Nitrogen dioxide at the air–water interface: trapping, absorption, and solvation in the bulk and at the surface

Abstract

The interaction of NO(2) with water surfaces in the troposphere is of major interest in atmospheric chemistry. We examined an initial step in this process, the uptake of NO(2) by water through the use of molecular dynamics simulations. An NO(2)-H(2)O intermolecular potential was obtained by fitting to high-level ab initio calculations. We determined the binding of NO(2)-H(2)O to be about two times stronger than that previously calculated. From scattering simulations of an NO(2) molecule interacting with a water slab we observed that the majority of the scattering events resulted in outcomes in which the NO(2) molecule became trapped at the surface or in the interior of the water slab. Typical surface-trapped/adsorbed and bulk-solvated/absorbed trajectories were analyzed to obtain radial distribution functions and the orientational propensity of NO(2) with respect to the water surface. We observed an affinity of the nitrogen atom for the oxygen in water, rather than hydrogen-bonding which was rare. The water solvation shell was less tight for the bulk-absorbed NO(2) than for the surface-adsorbed NO(2). Adsorbed NO(2) demonstrated a marked orientational preference, with the oxygens pointing into the vacuum. Such behavior is expected for a mildly hydrophobic and surfactant molecule like NO(2). Estimates based on our results suggest that at high NO(2) concentrations encountered, for example, in some sampling systems, adsorption and reaction of NO(2) at the surface may contribute to the formation of gas-phase HONO.

Raman spectroscopy of solutions and interfaces containing nitrogen dioxide, water, and 1,4 dioxane: Evidence for repulsion of surface water by NO2 gas

“…A recent theoretical study 2 of the interaction of nitrogen dioxide with the surface of water led to the conclusion that, even though the binding energy of the O 2 N-OH 2 complex was found to be 9.5 kJ mol −1 , a factor of 2 larger than previously calculated, nitrogen dioxide is at least "mildly" hydrophobic. Instead of taking part in hydrogen bonds, the oxygen atoms of NO 2 were found to be repelled by water molecules, which led to an unexpected preferential orientation of NO 2 at the surface, with the oxygen atoms pointing out of the interface, and suggested that, in a system with mixed solvents, the surface might actually be depleted of water.…”

“…Kolb et al 1 have presented a thorough review, up to 2010, of outstanding theoretical and experimental problems relating to the reactions of atmospheric trace gases, including NO 2 , with a variety of wet and dry surfaces, and it is clear that there are still many interesting problems that need to be investigated.…”

“…The absence of large red shifts in the IR upon formation of the NO 2 -H 2 O complex is another indication that normal hydrogen bonds are not formed, but rather the relatively weaker and longer bonds discussed in Ref. 2.…”

Multiscale Modeling of Multiphase Fluid Flow

“…Between the runs, the systems were again equilibrated in constant volume simulation and constant target temperature. The condensation probability, , was computed as = , where was the total number of adsorbed and absorbed octane molecules, and included all adsorbed, absorbed, scattered, and desorbed octane molecules [164,184]. Five bulk temperatures, 290 K, 300 K, 310 K, 330 K, and 350 K, were considered to explore the range of existing experimental setup [185] and to extend the range of available literature data [161].…”

“…Since at equilibrium, the evaporation and condensation coefficients are the same, throughout this work, mass accommodation and condensation coefficient are used interchangeably. The mass uptake and interactions at the liquid-gas interfaces are important and studied in other areas including physics of atmospheric aerosols [162][163][164].…”