Hydrogen peroxide forms spontaneously in water (bulk, film, or microdroplet) via reduction of dissolved oxygen at solid-water interface

Zare and co-workers have recently claimed that hydrogen peroxide is spontaneously generated on the air-water interface of sprayed microdroplets, i.e., that H2O2 forms without an external energy source or co-reactant or catalyst. Specifically, they find that the H2O2(aq) concentration in sprayed microdroplets increases by a factor of 3.5 (or 2.5) as the spray chamber's relative humidity (RH) is changed from 15 Building on these results, they imply causation for the seasonality of viral infections arising from the RH-dependent H2O2 generation in environmental microdroplets. Here, we present an alternative explanation for their observations.