Thermal-assisted photo-driven nitrogen oxidation to nitric oxide (NO) by using air as reactants is a promising way to supersede the traditional NO synthesis industry accompanied by huge energy expenditure and greenhouse gas emission. Meanwhile, breaking the N ≡ N triple bond (941 kJ•mol -1 ) in nitrogen is still challenging, and the development of efficient catalysts is highly required. Herein, Ru single atoms decorated TiO 2 nanosheets (Ru SAs/TiO 2 ) were constructed and achieved superior performance for NO photosynthesis with a product rate of 192 μmol g -1 h -1 and a quantum efficiency of 0.77 % at 365 nm. Both 15 N isotope labelling experiments and in situ near ambient pressure X-ray photoelectron spectroscopy (in situ NAP-XPS) proved the origin of NO from N 2 photooxidation. A series of in situ characterizations and theoretical calculations unveiled the reaction pathway of nitrogen photooxidation. Breaking O-O bond to form (N-O) 2 -Ru intermediates was demonstrated as the rate-determining step. Importantly, the single atomic structure was proved to inhibit the aggregation and inactivation of Ru, leading to outstanding durability.