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.