Ground hogs

Paving stones that soak up pollutants are being developed by researchers at
Mitsubishi Materials in Tokyo. The slabs have a concrete base topped with a
1-centimetre layer of a mixture containing titanium dioxide, zeolite and either
sand, crushed quartz or ground glass. The titanium absorbs ultraviolet light
from the Sun and allows this energy to transform nitrogen oxides into harmless
salts.