Abstract
The reactive uptake of N2O5 to aqueous aerosol is a major loss channel for nitrogen oxides in the troposphere. Despite its importance, a quantitative picture of the uptake mechanism is missing. Here we use molecular dynamics simulations with a data-driven many-body model of coupled-cluster accuracy to quantify thermodynamics and kinetics of solvation and adsorption of N2O5 in water. The free energy profile highlights that N2O5 is selectively adsorbed to the liquid–vapor interface and weakly solvated. Accommodation into bulk water occurs slowly, competing with evaporation upon adsorption from gas phase. Leveraging the quantitative accuracy of the model, we parameterize and solve a reaction–diffusion equation to determine hydrolysis rates consistent with experimental observations. We find a short reaction–diffusion length, indicating that the uptake is dominated by interfacial features. The parameters deduced here, including solubility, accommodation coefficient, and hydrolysis rate, afford a foundation for which to consider the reactive loss of N2O5 in more complex solutions.
Highlights
The reactive uptake of N2O5 to aqueous aerosol is a major loss channel for nitrogen oxides in the troposphere
We find a short reaction–diffusion length, indicating that the uptake is dominated by interfacial features in the vicinity of the liquid/vapor interface
The interfacial adsorption indicates N2O5 is relatively hydrophobic, consistent with previous observations of its relatively weak solvation[13,15,51]. This free energy profile dictates that the equilibrium density profile of N2O5 would be inhomogeneous in the vicinity of the liquid–vapor interface, a feature neglected in typical kinetic models
Summary
The reactive uptake of N2O5 to aqueous aerosol is a major loss channel for nitrogen oxides in the troposphere. Using training data obtained from density functional theory, this study found that the hydrolysis rate was sufficiently fast at the interface that bulk phase partitioning cannot kinetically compete, and the uptake was determined by a competition between interfacial hydrolysis and evaporation These calculations found modest agreement with experimental uptake coefficient values, consistent with the expected qualitative accuracy of the model employed. It has been shown that MB-pol[26,27] yields quantitative accuracy for a variety of molecular properties across water’s phase diagram[26–43] including at the water-vapor interface[44] Extensions of this modeling framework to describe mono-atomic ions and small molecules in aqueous solutions as well as generic mixtures of molecules have been recently realized[45–49]. We find a short reaction–diffusion length, indicating that the uptake is dominated by interfacial features in the vicinity of the liquid/vapor interface
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
