Accelerated Photolysis of H₂O₂ at the Air–Water Interface of a Microdroplet

Photochemical homolysis of hydrogen peroxide (H 2 O 2 ) occurs widely in nature and is a key source of hydroxyl radicals (·OH). The kinetics of H 2 O 2 photolysis play a pivotal role in determining the efficiency of ·OH production, which is currently mainly investigated in bulk systems. Here, we report considerably accelerated H 2 O 2 photolysis at the air–water interface of microdroplets, with a rate 1.9 × 10 3 times faster than that in bulk water. Our simulations show that due to the trans quasiplanar conformational preference of H 2 O 2 at the air–water interface compared to the bulk or gas phase, the absorption peak in the spectrum of H 2 O 2 is significantly redshifted by 45 nm, corresponding to greater absorbance of photons in the sunlight spectrum and faster photolysis of H 2 O 2 . This discovery has great potential to solve current problems associated with ·OH-centered heterogeneous photochemical processes in aerosols. For instance, we show that accelerated H 2 O 2 photolysis in microdroplets could lead to markedly enhanced oxidation of SO 2 and volatile organic compounds.