Heterogeneous Photochemical Reaction between H₂O₂ and NO as a Potential Source of Daytime HONO in the Atmosphere

H₂O₂ is a vital atmospheric oxidant, while its photolysis in the troposphere is negligible in conventional view. For the first time, we find that gas-phase H₂O₂ can undergo heterogeneous photolysis to produce OH radicals on the surfaces of particles such as SiO₂, Fe₂O₃, and Na₂SO₄ under solar irradiation, which further convert NO to produce HONO and NO₂. It is demonstrated that acidity can inhibit the formation of HONO and promote the formation of NO₂ significantly. Moreover, the heterogeneous photolysis of H₂O₂ is dependent on the reactivity of particles, with inert surfaces being more conducive to the generation of OH radicals. A MCM box model indicates that the HONO formation rate via the H₂O₂ heterogeneous reaction can reach 0.10 ppb·h^-1 at 9 a.m., and the relative contribution to the total daytime HONO production can account for approximately 5% at 1 p.m. Given the ubiquitous presence of SiO₂ in mineral dust particles, glass curtain walls, and terrestrial soils, these findings indicate that heterogeneous photolysis of H₂O₂ on the particle surface could be a potential source of daytime HONO. Our research also underscores the importance of atmospheric interfacial chemistry and its contribution to unknown sources of atmospheric oxidizing capacity.