  Nearly one third of all nitrogen oxides are removed from the atmosphere
through the reactive uptake of N$_2$O$_5$ into aqueous aerosol. The primary
step in reactive uptake is the rapid hydrolysis of N$_2$O$_5$, yet despite
significant study, the mechanism and rate of this process are unknown. Here we
use machine learning-based reactive many body potentials and methods of
importance sampling molecular dynamics simulations to study the solvation and
subsequent hydrolysis of N$_2$O$_5$. We find that hydrolysis to nitric acid
proceeds through the coordinated fluctuation of intramolecular charge
separation and solvation, and its characteristic rate is 4.1 ns$^{-1}$, orders
of magnitude faster than traditionally assumed. This large rate calls into
question standard models of reactive uptake that envision local equilibration
between the gas and the bulk solution. We propose an alternative model based on
interfacial reactivity that can explain existing experimental observations and
is corroborated by explicit simulations.
