Enhanced ClNO$_2$ formation at the interface of sea-salt aerosol

TL;DR

This study uses molecular simulation and theory to reveal that ClNO$_2$ formation from N$_2$O$_5$ is significantly enhanced at sea-salt aerosol interfaces, impacting atmospheric NO$_x$ regulation.

Contribution

It provides a microscopic understanding of N$_2$O$_5$ heterogeneous reactivity at sea-salt aerosol interfaces, highlighting the role of interfacial charge stabilization.

Findings

ClNO$_2$ formation is enhanced at the air-water interface.

Interfacial charge stabilization influences reaction rates.

Current aerosol branching ratio interpretations may need revision.

Abstract

The reactive uptake of $\mathrm{N_2O_5}$ on sea-spray aerosol plays a key role in regulating NO$_\mathrm{x}$ concentration in the troposphere. Despite numerous field and laboratory studies, a microscopic understanding of its heterogeneous reactivity remains unclear. Here, we use molecular simulation and theory to elucidate the chlorination of $\mathrm{N_2O_5}$ to form ClNO$_2$, the primary reactive channel within sea-spray aerosol. We find the formation of ClNO$_2$ is markedly enhanced at the air-water interface due to the stabilization of the charge-delocalized transition state, as evident from the formulation of bimolecular rate theory in heterogeneous environments. We explore the consequences of the enhanced interfacial reactivity in the uptake of $\mathrm{N_2O_5}$ using numerical solutions of molecular reaction-diffusion equations as well as their analytical approximations. Our results suggest that the current interpretation of aerosol branching ratios needs to be revisited.