The Aqueous Surface as an Efficient Transient Stop for the Reactivity of Gaseous NO₂ in Liquid Water

The heterogeneous reaction of NO₂ with water on diverse surfaces is broadly considered as a possible source of atmospheric HONO in dark conditions, but the associated mechanisms are not fully understood. We report data from first-principles simulations showing that the lifetime of the putative reactive NO₂ dimer on the surface of pure water droplets is too small to host the whole process. One infers from our results that the hydrolysis of NO₂ in clouds must be catalyzed by organic or inorganic species adsorbed on the droplets.