Hannover 2016 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 15: Atomic clusters II (with MO)
A 15.7: Vortrag
Dienstag, 1. März 2016, 16:00–16:15, f107
Surface composition of free mixed NaCl/Na2SO4 nanoscale aerosols — •Burkhard Langer, Egill Antonsson, Christopher Raschpichler, Dmitry Marchenko, and Eckart Rühl — Physikalische Chemie, Freie Universität Berlin
Nanoscopic NaCl/Na2SO4 aerosols (d ≈ 70 nm) serve as a model for marine salt aerosols.
The crystallization process of droplets of such binary salt solutions was measured using synchrotron radiation from BESSY II by photoelectron spectroscopy, which is particularly surface sensitive.
Intensities of the chlorine 2p and the sulfur 2p lines in photoelectron spectra taken at a photon energy of 270 eV are compared for different mixing ratios of the salts. This allows us to determine the chemical surface composition of free, mixed NaCl/Na2SO4 aerosols grown by drying aqueous saline droplets.
It turns out that the ratio of the surface constituents deviates significantly from the mixing ratio in the aqueous solution, whereby the minority species in droplets are increasingly found on the surface of the solid mixed aerosols.
This result can be explained by the nucleation process during crystallization, in which
each of the two salts produces its own pure crystal nuclei rather than crystallizing together.
The variation of the surface ion concentration as a function of the mixing ratio in the droplets,
as observed here for nanoscopic aerosols,
is in contrast to earlier findings suggesting a core-shell structure of mixed salt aerosols that are in the micron range [1].
Z. Ge et al., J. Colloid Interface Sci. 183, 68-77 (1996).