Figure 2. Photocatalytic NOx gas breakdown reactions on the surface of construction materials containing TiO2.

TiO₂ + hv → h⁺ + e^-

h⁺ + OH^- → OH^●

e^- + O₂ → O₂^-

H⁺ + O₂^- → HO₂^●

NO + HO₂^● → NO₂ + OH^●

NO₂ + OH^● → HNO₃