1) Concrete 
Noxer blocks are concrete pavers that feature a 5-7 mm thick coating of titanium dioxide (TiO2) atop a cement mortar layer. Titanium dioxide is a heterogeneous photocatalyst that uses sunlight to absorb and render oxides of nitrogen (NO and NO2) harmless by converting them to nitrate ions (NO3-), which are then either washed away by rain or soaked...