Sprayed Water Microdroplets Are Able to Generate Hydrogen Peroxide Spontaneously

Ultrapure N 2 gas was bubbled through water, and the humidified output containing undetectable concentrations of ozone filled a closed chamber in which 18 MΩ-cm water was sprayed through a silica capillary to form microdroplets. Analysis of the collected microdroplets by NMR spectroscopy showed the presence of hydrogen peroxide at a concentration level ranging from 0.3 to 1.5 μM depending on the flow conditions. This was confirmed using a spectrofluorometric assay. We suggest that this finding establishes that when sprayed to form microdroplets, water has the ability to produce hydrogen peroxide by itself. When the N 2 gas is replaced by compressed air or O 2 gas, the concentration of hydrogen peroxide is found to increase, indicating that gas–surface interactions with O 2 in aqueous microdroplets promote the formation of hydrogen peroxide.