Increasing the solar reflectance of urban surfaces reduces their solar heat gain, lowers their temperatures, and avoids transferring heat back into the atmosphere. Over 50% of the world population now lives in urban areas, and by 2040 that fraction is expected to reach 70%. Pavements and roofs comprise over 60% of urban surfaces (roofs 20 to 25%, pavements about 40%).
It's all about the benefits of titanium dioxide which not only reduces absorbed heat but additionally breaks down the nitrogen oxides that are emitted by burning fossil fuels.
This is an excellent article on the advantages to adding Tio2 to roofing and paving material:
This post goes into that age old category of ‘learn something everyday’. As regular readers of this blog know, I believe that we must do everything we can to both find alternative sources of energy and slow down the accelerating global warming trend. One of the key ways to accomplish both of these is through technological innovation.
A while ago I read an article in the New York Times that was nothing less than thrilling regarding technology and global warming. Six years ago the architect Richard Meier designed a church in Rome. The dominant design element was curvilinear white concrete. To preserve the whiteness the primary technical sponsor worked on coming up with a coating for the concrete. Six years later, the coated concrete is as white as it was when constructed, while other parts of the building have grayed due to atmospheric pollution. Now the thrilling part: the white pigment used actually ‘eats’ surrounding smog!
It was determined through testing that construction materials that contain titanium dioxide, the key ingredient in the pigment, destroy the pollutants found in car exhaust and heating emissions. In other words, titanium dioxide breaks down the nitrogen oxides that are emitted by burning fossil fuels. It is called photocatalytic cement. The maker of the pigment, Italcementi, has conducted numerous tests that have determined that some pollutants could be reduced by 20 to 70 percent. The reduction of pollutants is greatest within a distance of 8 feet. In one test a 1,000 foot stretch of highway outside Milan, with a high level of vehicular traffic was paved with titanium dioxide and it was found that there was a 60 percent reduction of nitrogen oxides at street level.
This is not only a wonderful unintended consequence, it really is an innovative technological breakthrough of the highest order in our effort to cut down or emissions that lead to global warming. Think about the concept of having the buildings and streets of cities treated with photocatalytic cement. Everyone walking down the street would be less than eight feet from sideways, streets and buildings, so the pollution people would inhale would be dramatically reduced. We could institutionalize through building codes that all concrete be coated with these materials and that regular reapplications would be mandatory.
Another positive aspect of this discovery is that one of the things that humanity has done that contributes to global warming is the vast paving of the land in the U.S. and around the world, since all this asphalt and concrete retains heat and prevents water absorption. We can now take one of our more egregious assaults on the environment and negate it to some degree. Make all our building materials act like trees!
It will take dozens, if not hundreds of such technological breakthroughs and their implementation to make substantial inroads in our effort to slow and ultimately reverse global warming. We must look at everything we do regarding energy use and consistently find ways to change our behavior and correct damage done. However, for each breakthrough we must celebrate a small victory. Three cheers for titanium oxide!
Three Cheers for Titanium Dioxide!