MD Investigation of the organic/inorganic ions selectivity at the air-liquid interface
Résumé
Aerosol particles are known to have a direct impact on the climate by directly absorbing and scattering solar radiation and indirectly by acting as cloud condensation nuclei. The main contribution to aerosol emission comes from the ocean through the production of sea spray aerosols (SSA), that mainly consist of organic and inorganic species, formed in different sizes and shapes, depending on their mixing ratios.
Experimentally Cochran et al (2016) showed how surface activity impacts the selective transfer of species from solution to the aerosol phase. Our study aims at verifying their observations by means of molecular level simulations. We chose a series of mono- and dicarboxylates (containing 4, 6 or 8 carbon atoms) with their possible counterions (K+, Na+, Ca2+, Mg2+). Firstly, equilibrium energies of carboxylate-inorganic ion complexes in gaseous phase were obtained by quantum chemical calculations (DFT & post-HF) to compare them with force-field results. Then, we employed classical molecular dynamics approach to model these ions solvated in a water slab. Polarizable force-field water model are applied to quantify the effect of polarization.
These calculations will allow to derive some trends on the enrichment f ions at the liquid-air interface compared to their eventual partitioning in the bulk phase. This work will overall contribute to a better understanding of the aerosol reactivity.
REFERENCES
[1] Cochran, R. E., Jayarathne, T., Stone, E.A., Grassian, V. H., " Selectivity across the interface: a test of surface activity in the composition of organic-enriched aerosols from bubble bursting", The Journal of Physical Chemistry Letters 7, 1692-1696 (2016)
Experimentally Cochran et al (2016) showed how surface activity impacts the selective transfer of species from solution to the aerosol phase. Our study aims at verifying their observations by means of molecular level simulations. We chose a series of mono- and dicarboxylates (containing 4, 6 or 8 carbon atoms) with their possible counterions (K+, Na+, Ca2+, Mg2+). Firstly, equilibrium energies of carboxylate-inorganic ion complexes in gaseous phase were obtained by quantum chemical calculations (DFT & post-HF) to compare them with force-field results. Then, we employed classical molecular dynamics approach to model these ions solvated in a water slab. Polarizable force-field water model are applied to quantify the effect of polarization.
These calculations will allow to derive some trends on the enrichment f ions at the liquid-air interface compared to their eventual partitioning in the bulk phase. This work will overall contribute to a better understanding of the aerosol reactivity.
REFERENCES
[1] Cochran, R. E., Jayarathne, T., Stone, E.A., Grassian, V. H., " Selectivity across the interface: a test of surface activity in the composition of organic-enriched aerosols from bubble bursting", The Journal of Physical Chemistry Letters 7, 1692-1696 (2016)