensive laboratory testing and field studies conducted by a European Union consortium of academic and industry experts from 2002 to 2006.

The tile adds about $800 to the cost of the average 2,000-square-foot house.

Question for class discussion: What should government policy be regarding these new roof tiles?