From ENN, an interesting article on research in Sweden to “[develop] ‘smart’ building materials designed to clean the air with a little help from the elements.” The concept:
UV rays hitting the titanium dioxide trigger a catalytic reaction that destroys the molecules of pollutants, including nitrogen oxides, which are emitted in the burning of fossil fuels and create smog when combined with volatile organic compounds.
Exposure to high levels of nitrogen oxides can trigger serious respiratory problems, including lung damage.
The catalytic reaction also prevents bacteria and dirt from sticking to a surface, making them easily removed by a splash of water or rain.
This is in the experimental stages, and researcher Bo-Erik Eriksson notes that there are still questions about large-scale effects and the costs of the technology. Still, this seems an idea worthy of further study.