KB Homes Model Home, Lancaster, CA. Image Source
Though I am not a chemist, to help explain, the tiles in question contain titanium dioxide which - when lighted by UV rays from the sun - degrades the nitrogen oxides, releasing oxygen into the atmosphere and leaving a veneer of nitrates on the tile. When the next rainstorm hits, the left over residue (a passivating layer) gets washed off and the oxidation process begins with renewed vigor. Of course, the lifetime use of the tile is yet to be determined, but the beauty of this process is that the former pollutant gets broken down into two seemingly harmless byproducts: oxygen which gets released back into the atmosphere and nitrates that go into the rain gutter to ground. The nitrogen-infused runoff is even marketed as a fertilizer for any garden or lawn found underneath. Pretty good, but there is little comment (or study) about the possible effects of over-fertilization or water contamination when an entire housing community sports such roofing.
Oxidation Process. Image Source.
The companies estimate that 10,800 miles of released nitrogen oxides can be cleared up by 2,000 square feet of tile, an average American roof. Yet, as you and I both know, car exhaust is not entirely made up of nitrogen oxides. In fact, it is only one part of what currently spills out the tailpipe. The bulk of emissions is carbon dioxide, responsible for most of the current debate about climate change and causation for Americans everywhere to renege any seemingly illicit relationships with the molecule. Other emissions include carbon monoxide, sulfur dioxide, benzene, formaldehyde, polycyclic hydrocarbons, and particulate matter, better known as soot. Each is, needless to say, pretty bad for both humans and environment.
Utah often tops the charts in particulate matter pollution, and so to curb or offset any pollutant in this state is a step towards responsible environmental stewardship. For anyone interested in purchasing these tiles, KB Homes estimates that an average roof will cost around $800 more than the normal concrete tile roofing. Though tiled roofs in Utah seem few and far between (except for maybe southern Utah), a bevy of new home materials that are more environmentally sound - such as Bionictile by Ceracasa, tile siding which effectively does the same thing by removing nitrogen oxides from the air - are creeping into the market.