Chemistry at the air–water interface of atmospherically relevant radicals is different from both the bulk and the gas phase. In their Communication on page 5413 ff., M. F. Ruiz-López and co-workers carried out computer simulations on HO2. and O2.− radicals. The effective ionic dissociation constant of the HO2. radical and the redox potential of the O2.− radical are lower at the interface than in the bulk.